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Rack/dep/speexdsp-SpeexDSP-1.2rc3/doc/manual.lyx

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  1. #LyX 1.6.1 created this file. For more info see http://www.lyx.org/

  2. \lyxformat 345

  3. \begin_document

  4. \begin_header

  5. \textclass scrbook

  6. \use_default_options true

  7. \language english

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  43. \author "" 

  44. \author "" 

  45. \end_header

  46. 

  47. \begin_body

  48. 

  49. \begin_layout Title

  50. The Speex Manual

  51. \begin_inset Newline newline

  52. \end_inset

  53. 

  54. Version 1.2

  55. \end_layout

  56. 

  57. \begin_layout Author

  58. Jean-Marc Valin

  59. \end_layout

  60. 

  61. \begin_layout Standard

  62. \begin_inset Newpage newpage

  63. \end_inset

  64. 

  65. 

  66. \end_layout

  67. 

  68. \begin_layout Standard

  69. Copyright 

  70. \begin_inset ERT

  71. status collapsed

  72. 

  73. \begin_layout Plain Layout

  74. 

  75. 

  76. \backslash

  77. copyright

  78. \end_layout

  79. 

  80. \end_inset

  81. 

  82.  2002-2008 Jean-Marc Valin/Xiph.org Foundation

  83. \end_layout

  84. 

  85. \begin_layout Standard

  86. Permission is granted to copy, distribute and/or modify this document under

  87.  the terms of the GNU Free Documentation License, Version 1.1 or any later

  88.  version published by the Free Software Foundation; with no Invariant Section,

  89.  with no Front-Cover Texts, and with no Back-Cover.

  90.  A copy of the license is included in the section entitled "GNU Free Documentati

  91. on License".

  92.  

  93. \end_layout

  94. 

  95. \begin_layout Standard

  96. \begin_inset Newpage newpage

  97. \end_inset

  98. 

  99. 

  100. \begin_inset CommandInset toc

  101. LatexCommand tableofcontents

  102. 

  103. \end_inset

  104. 

  105. 

  106. \begin_inset Newpage newpage

  107. \end_inset

  108. 

  109. 

  110. \end_layout

  111. 

  112. \begin_layout Standard

  113. \begin_inset FloatList table

  114. 

  115. \end_inset

  116. 

  117. 

  118. \begin_inset Newpage newpage

  119. \end_inset

  120. 

  121. 

  122. \end_layout

  123. 

  124. \begin_layout Chapter

  125. Introduction to Speex

  126. \end_layout

  127. 

  128. \begin_layout Standard

  129. The Speex codec (

  130. \family typewriter

  131. http://www.speex.org/

  132. \family default

  133. ) exists because there is a need for a speech codec that is open-source

  134.  and free from software patent royalties.

  135.  These are essential conditions for being usable in any open-source software.

  136.  In essence, Speex is to speech what Vorbis is to audio/music.

  137.  Unlike many other speech codecs, Speex is not designed for mobile phones

  138.  but rather for packet networks and voice over IP (VoIP) applications.

  139.  File-based compression is of course also supported.

  140.  

  141. \end_layout

  142. 

  143. \begin_layout Standard

  144. The Speex codec is designed to be very flexible and support a wide range

  145.  of speech quality and bit-rate.

  146.  Support for very good quality speech also means that Speex can encode wideband

  147.  speech (16 kHz sampling rate) in addition to narrowband speech (telephone

  148.  quality, 8 kHz sampling rate).

  149. \end_layout

  150. 

  151. \begin_layout Standard

  152. Designing for VoIP instead of mobile phones means that Speex is robust to

  153.  lost packets, but not to corrupted ones.

  154.  This is based on the assumption that in VoIP, packets either arrive unaltered

  155.  or don't arrive at all.

  156.  Because Speex is targeted at a wide range of devices, it has modest (adjustable

  157. ) complexity and a small memory footprint.

  158. \end_layout

  159. 

  160. \begin_layout Standard

  161. All the design goals led to the choice of CELP

  162. \begin_inset Index

  163. status collapsed

  164. 

  165. \begin_layout Plain Layout

  166. CELP

  167. \end_layout

  168. 

  169. \end_inset

  170. 

  171.  as the encoding technique.

  172.  One of the main reasons is that CELP has long proved that it could work

  173.  reliably and scale well to both low bit-rates (e.g.

  174.  DoD CELP @ 4.8 kbps) and high bit-rates (e.g.

  175.  G.728 @ 16 kbps).

  176.  

  177. \end_layout

  178. 

  179. \begin_layout Section

  180. Getting help

  181. \begin_inset CommandInset label

  182. LatexCommand label

  183. name "sec:Getting-help"

  184. 

  185. \end_inset

  186. 

  187. 

  188. \end_layout

  189. 

  190. \begin_layout Standard

  191. As for many open source projects, there are many ways to get help with Speex.

  192.  These include:

  193. \end_layout

  194. 

  195. \begin_layout Itemize

  196. This manual

  197. \end_layout

  198. 

  199. \begin_layout Itemize

  200. Other documentation on the Speex website (http://www.speex.org/)

  201. \end_layout

  202. 

  203. \begin_layout Itemize

  204. Mailing list: Discuss any Speex-related topic on speex-dev@xiph.org (not

  205.  just for developers)

  206. \end_layout

  207. 

  208. \begin_layout Itemize

  209. IRC: The main channel is #speex on irc.freenode.net.

  210.  Note that due to time differences, it may take a while to get someone,

  211.  so please be patient.

  212. \end_layout

  213. 

  214. \begin_layout Itemize

  215. Email the author privately at jean-marc.valin@usherbrooke.ca 

  216. \series bold

  217. only

  218. \series default

  219.  for private/delicate topics you do not wish to discuss publicly.

  220. \end_layout

  221. 

  222. \begin_layout Standard

  223. Before asking for help (mailing list or IRC), 

  224. \series bold

  225. it is important to first read this manual

  226. \series default

  227.  (OK, so if you made it here it's already a good sign).

  228.  It is generally considered rude to ask on a mailing list about topics that

  229.  are clearly detailed in the documentation.

  230.  On the other hand, it's perfectly OK (and encouraged) to ask for clarifications

  231.  about something covered in the manual.

  232.  This manual does not (yet) cover everything about Speex, so everyone is

  233.  encouraged to ask questions, send comments, feature requests, or just let

  234.  us know how Speex is being used.

  235.  

  236. \end_layout

  237. 

  238. \begin_layout Standard

  239. Here are some additional guidelines related to the mailing list.

  240.  Before reporting bugs in Speex to the list, it is strongly recommended

  241.  (if possible) to first test whether these bugs can be reproduced using

  242.  the speexenc and speexdec (see Section 

  243. \begin_inset CommandInset ref

  244. LatexCommand ref

  245. reference "sec:Command-line-encoder/decoder"

  246. 

  247. \end_inset

  248. 

  249. ) command-line utilities.

  250.  Bugs reported based on 3rd party code are both harder to find and far too

  251.  often caused by errors that have nothing to do with Speex.

  252.  

  253. \end_layout

  254. 

  255. \begin_layout Section

  256. About this document

  257. \end_layout

  258. 

  259. \begin_layout Standard

  260. This document is divided in the following way.

  261.  Section 

  262. \begin_inset CommandInset ref

  263. LatexCommand ref

  264. reference "sec:Feature-description"

  265. 

  266. \end_inset

  267. 

  268.  describes the different Speex features and defines many basic terms that

  269.  are used throughout this manual.

  270.  Section 

  271. \begin_inset CommandInset ref

  272. LatexCommand ref

  273. reference "sec:Command-line-encoder/decoder"

  274. 

  275. \end_inset

  276. 

  277.  documents the standard command-line tools provided in the Speex distribution.

  278.  Section 

  279. \begin_inset CommandInset ref

  280. LatexCommand ref

  281. reference "sec:Programming-with-Speex"

  282. 

  283. \end_inset

  284. 

  285.  includes detailed instructions about programming using the libspeex

  286. \begin_inset Index

  287. status collapsed

  288. 

  289. \begin_layout Plain Layout

  290. libspeex

  291. \end_layout

  292. 

  293. \end_inset

  294. 

  295.  API.

  296.  Section 

  297. \begin_inset CommandInset ref

  298. LatexCommand ref

  299. reference "sec:Formats-and-standards"

  300. 

  301. \end_inset

  302. 

  303.  has some information related to Speex and standards.

  304.  

  305. \end_layout

  306. 

  307. \begin_layout Standard

  308. The three last sections describe the algorithms used in Speex.

  309.  These sections require signal processing knowledge, but are not required

  310.  for merely using Speex.

  311.  They are intended for people who want to understand how Speex really works

  312.  and/or want to do research based on Speex.

  313.  Section 

  314. \begin_inset CommandInset ref

  315. LatexCommand ref

  316. reference "sec:Introduction-to-CELP"

  317. 

  318. \end_inset

  319. 

  320.  explains the general idea behind CELP, while sections 

  321. \begin_inset CommandInset ref

  322. LatexCommand ref

  323. reference "sec:Speex-narrowband-mode"

  324. 

  325. \end_inset

  326. 

  327.  and 

  328. \begin_inset CommandInset ref

  329. LatexCommand ref

  330. reference "sec:Speex-wideband-mode"

  331. 

  332. \end_inset

  333. 

  334.  are specific to Speex.

  335. \end_layout

  336. 

  337. \begin_layout Standard

  338. \begin_inset Newpage newpage

  339. \end_inset

  340. 

  341. 

  342. \end_layout

  343. 

  344. \begin_layout Chapter

  345. Codec description

  346. \begin_inset CommandInset label

  347. LatexCommand label

  348. name "sec:Feature-description"

  349. 

  350. \end_inset

  351. 

  352. 

  353. \end_layout

  354. 

  355. \begin_layout Standard

  356. This section describes Speex and its features into more details.

  357. \end_layout

  358. 

  359. \begin_layout Section

  360. Concepts

  361. \end_layout

  362. 

  363. \begin_layout Standard

  364. Before introducing all the Speex features, here are some concepts in speech

  365.  coding that help better understand the rest of the manual.

  366.  Although some are general concepts in speech/audio processing, others are

  367.  specific to Speex.

  368. \end_layout

  369. 

  370. \begin_layout Subsection*

  371. Sampling rate

  372. \begin_inset Index

  373. status collapsed

  374. 

  375. \begin_layout Plain Layout

  376. sampling rate

  377. \end_layout

  378. 

  379. \end_inset

  380. 

  381. 

  382. \end_layout

  383. 

  384. \begin_layout Standard

  385. The sampling rate expressed in Hertz (Hz) is the number of samples taken

  386.  from a signal per second.

  387.  For a sampling rate of 

  388. \begin_inset Formula $F_{s}$

  389. \end_inset

  390. 

  391.  kHz, the highest frequency that can be represented is equal to 

  392. \begin_inset Formula $F_{s}/2$

  393. \end_inset

  394. 

  395.  kHz (

  396. \begin_inset Formula $F_{s}/2$

  397. \end_inset

  398. 

  399.  is known as the Nyquist frequency).

  400.  This is a fundamental property in signal processing and is described by

  401.  the sampling theorem.

  402.  Speex is mainly designed for three different sampling rates: 8 kHz, 16

  403.  kHz, and 32 kHz.

  404.  These are respectively referred to as narrowband

  405. \begin_inset Index

  406. status collapsed

  407. 

  408. \begin_layout Plain Layout

  409. narrowband

  410. \end_layout

  411. 

  412. \end_inset

  413. 

  414. , wideband

  415. \begin_inset Index

  416. status collapsed

  417. 

  418. \begin_layout Plain Layout

  419. wideband

  420. \end_layout

  421. 

  422. \end_inset

  423. 

  424.  and ultra-wideband

  425. \begin_inset Index

  426. status collapsed

  427. 

  428. \begin_layout Plain Layout

  429. ultra-wideband

  430. \end_layout

  431. 

  432. \end_inset

  433. 

  434. .

  435.  

  436. \end_layout

  437. 

  438. \begin_layout Subsection*

  439. Bit-rate

  440. \end_layout

  441. 

  442. \begin_layout Standard

  443. When encoding a speech signal, the bit-rate is defined as the number of

  444.  bits per unit of time required to encode the speech.

  445.  It is measured in 

  446. \emph on

  447. bits per second

  448. \emph default

  449.  (bps), or generally 

  450. \emph on

  451. kilobits per second

  452. \emph default

  453. .

  454.  It is important to make the distinction between 

  455. \emph on

  456. kilo

  457. \series bold

  458. bits

  459. \series default

  460. \emph default

  461.  

  462. \emph on

  463. per second

  464. \emph default

  465.  (k

  466. \series bold

  467. b

  468. \series default

  469. ps) and 

  470. \emph on

  471. kilo

  472. \series bold

  473. bytes

  474. \series default

  475. \emph default

  476.  

  477. \emph on

  478. per second

  479. \emph default

  480.  (k

  481. \series bold

  482. B

  483. \series default

  484. ps).

  485. \end_layout

  486. 

  487. \begin_layout Subsection*

  488. Quality

  489. \begin_inset Index

  490. status collapsed

  491. 

  492. \begin_layout Plain Layout

  493. quality

  494. \end_layout

  495. 

  496. \end_inset

  497. 

  498.  (variable)

  499. \end_layout

  500. 

  501. \begin_layout Standard

  502. Speex is a lossy codec, which means that it achieves compression at the

  503.  expense of fidelity of the input speech signal.

  504.  Unlike some other speech codecs, it is possible to control the trade-off

  505.  made between quality and bit-rate.

  506.  The Speex encoding process is controlled most of the time by a quality

  507.  parameter that ranges from 0 to 10.

  508.  In constant bit-rate

  509. \begin_inset Index

  510. status collapsed

  511. 

  512. \begin_layout Plain Layout

  513. constant bit-rate

  514. \end_layout

  515. 

  516. \end_inset

  517. 

  518.  (CBR) operation, the quality parameter is an integer, while for variable

  519.  bit-rate (VBR), the parameter is a float.

  520.  

  521. \end_layout

  522. 

  523. \begin_layout Subsection*

  524. Complexity

  525. \begin_inset Index

  526. status collapsed

  527. 

  528. \begin_layout Plain Layout

  529. complexity

  530. \end_layout

  531. 

  532. \end_inset

  533. 

  534.  (variable)

  535. \end_layout

  536. 

  537. \begin_layout Standard

  538. With Speex, it is possible to vary the complexity allowed for the encoder.

  539.  This is done by controlling how the search is performed with an integer

  540.  ranging from 1 to 10 in a way that's similar to the -1 to -9 options to

  541.  

  542. \emph on

  543. gzip

  544. \emph default

  545.  and 

  546. \emph on

  547. bzip2

  548. \emph default

  549.  compression utilities.

  550.  For normal use, the noise level at complexity 1 is between 1 and 2 dB higher

  551.  than at complexity 10, but the CPU requirements for complexity 10 is about

  552.  5 times higher than for complexity 1.

  553.  In practice, the best trade-off is between complexity 2 and 4, though higher

  554.  settings are often useful when encoding non-speech sounds like DTMF

  555. \begin_inset Index

  556. status collapsed

  557. 

  558. \begin_layout Plain Layout

  559. DTMF

  560. \end_layout

  561. 

  562. \end_inset

  563. 

  564.  tones.

  565. \end_layout

  566. 

  567. \begin_layout Subsection*

  568. Variable Bit-Rate

  569. \begin_inset Index

  570. status collapsed

  571. 

  572. \begin_layout Plain Layout

  573. variable bit-rate

  574. \end_layout

  575. 

  576. \end_inset

  577. 

  578.  (VBR)

  579. \end_layout

  580. 

  581. \begin_layout Standard

  582. Variable bit-rate (VBR) allows a codec to change its bit-rate dynamically

  583.  to adapt to the 

  584. \begin_inset Quotes eld

  585. \end_inset

  586. 

  587. difficulty

  588. \begin_inset Quotes erd

  589. \end_inset

  590. 

  591.  of the audio being encoded.

  592.  In the example of Speex, sounds like vowels and high-energy transients

  593.  require a higher bit-rate to achieve good quality, while fricatives (e.g.

  594.  s,f sounds) can be coded adequately with less bits.

  595.  For this reason, VBR can achieve lower bit-rate for the same quality, or

  596.  a better quality for a certain bit-rate.

  597.  Despite its advantages, VBR has two main drawbacks: first, by only specifying

  598.  quality, there's no guaranty about the final average bit-rate.

  599.  Second, for some real-time applications like voice over IP (VoIP), what

  600.  counts is the maximum bit-rate, which must be low enough for the communication

  601.  channel.

  602. \end_layout

  603. 

  604. \begin_layout Subsection*

  605. Average Bit-Rate

  606. \begin_inset Index

  607. status collapsed

  608. 

  609. \begin_layout Plain Layout

  610. average bit-rate

  611. \end_layout

  612. 

  613. \end_inset

  614. 

  615.  (ABR)

  616. \end_layout

  617. 

  618. \begin_layout Standard

  619. Average bit-rate solves one of the problems of VBR, as it dynamically adjusts

  620.  VBR quality in order to meet a specific target bit-rate.

  621.  Because the quality/bit-rate is adjusted in real-time (open-loop), the

  622.  global quality will be slightly lower than that obtained by encoding in

  623.  VBR with exactly the right quality setting to meet the target average bit-rate.

  624. \end_layout

  625. 

  626. \begin_layout Subsection*

  627. Voice Activity Detection

  628. \begin_inset Index

  629. status collapsed

  630. 

  631. \begin_layout Plain Layout

  632. voice activity detection

  633. \end_layout

  634. 

  635. \end_inset

  636. 

  637.  (VAD)

  638. \end_layout

  639. 

  640. \begin_layout Standard

  641. When enabled, voice activity detection detects whether the audio being encoded

  642.  is speech or silence/background noise.

  643.  VAD is always implicitly activated when encoding in VBR, so the option

  644.  is only useful in non-VBR operation.

  645.  In this case, Speex detects non-speech periods and encode them with just

  646.  enough bits to reproduce the background noise.

  647.  This is called 

  648. \begin_inset Quotes eld

  649. \end_inset

  650. 

  651. comfort noise generation

  652. \begin_inset Quotes erd

  653. \end_inset

  654. 

  655.  (CNG).

  656. \end_layout

  657. 

  658. \begin_layout Subsection*

  659. Discontinuous Transmission

  660. \begin_inset Index

  661. status collapsed

  662. 

  663. \begin_layout Plain Layout

  664. discontinuous transmission

  665. \end_layout

  666. 

  667. \end_inset

  668. 

  669.  (DTX)

  670. \end_layout

  671. 

  672. \begin_layout Standard

  673. Discontinuous transmission is an addition to VAD/VBR operation, that allows

  674.  to stop transmitting completely when the background noise is stationary.

  675.  In file-based operation, since we cannot just stop writing to the file,

  676.  only 5 bits are used for such frames (corresponding to 250 bps).

  677. \end_layout

  678. 

  679. \begin_layout Subsection*

  680. Perceptual enhancement

  681. \begin_inset Index

  682. status collapsed

  683. 

  684. \begin_layout Plain Layout

  685. perceptual enhancement

  686. \end_layout

  687. 

  688. \end_inset

  689. 

  690. 

  691. \end_layout

  692. 

  693. \begin_layout Standard

  694. Perceptual enhancement is a part of the decoder which, when turned on, attempts

  695.  to reduce the perception of the noise/distortion produced by the encoding/decod

  696. ing process.

  697.  In most cases, perceptual enhancement brings the sound further from the

  698.  original 

  699. \emph on

  700. objectively

  701. \emph default

  702.  (e.g.

  703.  considering only SNR), but in the end it still 

  704. \emph on

  705. sounds

  706. \emph default

  707.  better (subjective improvement).

  708. \end_layout

  709. 

  710. \begin_layout Subsection*

  711. Latency and algorithmic delay

  712. \begin_inset Index

  713. status collapsed

  714. 

  715. \begin_layout Plain Layout

  716. algorithmic delay

  717. \end_layout

  718. 

  719. \end_inset

  720. 

  721. 

  722. \end_layout

  723. 

  724. \begin_layout Standard

  725. Every speech codec introduces a delay in the transmission.

  726.  For Speex, this delay is equal to the frame size, plus some amount of 

  727. \begin_inset Quotes eld

  728. \end_inset

  729. 

  730. look-ahead

  731. \begin_inset Quotes erd

  732. \end_inset

  733. 

  734.  required to process each frame.

  735.  In narrowband operation (8 kHz), the look-ahead is 10 ms, in wideband operation

  736.  (16 kHz), the look-ahead is 13.9 ms and in ultra-wideband operation (32

  737.  kHz) look-ahead is 15.9 ms, resulting in the algorithic delays of 30 ms,

  738.  33.9 ms and 35.9 ms accordingly.

  739.  These values don't account for the CPU time it takes to encode or decode

  740.  the frames.

  741. \end_layout

  742. 

  743. \begin_layout Section

  744. Codec

  745. \end_layout

  746. 

  747. \begin_layout Standard

  748. The main characteristics of Speex can be summarized as follows:

  749. \end_layout

  750. 

  751. \begin_layout Itemize

  752. Free software/open-source

  753. \begin_inset Index

  754. status collapsed

  755. 

  756. \begin_layout Plain Layout

  757. open-source

  758. \end_layout

  759. 

  760. \end_inset

  761. 

  762. , patent

  763. \begin_inset Index

  764. status collapsed

  765. 

  766. \begin_layout Plain Layout

  767. patent

  768. \end_layout

  769. 

  770. \end_inset

  771. 

  772.  and royalty-free

  773. \end_layout

  774. 

  775. \begin_layout Itemize

  776. Integration of narrowband

  777. \begin_inset Index

  778. status collapsed

  779. 

  780. \begin_layout Plain Layout

  781. narrowband

  782. \end_layout

  783. 

  784. \end_inset

  785. 

  786.  and wideband

  787. \begin_inset Index

  788. status collapsed

  789. 

  790. \begin_layout Plain Layout

  791. wideband

  792. \end_layout

  793. 

  794. \end_inset

  795. 

  796.  using an embedded bit-stream

  797. \end_layout

  798. 

  799. \begin_layout Itemize

  800. Wide range of bit-rates available (from 2.15 kbps to 44 kbps)

  801. \end_layout

  802. 

  803. \begin_layout Itemize

  804. Dynamic bit-rate switching (AMR) and Variable Bit-Rate

  805. \begin_inset Index

  806. status collapsed

  807. 

  808. \begin_layout Plain Layout

  809. variable bit-rate

  810. \end_layout

  811. 

  812. \end_inset

  813. 

  814.  (VBR) operation

  815. \end_layout

  816. 

  817. \begin_layout Itemize

  818. Voice Activity Detection

  819. \begin_inset Index

  820. status collapsed

  821. 

  822. \begin_layout Plain Layout

  823. voice activity detection

  824. \end_layout

  825. 

  826. \end_inset

  827. 

  828.  (VAD, integrated with VBR) and discontinuous transmission (DTX)

  829. \end_layout

  830. 

  831. \begin_layout Itemize

  832. Variable complexity

  833. \begin_inset Index

  834. status collapsed

  835. 

  836. \begin_layout Plain Layout

  837. complexity

  838. \end_layout

  839. 

  840. \end_inset

  841. 

  842. 

  843. \end_layout

  844. 

  845. \begin_layout Itemize

  846. Embedded wideband structure (scalable sampling rate)

  847. \end_layout

  848. 

  849. \begin_layout Itemize

  850. Ultra-wideband sampling rate at 32 kHz

  851. \end_layout

  852. 

  853. \begin_layout Itemize

  854. Intensity stereo encoding option

  855. \end_layout

  856. 

  857. \begin_layout Itemize

  858. Fixed-point implementation

  859. \end_layout

  860. 

  861. \begin_layout Section

  862. Preprocessor

  863. \end_layout

  864. 

  865. \begin_layout Standard

  866. This part refers to the preprocessor module introduced in the 1.1.x branch.

  867.  The preprocessor is designed to be used on the audio 

  868. \emph on

  869. before

  870. \emph default

  871.  running the encoder.

  872.  The preprocessor provides three main functionalities:

  873. \end_layout

  874. 

  875. \begin_layout Itemize

  876. noise suppression

  877. \end_layout

  878. 

  879. \begin_layout Itemize

  880. automatic gain control (AGC)

  881. \end_layout

  882. 

  883. \begin_layout Itemize

  884. voice activity detection (VAD)

  885. \end_layout

  886. 

  887. \begin_layout Standard

  888. The denoiser can be used to reduce the amount of background noise present

  889.  in the input signal.

  890.  This provides higher quality speech whether or not the denoised signal

  891.  is encoded with Speex (or at all).

  892.  However, when using the denoised signal with the codec, there is an additional

  893.  benefit.

  894.  Speech codecs in general (Speex included) tend to perform poorly on noisy

  895.  input, which tends to amplify the noise.

  896.  The denoiser greatly reduces this effect.

  897. \end_layout

  898. 

  899. \begin_layout Standard

  900. Automatic gain control (AGC) is a feature that deals with the fact that

  901.  the recording volume may vary by a large amount between different setups.

  902.  The AGC provides a way to adjust a signal to a reference volume.

  903.  This is useful for voice over IP because it removes the need for manual

  904.  adjustment of the microphone gain.

  905.  A secondary advantage is that by setting the microphone gain to a conservative

  906.  (low) level, it is easier to avoid clipping.

  907. \end_layout

  908. 

  909. \begin_layout Standard

  910. The voice activity detector (VAD) provided by the preprocessor is more advanced

  911.  than the one directly provided in the codec.

  912.  

  913. \end_layout

  914. 

  915. \begin_layout Section

  916. Adaptive Jitter Buffer

  917. \end_layout

  918. 

  919. \begin_layout Standard

  920. When transmitting voice (or any content for that matter) over UDP or RTP,

  921.  packet may be lost, arrive with different delay, or even out of order.

  922.  The purpose of a jitter buffer is to reorder packets and buffer them long

  923.  enough (but no longer than necessary) so they can be sent to be decoded.

  924.  

  925. \end_layout

  926. 

  927. \begin_layout Section

  928. Acoustic Echo Canceller

  929. \end_layout

  930. 

  931. \begin_layout Standard

  932. In any hands-free communication system (Fig.

  933.  

  934. \begin_inset CommandInset ref

  935. LatexCommand ref

  936. reference "fig:Acoustic-echo-model"

  937. 

  938. \end_inset

  939. 

  940. ), speech from the remote end is played in the local loudspeaker, propagates

  941.  in the room and is captured by the microphone.

  942.  If the audio captured from the microphone is sent directly to the remote

  943.  end, then the remote user hears an echo of his voice.

  944.  An acoustic echo canceller is designed to remove the acoustic echo before

  945.  it is sent to the remote end.

  946.  It is important to understand that the echo canceller is meant to improve

  947.  the quality on the 

  948. \series bold

  949. remote

  950. \series default

  951.  end.

  952.  For those who care a lot about mouth-to-ear delays it should be noted that

  953.  unlike Speex codec, resampler and preprocessor, this Acoustic Echo Canceller

  954.  does not introduce any latency.

  955. \end_layout

  956. 

  957. \begin_layout Standard

  958. \begin_inset Float figure

  959. wide false

  960. sideways false

  961. status open

  962. 

  963. \begin_layout Plain Layout

  964. \begin_inset ERT

  965. status collapsed

  966. 

  967. \begin_layout Plain Layout

  968. 

  969. 

  970. \backslash

  971. begin{center}

  972. \end_layout

  973. 

  974. \end_inset

  975. 

  976. 

  977. \begin_inset Graphics

  978. 	filename echo_path.eps

  979. 	width 10cm

  980. 

  981. \end_inset

  982. 

  983. 

  984. \begin_inset ERT

  985. status collapsed

  986. 

  987. \begin_layout Plain Layout

  988. 

  989. 

  990. \backslash

  991. end{center}

  992. \end_layout

  993. 

  994. \end_inset

  995. 

  996. 

  997. \end_layout

  998. 

  999. \begin_layout Plain Layout

  1000. \begin_inset Caption

  1001. 

  1002. \begin_layout Plain Layout

  1003. Acoustic echo model

  1004. \begin_inset CommandInset label

  1005. LatexCommand label

  1006. name "fig:Acoustic-echo-model"

  1007. 

  1008. \end_inset

  1009. 

  1010. 

  1011. \end_layout

  1012. 

  1013. \end_inset

  1014. 

  1015. 

  1016. \end_layout

  1017. 

  1018. \end_inset

  1019. 

  1020. 

  1021. \end_layout

  1022. 

  1023. \begin_layout Section

  1024. Resampler

  1025. \end_layout

  1026. 

  1027. \begin_layout Standard

  1028. In some cases, it may be useful to convert audio from one sampling rate

  1029.  to another.

  1030.  There are many reasons for that.

  1031.  It can be for mixing streams that have different sampling rates, for supporting

  1032.  sampling rates that the soundcard doesn't support, for transcoding, etc.

  1033.  That's why there is now a resampler that is part of the Speex project.

  1034.  This resampler can be used to convert between any two arbitrary rates (the

  1035.  ratio must only be a rational number) and there is control over the quality/com

  1036. plexity tradeoff.

  1037.  Keep in mind, that resampler introduce some delay in audio stream, which

  1038.  size depends on resampler quality setting.

  1039.  Refer to resampler API documentation to know how to get exact delay values.

  1040. \end_layout

  1041. 

  1042. \begin_layout Section

  1043. Integration

  1044. \end_layout

  1045. 

  1046. \begin_layout Standard

  1047. Knowing 

  1048. \emph on

  1049. how

  1050. \emph default

  1051.  to use each of the components is not that useful unless we know 

  1052. \emph on

  1053. where

  1054. \emph default

  1055.  to use them.

  1056.  Figure 

  1057. \begin_inset CommandInset ref

  1058. LatexCommand ref

  1059. reference "fig:Integration-VoIP"

  1060. 

  1061. \end_inset

  1062. 

  1063.  shows where each of the components would be used in a typical VoIP client.

  1064.  Components in dotted lines are optional, though they may be very useful

  1065.  in some circumstances.

  1066.  There are several important things to note from there.

  1067.  The AEC must be placed as close as possible to the playback and capture.

  1068.  Only the resampling may be closer.

  1069.  Also, it is very important to use the same clock for both mic capture and

  1070.  speaker/headphones playback.

  1071. \end_layout

  1072. 

  1073. \begin_layout Standard

  1074. \begin_inset Float figure

  1075. wide false

  1076. sideways false

  1077. status open

  1078. 

  1079. \begin_layout Plain Layout

  1080. \begin_inset ERT

  1081. status collapsed

  1082. 

  1083. \begin_layout Plain Layout

  1084. 

  1085. 

  1086. \backslash

  1087. begin{center}

  1088. \end_layout

  1089. 

  1090. \end_inset

  1091. 

  1092. 

  1093. \begin_inset Graphics

  1094. 	filename components.eps

  1095. 	width 80text%

  1096. 

  1097. \end_inset

  1098. 

  1099. 

  1100. \begin_inset ERT

  1101. status collapsed

  1102. 

  1103. \begin_layout Plain Layout

  1104. 

  1105. 

  1106. \backslash

  1107. end{center}

  1108. \end_layout

  1109. 

  1110. \end_inset

  1111. 

  1112. 

  1113. \end_layout

  1114. 

  1115. \begin_layout Plain Layout

  1116. \begin_inset Caption

  1117. 

  1118. \begin_layout Plain Layout

  1119. Integration of all the components in a VoIP client.

  1120. \begin_inset CommandInset label

  1121. LatexCommand label

  1122. name "fig:Integration-VoIP"

  1123. 

  1124. \end_inset

  1125. 

  1126. 

  1127. \end_layout

  1128. 

  1129. \end_inset

  1130. 

  1131. 

  1132. \end_layout

  1133. 

  1134. \end_inset

  1135. 

  1136. 

  1137. \end_layout

  1138. 

  1139. \begin_layout Standard

  1140. \begin_inset Newpage newpage

  1141. \end_inset

  1142. 

  1143. 

  1144. \end_layout

  1145. 

  1146. \begin_layout Chapter

  1147. Compiling and Porting

  1148. \end_layout

  1149. 

  1150. \begin_layout Standard

  1151. Compiling Speex under UNIX/Linux or any other platform supported by autoconf

  1152.  (e.g.

  1153.  Win32/cygwin) is as easy as typing:

  1154. \end_layout

  1155. 

  1156. \begin_layout LyX-Code

  1157. % ./configure [options]

  1158. \end_layout

  1159. 

  1160. \begin_layout LyX-Code

  1161. % make

  1162. \end_layout

  1163. 

  1164. \begin_layout LyX-Code

  1165. % make install

  1166. \end_layout

  1167. 

  1168. \begin_layout Standard

  1169. The options supported by the Speex configure script are:

  1170. \end_layout

  1171. 

  1172. \begin_layout Description

  1173. --prefix=<path> Specifies the base path for installing Speex (e.g.

  1174.  /usr)

  1175. \end_layout

  1176. 

  1177. \begin_layout Description

  1178. --enable-shared/--disable-shared Whether to compile shared libraries

  1179. \end_layout

  1180. 

  1181. \begin_layout Description

  1182. --enable-static/--disable-static Whether to compile static libraries

  1183. \end_layout

  1184. 

  1185. \begin_layout Description

  1186. --disable-wideband Disable the wideband part of Speex (typically to save

  1187.  space)

  1188. \end_layout

  1189. 

  1190. \begin_layout Description

  1191. --enable-valgrind Enable extra hits for valgrind for debugging purposes

  1192.  (do not use by default)

  1193. \end_layout

  1194. 

  1195. \begin_layout Description

  1196. --enable-sse Enable use of SSE instructions (x86/float only)

  1197. \end_layout

  1198. 

  1199. \begin_layout Description

  1200. --enable-fixed-point

  1201. \begin_inset Index

  1202. status collapsed

  1203. 

  1204. \begin_layout Plain Layout

  1205. fixed-point

  1206. \end_layout

  1207. 

  1208. \end_inset

  1209. 

  1210.  Compile Speex for a processor that does not have a floating point unit

  1211.  (FPU)

  1212. \end_layout

  1213. 

  1214. \begin_layout Description

  1215. --enable-arm4-asm Enable assembly specific to the ARMv4 architecture (gcc

  1216.  only)

  1217. \end_layout

  1218. 

  1219. \begin_layout Description

  1220. --enable-arm5e-asm Enable assembly specific to the ARMv5E architecture (gcc

  1221.  only)

  1222. \end_layout

  1223. 

  1224. \begin_layout Description

  1225. --enable-fixed-point-debug Use only for debugging the fixed-point

  1226. \begin_inset Index

  1227. status collapsed

  1228. 

  1229. \begin_layout Plain Layout

  1230. fixed-point

  1231. \end_layout

  1232. 

  1233. \end_inset

  1234. 

  1235.  code (very slow)

  1236. \end_layout

  1237. 

  1238. \begin_layout Description

  1239. --enable-ti-c55x Enable support for the TI C5x family

  1240. \end_layout

  1241. 

  1242. \begin_layout Description

  1243. --enable-blackfin-asm Enable assembly specific to the Blackfin DSP architecture

  1244.  (gcc only)

  1245. \end_layout

  1246. 

  1247. \begin_layout Section

  1248. Platforms

  1249. \end_layout

  1250. 

  1251. \begin_layout Standard

  1252. Speex is known to compile and work on a large number of architectures, both

  1253.  floating-point and fixed-point.

  1254.  In general, any architecture that can natively compute the multiplication

  1255.  of two signed 16-bit numbers (32-bit result) and runs at a sufficient clock

  1256.  rate (architecture-dependent) is capable of running Speex.

  1257.  Architectures on which Speex is 

  1258. \series bold

  1259. known

  1260. \series default

  1261.  to work (it probably works on many others) are:

  1262. \end_layout

  1263. 

  1264. \begin_layout Itemize

  1265. x86 & x86-64

  1266. \end_layout

  1267. 

  1268. \begin_layout Itemize

  1269. Power

  1270. \end_layout

  1271. 

  1272. \begin_layout Itemize

  1273. SPARC

  1274. \end_layout

  1275. 

  1276. \begin_layout Itemize

  1277. ARM

  1278. \end_layout

  1279. 

  1280. \begin_layout Itemize

  1281. Blackfin

  1282. \end_layout

  1283. 

  1284. \begin_layout Itemize

  1285. Coldfire (68k family)

  1286. \end_layout

  1287. 

  1288. \begin_layout Itemize

  1289. TI C54xx & C55xx

  1290. \end_layout

  1291. 

  1292. \begin_layout Itemize

  1293. TI C6xxx

  1294. \end_layout

  1295. 

  1296. \begin_layout Itemize

  1297. TriMedia (experimental)

  1298. \end_layout

  1299. 

  1300. \begin_layout Standard

  1301. Operating systems on top of which Speex is known to work include (it probably

  1302.  works on many others):

  1303. \end_layout

  1304. 

  1305. \begin_layout Itemize

  1306. Linux

  1307. \end_layout

  1308. 

  1309. \begin_layout Itemize

  1310. \begin_inset Formula $\mu$

  1311. \end_inset

  1312. 

  1313. Clinux

  1314. \end_layout

  1315. 

  1316. \begin_layout Itemize

  1317. MacOS X

  1318. \end_layout

  1319. 

  1320. \begin_layout Itemize

  1321. BSD

  1322. \end_layout

  1323. 

  1324. \begin_layout Itemize

  1325. Other UNIX/POSIX variants

  1326. \end_layout

  1327. 

  1328. \begin_layout Itemize

  1329. Symbian

  1330. \end_layout

  1331. 

  1332. \begin_layout Standard

  1333. The source code directory include additional information for compiling on

  1334.  certain architectures or operating systems in README.xxx files.

  1335. \end_layout

  1336. 

  1337. \begin_layout Section

  1338. Porting and Optimising

  1339. \end_layout

  1340. 

  1341. \begin_layout Standard

  1342. Here are a few things to consider when porting or optimising Speex for a

  1343.  new platform or an existing one.

  1344. \end_layout

  1345. 

  1346. \begin_layout Subsection

  1347. CPU optimisation

  1348. \end_layout

  1349. 

  1350. \begin_layout Standard

  1351. The single factor that will affect the CPU usage of Speex the most is whether

  1352.  it is compiled for floating point or fixed-point.

  1353.  If your CPU/DSP does not have a floating-point unit FPU, then compiling

  1354.  as fixed-point will be orders of magnitudes faster.

  1355.  If there is an FPU present, then it is important to test which version

  1356.  is faster.

  1357.  On the x86 architecture, floating-point is 

  1358. \series bold

  1359. generally

  1360. \series default

  1361.  faster, but not always.

  1362.  To compile Speex as fixed-point, you need to pass --fixed-point to the

  1363.  configure script or define the FIXED_POINT macro for the compiler.

  1364.  As of 1.2beta3, it is now possible to disable the floating-point compatibility

  1365.  API, which means that your code can link without a float emulation library.

  1366.  To do that configure with --disable-float-api or define the DISABLE_FLOAT_API

  1367.  macro.

  1368.  Until the VBR feature is ported to fixed-point, you will also need to configure

  1369.  with --disable-vbr or define DISABLE_VBR.

  1370. \end_layout

  1371. 

  1372. \begin_layout Standard

  1373. Other important things to check on some DSP architectures are:

  1374. \end_layout

  1375. 

  1376. \begin_layout Itemize

  1377. Make sure the cache is set to write-back mode

  1378. \end_layout

  1379. 

  1380. \begin_layout Itemize

  1381. If the chip has SRAM instead of cache, make sure as much code and data are

  1382.  in SRAM, rather than in RAM

  1383. \end_layout

  1384. 

  1385. \begin_layout Standard

  1386. If you are going to be writing assembly, then the following functions are

  1387.  

  1388. \series bold

  1389. usually

  1390. \series default

  1391.  the first ones you should consider optimising:

  1392. \end_layout

  1393. 

  1394. \begin_layout Itemize

  1395. \begin_inset listings

  1396. inline true

  1397. status collapsed

  1398. 

  1399. \begin_layout Plain Layout

  1400. 

  1401. filter_mem16()

  1402. \end_layout

  1403. 

  1404. \end_inset

  1405. 

  1406. 

  1407. \end_layout

  1408. 

  1409. \begin_layout Itemize

  1410. \begin_inset listings

  1411. inline true

  1412. status collapsed

  1413. 

  1414. \begin_layout Plain Layout

  1415. 

  1416. iir_mem16()

  1417. \end_layout

  1418. 

  1419. \end_inset

  1420. 

  1421. 

  1422. \end_layout

  1423. 

  1424. \begin_layout Itemize

  1425. \begin_inset listings

  1426. inline true

  1427. status collapsed

  1428. 

  1429. \begin_layout Plain Layout

  1430. 

  1431. vq_nbest()

  1432. \end_layout

  1433. 

  1434. \end_inset

  1435. 

  1436. 

  1437. \end_layout

  1438. 

  1439. \begin_layout Itemize

  1440. \begin_inset listings

  1441. inline true

  1442. status collapsed

  1443. 

  1444. \begin_layout Plain Layout

  1445. 

  1446. pitch_xcorr()

  1447. \end_layout

  1448. 

  1449. \end_inset

  1450. 

  1451. 

  1452. \end_layout

  1453. 

  1454. \begin_layout Itemize

  1455. \begin_inset listings

  1456. inline true

  1457. status collapsed

  1458. 

  1459. \begin_layout Plain Layout

  1460. 

  1461. interp_pitch()

  1462. \end_layout

  1463. 

  1464. \end_inset

  1465. 

  1466. 

  1467. \end_layout

  1468. 

  1469. \begin_layout Standard

  1470. The filtering functions 

  1471. \begin_inset listings

  1472. inline true

  1473. status collapsed

  1474. 

  1475. \begin_layout Plain Layout

  1476. 

  1477. filter_mem16()

  1478. \end_layout

  1479. 

  1480. \end_inset

  1481. 

  1482.  and 

  1483. \begin_inset listings

  1484. inline true

  1485. status collapsed

  1486. 

  1487. \begin_layout Plain Layout

  1488. 

  1489. iir_mem16()

  1490. \end_layout

  1491. 

  1492. \end_inset

  1493. 

  1494.  are implemented in the direct form II transposed (DF2T).

  1495.  However, for architectures based on multiply-accumulate (MAC), DF2T requires

  1496.  frequent reload of the accumulator, which can make the code very slow.

  1497.  For these architectures (e.g.

  1498.  Blackfin and Coldfire), a better approach is to implement those functions

  1499.  as direct form I (DF1), which is easier to express in terms of MAC.

  1500.  When doing that however, 

  1501. \series bold

  1502. it is important to make sure that the DF1 implementation still behaves like

  1503.  the original DF2T behaviour when it comes to memory values

  1504. \series default

  1505. .

  1506.  This is necessary because the filter is time-varying and must compute exactly

  1507.  the same value (not counting machine rounding) on any encoder or decoder.

  1508. \end_layout

  1509. 

  1510. \begin_layout Subsection

  1511. Memory optimisation

  1512. \end_layout

  1513. 

  1514. \begin_layout Standard

  1515. Memory optimisation is mainly something that should be considered for small

  1516.  embedded platforms.

  1517.  For PCs, Speex is already so tiny that it's just not worth doing any of

  1518.  the things suggested here.

  1519.  There are several ways to reduce the memory usage of Speex, both in terms

  1520.  of code size and data size.

  1521.  For optimising code size, the trick is to first remove features you do

  1522.  not need.

  1523.  Some examples of things that can easily be disabled 

  1524. \series bold

  1525. if you don't need them

  1526. \series default

  1527.  are:

  1528. \end_layout

  1529. 

  1530. \begin_layout Itemize

  1531. Wideband support (--disable-wideband)

  1532. \end_layout

  1533. 

  1534. \begin_layout Itemize

  1535. Support for stereo (removing stereo.c)

  1536. \end_layout

  1537. 

  1538. \begin_layout Itemize

  1539. VBR support (--disable-vbr or DISABLE_VBR)

  1540. \end_layout

  1541. 

  1542. \begin_layout Itemize

  1543. Static codebooks that are not needed for the bit-rates you are using (*_table.c

  1544.  files)

  1545. \end_layout

  1546. 

  1547. \begin_layout Standard

  1548. Speex also has several methods for allocating temporary arrays.

  1549.  When using a compiler that supports C99 properly (as of 2007, Microsoft

  1550.  compilers don't, but gcc does), it is best to define VAR_ARRAYS.

  1551.  That makes use of the variable-size array feature of C99.

  1552.  The next best is to define USE_ALLOCA so that Speex can use alloca() to

  1553.  allocate the temporary arrays.

  1554.  Note that on many systems, alloca() is buggy so it may not work.

  1555.  If none of VAR_ARRAYS and USE_ALLOCA are defined, then Speex falls back

  1556.  to allocating a large 

  1557. \begin_inset Quotes eld

  1558. \end_inset

  1559. 

  1560. scratch space

  1561. \begin_inset Quotes erd

  1562. \end_inset

  1563. 

  1564.  and doing its own internal allocation.

  1565.  The main disadvantage of this solution is that it is wasteful.

  1566.  It needs to allocate enough stack for the worst case scenario (worst bit-rate,

  1567.  highest complexity setting, ...) and by default, the memory isn't shared between

  1568.  multiple encoder/decoder states.

  1569.  Still, if the 

  1570. \begin_inset Quotes eld

  1571. \end_inset

  1572. 

  1573. manual

  1574. \begin_inset Quotes erd

  1575. \end_inset

  1576. 

  1577.  allocation is the only option left, there are a few things that can be

  1578.  improved.

  1579.  By overriding the speex_alloc_scratch() call in os_support.h, it is possible

  1580.  to always return the same memory area for all states

  1581. \begin_inset Foot

  1582. status collapsed

  1583. 

  1584. \begin_layout Plain Layout

  1585. In this case, one must be careful with threads

  1586. \end_layout

  1587. 

  1588. \end_inset

  1589. 

  1590. .

  1591.  In addition to that, by redefining the NB_ENC_STACK and NB_DEC_STACK (or

  1592.  similar for wideband), it is possible to only allocate memory for a scenario

  1593.  that is known in advance.

  1594.  In this case, it is important to measure the amount of memory required

  1595.  for the specific sampling rate, bit-rate and complexity level being used.

  1596. \end_layout

  1597. 

  1598. \begin_layout Standard

  1599. \begin_inset Newpage newpage

  1600. \end_inset

  1601. 

  1602. 

  1603. \end_layout

  1604. 

  1605. \begin_layout Chapter

  1606. Command-line encoder/decoder

  1607. \begin_inset CommandInset label

  1608. LatexCommand label

  1609. name "sec:Command-line-encoder/decoder"

  1610. 

  1611. \end_inset

  1612. 

  1613. 

  1614. \end_layout

  1615. 

  1616. \begin_layout Standard

  1617. The base Speex distribution includes a command-line encoder (

  1618. \emph on

  1619. speexenc

  1620. \emph default

  1621. ) and decoder (

  1622. \emph on

  1623. speexdec

  1624. \emph default

  1625. ).

  1626.  Those tools produce and read Speex files encapsulated in the Ogg container.

  1627.  Although it is possible to encapsulate Speex in any container, Ogg is the

  1628.  recommended container for files.

  1629.  This section describes how to use the command line tools for Speex files

  1630.  in Ogg.

  1631. \end_layout

  1632. 

  1633. \begin_layout Section

  1634. 

  1635. \emph on

  1636. speexenc

  1637. \begin_inset Index

  1638. status collapsed

  1639. 

  1640. \begin_layout Plain Layout

  1641. speexenc

  1642. \end_layout

  1643. 

  1644. \end_inset

  1645. 

  1646. 

  1647. \end_layout

  1648. 

  1649. \begin_layout Standard

  1650. The 

  1651. \emph on

  1652. speexenc

  1653. \emph default

  1654.  utility is used to create Speex files from raw PCM or wave files.

  1655.  It can be used by calling: 

  1656. \end_layout

  1657. 

  1658. \begin_layout LyX-Code

  1659. speexenc [options] input_file output_file

  1660. \end_layout

  1661. 

  1662. \begin_layout Standard

  1663. The value '-' for input_file or output_file corresponds respectively to

  1664.  stdin and stdout.

  1665.  The valid options are:

  1666. \end_layout

  1667. 

  1668. \begin_layout Description

  1669. --narrowband

  1670. \begin_inset space ~

  1671. \end_inset

  1672. 

  1673. (-n) Tell Speex to treat the input as narrowband (8 kHz).

  1674.  This is the default

  1675. \end_layout

  1676. 

  1677. \begin_layout Description

  1678. --wideband

  1679. \begin_inset space ~

  1680. \end_inset

  1681. 

  1682. (-w) Tell Speex to treat the input as wideband (16 kHz)

  1683. \end_layout

  1684. 

  1685. \begin_layout Description

  1686. --ultra-wideband

  1687. \begin_inset space ~

  1688. \end_inset

  1689. 

  1690. (-u) Tell Speex to treat the input as 

  1691. \begin_inset Quotes eld

  1692. \end_inset

  1693. 

  1694. ultra-wideband

  1695. \begin_inset Quotes erd

  1696. \end_inset

  1697. 

  1698.  (32 kHz)

  1699. \end_layout

  1700. 

  1701. \begin_layout Description

  1702. --quality

  1703. \begin_inset space ~

  1704. \end_inset

  1705. 

  1706. n Set the encoding quality (0-10), default is 8

  1707. \end_layout

  1708. 

  1709. \begin_layout Description

  1710. --bitrate

  1711. \begin_inset space ~

  1712. \end_inset

  1713. 

  1714. n Encoding bit-rate (use bit-rate n or lower) 

  1715. \end_layout

  1716. 

  1717. \begin_layout Description

  1718. --vbr Enable VBR (Variable Bit-Rate), disabled by default

  1719. \end_layout

  1720. 

  1721. \begin_layout Description

  1722. --abr

  1723. \begin_inset space ~

  1724. \end_inset

  1725. 

  1726. n Enable ABR (Average Bit-Rate) at n kbps, disabled by default

  1727. \end_layout

  1728. 

  1729. \begin_layout Description

  1730. --vad Enable VAD (Voice Activity Detection), disabled by default

  1731. \end_layout

  1732. 

  1733. \begin_layout Description

  1734. --dtx Enable DTX (Discontinuous Transmission), disabled by default

  1735. \end_layout

  1736. 

  1737. \begin_layout Description

  1738. --nframes

  1739. \begin_inset space ~

  1740. \end_inset

  1741. 

  1742. n Pack n frames in each Ogg packet (this saves space at low bit-rates)

  1743. \end_layout

  1744. 

  1745. \begin_layout Description

  1746. --comp

  1747. \begin_inset space ~

  1748. \end_inset

  1749. 

  1750. n Set encoding speed/quality tradeoff.

  1751.  The higher the value of n, the slower the encoding (default is 3)

  1752. \end_layout

  1753. 

  1754. \begin_layout Description

  1755. -V Verbose operation, print bit-rate currently in use

  1756. \end_layout

  1757. 

  1758. \begin_layout Description

  1759. --help

  1760. \begin_inset space ~

  1761. \end_inset

  1762. 

  1763. (-h) Print the help

  1764. \end_layout

  1765. 

  1766. \begin_layout Description

  1767. --version

  1768. \begin_inset space ~

  1769. \end_inset

  1770. 

  1771. (-v) Print version information

  1772. \end_layout

  1773. 

  1774. \begin_layout Subsection*

  1775. Speex comments

  1776. \end_layout

  1777. 

  1778. \begin_layout Description

  1779. --comment Add the given string as an extra comment.

  1780.  This may be used multiple times.

  1781.  

  1782. \end_layout

  1783. 

  1784. \begin_layout Description

  1785. --author Author of this track.

  1786.  

  1787. \end_layout

  1788. 

  1789. \begin_layout Description

  1790. --title Title for this track.

  1791.  

  1792. \end_layout

  1793. 

  1794. \begin_layout Subsection*

  1795. Raw input options

  1796. \end_layout

  1797. 

  1798. \begin_layout Description

  1799. --rate

  1800. \begin_inset space ~

  1801. \end_inset

  1802. 

  1803. n Sampling rate for raw input

  1804. \end_layout

  1805. 

  1806. \begin_layout Description

  1807. --stereo Consider raw input as stereo 

  1808. \end_layout

  1809. 

  1810. \begin_layout Description

  1811. --le Raw input is little-endian 

  1812. \end_layout

  1813. 

  1814. \begin_layout Description

  1815. --be Raw input is big-endian 

  1816. \end_layout

  1817. 

  1818. \begin_layout Description

  1819. --8bit Raw input is 8-bit unsigned 

  1820. \end_layout

  1821. 

  1822. \begin_layout Description

  1823. --16bit Raw input is 16-bit signed 

  1824. \end_layout

  1825. 

  1826. \begin_layout Section

  1827. 

  1828. \emph on

  1829. speexdec

  1830. \begin_inset Index

  1831. status collapsed

  1832. 

  1833. \begin_layout Plain Layout

  1834. speexdec

  1835. \end_layout

  1836. 

  1837. \end_inset

  1838. 

  1839. 

  1840. \end_layout

  1841. 

  1842. \begin_layout Standard

  1843. The 

  1844. \emph on

  1845. speexdec

  1846. \emph default

  1847.  utility is used to decode Speex files and can be used by calling: 

  1848. \end_layout

  1849. 

  1850. \begin_layout LyX-Code

  1851. speexdec [options] speex_file [output_file]

  1852. \end_layout

  1853. 

  1854. \begin_layout Standard

  1855. The value '-' for input_file or output_file corresponds respectively to

  1856.  stdin and stdout.

  1857.  Also, when no output_file is specified, the file is played to the soundcard.

  1858.  The valid options are:

  1859. \end_layout

  1860. 

  1861. \begin_layout Description

  1862. --enh enable post-filter (default)

  1863. \end_layout

  1864. 

  1865. \begin_layout Description

  1866. --no-enh disable post-filter

  1867. \end_layout

  1868. 

  1869. \begin_layout Description

  1870. --force-nb Force decoding in narrowband 

  1871. \end_layout

  1872. 

  1873. \begin_layout Description

  1874. --force-wb Force decoding in wideband 

  1875. \end_layout

  1876. 

  1877. \begin_layout Description

  1878. --force-uwb Force decoding in ultra-wideband 

  1879. \end_layout

  1880. 

  1881. \begin_layout Description

  1882. --mono Force decoding in mono 

  1883. \end_layout

  1884. 

  1885. \begin_layout Description

  1886. --stereo Force decoding in stereo 

  1887. \end_layout

  1888. 

  1889. \begin_layout Description

  1890. --rate

  1891. \begin_inset space ~

  1892. \end_inset

  1893. 

  1894. n Force decoding at n Hz sampling rate

  1895. \end_layout

  1896. 

  1897. \begin_layout Description

  1898. --packet-loss

  1899. \begin_inset space ~

  1900. \end_inset

  1901. 

  1902. n Simulate n % random packet loss

  1903. \end_layout

  1904. 

  1905. \begin_layout Description

  1906. -V Verbose operation, print bit-rate currently in use

  1907. \end_layout

  1908. 

  1909. \begin_layout Description

  1910. --help

  1911. \begin_inset space ~

  1912. \end_inset

  1913. 

  1914. (-h) Print the help

  1915. \end_layout

  1916. 

  1917. \begin_layout Description

  1918. --version

  1919. \begin_inset space ~

  1920. \end_inset

  1921. 

  1922. (-v) Print version information

  1923. \end_layout

  1924. 

  1925. \begin_layout Standard

  1926. \begin_inset Newpage newpage

  1927. \end_inset

  1928. 

  1929. 

  1930. \end_layout

  1931. 

  1932. \begin_layout Chapter

  1933. Using the Speex Codec API (

  1934. \emph on

  1935. libspeex

  1936. \emph default

  1937. 

  1938. \begin_inset Index

  1939. status collapsed

  1940. 

  1941. \begin_layout Plain Layout

  1942. libspeex

  1943. \end_layout

  1944. 

  1945. \end_inset

  1946. 

  1947. )

  1948. \begin_inset CommandInset label

  1949. LatexCommand label

  1950. name "sec:Programming-with-Speex"

  1951. 

  1952. \end_inset

  1953. 

  1954. 

  1955. \end_layout

  1956. 

  1957. \begin_layout Standard

  1958. The 

  1959. \emph on

  1960. libspeex

  1961. \emph default

  1962.  library contains all the functions for encoding and decoding speech with

  1963.  the Speex codec.

  1964.  When linking on a UNIX system, one must add 

  1965. \emph on

  1966. -lspeex -lm

  1967. \emph default

  1968.  to the compiler command line.

  1969.  One important thing to know is that 

  1970. \series bold

  1971. libspeex calls are reentrant, but not thread-safe

  1972. \series default

  1973. .

  1974.  That means that it is fine to use calls from many threads, but 

  1975. \series bold

  1976. calls using the same state from multiple threads must be protected by mutexes

  1977. \series default

  1978. .

  1979.  Examples of code can also be found in Appendix 

  1980. \begin_inset CommandInset ref

  1981. LatexCommand ref

  1982. reference "sec:Sample-code"

  1983. 

  1984. \end_inset

  1985. 

  1986.  and the complete API documentation is included in the Documentation section

  1987.  of the Speex website (http://www.speex.org/).

  1988. \end_layout

  1989. 

  1990. \begin_layout Section

  1991. Encoding

  1992. \begin_inset CommandInset label

  1993. LatexCommand label

  1994. name "sub:Encoding"

  1995. 

  1996. \end_inset

  1997. 

  1998. 

  1999. \end_layout

  2000. 

  2001. \begin_layout Standard

  2002. In order to encode speech using Speex, one first needs to:

  2003. \end_layout

  2004. 

  2005. \begin_layout Standard

  2006. \begin_inset listings

  2007. inline false

  2008. status open

  2009. 

  2010. \begin_layout Plain Layout

  2011. 

  2012. #include <speex/speex.h>

  2013. \end_layout

  2014. 

  2015. \end_inset

  2016. 

  2017. Then in the code, a Speex bit-packing struct must be declared, along with

  2018.  a Speex encoder state:

  2019. \begin_inset listings

  2020. inline false

  2021. status open

  2022. 

  2023. \begin_layout Plain Layout

  2024. 

  2025. SpeexBits bits;

  2026. \end_layout

  2027. 

  2028. \begin_layout Plain Layout

  2029. 

  2030. void *enc_state;

  2031. \end_layout

  2032. 

  2033. \end_inset

  2034. 

  2035. The two are initialized by:

  2036. \begin_inset listings

  2037. inline false

  2038. status open

  2039. 

  2040. \begin_layout Plain Layout

  2041. 

  2042. speex_bits_init(&bits);

  2043. \end_layout

  2044. 

  2045. \begin_layout Plain Layout

  2046. 

  2047. enc_state = speex_encoder_init(&speex_nb_mode);

  2048. \end_layout

  2049. 

  2050. \end_inset

  2051. 

  2052. 

  2053. \end_layout

  2054. 

  2055. \begin_layout Standard

  2056. For wideband coding, 

  2057. \emph on

  2058. speex_nb_mode

  2059. \emph default

  2060.  will be replaced by 

  2061. \emph on

  2062. speex_wb_mode

  2063. \emph default

  2064. .

  2065.  In most cases, you will need to know the frame size used at the sampling

  2066.  rate you are using.

  2067.  You can get that value in the 

  2068. \emph on

  2069. frame_size

  2070. \emph default

  2071.  variable (expressed in 

  2072. \series bold

  2073. samples

  2074. \series default

  2075. , not bytes) with:

  2076. \end_layout

  2077. 

  2078. \begin_layout Standard

  2079. \begin_inset listings

  2080. inline false

  2081. status open

  2082. 

  2083. \begin_layout Plain Layout

  2084. 

  2085. speex_encoder_ctl(enc_state,SPEEX_GET_FRAME_SIZE,&frame_size);

  2086. \end_layout

  2087. 

  2088. \end_inset

  2089. 

  2090. 

  2091. \end_layout

  2092. 

  2093. \begin_layout Standard

  2094. In practice, 

  2095. \emph on

  2096. frame_size

  2097. \emph default

  2098.  will correspond to 20 ms when using 8, 16, or 32 kHz sampling rate.

  2099.  There are many parameters that can be set for the Speex encoder, but the

  2100.  most useful one is the quality parameter that controls the quality vs bit-rate

  2101.  tradeoff.

  2102.  This is set by:

  2103. \end_layout

  2104. 

  2105. \begin_layout Standard

  2106. \begin_inset listings

  2107. inline false

  2108. status open

  2109. 

  2110. \begin_layout Plain Layout

  2111. 

  2112. speex_encoder_ctl(enc_state,SPEEX_SET_QUALITY,&quality);

  2113. \end_layout

  2114. 

  2115. \end_inset

  2116. 

  2117. where 

  2118. \emph on

  2119. quality

  2120. \emph default

  2121.  is an integer value ranging from 0 to 10 (inclusively).

  2122.  The mapping between quality and bit-rate is described in Fig.

  2123.  

  2124. \begin_inset CommandInset ref

  2125. LatexCommand ref

  2126. reference "cap:quality_vs_bps"

  2127. 

  2128. \end_inset

  2129. 

  2130.  for narrowband.

  2131. \end_layout

  2132. 

  2133. \begin_layout Standard

  2134. Once the initialization is done, for every input frame:

  2135. \end_layout

  2136. 

  2137. \begin_layout Standard

  2138. \begin_inset listings

  2139. inline false

  2140. status open

  2141. 

  2142. \begin_layout Plain Layout

  2143. 

  2144. speex_bits_reset(&bits);

  2145. \end_layout

  2146. 

  2147. \begin_layout Plain Layout

  2148. 

  2149. speex_encode_int(enc_state, input_frame, &bits);

  2150. \end_layout

  2151. 

  2152. \begin_layout Plain Layout

  2153. 

  2154. nbBytes = speex_bits_write(&bits, byte_ptr, MAX_NB_BYTES);

  2155. \end_layout

  2156. 

  2157. \end_inset

  2158. 

  2159. 

  2160. \end_layout

  2161. 

  2162. \begin_layout Standard

  2163. where 

  2164. \emph on

  2165. input_frame

  2166. \emph default

  2167.  is a 

  2168. \emph on

  2169. (

  2170. \emph default

  2171. short 

  2172. \emph on

  2173. *)

  2174. \emph default

  2175.  pointing to the beginning of a speech frame, 

  2176. \emph on

  2177. byte_ptr

  2178. \emph default

  2179.  is a 

  2180. \emph on

  2181. (char *)

  2182. \emph default

  2183.  where the encoded frame will be written, 

  2184. \emph on

  2185. MAX_NB_BYTES

  2186. \emph default

  2187.  is the maximum number of bytes that can be written to 

  2188. \emph on

  2189. byte_ptr

  2190. \emph default

  2191.  without causing an overflow and 

  2192. \emph on

  2193. nbBytes

  2194. \emph default

  2195.  is the number of bytes actually written to 

  2196. \emph on

  2197. byte_ptr

  2198. \emph default

  2199.  (the encoded size in bytes).

  2200.  Before calling speex_bits_write, it is possible to find the number of bytes

  2201.  that need to be written by calling 

  2202. \family typewriter

  2203. speex_bits_nbytes(&bits)

  2204. \family default

  2205. , which returns a number of bytes.

  2206. \end_layout

  2207. 

  2208. \begin_layout Standard

  2209. It is still possible to use the 

  2210. \emph on

  2211. speex_encode()

  2212. \emph default

  2213.  function, which takes a 

  2214. \emph on

  2215. (float *)

  2216. \emph default

  2217.  for the audio.

  2218.  However, this would make an eventual port to an FPU-less platform (like

  2219.  ARM) more complicated.

  2220.  Internally, 

  2221. \emph on

  2222. speex_encode()

  2223. \emph default

  2224.  and 

  2225. \emph on

  2226. speex_encode_int()

  2227. \emph default

  2228.  are processed in the same way.

  2229.  Whether the encoder uses the fixed-point version is only decided by the

  2230.  compile-time flags, not at the API level.

  2231. \end_layout

  2232. 

  2233. \begin_layout Standard

  2234. After you're done with the encoding, free all resources with:

  2235. \end_layout

  2236. 

  2237. \begin_layout Standard

  2238. \begin_inset listings

  2239. inline false

  2240. status open

  2241. 

  2242. \begin_layout Plain Layout

  2243. 

  2244. speex_bits_destroy(&bits);

  2245. \end_layout

  2246. 

  2247. \begin_layout Plain Layout

  2248. 

  2249. speex_encoder_destroy(enc_state);

  2250. \end_layout

  2251. 

  2252. \end_inset

  2253. 

  2254. 

  2255. \end_layout

  2256. 

  2257. \begin_layout Standard

  2258. That's about it for the encoder.

  2259.  

  2260. \end_layout

  2261. 

  2262. \begin_layout Section

  2263. Decoding

  2264. \begin_inset CommandInset label

  2265. LatexCommand label

  2266. name "sub:Decoding"

  2267. 

  2268. \end_inset

  2269. 

  2270. 

  2271. \end_layout

  2272. 

  2273. \begin_layout Standard

  2274. In order to decode speech using Speex, you first need to:

  2275. \begin_inset listings

  2276. inline false

  2277. status open

  2278. 

  2279. \begin_layout Plain Layout

  2280. 

  2281. #include <speex/speex.h>

  2282. \end_layout

  2283. 

  2284. \end_inset

  2285. 

  2286. You also need to declare a Speex bit-packing struct

  2287. \begin_inset listings

  2288. inline false

  2289. status open

  2290. 

  2291. \begin_layout Plain Layout

  2292. 

  2293. SpeexBits bits;

  2294. \end_layout

  2295. 

  2296. \end_inset

  2297. 

  2298. and a Speex decoder state

  2299. \begin_inset listings

  2300. inline false

  2301. status open

  2302. 

  2303. \begin_layout Plain Layout

  2304. 

  2305. void *dec_state;

  2306. \end_layout

  2307. 

  2308. \end_inset

  2309. 

  2310. The two are initialized by:

  2311. \begin_inset listings

  2312. inline false

  2313. status open

  2314. 

  2315. \begin_layout Plain Layout

  2316. 

  2317. speex_bits_init(&bits);

  2318. \end_layout

  2319. 

  2320. \begin_layout Plain Layout

  2321. 

  2322. dec_state = speex_decoder_init(&speex_nb_mode);

  2323. \end_layout

  2324. 

  2325. \end_inset

  2326. 

  2327. 

  2328. \end_layout

  2329. 

  2330. \begin_layout Standard

  2331. For wideband decoding, 

  2332. \emph on

  2333. speex_nb_mode

  2334. \emph default

  2335.  will be replaced by 

  2336. \emph on

  2337. speex_wb_mode

  2338. \emph default

  2339. .

  2340.  If you need to obtain the size of the frames that will be used by the decoder,

  2341.  you can get that value in the 

  2342. \emph on

  2343. frame_size

  2344. \emph default

  2345.  variable (expressed in 

  2346. \series bold

  2347. samples

  2348. \series default

  2349. , not bytes) with:

  2350. \end_layout

  2351. 

  2352. \begin_layout Standard

  2353. \begin_inset listings

  2354. inline false

  2355. status open

  2356. 

  2357. \begin_layout Plain Layout

  2358. 

  2359. speex_decoder_ctl(dec_state, SPEEX_GET_FRAME_SIZE, &frame_size);

  2360. \end_layout

  2361. 

  2362. \end_inset

  2363. 

  2364. 

  2365. \end_layout

  2366. 

  2367. \begin_layout Standard

  2368. There is also a parameter that can be set for the decoder: whether or not

  2369.  to use a perceptual enhancer.

  2370.  This can be set by: 

  2371. \end_layout

  2372. 

  2373. \begin_layout Standard

  2374. \begin_inset listings

  2375. inline false

  2376. status open

  2377. 

  2378. \begin_layout Plain Layout

  2379. 

  2380. speex_decoder_ctl(dec_state, SPEEX_SET_ENH, &enh);

  2381. \end_layout

  2382. 

  2383. \end_inset

  2384. 

  2385. 

  2386. \end_layout

  2387. 

  2388. \begin_layout Standard

  2389. where 

  2390. \emph on

  2391. enh

  2392. \emph default

  2393.  is an int with value 0 to have the enhancer disabled and 1 to have it enabled.

  2394.  As of 1.2-beta1, the default is now to enable the enhancer.

  2395. \end_layout

  2396. 

  2397. \begin_layout Standard

  2398. Again, once the decoder initialization is done, for every input frame:

  2399. \end_layout

  2400. 

  2401. \begin_layout Standard

  2402. \begin_inset listings

  2403. inline false

  2404. status open

  2405. 

  2406. \begin_layout Plain Layout

  2407. 

  2408. speex_bits_read_from(&bits, input_bytes, nbBytes);

  2409. \end_layout

  2410. 

  2411. \begin_layout Plain Layout

  2412. 

  2413. speex_decode_int(dec_state, &bits, output_frame);

  2414. \end_layout

  2415. 

  2416. \end_inset

  2417. 

  2418. where input_bytes is a 

  2419. \emph on

  2420. (char *)

  2421. \emph default

  2422.  containing the bit-stream data received for a frame, 

  2423. \emph on

  2424. nbBytes

  2425. \emph default

  2426.  is the size (in bytes) of that bit-stream, and 

  2427. \emph on

  2428. output_frame

  2429. \emph default

  2430.  is a 

  2431. \emph on

  2432. (short *)

  2433. \emph default

  2434.  and points to the area where the decoded speech frame will be written.

  2435.  A NULL value as the second argument indicates that we don't have the bits

  2436.  for the current frame.

  2437.  When a frame is lost, the Speex decoder will do its best to "guess" the

  2438.  correct signal.

  2439. \end_layout

  2440. 

  2441. \begin_layout Standard

  2442. As for the encoder, the 

  2443. \emph on

  2444. speex_decode()

  2445. \emph default

  2446.  function can still be used, with a 

  2447. \emph on

  2448. (float *)

  2449. \emph default

  2450.  as the output for the audio.

  2451.  After you're done with the decoding, free all resources with:

  2452. \end_layout

  2453. 

  2454. \begin_layout Standard

  2455. \begin_inset listings

  2456. inline false

  2457. status open

  2458. 

  2459. \begin_layout Plain Layout

  2460. 

  2461. speex_bits_destroy(&bits);

  2462. \end_layout

  2463. 

  2464. \begin_layout Plain Layout

  2465. 

  2466. speex_decoder_destroy(dec_state);

  2467. \end_layout

  2468. 

  2469. \end_inset

  2470. 

  2471. 

  2472. \end_layout

  2473. 

  2474. \begin_layout Section

  2475. Codec Options (speex_*_ctl)

  2476. \begin_inset CommandInset label

  2477. LatexCommand label

  2478. name "sub:Codec-Options"

  2479. 

  2480. \end_inset

  2481. 

  2482. 

  2483. \end_layout

  2484. 

  2485. \begin_layout Quote

  2486. \align center

  2487. 

  2488. \emph on

  2489. Entities should not be multiplied beyond necessity -- William of Ockham.

  2490. \end_layout

  2491. 

  2492. \begin_layout Quote

  2493. \align center

  2494. 

  2495. \emph on

  2496. Just because there's an option for it doesn't mean you have to turn it on

  2497.  -- me.

  2498. \end_layout

  2499. 

  2500. \begin_layout Standard

  2501. The Speex encoder and decoder support many options and requests that can

  2502.  be accessed through the 

  2503. \emph on

  2504. speex_encoder_ctl

  2505. \emph default

  2506.  and 

  2507. \emph on

  2508. speex_decoder_ctl

  2509. \emph default

  2510.  functions.

  2511.  These functions are similar to the 

  2512. \emph on

  2513. ioctl

  2514. \emph default

  2515.  system call and their prototypes are:

  2516. \end_layout

  2517. 

  2518. \begin_layout Standard

  2519. \begin_inset listings

  2520. inline false

  2521. status open

  2522. 

  2523. \begin_layout Plain Layout

  2524. 

  2525. void speex_encoder_ctl(void *encoder, int request, void *ptr);

  2526. \end_layout

  2527. 

  2528. \begin_layout Plain Layout

  2529. 

  2530. void speex_decoder_ctl(void *encoder, int request, void *ptr);

  2531. \end_layout

  2532. 

  2533. \end_inset

  2534. 

  2535. 

  2536. \end_layout

  2537. 

  2538. \begin_layout Standard

  2539. Despite those functions, the defaults are usually good for many applications

  2540.  and 

  2541. \series bold

  2542. optional settings should only be used when one understands them and knows

  2543.  that they are needed

  2544. \series default

  2545. .

  2546.  A common error is to attempt to set many unnecessary settings.

  2547.  

  2548. \end_layout

  2549. 

  2550. \begin_layout Standard

  2551. Here is a list of the values allowed for the requests.

  2552.  Some only apply to the encoder or the decoder.

  2553.  Because the last argument is of type 

  2554. \begin_inset listings

  2555. inline true

  2556. status collapsed

  2557. 

  2558. \begin_layout Plain Layout

  2559. 

  2560. void *

  2561. \end_layout

  2562. 

  2563. \end_inset

  2564. 

  2565. , the 

  2566. \begin_inset listings

  2567. inline true

  2568. status collapsed

  2569. 

  2570. \begin_layout Plain Layout

  2571. 

  2572. _ctl()

  2573. \end_layout

  2574. 

  2575. \end_inset

  2576. 

  2577.  functions are 

  2578. \series bold

  2579. not type safe

  2580. \series default

  2581. , and should thus be used with care.

  2582.  The type 

  2583. \begin_inset listings

  2584. inline true

  2585. status collapsed

  2586. 

  2587. \begin_layout Plain Layout

  2588. 

  2589. spx_int32_t

  2590. \end_layout

  2591. 

  2592. \end_inset

  2593. 

  2594.  is the same as the C99 

  2595. \begin_inset listings

  2596. inline true

  2597. status collapsed

  2598. 

  2599. \begin_layout Plain Layout

  2600. 

  2601. int32_t

  2602. \end_layout

  2603. 

  2604. \end_inset

  2605. 

  2606.  type.

  2607. \end_layout

  2608. 

  2609. \begin_layout Description

  2610. SPEEX_SET_ENH

  2611. \begin_inset Formula $\ddagger$

  2612. \end_inset

  2613. 

  2614.  Set perceptual enhancer

  2615. \begin_inset Index

  2616. status collapsed

  2617. 

  2618. \begin_layout Plain Layout

  2619. perceptual enhancement

  2620. \end_layout

  2621. 

  2622. \end_inset

  2623. 

  2624.  to on (1) or off (0) (

  2625. \begin_inset listings

  2626. inline true

  2627. status collapsed

  2628. 

  2629. \begin_layout Plain Layout

  2630. 

  2631. spx_int32_t

  2632. \end_layout

  2633. 

  2634. \end_inset

  2635. 

  2636. , default is on)

  2637. \end_layout

  2638. 

  2639. \begin_layout Description

  2640. SPEEX_GET_ENH

  2641. \begin_inset Formula $\ddagger$

  2642. \end_inset

  2643. 

  2644.  Get perceptual enhancer status (

  2645. \begin_inset listings

  2646. inline true

  2647. status collapsed

  2648. 

  2649. \begin_layout Plain Layout

  2650. 

  2651. spx_int32_t

  2652. \end_layout

  2653. 

  2654. \end_inset

  2655. 

  2656. )

  2657. \end_layout

  2658. 

  2659. \begin_layout Description

  2660. SPEEX_GET_FRAME_SIZE Get the number of samples per frame for the current

  2661.  mode (

  2662. \begin_inset listings

  2663. inline true

  2664. status collapsed

  2665. 

  2666. \begin_layout Plain Layout

  2667. 

  2668. spx_int32_t

  2669. \end_layout

  2670. 

  2671. \end_inset

  2672. 

  2673. )

  2674. \end_layout

  2675. 

  2676. \begin_layout Description

  2677. SPEEX_SET_QUALITY

  2678. \begin_inset Formula $\dagger$

  2679. \end_inset

  2680. 

  2681.  Set the encoder speech quality (

  2682. \begin_inset listings

  2683. inline true

  2684. status collapsed

  2685. 

  2686. \begin_layout Plain Layout

  2687. 

  2688. spx_int32_t

  2689. \end_layout

  2690. 

  2691. \end_inset

  2692. 

  2693.  from 0 to 10, default is 8)

  2694. \end_layout

  2695. 

  2696. \begin_layout Description

  2697. SPEEX_GET_QUALITY

  2698. \begin_inset Formula $\dagger$

  2699. \end_inset

  2700. 

  2701.  Get the current encoder speech quality (

  2702. \begin_inset listings

  2703. inline true

  2704. status collapsed

  2705. 

  2706. \begin_layout Plain Layout

  2707. 

  2708. spx_int32_t

  2709. \end_layout

  2710. 

  2711. \end_inset

  2712. 

  2713.  from 0 to 10)

  2714. \end_layout

  2715. 

  2716. \begin_layout Description

  2717. SPEEX_SET_MODE

  2718. \begin_inset Formula $\dagger$

  2719. \end_inset

  2720. 

  2721.  Set the mode number, as specified in the RTP spec (

  2722. \begin_inset listings

  2723. inline true

  2724. status collapsed

  2725. 

  2726. \begin_layout Plain Layout

  2727. 

  2728. spx_int32_t

  2729. \end_layout

  2730. 

  2731. \end_inset

  2732. 

  2733. )

  2734. \end_layout

  2735. 

  2736. \begin_layout Description

  2737. SPEEX_GET_MODE

  2738. \begin_inset Formula $\dagger$

  2739. \end_inset

  2740. 

  2741.  Get the current mode number, as specified in the RTP spec (

  2742. \begin_inset listings

  2743. inline true

  2744. status collapsed

  2745. 

  2746. \begin_layout Plain Layout

  2747. 

  2748. spx_int32_t

  2749. \end_layout

  2750. 

  2751. \end_inset

  2752. 

  2753. )

  2754. \end_layout

  2755. 

  2756. \begin_layout Description

  2757. SPEEX_SET_VBR

  2758. \begin_inset Formula $\dagger$

  2759. \end_inset

  2760. 

  2761.  Set variable bit-rate (VBR) to on (1) or off (0) (

  2762. \begin_inset listings

  2763. inline true

  2764. status collapsed

  2765. 

  2766. \begin_layout Plain Layout

  2767. 

  2768. spx_int32_t

  2769. \end_layout

  2770. 

  2771. \end_inset

  2772. 

  2773. , default is off)

  2774. \end_layout

  2775. 

  2776. \begin_layout Description

  2777. SPEEX_GET_VBR

  2778. \begin_inset Formula $\dagger$

  2779. \end_inset

  2780. 

  2781.  Get variable bit-rate

  2782. \begin_inset Index

  2783. status collapsed

  2784. 

  2785. \begin_layout Plain Layout

  2786. variable bit-rate

  2787. \end_layout

  2788. 

  2789. \end_inset

  2790. 

  2791.  (VBR) status (

  2792. \begin_inset listings

  2793. inline true

  2794. status collapsed

  2795. 

  2796. \begin_layout Plain Layout

  2797. 

  2798. spx_int32_t

  2799. \end_layout

  2800. 

  2801. \end_inset

  2802. 

  2803. )

  2804. \end_layout

  2805. 

  2806. \begin_layout Description

  2807. SPEEX_SET_VBR_QUALITY

  2808. \begin_inset Formula $\dagger$

  2809. \end_inset

  2810. 

  2811.  Set the encoder VBR speech quality (float 0.0 to 10.0, default is 8.0)

  2812. \end_layout

  2813. 

  2814. \begin_layout Description

  2815. SPEEX_GET_VBR_QUALITY

  2816. \begin_inset Formula $\dagger$

  2817. \end_inset

  2818. 

  2819.  Get the current encoder VBR speech quality (float 0 to 10)

  2820. \end_layout

  2821. 

  2822. \begin_layout Description

  2823. SPEEX_SET_COMPLEXITY

  2824. \begin_inset Formula $\dagger$

  2825. \end_inset

  2826. 

  2827.  Set the CPU resources allowed for the encoder (

  2828. \begin_inset listings

  2829. inline true

  2830. status collapsed

  2831. 

  2832. \begin_layout Plain Layout

  2833. 

  2834. spx_int32_t

  2835. \end_layout

  2836. 

  2837. \end_inset

  2838. 

  2839.  from 1 to 10, default is 2)

  2840. \end_layout

  2841. 

  2842. \begin_layout Description

  2843. SPEEX_GET_COMPLEXITY

  2844. \begin_inset Formula $\dagger$

  2845. \end_inset

  2846. 

  2847.  Get the CPU resources allowed for the encoder (

  2848. \begin_inset listings

  2849. inline true

  2850. status collapsed

  2851. 

  2852. \begin_layout Plain Layout

  2853. 

  2854. spx_int32_t

  2855. \end_layout

  2856. 

  2857. \end_inset

  2858. 

  2859.  from 1 to 10, default is 2)

  2860. \end_layout

  2861. 

  2862. \begin_layout Description

  2863. SPEEX_SET_BITRATE

  2864. \begin_inset Formula $\dagger$

  2865. \end_inset

  2866. 

  2867.  Set the bit-rate to use the closest value not exceeding the parameter (

  2868. \begin_inset listings

  2869. inline true

  2870. status collapsed

  2871. 

  2872. \begin_layout Plain Layout

  2873. 

  2874. spx_int32_t

  2875. \end_layout

  2876. 

  2877. \end_inset

  2878. 

  2879.  in bits per second)

  2880. \end_layout

  2881. 

  2882. \begin_layout Description

  2883. SPEEX_GET_BITRATE Get the current bit-rate in use (

  2884. \begin_inset listings

  2885. inline true

  2886. status collapsed

  2887. 

  2888. \begin_layout Plain Layout

  2889. 

  2890. spx_int32_t

  2891. \end_layout

  2892. 

  2893. \end_inset

  2894. 

  2895.  in bits per second)

  2896. \end_layout

  2897. 

  2898. \begin_layout Description

  2899. SPEEX_SET_SAMPLING_RATE Set real sampling rate (

  2900. \begin_inset listings

  2901. inline true

  2902. status collapsed

  2903. 

  2904. \begin_layout Plain Layout

  2905. 

  2906. spx_int32_t

  2907. \end_layout

  2908. 

  2909. \end_inset

  2910. 

  2911.  in Hz)

  2912. \end_layout

  2913. 

  2914. \begin_layout Description

  2915. SPEEX_GET_SAMPLING_RATE Get real sampling rate (

  2916. \begin_inset listings

  2917. inline true

  2918. status collapsed

  2919. 

  2920. \begin_layout Plain Layout

  2921. 

  2922. spx_int32_t

  2923. \end_layout

  2924. 

  2925. \end_inset

  2926. 

  2927.  in Hz)

  2928. \end_layout

  2929. 

  2930. \begin_layout Description

  2931. SPEEX_RESET_STATE Reset the encoder/decoder state to its original state,

  2932.  clearing all memories (no argument)

  2933. \end_layout

  2934. 

  2935. \begin_layout Description

  2936. SPEEX_SET_VAD

  2937. \begin_inset Formula $\dagger$

  2938. \end_inset

  2939. 

  2940.  Set voice activity detection

  2941. \begin_inset Index

  2942. status collapsed

  2943. 

  2944. \begin_layout Plain Layout

  2945. voice activity detection

  2946. \end_layout

  2947. 

  2948. \end_inset

  2949. 

  2950.  (VAD) to on (1) or off (0) (

  2951. \begin_inset listings

  2952. inline true

  2953. status collapsed

  2954. 

  2955. \begin_layout Plain Layout

  2956. 

  2957. spx_int32_t

  2958. \end_layout

  2959. 

  2960. \end_inset

  2961. 

  2962. , default is off)

  2963. \end_layout

  2964. 

  2965. \begin_layout Description

  2966. SPEEX_GET_VAD

  2967. \begin_inset Formula $\dagger$

  2968. \end_inset

  2969. 

  2970.  Get voice activity detection (VAD) status (

  2971. \begin_inset listings

  2972. inline true

  2973. status collapsed

  2974. 

  2975. \begin_layout Plain Layout

  2976. 

  2977. spx_int32_t

  2978. \end_layout

  2979. 

  2980. \end_inset

  2981. 

  2982. )

  2983. \end_layout

  2984. 

  2985. \begin_layout Description

  2986. SPEEX_SET_DTX

  2987. \begin_inset Formula $\dagger$

  2988. \end_inset

  2989. 

  2990.  Set discontinuous transmission

  2991. \begin_inset Index

  2992. status collapsed

  2993. 

  2994. \begin_layout Plain Layout

  2995. discontinuous transmission

  2996. \end_layout

  2997. 

  2998. \end_inset

  2999. 

  3000.  (DTX) to on (1) or off (0) (

  3001. \begin_inset listings

  3002. inline true

  3003. status collapsed

  3004. 

  3005. \begin_layout Plain Layout

  3006. 

  3007. spx_int32_t

  3008. \end_layout

  3009. 

  3010. \end_inset

  3011. 

  3012. , default is off)

  3013. \end_layout

  3014. 

  3015. \begin_layout Description

  3016. SPEEX_GET_DTX

  3017. \begin_inset Formula $\dagger$

  3018. \end_inset

  3019. 

  3020.  Get discontinuous transmission (DTX) status (

  3021. \begin_inset listings

  3022. inline true

  3023. status collapsed

  3024. 

  3025. \begin_layout Plain Layout

  3026. 

  3027. spx_int32_t

  3028. \end_layout

  3029. 

  3030. \end_inset

  3031. 

  3032. )

  3033. \end_layout

  3034. 

  3035. \begin_layout Description

  3036. SPEEX_SET_ABR

  3037. \begin_inset Formula $\dagger$

  3038. \end_inset

  3039. 

  3040.  Set average bit-rate

  3041. \begin_inset Index

  3042. status collapsed

  3043. 

  3044. \begin_layout Plain Layout

  3045. average bit-rate

  3046. \end_layout

  3047. 

  3048. \end_inset

  3049. 

  3050.  (ABR) to a value n in bits per second (

  3051. \begin_inset listings

  3052. inline true

  3053. status collapsed

  3054. 

  3055. \begin_layout Plain Layout

  3056. 

  3057. spx_int32_t

  3058. \end_layout

  3059. 

  3060. \end_inset

  3061. 

  3062.  in bits per second)

  3063. \end_layout

  3064. 

  3065. \begin_layout Description

  3066. SPEEX_GET_ABR

  3067. \begin_inset Formula $\dagger$

  3068. \end_inset

  3069. 

  3070.  Get average bit-rate (ABR) setting (

  3071. \begin_inset listings

  3072. inline true

  3073. status collapsed

  3074. 

  3075. \begin_layout Plain Layout

  3076. 

  3077. spx_int32_t

  3078. \end_layout

  3079. 

  3080. \end_inset

  3081. 

  3082.  in bits per second)

  3083. \end_layout

  3084. 

  3085. \begin_layout Description

  3086. SPEEX_SET_PLC_TUNING

  3087. \begin_inset Formula $\dagger$

  3088. \end_inset

  3089. 

  3090.  Tell the encoder to optimize encoding for a certain percentage of packet

  3091.  loss (

  3092. \begin_inset listings

  3093. inline true

  3094. status collapsed

  3095. 

  3096. \begin_layout Plain Layout

  3097. 

  3098. spx_int32_t

  3099. \end_layout

  3100. 

  3101. \end_inset

  3102. 

  3103.  in percent)

  3104. \end_layout

  3105. 

  3106. \begin_layout Description

  3107. SPEEX_GET_PLC_TUNING

  3108. \begin_inset Formula $\dagger$

  3109. \end_inset

  3110. 

  3111.  Get the current tuning of the encoder for PLC (

  3112. \begin_inset listings

  3113. inline true

  3114. status collapsed

  3115. 

  3116. \begin_layout Plain Layout

  3117. 

  3118. spx_int32_t

  3119. \end_layout

  3120. 

  3121. \end_inset

  3122. 

  3123.  in percent)

  3124. \end_layout

  3125. 

  3126. \begin_layout Description

  3127. SPEEX_GET_LOOKAHEAD Returns the lookahead used by Speex separately for an

  3128.  encoder and a decoder.

  3129.  Sum encoder and decoder lookahead values to get the total codec lookahead.

  3130. \end_layout

  3131. 

  3132. \begin_layout Description

  3133. SPEEX_SET_VBR_MAX_BITRATE

  3134. \begin_inset Formula $\dagger$

  3135. \end_inset

  3136. 

  3137.  Set the maximum bit-rate allowed in VBR operation (

  3138. \begin_inset listings

  3139. inline true

  3140. status collapsed

  3141. 

  3142. \begin_layout Plain Layout

  3143. 

  3144. spx_int32_t

  3145. \end_layout

  3146. 

  3147. \end_inset

  3148. 

  3149.  in bits per second)

  3150. \end_layout

  3151. 

  3152. \begin_layout Description

  3153. SPEEX_GET_VBR_MAX_BITRATE

  3154. \begin_inset Formula $\dagger$

  3155. \end_inset

  3156. 

  3157.  Get the current maximum bit-rate allowed in VBR operation (

  3158. \begin_inset listings

  3159. inline true

  3160. status collapsed

  3161. 

  3162. \begin_layout Plain Layout

  3163. 

  3164. spx_int32_t

  3165. \end_layout

  3166. 

  3167. \end_inset

  3168. 

  3169.  in bits per second)

  3170. \end_layout

  3171. 

  3172. \begin_layout Description

  3173. SPEEX_SET_HIGHPASS Set the high-pass filter on (1) or off (0) (

  3174. \begin_inset listings

  3175. inline true

  3176. status collapsed

  3177. 

  3178. \begin_layout Plain Layout

  3179. 

  3180. spx_int32_t

  3181. \end_layout

  3182. 

  3183. \end_inset

  3184. 

  3185. , default is on)

  3186. \end_layout

  3187. 

  3188. \begin_layout Description

  3189. SPEEX_GET_HIGHPASS Get the current high-pass filter status (

  3190. \begin_inset listings

  3191. inline true

  3192. status collapsed

  3193. 

  3194. \begin_layout Plain Layout

  3195. 

  3196. spx_int32_t

  3197. \end_layout

  3198. 

  3199. \end_inset

  3200. 

  3201. )

  3202. \end_layout

  3203. 

  3204. \begin_layout Description

  3205. \begin_inset Formula $\dagger$

  3206. \end_inset

  3207. 

  3208.  applies only to the encoder

  3209. \end_layout

  3210. 

  3211. \begin_layout Description

  3212. \begin_inset Formula $\ddagger$

  3213. \end_inset

  3214. 

  3215.  applies only to the decoder

  3216. \end_layout

  3217. 

  3218. \begin_layout Section

  3219. Mode queries

  3220. \begin_inset CommandInset label

  3221. LatexCommand label

  3222. name "sub:Mode-queries"

  3223. 

  3224. \end_inset

  3225. 

  3226. 

  3227. \end_layout

  3228. 

  3229. \begin_layout Standard

  3230. Speex modes have a query system similar to the speex_encoder_ctl and speex_decod

  3231. er_ctl calls.

  3232.  Since modes are read-only, it is only possible to get information about

  3233.  a particular mode.

  3234.  The function used to do that is:

  3235. \begin_inset listings

  3236. inline false

  3237. status open

  3238. 

  3239. \begin_layout Plain Layout

  3240. 

  3241. void speex_mode_query(SpeexMode *mode, int request, void *ptr);

  3242. \end_layout

  3243. 

  3244. \end_inset

  3245. 

  3246. The admissible values for request are (unless otherwise note, the values

  3247.  are returned through 

  3248. \emph on

  3249. ptr

  3250. \emph default

  3251. ):

  3252. \end_layout

  3253. 

  3254. \begin_layout Description

  3255. SPEEX_MODE_FRAME_SIZE Get the frame size (in samples) for the mode

  3256. \end_layout

  3257. 

  3258. \begin_layout Description

  3259. SPEEX_SUBMODE_BITRATE Get the bit-rate for a submode number specified through

  3260.  

  3261. \emph on

  3262. ptr

  3263. \emph default

  3264.  (integer in bps).

  3265.  

  3266. \end_layout

  3267. 

  3268. \begin_layout Section

  3269. Packing and in-band signalling

  3270. \begin_inset Index

  3271. status collapsed

  3272. 

  3273. \begin_layout Plain Layout

  3274. in-band signalling

  3275. \end_layout

  3276. 

  3277. \end_inset

  3278. 

  3279. 

  3280. \end_layout

  3281. 

  3282. \begin_layout Standard

  3283. Sometimes it is desirable to pack more than one frame per packet (or other

  3284.  basic unit of storage).

  3285.  The proper way to do it is to call speex_encode 

  3286. \begin_inset Formula $N$

  3287. \end_inset

  3288. 

  3289.  times before writing the stream with speex_bits_write.

  3290.  In cases where the number of frames is not determined by an out-of-band

  3291.  mechanism, it is possible to include a terminator code.

  3292.  That terminator consists of the code 15 (decimal) encoded with 5 bits,

  3293.  as shown in Table 

  3294. \begin_inset CommandInset ref

  3295. LatexCommand ref

  3296. reference "cap:quality_vs_bps"

  3297. 

  3298. \end_inset

  3299. 

  3300. .

  3301.  Note that as of version 1.0.2, calling speex_bits_write automatically inserts

  3302.  the terminator so as to fill the last byte.

  3303.  This doesn't involves any overhead and makes sure Speex can always detect

  3304.  when there is no more frame in a packet.

  3305. \end_layout

  3306. 

  3307. \begin_layout Standard

  3308. It is also possible to send in-band 

  3309. \begin_inset Quotes eld

  3310. \end_inset

  3311. 

  3312. messages

  3313. \begin_inset Quotes erd

  3314. \end_inset

  3315. 

  3316.  to the other side.

  3317.  All these messages are encoded as 

  3318. \begin_inset Quotes eld

  3319. \end_inset

  3320. 

  3321. pseudo-frames

  3322. \begin_inset Quotes erd

  3323. \end_inset

  3324. 

  3325.  of mode 14 which contain a 4-bit message type code, followed by the message.

  3326.  Table 

  3327. \begin_inset CommandInset ref

  3328. LatexCommand ref

  3329. reference "cap:In-band-signalling-codes"

  3330. 

  3331. \end_inset

  3332. 

  3333.  lists the available codes, their meaning and the size of the message that

  3334.  follows.

  3335.  Most of these messages are requests that are sent to the encoder or decoder

  3336.  on the other end, which is free to comply or ignore them.

  3337.  By default, all in-band messages are ignored.

  3338. \end_layout

  3339. 

  3340. \begin_layout Standard

  3341. \begin_inset Float table

  3342. placement htbp

  3343. wide false

  3344. sideways false

  3345. status open

  3346. 

  3347. \begin_layout Plain Layout

  3348. \begin_inset ERT

  3349. status collapsed

  3350. 

  3351. \begin_layout Plain Layout

  3352. 

  3353. 

  3354. \backslash

  3355. begin{center}

  3356. \end_layout

  3357. 

  3358. \end_inset

  3359. 

  3360. 

  3361. \begin_inset Tabular

  3362. <lyxtabular version="3" rows="17" columns="3">

  3363. <features>

  3364. <column alignment="center" valignment="top" width="0pt">

  3365. <column alignment="center" valignment="top" width="0pt">

  3366. <column alignment="center" valignment="top" width="0pt">

  3367. <row>

  3368. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  3369. \begin_inset Text

  3370. 

  3371. \begin_layout Plain Layout

  3372. Code

  3373. \end_layout

  3374. 

  3375. \end_inset

  3376. </cell>

  3377. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  3378. \begin_inset Text

  3379. 

  3380. \begin_layout Plain Layout

  3381. Size (bits)

  3382. \end_layout

  3383. 

  3384. \end_inset

  3385. </cell>

  3386. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">

  3387. \begin_inset Text

  3388. 

  3389. \begin_layout Plain Layout

  3390. Content

  3391. \end_layout

  3392. 

  3393. \end_inset

  3394. </cell>

  3395. </row>

  3396. <row>

  3397. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3398. \begin_inset Text

  3399. 

  3400. \begin_layout Plain Layout

  3401. 0

  3402. \end_layout

  3403. 

  3404. \end_inset

  3405. </cell>

  3406. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3407. \begin_inset Text

  3408. 

  3409. \begin_layout Plain Layout

  3410. 1

  3411. \end_layout

  3412. 

  3413. \end_inset

  3414. </cell>

  3415. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3416. \begin_inset Text

  3417. 

  3418. \begin_layout Plain Layout

  3419. Asks decoder to set perceptual enhancement off (0) or on(1)

  3420. \end_layout

  3421. 

  3422. \end_inset

  3423. </cell>

  3424. </row>

  3425. <row>

  3426. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3427. \begin_inset Text

  3428. 

  3429. \begin_layout Plain Layout

  3430. 1

  3431. \end_layout

  3432. 

  3433. \end_inset

  3434. </cell>

  3435. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3436. \begin_inset Text

  3437. 

  3438. \begin_layout Plain Layout

  3439. 1

  3440. \end_layout

  3441. 

  3442. \end_inset

  3443. </cell>

  3444. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3445. \begin_inset Text

  3446. 

  3447. \begin_layout Plain Layout

  3448. Asks (if 1) the encoder to be less 

  3449. \begin_inset Quotes eld

  3450. \end_inset

  3451. 

  3452. aggressive

  3453. \begin_inset Quotes erd

  3454. \end_inset

  3455. 

  3456.  due to high packet loss

  3457. \end_layout

  3458. 

  3459. \end_inset

  3460. </cell>

  3461. </row>

  3462. <row>

  3463. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3464. \begin_inset Text

  3465. 

  3466. \begin_layout Plain Layout

  3467. 2

  3468. \end_layout

  3469. 

  3470. \end_inset

  3471. </cell>

  3472. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3473. \begin_inset Text

  3474. 

  3475. \begin_layout Plain Layout

  3476. 4

  3477. \end_layout

  3478. 

  3479. \end_inset

  3480. </cell>

  3481. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3482. \begin_inset Text

  3483. 

  3484. \begin_layout Plain Layout

  3485. Asks encoder to switch to mode N

  3486. \end_layout

  3487. 

  3488. \end_inset

  3489. </cell>

  3490. </row>

  3491. <row>

  3492. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3493. \begin_inset Text

  3494. 

  3495. \begin_layout Plain Layout

  3496. 3

  3497. \end_layout

  3498. 

  3499. \end_inset

  3500. </cell>

  3501. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3502. \begin_inset Text

  3503. 

  3504. \begin_layout Plain Layout

  3505. 4

  3506. \end_layout

  3507. 

  3508. \end_inset

  3509. </cell>

  3510. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3511. \begin_inset Text

  3512. 

  3513. \begin_layout Plain Layout

  3514. Asks encoder to switch to mode N for low-band

  3515. \end_layout

  3516. 

  3517. \end_inset

  3518. </cell>

  3519. </row>

  3520. <row>

  3521. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3522. \begin_inset Text

  3523. 

  3524. \begin_layout Plain Layout

  3525. 4

  3526. \end_layout

  3527. 

  3528. \end_inset

  3529. </cell>

  3530. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3531. \begin_inset Text

  3532. 

  3533. \begin_layout Plain Layout

  3534. 4

  3535. \end_layout

  3536. 

  3537. \end_inset

  3538. </cell>

  3539. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3540. \begin_inset Text

  3541. 

  3542. \begin_layout Plain Layout

  3543. Asks encoder to switch to mode N for high-band

  3544. \end_layout

  3545. 

  3546. \end_inset

  3547. </cell>

  3548. </row>

  3549. <row>

  3550. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3551. \begin_inset Text

  3552. 

  3553. \begin_layout Plain Layout

  3554. 5

  3555. \end_layout

  3556. 

  3557. \end_inset

  3558. </cell>

  3559. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3560. \begin_inset Text

  3561. 

  3562. \begin_layout Plain Layout

  3563. 4

  3564. \end_layout

  3565. 

  3566. \end_inset

  3567. </cell>

  3568. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3569. \begin_inset Text

  3570. 

  3571. \begin_layout Plain Layout

  3572. Asks encoder to switch to quality N for VBR

  3573. \end_layout

  3574. 

  3575. \end_inset

  3576. </cell>

  3577. </row>

  3578. <row>

  3579. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3580. \begin_inset Text

  3581. 

  3582. \begin_layout Plain Layout

  3583. 6

  3584. \end_layout

  3585. 

  3586. \end_inset

  3587. </cell>

  3588. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3589. \begin_inset Text

  3590. 

  3591. \begin_layout Plain Layout

  3592. 4

  3593. \end_layout

  3594. 

  3595. \end_inset

  3596. </cell>

  3597. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3598. \begin_inset Text

  3599. 

  3600. \begin_layout Plain Layout

  3601. Request acknowledge (0=no, 1=all, 2=only for in-band data)

  3602. \end_layout

  3603. 

  3604. \end_inset

  3605. </cell>

  3606. </row>

  3607. <row>

  3608. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3609. \begin_inset Text

  3610. 

  3611. \begin_layout Plain Layout

  3612. 7

  3613. \end_layout

  3614. 

  3615. \end_inset

  3616. </cell>

  3617. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3618. \begin_inset Text

  3619. 

  3620. \begin_layout Plain Layout

  3621. 4

  3622. \end_layout

  3623. 

  3624. \end_inset

  3625. </cell>

  3626. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3627. \begin_inset Text

  3628. 

  3629. \begin_layout Plain Layout

  3630. Asks encoder to set CBR (0), VAD(1), DTX(3), VBR(5), VBR+DTX(7)

  3631. \end_layout

  3632. 

  3633. \end_inset

  3634. </cell>

  3635. </row>

  3636. <row>

  3637. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3638. \begin_inset Text

  3639. 

  3640. \begin_layout Plain Layout

  3641. 8

  3642. \end_layout

  3643. 

  3644. \end_inset

  3645. </cell>

  3646. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3647. \begin_inset Text

  3648. 

  3649. \begin_layout Plain Layout

  3650. 8

  3651. \end_layout

  3652. 

  3653. \end_inset

  3654. </cell>

  3655. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3656. \begin_inset Text

  3657. 

  3658. \begin_layout Plain Layout

  3659. Transmit (8-bit) character to the other end

  3660. \end_layout

  3661. 

  3662. \end_inset

  3663. </cell>

  3664. </row>

  3665. <row>

  3666. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3667. \begin_inset Text

  3668. 

  3669. \begin_layout Plain Layout

  3670. 9

  3671. \end_layout

  3672. 

  3673. \end_inset

  3674. </cell>

  3675. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3676. \begin_inset Text

  3677. 

  3678. \begin_layout Plain Layout

  3679. 8

  3680. \end_layout

  3681. 

  3682. \end_inset

  3683. </cell>

  3684. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3685. \begin_inset Text

  3686. 

  3687. \begin_layout Plain Layout

  3688. Intensity stereo information

  3689. \end_layout

  3690. 

  3691. \end_inset

  3692. </cell>

  3693. </row>

  3694. <row>

  3695. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3696. \begin_inset Text

  3697. 

  3698. \begin_layout Plain Layout

  3699. 10

  3700. \end_layout

  3701. 

  3702. \end_inset

  3703. </cell>

  3704. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3705. \begin_inset Text

  3706. 

  3707. \begin_layout Plain Layout

  3708. 16

  3709. \end_layout

  3710. 

  3711. \end_inset

  3712. </cell>

  3713. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3714. \begin_inset Text

  3715. 

  3716. \begin_layout Plain Layout

  3717. Announce maximum bit-rate acceptable (N in bytes/second)

  3718. \end_layout

  3719. 

  3720. \end_inset

  3721. </cell>

  3722. </row>

  3723. <row>

  3724. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3725. \begin_inset Text

  3726. 

  3727. \begin_layout Plain Layout

  3728. 11

  3729. \end_layout

  3730. 

  3731. \end_inset

  3732. </cell>

  3733. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3734. \begin_inset Text

  3735. 

  3736. \begin_layout Plain Layout

  3737. 16

  3738. \end_layout

  3739. 

  3740. \end_inset

  3741. </cell>

  3742. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3743. \begin_inset Text

  3744. 

  3745. \begin_layout Plain Layout

  3746. reserved

  3747. \end_layout

  3748. 

  3749. \end_inset

  3750. </cell>

  3751. </row>

  3752. <row>

  3753. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3754. \begin_inset Text

  3755. 

  3756. \begin_layout Plain Layout

  3757. 12

  3758. \end_layout

  3759. 

  3760. \end_inset

  3761. </cell>

  3762. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3763. \begin_inset Text

  3764. 

  3765. \begin_layout Plain Layout

  3766. 32

  3767. \end_layout

  3768. 

  3769. \end_inset

  3770. </cell>

  3771. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3772. \begin_inset Text

  3773. 

  3774. \begin_layout Plain Layout

  3775. Acknowledge receiving packet N

  3776. \end_layout

  3777. 

  3778. \end_inset

  3779. </cell>

  3780. </row>

  3781. <row>

  3782. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3783. \begin_inset Text

  3784. 

  3785. \begin_layout Plain Layout

  3786. 13

  3787. \end_layout

  3788. 

  3789. \end_inset

  3790. </cell>

  3791. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3792. \begin_inset Text

  3793. 

  3794. \begin_layout Plain Layout

  3795. 32

  3796. \end_layout

  3797. 

  3798. \end_inset

  3799. </cell>

  3800. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3801. \begin_inset Text

  3802. 

  3803. \begin_layout Plain Layout

  3804. reserved

  3805. \end_layout

  3806. 

  3807. \end_inset

  3808. </cell>

  3809. </row>

  3810. <row>

  3811. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3812. \begin_inset Text

  3813. 

  3814. \begin_layout Plain Layout

  3815. 14

  3816. \end_layout

  3817. 

  3818. \end_inset

  3819. </cell>

  3820. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  3821. \begin_inset Text

  3822. 

  3823. \begin_layout Plain Layout

  3824. 64

  3825. \end_layout

  3826. 

  3827. \end_inset

  3828. </cell>

  3829. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  3830. \begin_inset Text

  3831. 

  3832. \begin_layout Plain Layout

  3833. reserved

  3834. \end_layout

  3835. 

  3836. \end_inset

  3837. </cell>

  3838. </row>

  3839. <row>

  3840. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  3841. \begin_inset Text

  3842. 

  3843. \begin_layout Plain Layout

  3844. 15

  3845. \end_layout

  3846. 

  3847. \end_inset

  3848. </cell>

  3849. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  3850. \begin_inset Text

  3851. 

  3852. \begin_layout Plain Layout

  3853. 64

  3854. \end_layout

  3855. 

  3856. \end_inset

  3857. </cell>

  3858. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">

  3859. \begin_inset Text

  3860. 

  3861. \begin_layout Plain Layout

  3862. reserved

  3863. \end_layout

  3864. 

  3865. \end_inset

  3866. </cell>

  3867. </row>

  3868. </lyxtabular>

  3869. 

  3870. \end_inset

  3871. 

  3872. 

  3873. \begin_inset ERT

  3874. status collapsed

  3875. 

  3876. \begin_layout Plain Layout

  3877. 

  3878. 

  3879. \backslash

  3880. end{center}

  3881. \end_layout

  3882. 

  3883. \end_inset

  3884. 

  3885. 

  3886. \end_layout

  3887. 

  3888. \begin_layout Plain Layout

  3889. \begin_inset Caption

  3890. 

  3891. \begin_layout Plain Layout

  3892. In-band signalling codes

  3893. \begin_inset CommandInset label

  3894. LatexCommand label

  3895. name "cap:In-band-signalling-codes"

  3896. 

  3897. \end_inset

  3898. 

  3899. 

  3900. \end_layout

  3901. 

  3902. \end_inset

  3903. 

  3904. 

  3905. \end_layout

  3906. 

  3907. \end_inset

  3908. 

  3909. 

  3910. \end_layout

  3911. 

  3912. \begin_layout Standard

  3913. Finally, applications may define custom in-band messages using mode 13.

  3914.  The size of the message in bytes is encoded with 5 bits, so that the decoder

  3915.  can skip it if it doesn't know how to interpret it.

  3916. \begin_inset Newpage newpage

  3917. \end_inset

  3918. 

  3919. 

  3920. \end_layout

  3921. 

  3922. \begin_layout Chapter

  3923. Speech Processing API (

  3924. \emph on

  3925. libspeexdsp

  3926. \emph default

  3927. )

  3928. \end_layout

  3929. 

  3930. \begin_layout Standard

  3931. As of version 1.2beta3, the non-codec parts of the Speex package are now

  3932.  in a separate library called 

  3933. \emph on

  3934. libspeexdsp

  3935. \emph default

  3936. .

  3937.  This library includes the preprocessor, the acoustic echo canceller, the

  3938.  jitter buffer, and the resampler.

  3939.  In a UNIX environment, it can be linked into a program by adding 

  3940. \emph on

  3941. -lspeexdsp -lm

  3942. \emph default

  3943.  to the compiler command line.

  3944.  Just like for libspeex, 

  3945. \series bold

  3946. libspeexdsp calls are reentrant, but not thread-safe

  3947. \series default

  3948. .

  3949.  That means that it is fine to use calls from many threads, but 

  3950. \series bold

  3951. calls using the same state from multiple threads must be protected by mutexes

  3952. \series default

  3953. .

  3954. \end_layout

  3955. 

  3956. \begin_layout Section

  3957. Preprocessor

  3958. \begin_inset CommandInset label

  3959. LatexCommand label

  3960. name "sub:Preprocessor"

  3961. 

  3962. \end_inset

  3963. 

  3964. 

  3965. \end_layout

  3966. 

  3967. \begin_layout Standard

  3968. \noindent

  3969. In order to use the Speex preprocessor

  3970. \begin_inset Index

  3971. status collapsed

  3972. 

  3973. \begin_layout Plain Layout

  3974. preprocessor

  3975. \end_layout

  3976. 

  3977. \end_inset

  3978. 

  3979. , you first need to:

  3980. \begin_inset listings

  3981. inline false

  3982. status open

  3983. 

  3984. \begin_layout Plain Layout

  3985. 

  3986. #include <speex/speex_preprocess.h>

  3987. \end_layout

  3988. 

  3989. \end_inset

  3990. 

  3991. 

  3992. \end_layout

  3993. 

  3994. \begin_layout Standard

  3995. \noindent

  3996. Then, a preprocessor state can be created as:

  3997. \begin_inset listings

  3998. inline false

  3999. status open

  4000. 

  4001. \begin_layout Plain Layout

  4002. 

  4003. SpeexPreprocessState *preprocess_state = speex_preprocess_state_init(frame_size,

  4004.  sampling_rate);

  4005. \end_layout

  4006. 

  4007. \end_inset

  4008. 

  4009. 

  4010. \end_layout

  4011. 

  4012. \begin_layout Standard

  4013. \noindent

  4014. and it is recommended to use the same value for 

  4015. \family typewriter

  4016. frame_size

  4017. \family default

  4018.  as is used by the encoder (20 

  4019. \emph on

  4020. ms

  4021. \emph default

  4022. ).

  4023. \end_layout

  4024. 

  4025. \begin_layout Standard

  4026. For each input frame, you need to call:

  4027. \end_layout

  4028. 

  4029. \begin_layout Standard

  4030. \begin_inset listings

  4031. inline false

  4032. status open

  4033. 

  4034. \begin_layout Plain Layout

  4035. 

  4036. speex_preprocess_run(preprocess_state, audio_frame);

  4037. \end_layout

  4038. 

  4039. \end_inset

  4040. 

  4041. 

  4042. \end_layout

  4043. 

  4044. \begin_layout Standard

  4045. \noindent

  4046. where 

  4047. \family typewriter

  4048. audio_frame

  4049. \family default

  4050.  is used both as input and output.

  4051.  In cases where the output audio is not useful for a certain frame, it is

  4052.  possible to use instead:

  4053. \end_layout

  4054. 

  4055. \begin_layout Standard

  4056. \begin_inset listings

  4057. inline false

  4058. status open

  4059. 

  4060. \begin_layout Plain Layout

  4061. 

  4062. speex_preprocess_estimate_update(preprocess_state, audio_frame);

  4063. \end_layout

  4064. 

  4065. \end_inset

  4066. 

  4067. 

  4068. \end_layout

  4069. 

  4070. \begin_layout Standard

  4071. \noindent

  4072. This call will update all the preprocessor internal state variables without

  4073.  computing the output audio, thus saving some CPU cycles.

  4074. \end_layout

  4075. 

  4076. \begin_layout Standard

  4077. The behaviour of the preprocessor can be changed using:

  4078. \end_layout

  4079. 

  4080. \begin_layout Standard

  4081. \begin_inset listings

  4082. inline false

  4083. status open

  4084. 

  4085. \begin_layout Plain Layout

  4086. 

  4087. speex_preprocess_ctl(preprocess_state, request, ptr);

  4088. \end_layout

  4089. 

  4090. \end_inset

  4091. 

  4092. 

  4093. \end_layout

  4094. 

  4095. \begin_layout Standard

  4096. \noindent

  4097. which is used in the same way as the encoder and decoder equivalent.

  4098.  Options are listed in Section 

  4099. \begin_inset CommandInset ref

  4100. LatexCommand ref

  4101. reference "sub:Preprocessor-options"

  4102. 

  4103. \end_inset

  4104. 

  4105. .

  4106. \end_layout

  4107. 

  4108. \begin_layout Standard

  4109. The preprocessor state can be destroyed using:

  4110. \end_layout

  4111. 

  4112. \begin_layout Standard

  4113. \begin_inset listings

  4114. inline false

  4115. status open

  4116. 

  4117. \begin_layout Plain Layout

  4118. 

  4119. speex_preprocess_state_destroy(preprocess_state);

  4120. \end_layout

  4121. 

  4122. \end_inset

  4123. 

  4124. 

  4125. \end_layout

  4126. 

  4127. \begin_layout Subsection

  4128. Preprocessor options

  4129. \begin_inset CommandInset label

  4130. LatexCommand label

  4131. name "sub:Preprocessor-options"

  4132. 

  4133. \end_inset

  4134. 

  4135. 

  4136. \end_layout

  4137. 

  4138. \begin_layout Standard

  4139. As with the codec, the preprocessor also has options that can be controlled

  4140.  using an ioctl()-like call.

  4141.  The available options are:

  4142. \end_layout

  4143. 

  4144. \begin_layout Description

  4145. SPEEX_PREPROCESS_SET_DENOISE Turns denoising on(1) or off(0) (

  4146. \begin_inset listings

  4147. inline true

  4148. status collapsed

  4149. 

  4150. \begin_layout Plain Layout

  4151. 

  4152. spx_int32_t

  4153. \end_layout

  4154. 

  4155. \end_inset

  4156. 

  4157. )

  4158. \end_layout

  4159. 

  4160. \begin_layout Description

  4161. SPEEX_PREPROCESS_GET_DENOISE Get denoising status (

  4162. \begin_inset listings

  4163. inline true

  4164. status collapsed

  4165. 

  4166. \begin_layout Plain Layout

  4167. 

  4168. spx_int32_t

  4169. \end_layout

  4170. 

  4171. \end_inset

  4172. 

  4173. )

  4174. \end_layout

  4175. 

  4176. \begin_layout Description

  4177. SPEEX_PREPROCESS_SET_AGC Turns automatic gain control (AGC) on(1) or off(0)

  4178.  (

  4179. \begin_inset listings

  4180. inline true

  4181. status collapsed

  4182. 

  4183. \begin_layout Plain Layout

  4184. 

  4185. spx_int32_t

  4186. \end_layout

  4187. 

  4188. \end_inset

  4189. 

  4190. )

  4191. \end_layout

  4192. 

  4193. \begin_layout Description

  4194. SPEEX_PREPROCESS_GET_AGC Get AGC status (

  4195. \begin_inset listings

  4196. inline true

  4197. status collapsed

  4198. 

  4199. \begin_layout Plain Layout

  4200. 

  4201. spx_int32_t

  4202. \end_layout

  4203. 

  4204. \end_inset

  4205. 

  4206. )

  4207. \end_layout

  4208. 

  4209. \begin_layout Description

  4210. SPEEX_PREPROCESS_SET_VAD Turns voice activity detector (VAD) on(1) or off(0)

  4211.  (

  4212. \begin_inset listings

  4213. inline true

  4214. status collapsed

  4215. 

  4216. \begin_layout Plain Layout

  4217. 

  4218. spx_int32_t

  4219. \end_layout

  4220. 

  4221. \end_inset

  4222. 

  4223. )

  4224. \end_layout

  4225. 

  4226. \begin_layout Description

  4227. SPEEX_PREPROCESS_GET_VAD Get VAD status (

  4228. \begin_inset listings

  4229. inline true

  4230. status collapsed

  4231. 

  4232. \begin_layout Plain Layout

  4233. 

  4234. spx_int32_t

  4235. \end_layout

  4236. 

  4237. \end_inset

  4238. 

  4239. )

  4240. \end_layout

  4241. 

  4242. \begin_layout Description

  4243. SPEEX_PREPROCESS_SET_AGC_LEVEL

  4244. \end_layout

  4245. 

  4246. \begin_layout Description

  4247. SPEEX_PREPROCESS_GET_AGC_LEVEL

  4248. \end_layout

  4249. 

  4250. \begin_layout Description

  4251. SPEEX_PREPROCESS_SET_DEREVERB Turns reverberation removal on(1) or off(0)

  4252.  (

  4253. \begin_inset listings

  4254. inline true

  4255. status collapsed

  4256. 

  4257. \begin_layout Plain Layout

  4258. 

  4259. spx_int32_t

  4260. \end_layout

  4261. 

  4262. \end_inset

  4263. 

  4264. )

  4265. \end_layout

  4266. 

  4267. \begin_layout Description

  4268. SPEEX_PREPROCESS_GET_DEREVERB Get reverberation removal status (

  4269. \begin_inset listings

  4270. inline true

  4271. status collapsed

  4272. 

  4273. \begin_layout Plain Layout

  4274. 

  4275. spx_int32_t

  4276. \end_layout

  4277. 

  4278. \end_inset

  4279. 

  4280. )

  4281. \end_layout

  4282. 

  4283. \begin_layout Description

  4284. SPEEX_PREPROCESS_SET_DEREVERB_LEVEL Not working yet, do not use

  4285. \end_layout

  4286. 

  4287. \begin_layout Description

  4288. SPEEX_PREPROCESS_GET_DEREVERB_LEVEL Not working yet, do not use

  4289. \end_layout

  4290. 

  4291. \begin_layout Description

  4292. SPEEX_PREPROCESS_SET_DEREVERB_DECAY Not working yet, do not use

  4293. \end_layout

  4294. 

  4295. \begin_layout Description

  4296. SPEEX_PREPROCESS_GET_DEREVERB_DECAY Not working yet, do not use

  4297. \end_layout

  4298. 

  4299. \begin_layout Description

  4300. SPEEX_PREPROCESS_SET_PROB_START

  4301. \end_layout

  4302. 

  4303. \begin_layout Description

  4304. SPEEX_PREPROCESS_GET_PROB_START

  4305. \end_layout

  4306. 

  4307. \begin_layout Description

  4308. SPEEX_PREPROCESS_SET_PROB_CONTINUE

  4309. \end_layout

  4310. 

  4311. \begin_layout Description

  4312. SPEEX_PREPROCESS_GET_PROB_CONTINUE

  4313. \end_layout

  4314. 

  4315. \begin_layout Description

  4316. SPEEX_PREPROCESS_SET_NOISE_SUPPRESS Set maximum attenuation of the noise

  4317.  in dB (negative 

  4318. \begin_inset listings

  4319. inline true

  4320. status collapsed

  4321. 

  4322. \begin_layout Plain Layout

  4323. 

  4324. spx_int32_t

  4325. \end_layout

  4326. 

  4327. \end_inset

  4328. 

  4329. )

  4330. \end_layout

  4331. 

  4332. \begin_layout Description

  4333. SPEEX_PREPROCESS_GET_NOISE_SUPPRESS Get maximum attenuation of the noise

  4334.  in dB (negative 

  4335. \begin_inset listings

  4336. inline true

  4337. status collapsed

  4338. 

  4339. \begin_layout Plain Layout

  4340. 

  4341. spx_int32_t

  4342. \end_layout

  4343. 

  4344. \end_inset

  4345. 

  4346. )

  4347. \end_layout

  4348. 

  4349. \begin_layout Description

  4350. SPEEX_PREPROCESS_SET_ECHO_SUPPRESS Set maximum attenuation of the residual

  4351.  echo in dB (negative 

  4352. \begin_inset listings

  4353. inline true

  4354. status collapsed

  4355. 

  4356. \begin_layout Plain Layout

  4357. 

  4358. spx_int32_t

  4359. \end_layout

  4360. 

  4361. \end_inset

  4362. 

  4363. )

  4364. \end_layout

  4365. 

  4366. \begin_layout Description

  4367. SPEEX_PREPROCESS_GET_ECHO_SUPPRESS Get maximum attenuation of the residual

  4368.  echo in dB (negative 

  4369. \begin_inset listings

  4370. inline true

  4371. status collapsed

  4372. 

  4373. \begin_layout Plain Layout

  4374. 

  4375. spx_int32_t

  4376. \end_layout

  4377. 

  4378. \end_inset

  4379. 

  4380. )

  4381. \end_layout

  4382. 

  4383. \begin_layout Description

  4384. SPEEX_PREPROCESS_SET_ECHO_SUPPRESS_ACTIVE Set maximum attenuation of the

  4385.  echo in dB when near end is active (negative 

  4386. \begin_inset listings

  4387. inline true

  4388. status collapsed

  4389. 

  4390. \begin_layout Plain Layout

  4391. 

  4392. spx_int32_t

  4393. \end_layout

  4394. 

  4395. \end_inset

  4396. 

  4397. )

  4398. \end_layout

  4399. 

  4400. \begin_layout Description

  4401. SPEEX_PREPROCESS_GET_ECHO_SUPPRESS_ACTIVE Get maximum attenuation of the

  4402.  echo in dB when near end is active (negative 

  4403. \begin_inset listings

  4404. inline true

  4405. status collapsed

  4406. 

  4407. \begin_layout Plain Layout

  4408. 

  4409. spx_int32_t

  4410. \end_layout

  4411. 

  4412. \end_inset

  4413. 

  4414. )

  4415. \end_layout

  4416. 

  4417. \begin_layout Description

  4418. SPEEX_PREPROCESS_SET_ECHO_STATE Set the associated echo canceller for residual

  4419.  echo suppression (pointer or NULL for no residual echo suppression)

  4420. \end_layout

  4421. 

  4422. \begin_layout Description

  4423. SPEEX_PREPROCESS_GET_ECHO_STATE Get the associated echo canceller (pointer)

  4424. \end_layout

  4425. 

  4426. \begin_layout Section

  4427. Echo Cancellation

  4428. \begin_inset CommandInset label

  4429. LatexCommand label

  4430. name "sub:Echo-Cancellation"

  4431. 

  4432. \end_inset

  4433. 

  4434. 

  4435. \end_layout

  4436. 

  4437. \begin_layout Standard

  4438. The Speex library now includes an echo cancellation

  4439. \begin_inset Index

  4440. status collapsed

  4441. 

  4442. \begin_layout Plain Layout

  4443. echo cancellation

  4444. \end_layout

  4445. 

  4446. \end_inset

  4447. 

  4448.  algorithm suitable for Acoustic Echo Cancellation

  4449. \begin_inset Index

  4450. status collapsed

  4451. 

  4452. \begin_layout Plain Layout

  4453. acoustic echo cancellation

  4454. \end_layout

  4455. 

  4456. \end_inset

  4457. 

  4458.  (AEC).

  4459.  In order to use the echo canceller, you first need to

  4460. \end_layout

  4461. 

  4462. \begin_layout Standard

  4463. \begin_inset listings

  4464. inline false

  4465. status open

  4466. 

  4467. \begin_layout Plain Layout

  4468. 

  4469. #include <speex/speex_echo.h>

  4470. \end_layout

  4471. 

  4472. \end_inset

  4473. 

  4474. 

  4475. \end_layout

  4476. 

  4477. \begin_layout Standard

  4478. Then, an echo canceller state can be created by:

  4479. \end_layout

  4480. 

  4481. \begin_layout Standard

  4482. \begin_inset listings

  4483. inline false

  4484. status open

  4485. 

  4486. \begin_layout Plain Layout

  4487. 

  4488. SpeexEchoState *echo_state = speex_echo_state_init(frame_size, filter_length);

  4489. \end_layout

  4490. 

  4491. \end_inset

  4492. 

  4493. 

  4494. \end_layout

  4495. 

  4496. \begin_layout Standard

  4497. where 

  4498. \family typewriter

  4499. frame_size

  4500. \family default

  4501.  is the amount of data (in samples) you want to process at once and 

  4502. \family typewriter

  4503. filter_length

  4504. \family default

  4505.  is the length (in samples) of the echo cancelling filter you want to use

  4506.  (also known as 

  4507. \shape italic

  4508. tail length

  4509. \shape default

  4510. 

  4511. \begin_inset Index

  4512. status collapsed

  4513. 

  4514. \begin_layout Plain Layout

  4515. tail length

  4516. \end_layout

  4517. 

  4518. \end_inset

  4519. 

  4520. ).

  4521.  It is recommended to use a frame size in the order of 20 ms (or equal to

  4522.  the codec frame size) and make sure it is easy to perform an FFT of that

  4523.  size (powers of two are better than prime sizes).

  4524.  The recommended tail length is approximately the third of the room reverberatio

  4525. n time.

  4526.  For example, in a small room, reverberation time is in the order of 300

  4527.  ms, so a tail length of 100 ms is a good choice (800 samples at 8000 Hz

  4528.  sampling rate).

  4529. \end_layout

  4530. 

  4531. \begin_layout Standard

  4532. Once the echo canceller state is created, audio can be processed by:

  4533. \end_layout

  4534. 

  4535. \begin_layout Standard

  4536. \begin_inset listings

  4537. inline false

  4538. status open

  4539. 

  4540. \begin_layout Plain Layout

  4541. 

  4542. speex_echo_cancellation(echo_state, input_frame, echo_frame, output_frame);

  4543. \end_layout

  4544. 

  4545. \end_inset

  4546. 

  4547. 

  4548. \end_layout

  4549. 

  4550. \begin_layout Standard

  4551. where 

  4552. \family typewriter

  4553. input_frame

  4554. \family default

  4555.  is the audio as captured by the microphone, 

  4556. \family typewriter

  4557. echo_frame

  4558. \family default

  4559.  is the signal that was played in the speaker (and needs to be removed)

  4560.  and 

  4561. \family typewriter

  4562. output_frame

  4563. \family default

  4564.  is the signal with echo removed.

  4565.  

  4566. \end_layout

  4567. 

  4568. \begin_layout Standard

  4569. One important thing to keep in mind is the relationship between 

  4570. \family typewriter

  4571. input_frame

  4572. \family default

  4573.  and 

  4574. \family typewriter

  4575. echo_frame

  4576. \family default

  4577. .

  4578.  It is important that, at any time, any echo that is present in the input

  4579.  has already been sent to the echo canceller as 

  4580. \family typewriter

  4581. echo_frame

  4582. \family default

  4583. .

  4584.  In other words, the echo canceller cannot remove a signal that it hasn't

  4585.  yet received.

  4586.  On the other hand, the delay between the input signal and the echo signal

  4587.  must be small enough because otherwise part of the echo cancellation filter

  4588.  is inefficient.

  4589.  In the ideal case, you code would look like:

  4590. \begin_inset listings

  4591. lstparams "breaklines=true"

  4592. inline false

  4593. status open

  4594. 

  4595. \begin_layout Plain Layout

  4596. 

  4597. write_to_soundcard(echo_frame, frame_size);

  4598. \end_layout

  4599. 

  4600. \begin_layout Plain Layout

  4601. 

  4602. read_from_soundcard(input_frame, frame_size);

  4603. \end_layout

  4604. 

  4605. \begin_layout Plain Layout

  4606. 

  4607. speex_echo_cancellation(echo_state, input_frame, echo_frame, output_frame);

  4608. \end_layout

  4609. 

  4610. \end_inset

  4611. 

  4612. 

  4613. \end_layout

  4614. 

  4615. \begin_layout Standard

  4616. If you wish to further reduce the echo present in the signal, you can do

  4617.  so by associating the echo canceller to the preprocessor (see Section 

  4618. \begin_inset CommandInset ref

  4619. LatexCommand ref

  4620. reference "sub:Preprocessor"

  4621. 

  4622. \end_inset

  4623. 

  4624. ).

  4625.  This is done by calling:

  4626. \begin_inset listings

  4627. lstparams "breaklines=true"

  4628. inline false

  4629. status open

  4630. 

  4631. \begin_layout Plain Layout

  4632. 

  4633. speex_preprocess_ctl(preprocess_state, SPEEX_PREPROCESS_SET_ECHO_STATE,echo_stat

  4634. e);

  4635. \end_layout

  4636. 

  4637. \end_inset

  4638. 

  4639. in the initialisation.

  4640. \end_layout

  4641. 

  4642. \begin_layout Standard

  4643. As of version 1.2-beta2, there is an alternative, simpler API that can be

  4644.  used instead of 

  4645. \emph on

  4646. speex_echo_cancellation()

  4647. \emph default

  4648. .

  4649.  When audio capture and playback are handled asynchronously (e.g.

  4650.  in different threads or using the 

  4651. \emph on

  4652. poll()

  4653. \emph default

  4654.  or 

  4655. \emph on

  4656. select()

  4657. \emph default

  4658.  system call), it can be difficult to keep track of what input_frame comes

  4659.  with what echo_frame.

  4660.  Instead, the playback context/thread can simply call:

  4661. \end_layout

  4662. 

  4663. \begin_layout Standard

  4664. \begin_inset listings

  4665. inline false

  4666. status open

  4667. 

  4668. \begin_layout Plain Layout

  4669. 

  4670. speex_echo_playback(echo_state, echo_frame);

  4671. \end_layout

  4672. 

  4673. \end_inset

  4674. 

  4675. 

  4676. \end_layout

  4677. 

  4678. \begin_layout Standard

  4679. every time an audio frame is played.

  4680.  Then, the capture context/thread calls:

  4681. \end_layout

  4682. 

  4683. \begin_layout Standard

  4684. \begin_inset listings

  4685. inline false

  4686. status open

  4687. 

  4688. \begin_layout Plain Layout

  4689. 

  4690. speex_echo_capture(echo_state, input_frame, output_frame);

  4691. \end_layout

  4692. 

  4693. \end_inset

  4694. 

  4695. 

  4696. \end_layout

  4697. 

  4698. \begin_layout Standard

  4699. for every frame captured.

  4700.  Internally, 

  4701. \emph on

  4702. speex_echo_playback()

  4703. \emph default

  4704.  simply buffers the playback frame so it can be used by 

  4705. \emph on

  4706. speex_echo_capture()

  4707. \emph default

  4708.  to call 

  4709. \emph on

  4710. speex_echo_cancel()

  4711. \emph default

  4712. .

  4713.  A side effect of using this alternate API is that the playback audio is

  4714.  delayed by two frames, which is the normal delay caused by the soundcard.

  4715.  When capture and playback are already synchronised, 

  4716. \emph on

  4717. speex_echo_cancellation()

  4718. \emph default

  4719.  is preferable since it gives better control on the exact input/echo timing.

  4720. \end_layout

  4721. 

  4722. \begin_layout Standard

  4723. The echo cancellation state can be destroyed with:

  4724. \end_layout

  4725. 

  4726. \begin_layout Standard

  4727. \begin_inset listings

  4728. inline false

  4729. status open

  4730. 

  4731. \begin_layout Plain Layout

  4732. 

  4733. speex_echo_state_destroy(echo_state);

  4734. \end_layout

  4735. 

  4736. \end_inset

  4737. 

  4738. 

  4739. \end_layout

  4740. 

  4741. \begin_layout Standard

  4742. It is also possible to reset the state of the echo canceller so it can be

  4743.  reused without the need to create another state with:

  4744. \end_layout

  4745. 

  4746. \begin_layout Standard

  4747. \begin_inset listings

  4748. inline false

  4749. status open

  4750. 

  4751. \begin_layout Plain Layout

  4752. 

  4753. speex_echo_state_reset(echo_state);

  4754. \end_layout

  4755. 

  4756. \end_inset

  4757. 

  4758. 

  4759. \end_layout

  4760. 

  4761. \begin_layout Subsection

  4762. Troubleshooting

  4763. \end_layout

  4764. 

  4765. \begin_layout Standard

  4766. There are several things that may prevent the echo canceller from working

  4767.  properly.

  4768.  One of them is a bug (or something suboptimal) in the code, but there are

  4769.  many others you should consider first

  4770. \end_layout

  4771. 

  4772. \begin_layout Itemize

  4773. Using a different soundcard to do the capture and plaback will 

  4774. \series bold

  4775. not

  4776. \series default

  4777.  work, regardless of what you may think.

  4778.  The only exception to that is if the two cards can be made to have their

  4779.  sampling clock 

  4780. \begin_inset Quotes eld

  4781. \end_inset

  4782. 

  4783. locked

  4784. \begin_inset Quotes erd

  4785. \end_inset

  4786. 

  4787.  on the same clock source.

  4788.  If not, the clocks will always have a small amount of drift, which will

  4789.  prevent the echo canceller from adapting.

  4790. \end_layout

  4791. 

  4792. \begin_layout Itemize

  4793. The delay between the record and playback signals must be minimal.

  4794.  Any signal played has to 

  4795. \begin_inset Quotes eld

  4796. \end_inset

  4797. 

  4798. appear

  4799. \begin_inset Quotes erd

  4800. \end_inset

  4801. 

  4802.  on the playback (far end) signal slightly before the echo canceller 

  4803. \begin_inset Quotes eld

  4804. \end_inset

  4805. 

  4806. sees

  4807. \begin_inset Quotes erd

  4808. \end_inset

  4809. 

  4810.  it in the near end signal, but excessive delay means that part of the filter

  4811.  length is wasted.

  4812.  In the worst situations, the delay is such that it is longer than the filter

  4813.  length, in which case, no echo can be cancelled.

  4814. \end_layout

  4815. 

  4816. \begin_layout Itemize

  4817. When it comes to echo tail length (filter length), longer is 

  4818. \series bold

  4819. not

  4820. \series default

  4821.  better.

  4822.  Actually, the longer the tail length, the longer it takes for the filter

  4823.  to adapt.

  4824.  Of course, a tail length that is too short will not cancel enough echo,

  4825.  but the most common problem seen is that people set a very long tail length

  4826.  and then wonder why no echo is being cancelled.

  4827. \end_layout

  4828. 

  4829. \begin_layout Itemize

  4830. Non-linear distortion cannot (by definition) be modeled by the linear adaptive

  4831.  filter used in the echo canceller and thus cannot be cancelled.

  4832.  Use good audio gear and avoid saturation/clipping.

  4833. \end_layout

  4834. 

  4835. \begin_layout Standard

  4836. Also useful is reading 

  4837. \emph on

  4838. Echo Cancellation Demystified

  4839. \emph default

  4840.  by Alexey Frunze

  4841. \begin_inset Foot

  4842. status collapsed

  4843. 

  4844. \begin_layout Plain Layout

  4845. http://www.embeddedstar.com/articles/2003/7/article20030720-1.html

  4846. \end_layout

  4847. 

  4848. \end_inset

  4849. 

  4850. , which explains the fundamental principles of echo cancellation.

  4851.  The details of the algorithm described in the article are different, but

  4852.  the general ideas of echo cancellation through adaptive filters are the

  4853.  same.

  4854. \end_layout

  4855. 

  4856. \begin_layout Standard

  4857. As of version 1.2beta2, a new 

  4858. \family typewriter

  4859. echo_diagnostic.m

  4860. \family default

  4861.  tool is included in the source distribution.

  4862.  The first step is to define DUMP_ECHO_CANCEL_DATA during the build.

  4863.  This causes the echo canceller to automatically save the near-end, far-end

  4864.  and output signals to files (aec_rec.sw aec_play.sw and aec_out.sw).

  4865.  These are exactly what the AEC receives and outputs.

  4866.  From there, it is necessary to start Octave and type:

  4867. \end_layout

  4868. 

  4869. \begin_layout Standard

  4870. \begin_inset listings

  4871. lstparams "language=Matlab"

  4872. inline false

  4873. status open

  4874. 

  4875. \begin_layout Plain Layout

  4876. 

  4877. echo_diagnostic('aec_rec.sw', 'aec_play.sw', 'aec_diagnostic.sw', 1024);

  4878. \end_layout

  4879. 

  4880. \end_inset

  4881. 

  4882. 

  4883. \end_layout

  4884. 

  4885. \begin_layout Standard

  4886. The value of 1024 is the filter length and can be changed.

  4887.  There will be some (hopefully) useful messages printed and echo cancelled

  4888.  audio will be saved to aec_diagnostic.sw .

  4889.  If even that output is bad (almost no cancellation) then there is  probably

  4890.  problem with the playback or recording process.

  4891. \end_layout

  4892. 

  4893. \begin_layout Section

  4894. Jitter Buffer

  4895. \end_layout

  4896. 

  4897. \begin_layout Standard

  4898. The jitter buffer can be enabled by including:

  4899. \begin_inset listings

  4900. lstparams "breaklines=true"

  4901. inline false

  4902. status open

  4903. 

  4904. \begin_layout Plain Layout

  4905. 

  4906. #include <speex/speex_jitter.h>

  4907. \end_layout

  4908. 

  4909. \end_inset

  4910. 

  4911.  and a new jitter buffer state can be initialised by:

  4912. \end_layout

  4913. 

  4914. \begin_layout Standard

  4915. \begin_inset listings

  4916. lstparams "breaklines=true"

  4917. inline false

  4918. status open

  4919. 

  4920. \begin_layout Plain Layout

  4921. 

  4922. JitterBuffer *state = jitter_buffer_init(step);

  4923. \end_layout

  4924. 

  4925. \end_inset

  4926. 

  4927. 

  4928. \end_layout

  4929. 

  4930. \begin_layout Standard

  4931. where the 

  4932. \begin_inset listings

  4933. inline true

  4934. status collapsed

  4935. 

  4936. \begin_layout Plain Layout

  4937. 

  4938. step

  4939. \end_layout

  4940. 

  4941. \end_inset

  4942. 

  4943.  argument is the default time step (in timestamp units) used for adjusting

  4944.  the delay and doing concealment.

  4945.  A value of 1 is always correct, but higher values may be more convenient

  4946.  sometimes.

  4947.  For example, if you are only able to do concealment on 20ms frames, there

  4948.  is no point in the jitter buffer asking you to do it on one sample.

  4949.  Another example is that for video, it makes no sense to adjust the delay

  4950.  by less than a full frame.

  4951.  The value provided can always be changed at a later time.

  4952. \end_layout

  4953. 

  4954. \begin_layout Standard

  4955. The jitter buffer API is based on the 

  4956. \begin_inset listings

  4957. inline true

  4958. status open

  4959. 

  4960. \begin_layout Plain Layout

  4961. 

  4962. JitterBufferPacket

  4963. \end_layout

  4964. 

  4965. \end_inset

  4966. 

  4967.  type, which is defined as:

  4968. \begin_inset listings

  4969. inline false

  4970. status open

  4971. 

  4972. \begin_layout Plain Layout

  4973. 

  4974. typedef struct {

  4975. \end_layout

  4976. 

  4977. \begin_layout Plain Layout

  4978. 

  4979.    char        *data;       /* Data bytes contained in the packet */

  4980. \end_layout

  4981. 

  4982. \begin_layout Plain Layout

  4983. 

  4984.    spx_uint32_t len;        /* Length of the packet in bytes */

  4985. \end_layout

  4986. 

  4987. \begin_layout Plain Layout

  4988. 

  4989.    spx_uint32_t timestamp;  /* Timestamp for the packet */

  4990. \end_layout

  4991. 

  4992. \begin_layout Plain Layout

  4993. 

  4994.    spx_uint32_t span;       /* Time covered by the packet (timestamp units)

  4995.  */

  4996. \end_layout

  4997. 

  4998. \begin_layout Plain Layout

  4999. 

  5000. } JitterBufferPacket; 

  5001. \end_layout

  5002. 

  5003. \end_inset

  5004. 

  5005. 

  5006. \end_layout

  5007. 

  5008. \begin_layout Standard

  5009. As an example, for audio the timestamp field would be what is obtained from

  5010.  the RTP timestamp field and the span would be the number of samples that

  5011.  are encoded in the packet.

  5012.  For Speex narrowband, span would be 160 if only one frame is included in

  5013.  the packet.

  5014.  

  5015. \end_layout

  5016. 

  5017. \begin_layout Standard

  5018. When a packet arrives, it need to be inserter into the jitter buffer by:

  5019. \begin_inset listings

  5020. inline false

  5021. status open

  5022. 

  5023. \begin_layout Plain Layout

  5024. 

  5025. JitterBufferPacket packet;

  5026. \end_layout

  5027. 

  5028. \begin_layout Plain Layout

  5029. 

  5030. /* Fill in each field in the packet struct */

  5031. \end_layout

  5032. 

  5033. \begin_layout Plain Layout

  5034. 

  5035. jitter_buffer_put(state, &packet);

  5036. \end_layout

  5037. 

  5038. \end_inset

  5039. 

  5040. 

  5041. \end_layout

  5042. 

  5043. \begin_layout Standard

  5044. When the decoder is ready to decode a packet the packet to be decoded can

  5045.  be obtained by: 

  5046. \begin_inset listings

  5047. inline false

  5048. status open

  5049. 

  5050. \begin_layout Plain Layout

  5051. 

  5052. int start_offset;

  5053. \end_layout

  5054. 

  5055. \begin_layout Plain Layout

  5056. 

  5057. err = jitter_buffer_get(state, &packet, desired_span, &start_offset);

  5058. \end_layout

  5059. 

  5060. \end_inset

  5061. 

  5062. 

  5063. \end_layout

  5064. 

  5065. \begin_layout Standard

  5066. If 

  5067. \begin_inset listings

  5068. inline true

  5069. status open

  5070. 

  5071. \begin_layout Plain Layout

  5072. 

  5073. jitter_buffer_put()

  5074. \end_layout

  5075. 

  5076. \end_inset

  5077. 

  5078.  and 

  5079. \begin_inset listings

  5080. inline true

  5081. status collapsed

  5082. 

  5083. \begin_layout Plain Layout

  5084. 

  5085. jitter_buffer_get()

  5086. \end_layout

  5087. 

  5088. \end_inset

  5089. 

  5090.  are called from different threads, then 

  5091. \series bold

  5092. you need to protect the jitter buffer state with a mutex

  5093. \series default

  5094. .

  5095.  

  5096. \end_layout

  5097. 

  5098. \begin_layout Standard

  5099. Because the jitter buffer is designed not to use an explicit timer, it needs

  5100.  to be told about the time explicitly.

  5101.  This is done by calling: 

  5102. \begin_inset listings

  5103. inline false

  5104. status open

  5105. 

  5106. \begin_layout Plain Layout

  5107. 

  5108. jitter_buffer_tick(state);

  5109. \end_layout

  5110. 

  5111. \end_inset

  5112. 

  5113. 

  5114. \end_layout

  5115. 

  5116. \begin_layout Standard

  5117. This needs to be done periodically in the playing thread.

  5118.  This will be the last jitter buffer call before going to sleep (until more

  5119.  data is played back).

  5120.  In some cases, it may be preferable to use 

  5121. \begin_inset listings

  5122. inline false

  5123. status open

  5124. 

  5125. \begin_layout Plain Layout

  5126. 

  5127. jitter_buffer_remaining_span(state, remaining);

  5128. \end_layout

  5129. 

  5130. \end_inset

  5131. 

  5132. 

  5133. \end_layout

  5134. 

  5135. \begin_layout Standard

  5136. The second argument is used to specify that we are still holding data that

  5137.  has not been written to the playback device.

  5138.  For instance, if 256 samples were needed by the soundcard (specified by

  5139.  

  5140. \begin_inset listings

  5141. inline true

  5142. status collapsed

  5143. 

  5144. \begin_layout Plain Layout

  5145. 

  5146. desired_span

  5147. \end_layout

  5148. 

  5149. \end_inset

  5150. 

  5151. ), but 

  5152. \begin_inset listings

  5153. inline true

  5154. status collapsed

  5155. 

  5156. \begin_layout Plain Layout

  5157. 

  5158. jitter_buffer_get()

  5159. \end_layout

  5160. 

  5161. \end_inset

  5162. 

  5163.  returned 320 samples, we would have 

  5164. \begin_inset listings

  5165. inline true

  5166. status open

  5167. 

  5168. \begin_layout Plain Layout

  5169. 

  5170. remaining=64

  5171. \end_layout

  5172. 

  5173. \end_inset

  5174. 

  5175. .

  5176. \end_layout

  5177. 

  5178. \begin_layout Section

  5179. Resampler

  5180. \end_layout

  5181. 

  5182. \begin_layout Standard

  5183. Speex includes a resampling modules.

  5184.  To make use of the resampler, it is necessary to include its header file:

  5185. \end_layout

  5186. 

  5187. \begin_layout Standard

  5188. \begin_inset listings

  5189. inline false

  5190. status open

  5191. 

  5192. \begin_layout Plain Layout

  5193. 

  5194. #include <speex/speex_resampler.h>

  5195. \end_layout

  5196. 

  5197. \end_inset

  5198. 

  5199. 

  5200. \end_layout

  5201. 

  5202. \begin_layout Standard

  5203. For each stream that is to be resampled, it is necessary to create a resampler

  5204.  state with:

  5205. \end_layout

  5206. 

  5207. \begin_layout Standard

  5208. \begin_inset listings

  5209. inline false

  5210. status open

  5211. 

  5212. \begin_layout Plain Layout

  5213. 

  5214. SpeexResamplerState *resampler;

  5215. \end_layout

  5216. 

  5217. \begin_layout Plain Layout

  5218. 

  5219. resampler = speex_resampler_init(nb_channels, input_rate, output_rate, quality,

  5220.  &err);

  5221. \end_layout

  5222. 

  5223. \end_inset

  5224. 

  5225. 

  5226. \end_layout

  5227. 

  5228. \begin_layout Standard

  5229. where 

  5230. \begin_inset listings

  5231. inline true

  5232. status collapsed

  5233. 

  5234. \begin_layout Plain Layout

  5235. 

  5236. nb_channels

  5237. \end_layout

  5238. 

  5239. \end_inset

  5240. 

  5241.  is the number of channels that will be used (either interleaved or non-interlea

  5242. ved), 

  5243. \begin_inset listings

  5244. inline true

  5245. status collapsed

  5246. 

  5247. \begin_layout Plain Layout

  5248. 

  5249. input_rate

  5250. \end_layout

  5251. 

  5252. \end_inset

  5253. 

  5254.  is the sampling rate of the input stream, 

  5255. \begin_inset listings

  5256. inline true

  5257. status collapsed

  5258. 

  5259. \begin_layout Plain Layout

  5260. 

  5261. output_rate

  5262. \end_layout

  5263. 

  5264. \end_inset

  5265. 

  5266.  is the sampling rate of the output stream and 

  5267. \begin_inset listings

  5268. inline true

  5269. status collapsed

  5270. 

  5271. \begin_layout Plain Layout

  5272. 

  5273. quality

  5274. \end_layout

  5275. 

  5276. \end_inset

  5277. 

  5278.  is the requested quality setting (0 to 10).

  5279.  The quality parameter is useful for controlling the quality/complexity/latency

  5280.  tradeoff.

  5281.  Using a higher quality setting means less noise/aliasing, a higher complexity

  5282.  and a higher latency.

  5283.  Usually, a quality of 3 is acceptable for most desktop uses and quality

  5284.  10 is mostly recommended for pro audio work.

  5285.  Quality 0 usually has a decent sound (certainly better than using linear

  5286.  interpolation resampling), but artifacts may be heard.

  5287. \end_layout

  5288. 

  5289. \begin_layout Standard

  5290. The actual resampling is performed using

  5291. \end_layout

  5292. 

  5293. \begin_layout Standard

  5294. \begin_inset listings

  5295. inline false

  5296. status open

  5297. 

  5298. \begin_layout Plain Layout

  5299. 

  5300. err = speex_resampler_process_int(resampler, channelID, in, &in_length,

  5301.  out, &out_length);

  5302. \end_layout

  5303. 

  5304. \end_inset

  5305. 

  5306. where 

  5307. \begin_inset listings

  5308. inline true

  5309. status collapsed

  5310. 

  5311. \begin_layout Plain Layout

  5312. 

  5313. channelID

  5314. \end_layout

  5315. 

  5316. \end_inset

  5317. 

  5318.  is the ID of the channel to be processed.

  5319.  For a mono stream, use 0.

  5320.  The 

  5321. \emph on

  5322. in

  5323. \emph default

  5324.  pointer points to the first sample of the input buffer for the selected

  5325.  channel and 

  5326. \begin_inset listings

  5327. inline true

  5328. status collapsed

  5329. 

  5330. \begin_layout Plain Layout

  5331. 

  5332. out

  5333. \end_layout

  5334. 

  5335. \end_inset

  5336. 

  5337.  points to the first sample of the output.

  5338.  The size of the input and output buffers are specified by 

  5339. \begin_inset listings

  5340. inline true

  5341. status collapsed

  5342. 

  5343. \begin_layout Plain Layout

  5344. 

  5345. in_length

  5346. \end_layout

  5347. 

  5348. \end_inset

  5349. 

  5350.  and 

  5351. \begin_inset listings

  5352. inline true

  5353. status collapsed

  5354. 

  5355. \begin_layout Plain Layout

  5356. 

  5357. out_length

  5358. \end_layout

  5359. 

  5360. \end_inset

  5361. 

  5362.  respectively.

  5363.  Upon completion, these values are replaced by the number of samples read

  5364.  and written by the resampler.

  5365.  Unless an error occurs, either all input samples will be read or all output

  5366.  samples will be written to (or both).

  5367.  For floating-point samples, the function 

  5368. \begin_inset listings

  5369. inline true

  5370. status open

  5371. 

  5372. \begin_layout Plain Layout

  5373. 

  5374. speex_resampler_process_float()

  5375. \end_layout

  5376. 

  5377. \end_inset

  5378. 

  5379.  behaves similarly.

  5380. \end_layout

  5381. 

  5382. \begin_layout Standard

  5383. It is also possible to process multiple channels at once.

  5384.  To do that, you can use speex_resampler_process_interleaved_int() or 

  5385. \begin_inset listings

  5386. inline true

  5387. status open

  5388. 

  5389. \begin_layout Plain Layout

  5390. 

  5391. speex_resampler_process_interleaved_float()

  5392. \end_layout

  5393. 

  5394. \end_inset

  5395. 

  5396. .

  5397.  The arguments are the same except that there is no 

  5398. \begin_inset listings

  5399. inline true

  5400. status collapsed

  5401. 

  5402. \begin_layout Plain Layout

  5403. 

  5404. channelID

  5405. \end_layout

  5406. 

  5407. \end_inset

  5408. 

  5409.  argument.

  5410.  Note that the 

  5411. \series bold

  5412. length parameters are per-channel

  5413. \series default

  5414. .

  5415.  So if you have 1024 samples for each of 4 channels, you pass 1024 and not

  5416.  4096.

  5417. \end_layout

  5418. 

  5419. \begin_layout Standard

  5420. The resampler allows changing the quality and input/output sampling frequencies

  5421.  on the fly without glitches.

  5422.  This can be done with calls such as 

  5423. \begin_inset listings

  5424. inline true

  5425. status open

  5426. 

  5427. \begin_layout Plain Layout

  5428. 

  5429. speex_resampler_set_quality()

  5430. \end_layout

  5431. 

  5432. \end_inset

  5433. 

  5434.  and 

  5435. \begin_inset listings

  5436. inline true

  5437. status open

  5438. 

  5439. \begin_layout Plain Layout

  5440. 

  5441. speex_resampler_set_rate()

  5442. \end_layout

  5443. 

  5444. \end_inset

  5445. 

  5446. .

  5447.  The only side effect is that a new filter will have to be recomputed, consuming

  5448.  many CPU cycles.

  5449.  

  5450. \end_layout

  5451. 

  5452. \begin_layout Standard

  5453. When resampling a file, it is often desirable to have the output file perfectly

  5454.  synchronised with the input.

  5455.  To do that, you need to call 

  5456. \begin_inset listings

  5457. inline true

  5458. status open

  5459. 

  5460. \begin_layout Plain Layout

  5461. 

  5462. speex_resampler_skip_zeros()

  5463. \end_layout

  5464. 

  5465. \end_inset

  5466. 

  5467.  

  5468. \series bold

  5469. before

  5470. \series default

  5471.  you start processing any samples.

  5472.  For real-time applications (e.g.

  5473.  VoIP), it is not recommended to do that as the first process frame will

  5474.  be shorter to compensate for the delay (the skipped zeros).

  5475.  Instead, in real-time applications you may want to know how many delay

  5476.  is introduced by the resampler.

  5477.  This can be done at run-time with 

  5478. \begin_inset listings

  5479. inline true

  5480. status open

  5481. 

  5482. \begin_layout Plain Layout

  5483. 

  5484. speex_resampler_get_input_latency()

  5485. \end_layout

  5486. 

  5487. \end_inset

  5488. 

  5489.  and 

  5490. \begin_inset listings

  5491. inline true

  5492. status open

  5493. 

  5494. \begin_layout Plain Layout

  5495. 

  5496. speex_resampler_get_output_latency()

  5497. \end_layout

  5498. 

  5499. \end_inset

  5500. 

  5501.  functions.

  5502.  First function returns delay measured in samples at input samplerate, while

  5503.  second returns delay measured in samples at output samplerate.

  5504. \end_layout

  5505. 

  5506. \begin_layout Standard

  5507. To destroy a resampler state, just call 

  5508. \begin_inset listings

  5509. inline true

  5510. status open

  5511. 

  5512. \begin_layout Plain Layout

  5513. 

  5514. speex_resampler_destroy()

  5515. \end_layout

  5516. 

  5517. \end_inset

  5518. 

  5519. .

  5520. \end_layout

  5521. 

  5522. \begin_layout Section

  5523. Ring Buffer

  5524. \end_layout

  5525. 

  5526. \begin_layout Standard

  5527. In some cases, it is necessary to interface components that use different

  5528.  block sizes.

  5529.  For example, it is possible that the soundcard does not support reading/writing

  5530.  in blocks of 20

  5531. \begin_inset space ~

  5532. \end_inset

  5533. 

  5534. ms or sometimes, complicated resampling ratios mean that the blocks don't

  5535.  always have the same time.

  5536.  In thoses cases, it is often necessary to buffer a bit of audio using a

  5537.  ring buffer.

  5538. \end_layout

  5539. 

  5540. \begin_layout Standard

  5541. \begin_inset Newpage newpage

  5542. \end_inset

  5543. 

  5544. 

  5545. \end_layout

  5546. 

  5547. \begin_layout Chapter

  5548. Formats and standards

  5549. \begin_inset Index

  5550. status collapsed

  5551. 

  5552. \begin_layout Plain Layout

  5553. standards

  5554. \end_layout

  5555. 

  5556. \end_inset

  5557. 

  5558. 

  5559. \begin_inset CommandInset label

  5560. LatexCommand label

  5561. name "sec:Formats-and-standards"

  5562. 

  5563. \end_inset

  5564. 

  5565. 

  5566. \end_layout

  5567. 

  5568. \begin_layout Standard

  5569. Speex can encode speech in both narrowband and wideband and provides different

  5570.  bit-rates.

  5571.  However, not all features need to be supported by a certain implementation

  5572.  or device.

  5573.  In order to be called 

  5574. \begin_inset Quotes eld

  5575. \end_inset

  5576. 

  5577. Speex compatible

  5578. \begin_inset Quotes erd

  5579. \end_inset

  5580. 

  5581.  (whatever that means), an implementation must implement at least a basic

  5582.  set of features.

  5583. \end_layout

  5584. 

  5585. \begin_layout Standard

  5586. At the minimum, all narrowband modes of operation MUST be supported at the

  5587.  decoder.

  5588.  This includes the decoding of a wideband bit-stream by the narrowband decoder

  5589. \begin_inset Foot

  5590. status collapsed

  5591. 

  5592. \begin_layout Plain Layout

  5593. The wideband bit-stream contains an embedded narrowband bit-stream which

  5594.  can be decoded alone

  5595. \end_layout

  5596. 

  5597. \end_inset

  5598. 

  5599. .

  5600.  If present, a wideband decoder MUST be able to decode a narrowband stream,

  5601.  and MAY either be able to decode all wideband modes or be able to decode

  5602.  the embedded narrowband part of all modes (which includes ignoring the

  5603.  high-band bits).

  5604. \end_layout

  5605. 

  5606. \begin_layout Standard

  5607. For encoders, at least one narrowband or wideband mode MUST be supported.

  5608.  The main reason why all encoding modes do not have to be supported is that

  5609.  some platforms may not be able to handle the complexity of encoding in

  5610.  some modes.

  5611. \end_layout

  5612. 

  5613. \begin_layout Section

  5614. RTP

  5615. \begin_inset Index

  5616. status collapsed

  5617. 

  5618. \begin_layout Plain Layout

  5619. RTP

  5620. \end_layout

  5621. 

  5622. \end_inset

  5623. 

  5624.  Payload Format 

  5625. \end_layout

  5626. 

  5627. \begin_layout Standard

  5628. The RTP payload draft is included in appendix 

  5629. \begin_inset CommandInset ref

  5630. LatexCommand ref

  5631. reference "sec:IETF-draft"

  5632. 

  5633. \end_inset

  5634. 

  5635.  and the latest version is available at 

  5636. \begin_inset Flex URL

  5637. status collapsed

  5638. 

  5639. \begin_layout Plain Layout

  5640. 

  5641. http://www.speex.org/drafts/latest

  5642. \end_layout

  5643. 

  5644. \end_inset

  5645. 

  5646. .

  5647.  This draft has been sent (2003/02/26) to the Internet Engineering Task

  5648.  Force (IETF) and will be discussed at the March 18th meeting in San Francisco.

  5649.  

  5650. \end_layout

  5651. 

  5652. \begin_layout Section

  5653. MIME Type

  5654. \end_layout

  5655. 

  5656. \begin_layout Standard

  5657. For now, you should use the MIME type audio/x-speex for Speex-in-Ogg.

  5658.  We will apply for type 

  5659. \family typewriter

  5660. audio/speex

  5661. \family default

  5662.  in the near future.

  5663. \end_layout

  5664. 

  5665. \begin_layout Section

  5666. Ogg

  5667. \begin_inset Index

  5668. status collapsed

  5669. 

  5670. \begin_layout Plain Layout

  5671. Ogg

  5672. \end_layout

  5673. 

  5674. \end_inset

  5675. 

  5676.  file format

  5677. \end_layout

  5678. 

  5679. \begin_layout Standard

  5680. Speex bit-streams can be stored in Ogg files.

  5681.  In this case, the first packet of the Ogg file contains the Speex header

  5682.  described in table 

  5683. \begin_inset CommandInset ref

  5684. LatexCommand ref

  5685. reference "cap:ogg_speex_header"

  5686. 

  5687. \end_inset

  5688. 

  5689. .

  5690.  All integer fields in the headers are stored as little-endian.

  5691.  The 

  5692. \family typewriter

  5693. speex_string

  5694. \family default

  5695.  field must contain the 

  5696. \begin_inset Quotes eld

  5697. \end_inset

  5698. 

  5699. 

  5700. \family typewriter

  5701. Speex

  5702. \family default

  5703. 

  5704. \begin_inset space ~

  5705. \end_inset

  5706. 

  5707. 

  5708. \begin_inset space ~

  5709. \end_inset

  5710. 

  5711. 

  5712. \begin_inset space ~

  5713. \end_inset

  5714. 

  5715. 

  5716. \begin_inset Quotes erd

  5717. \end_inset

  5718. 

  5719.  (with 3 trailing spaces), which identifies the bit-stream.

  5720.  The next field, 

  5721. \family typewriter

  5722. speex_version

  5723. \family default

  5724.  contains the version of Speex that encoded the file.

  5725.  For now, refer to speex_header.[ch] for more info.

  5726.  The 

  5727. \emph on

  5728. beginning of stream

  5729. \emph default

  5730.  (

  5731. \family typewriter

  5732. b_o_s

  5733. \family default

  5734. ) flag is set to 1 for the header.

  5735.  The header packet has 

  5736. \family typewriter

  5737. packetno=0

  5738. \family default

  5739.  and 

  5740. \family typewriter

  5741. granulepos=0

  5742. \family default

  5743. .

  5744. \end_layout

  5745. 

  5746. \begin_layout Standard

  5747. The second packet contains the Speex comment header.

  5748.  The format used is the Vorbis comment format described here: http://www.xiph.org/

  5749. ogg/vorbis/doc/v-comment.html .

  5750.  This packet has 

  5751. \family typewriter

  5752. packetno=1

  5753. \family default

  5754.  and 

  5755. \family typewriter

  5756. granulepos=0

  5757. \family default

  5758. .

  5759. \end_layout

  5760. 

  5761. \begin_layout Standard

  5762. The third and subsequent packets each contain one or more (number found

  5763.  in header) Speex frames.

  5764.  These are identified with 

  5765. \family typewriter

  5766. packetno

  5767. \family default

  5768.  starting from 2 and the 

  5769. \family typewriter

  5770. granulepos

  5771. \family default

  5772.  is the number of the last sample encoded in that packet.

  5773.  The last of these packets has the 

  5774. \emph on

  5775. end of stream

  5776. \emph default

  5777.  (

  5778. \family typewriter

  5779. e_o_s

  5780. \family default

  5781. ) flag is set to 1.

  5782. \end_layout

  5783. 

  5784. \begin_layout Standard

  5785. \begin_inset Float table

  5786. placement htbp

  5787. wide true

  5788. sideways false

  5789. status open

  5790. 

  5791. \begin_layout Plain Layout

  5792. \begin_inset ERT

  5793. status collapsed

  5794. 

  5795. \begin_layout Plain Layout

  5796. 

  5797. 

  5798. \backslash

  5799. begin{center}

  5800. \end_layout

  5801. 

  5802. \end_inset

  5803. 

  5804. 

  5805. \begin_inset Tabular

  5806. <lyxtabular version="3" rows="16" columns="3">

  5807. <features>

  5808. <column alignment="center" valignment="top" width="0pt">

  5809. <column alignment="center" valignment="top" width="0pt">

  5810. <column alignment="center" valignment="top" width="0pt">

  5811. <row>

  5812. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  5813. \begin_inset Text

  5814. 

  5815. \begin_layout Plain Layout

  5816. Field

  5817. \end_layout

  5818. 

  5819. \end_inset

  5820. </cell>

  5821. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  5822. \begin_inset Text

  5823. 

  5824. \begin_layout Plain Layout

  5825. Type

  5826. \end_layout

  5827. 

  5828. \end_inset

  5829. </cell>

  5830. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">

  5831. \begin_inset Text

  5832. 

  5833. \begin_layout Plain Layout

  5834. Size

  5835. \end_layout

  5836. 

  5837. \end_inset

  5838. </cell>

  5839. </row>

  5840. <row>

  5841. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5842. \begin_inset Text

  5843. 

  5844. \begin_layout Plain Layout

  5845. speex_string

  5846. \end_layout

  5847. 

  5848. \end_inset

  5849. </cell>

  5850. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5851. \begin_inset Text

  5852. 

  5853. \begin_layout Plain Layout

  5854. char[]

  5855. \end_layout

  5856. 

  5857. \end_inset

  5858. </cell>

  5859. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  5860. \begin_inset Text

  5861. 

  5862. \begin_layout Plain Layout

  5863. 8

  5864. \end_layout

  5865. 

  5866. \end_inset

  5867. </cell>

  5868. </row>

  5869. <row>

  5870. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5871. \begin_inset Text

  5872. 

  5873. \begin_layout Plain Layout

  5874. speex_version

  5875. \end_layout

  5876. 

  5877. \end_inset

  5878. </cell>

  5879. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5880. \begin_inset Text

  5881. 

  5882. \begin_layout Plain Layout

  5883. char[]

  5884. \end_layout

  5885. 

  5886. \end_inset

  5887. </cell>

  5888. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  5889. \begin_inset Text

  5890. 

  5891. \begin_layout Plain Layout

  5892. 20

  5893. \end_layout

  5894. 

  5895. \end_inset

  5896. </cell>

  5897. </row>

  5898. <row>

  5899. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5900. \begin_inset Text

  5901. 

  5902. \begin_layout Plain Layout

  5903. speex_version_id

  5904. \end_layout

  5905. 

  5906. \end_inset

  5907. </cell>

  5908. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5909. \begin_inset Text

  5910. 

  5911. \begin_layout Plain Layout

  5912. int

  5913. \end_layout

  5914. 

  5915. \end_inset

  5916. </cell>

  5917. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  5918. \begin_inset Text

  5919. 

  5920. \begin_layout Plain Layout

  5921. 4

  5922. \end_layout

  5923. 

  5924. \end_inset

  5925. </cell>

  5926. </row>

  5927. <row>

  5928. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5929. \begin_inset Text

  5930. 

  5931. \begin_layout Plain Layout

  5932. header_size

  5933. \end_layout

  5934. 

  5935. \end_inset

  5936. </cell>

  5937. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5938. \begin_inset Text

  5939. 

  5940. \begin_layout Plain Layout

  5941. int

  5942. \end_layout

  5943. 

  5944. \end_inset

  5945. </cell>

  5946. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  5947. \begin_inset Text

  5948. 

  5949. \begin_layout Plain Layout

  5950. 4

  5951. \end_layout

  5952. 

  5953. \end_inset

  5954. </cell>

  5955. </row>

  5956. <row>

  5957. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5958. \begin_inset Text

  5959. 

  5960. \begin_layout Plain Layout

  5961. rate

  5962. \end_layout

  5963. 

  5964. \end_inset

  5965. </cell>

  5966. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5967. \begin_inset Text

  5968. 

  5969. \begin_layout Plain Layout

  5970. int

  5971. \end_layout

  5972. 

  5973. \end_inset

  5974. </cell>

  5975. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  5976. \begin_inset Text

  5977. 

  5978. \begin_layout Plain Layout

  5979. 4

  5980. \end_layout

  5981. 

  5982. \end_inset

  5983. </cell>

  5984. </row>

  5985. <row>

  5986. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5987. \begin_inset Text

  5988. 

  5989. \begin_layout Plain Layout

  5990. mode

  5991. \end_layout

  5992. 

  5993. \end_inset

  5994. </cell>

  5995. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  5996. \begin_inset Text

  5997. 

  5998. \begin_layout Plain Layout

  5999. int

  6000. \end_layout

  6001. 

  6002. \end_inset

  6003. </cell>

  6004. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  6005. \begin_inset Text

  6006. 

  6007. \begin_layout Plain Layout

  6008. 4

  6009. \end_layout

  6010. 

  6011. \end_inset

  6012. </cell>

  6013. </row>

  6014. <row>

  6015. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  6016. \begin_inset Text

  6017. 

  6018. \begin_layout Plain Layout

  6019. mode_bitstream_version

  6020. \end_layout

  6021. 

  6022. \end_inset

  6023. </cell>

  6024. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  6025. \begin_inset Text

  6026. 

  6027. \begin_layout Plain Layout

  6028. int

  6029. \end_layout

  6030. 

  6031. \end_inset

  6032. </cell>

  6033. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  6034. \begin_inset Text

  6035. 

  6036. \begin_layout Plain Layout

  6037. 4

  6038. \end_layout

  6039. 

  6040. \end_inset

  6041. </cell>

  6042. </row>

  6043. <row>

  6044. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  6045. \begin_inset Text

  6046. 

  6047. \begin_layout Plain Layout

  6048. nb_channels

  6049. \end_layout

  6050. 

  6051. \end_inset

  6052. </cell>

  6053. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  6054. \begin_inset Text

  6055. 

  6056. \begin_layout Plain Layout

  6057. int

  6058. \end_layout

  6059. 

  6060. \end_inset

  6061. </cell>

  6062. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  6063. \begin_inset Text

  6064. 

  6065. \begin_layout Plain Layout

  6066. 4

  6067. \end_layout

  6068. 

  6069. \end_inset

  6070. </cell>

  6071. </row>

  6072. <row>

  6073. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  6074. \begin_inset Text

  6075. 

  6076. \begin_layout Plain Layout

  6077. bitrate

  6078. \end_layout

  6079. 

  6080. \end_inset

  6081. </cell>

  6082. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  6083. \begin_inset Text

  6084. 

  6085. \begin_layout Plain Layout

  6086. int

  6087. \end_layout

  6088. 

  6089. \end_inset

  6090. </cell>

  6091. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  6092. \begin_inset Text

  6093. 

  6094. \begin_layout Plain Layout

  6095. 4

  6096. \end_layout

  6097. 

  6098. \end_inset

  6099. </cell>

  6100. </row>

  6101. <row>

  6102. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  6103. \begin_inset Text

  6104. 

  6105. \begin_layout Plain Layout

  6106. frame_size

  6107. \end_layout

  6108. 

  6109. \end_inset

  6110. </cell>

  6111. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  6112. \begin_inset Text

  6113. 

  6114. \begin_layout Plain Layout

  6115. int

  6116. \end_layout

  6117. 

  6118. \end_inset

  6119. </cell>

  6120. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  6121. \begin_inset Text

  6122. 

  6123. \begin_layout Plain Layout

  6124. 4

  6125. \end_layout

  6126. 

  6127. \end_inset

  6128. </cell>

  6129. </row>

  6130. <row>

  6131. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

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  6269. 4

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  6274. </row>

  6275. </lyxtabular>

  6276. 

  6277. \end_inset

  6278. 

  6279. 

  6280. \begin_inset ERT

  6281. status collapsed

  6282. 

  6283. \begin_layout Plain Layout

  6284. 

  6285. 

  6286. \backslash

  6287. end{center}

  6288. \end_layout

  6289. 

  6290. \end_inset

  6291. 

  6292. 

  6293. \end_layout

  6294. 

  6295. \begin_layout Plain Layout

  6296. \begin_inset Caption

  6297. 

  6298. \begin_layout Plain Layout

  6299. Ogg/Speex header packet

  6300. \begin_inset CommandInset label

  6301. LatexCommand label

  6302. name "cap:ogg_speex_header"

  6303. 

  6304. \end_inset

  6305. 

  6306. 

  6307. \end_layout

  6308. 

  6309. \end_inset

  6310. 

  6311. 

  6312. \end_layout

  6313. 

  6314. \end_inset

  6315. 

  6316. 

  6317. \end_layout

  6318. 

  6319. \begin_layout Standard

  6320. \begin_inset ERT

  6321. status collapsed

  6322. 

  6323. \begin_layout Plain Layout

  6324. 

  6325. 

  6326. \backslash

  6327. clearpage

  6328. \end_layout

  6329. 

  6330. \end_inset

  6331. 

  6332. 

  6333. \end_layout

  6334. 

  6335. \begin_layout Chapter

  6336. Introduction to CELP Coding

  6337. \begin_inset Index

  6338. status collapsed

  6339. 

  6340. \begin_layout Plain Layout

  6341. CELP

  6342. \end_layout

  6343. 

  6344. \end_inset

  6345. 

  6346. 

  6347. \begin_inset CommandInset label

  6348. LatexCommand label

  6349. name "sec:Introduction-to-CELP"

  6350. 

  6351. \end_inset

  6352. 

  6353. 

  6354. \end_layout

  6355. 

  6356. \begin_layout Quote

  6357. \align center

  6358. 

  6359. \emph on

  6360. Do not meddle in the affairs of poles, for they are subtle and quick to

  6361.  leave the unit circle.

  6362. \end_layout

  6363. 

  6364. \begin_layout Standard

  6365. Speex is based on CELP, which stands for Code Excited Linear Prediction.

  6366.  This section attempts to introduce the principles behind CELP, so if you

  6367.  are already familiar with CELP, you can safely skip to section 

  6368. \begin_inset CommandInset ref

  6369. LatexCommand ref

  6370. reference "sec:Speex-narrowband-mode"

  6371. 

  6372. \end_inset

  6373. 

  6374. .

  6375.  The CELP technique is based on three ideas:

  6376. \end_layout

  6377. 

  6378. \begin_layout Enumerate

  6379. The use of a linear prediction (LP) model to model the vocal tract

  6380. \end_layout

  6381. 

  6382. \begin_layout Enumerate

  6383. The use of (adaptive and fixed) codebook entries as input (excitation) of

  6384.  the LP model

  6385. \end_layout

  6386. 

  6387. \begin_layout Enumerate

  6388. The search performed in closed-loop in a 

  6389. \begin_inset Quotes eld

  6390. \end_inset

  6391. 

  6392. perceptually weighted domain

  6393. \begin_inset Quotes erd

  6394. \end_inset

  6395. 

  6396. 

  6397. \end_layout

  6398. 

  6399. \begin_layout Standard

  6400. This section describes the basic ideas behind CELP.

  6401.  This is still a work in progress.

  6402. \end_layout

  6403. 

  6404. \begin_layout Section

  6405. Source-Filter Model of Speech Prediction

  6406. \end_layout

  6407. 

  6408. \begin_layout Standard

  6409. The source-filter model of speech production assumes that the vocal cords

  6410.  are the source of spectrally flat sound (the excitation signal), and that

  6411.  the vocal tract acts as a filter to spectrally shape the various sounds

  6412.  of speech.

  6413.  While still an approximation, the model is widely used in speech coding

  6414.  because of its simplicity.Its use is also the reason why most speech codecs

  6415.  (Speex included) perform badly on music signals.

  6416.  The different phonemes can be distinguished by their excitation (source)

  6417.  and spectral shape (filter).

  6418.  Voiced sounds (e.g.

  6419.  vowels) have an excitation signal that is periodic and that can be approximated

  6420.  by an impulse train in the time domain or by regularly-spaced harmonics

  6421.  in the frequency domain.

  6422.  On the other hand, fricatives (such as the "s", "sh" and "f" sounds) have

  6423.  an excitation signal that is similar to white Gaussian noise.

  6424.  So called voice fricatives (such as "z" and "v") have excitation signal

  6425.  composed of an harmonic part and a noisy part.

  6426. \end_layout

  6427. 

  6428. \begin_layout Standard

  6429. The source-filter model is usually tied with the use of Linear prediction.

  6430.  The CELP model is based on source-filter model, as can be seen from the

  6431.  CELP decoder illustrated in Figure 

  6432. \begin_inset CommandInset ref

  6433. LatexCommand ref

  6434. reference "fig:The-CELP-model"

  6435. 

  6436. \end_inset

  6437. 

  6438. .

  6439.  

  6440. \end_layout

  6441. 

  6442. \begin_layout Standard

  6443. \begin_inset Float figure

  6444. wide false

  6445. sideways false

  6446. status open

  6447. 

  6448. \begin_layout Plain Layout

  6449. \begin_inset ERT

  6450. status collapsed

  6451. 

  6452. \begin_layout Plain Layout

  6453. 

  6454. 

  6455. \backslash

  6456. begin{center}

  6457. \end_layout

  6458. 

  6459. \end_inset

  6460. 

  6461. 

  6462. \begin_inset Graphics

  6463. 	filename celp_decoder.eps

  6464. 	width 45page%

  6465. 	keepAspectRatio

  6466. 

  6467. \end_inset

  6468. 

  6469. 

  6470. \begin_inset ERT

  6471. status collapsed

  6472. 

  6473. \begin_layout Plain Layout

  6474. 

  6475. 

  6476. \backslash

  6477. end{center}

  6478. \end_layout

  6479. 

  6480. \end_inset

  6481. 

  6482. 

  6483. \end_layout

  6484. 

  6485. \begin_layout Plain Layout

  6486. \begin_inset Caption

  6487. 

  6488. \begin_layout Plain Layout

  6489. The CELP model of speech synthesis (decoder)

  6490. \begin_inset CommandInset label

  6491. LatexCommand label

  6492. name "fig:The-CELP-model"

  6493. 

  6494. \end_inset

  6495. 

  6496.  

  6497. \end_layout

  6498. 

  6499. \end_inset

  6500. 

  6501. 

  6502. \end_layout

  6503. 

  6504. \end_inset

  6505. 

  6506. 

  6507. \end_layout

  6508. 

  6509. \begin_layout Section

  6510. Linear Prediction Coefficients (LPC)

  6511. \begin_inset Index

  6512. status collapsed

  6513. 

  6514. \begin_layout Plain Layout

  6515. linear prediction

  6516. \end_layout

  6517. 

  6518. \end_inset

  6519. 

  6520. 

  6521. \end_layout

  6522. 

  6523. \begin_layout Standard

  6524. Linear prediction is at the base of many speech coding techniques, including

  6525.  CELP.

  6526.  The idea behind it is to predict the signal 

  6527. \begin_inset Formula $x[n]$

  6528. \end_inset

  6529. 

  6530.  using a linear combination of its past samples:

  6531. \end_layout

  6532. 

  6533. \begin_layout Standard

  6534. \begin_inset Formula \[

  6535. y[n]=\sum_{i=1}^{N}a_{i}x[n-i]\]

  6536. 

  6537. \end_inset

  6538. 

  6539. where 

  6540. \begin_inset Formula $y[n]$

  6541. \end_inset

  6542. 

  6543.  is the linear prediction of 

  6544. \begin_inset Formula $x[n]$

  6545. \end_inset

  6546. 

  6547. .

  6548.  The prediction error is thus given by:

  6549. \begin_inset Formula \[

  6550. e[n]=x[n]-y[n]=x[n]-\sum_{i=1}^{N}a_{i}x[n-i]\]

  6551. 

  6552. \end_inset

  6553. 

  6554. 

  6555. \end_layout

  6556. 

  6557. \begin_layout Standard

  6558. The goal of the LPC analysis is to find the best prediction coefficients

  6559.  

  6560. \begin_inset Formula $a_{i}$

  6561. \end_inset

  6562. 

  6563.  which minimize the quadratic error function:

  6564. \begin_inset Formula \[

  6565. E=\sum_{n=0}^{L-1}\left[e[n]\right]^{2}=\sum_{n=0}^{L-1}\left[x[n]-\sum_{i=1}^{N}a_{i}x[n-i]\right]^{2}\]

  6566. 

  6567. \end_inset

  6568. 

  6569. That can be done by making all derivatives 

  6570. \begin_inset Formula $\frac{\partial E}{\partial a_{i}}$

  6571. \end_inset

  6572. 

  6573.  equal to zero:

  6574. \begin_inset Formula \[

  6575. \frac{\partial E}{\partial a_{i}}=\frac{\partial}{\partial a_{i}}\sum_{n=0}^{L-1}\left[x[n]-\sum_{i=1}^{N}a_{i}x[n-i]\right]^{2}=0\]

  6576. 

  6577. \end_inset

  6578. 

  6579. 

  6580. \end_layout

  6581. 

  6582. \begin_layout Standard

  6583. For an order 

  6584. \begin_inset Formula $N$

  6585. \end_inset

  6586. 

  6587.  filter, the filter coefficients 

  6588. \begin_inset Formula $a_{i}$

  6589. \end_inset

  6590. 

  6591.  are found by solving the system 

  6592. \begin_inset Formula $N\times N$

  6593. \end_inset

  6594. 

  6595.  linear system 

  6596. \begin_inset Formula $\mathbf{Ra}=\mathbf{r}$

  6597. \end_inset

  6598. 

  6599. , where

  6600. \begin_inset Formula \[

  6601. \mathbf{R}=\left[\begin{array}{cccc}

  6602. R(0) & R(1) & \cdots & R(N-1)\\

  6603. R(1) & R(0) & \cdots & R(N-2)\\

  6604. \vdots & \vdots & \ddots & \vdots\\

  6605. R(N-1) & R(N-2) & \cdots & R(0)\end{array}\right]\]

  6606. 

  6607. \end_inset

  6608. 

  6609. 

  6610. \begin_inset Formula \[

  6611. \mathbf{r}=\left[\begin{array}{c}

  6612. R(1)\\

  6613. R(2)\\

  6614. \vdots\\

  6615. R(N)\end{array}\right]\]

  6616. 

  6617. \end_inset

  6618. 

  6619. with 

  6620. \begin_inset Formula $R(m)$

  6621. \end_inset

  6622. 

  6623. , the auto-correlation

  6624. \begin_inset Index

  6625. status collapsed

  6626. 

  6627. \begin_layout Plain Layout

  6628. auto-correlation

  6629. \end_layout

  6630. 

  6631. \end_inset

  6632. 

  6633.  of the signal 

  6634. \begin_inset Formula $x[n]$

  6635. \end_inset

  6636. 

  6637. , computed as:

  6638. \end_layout

  6639. 

  6640. \begin_layout Standard

  6641. \begin_inset Formula \[

  6642. R(m)=\sum_{i=0}^{N-1}x[i]x[i-m]\]

  6643. 

  6644. \end_inset

  6645. 

  6646. 

  6647. \end_layout

  6648. 

  6649. \begin_layout Standard

  6650. Because 

  6651. \begin_inset Formula $\mathbf{R}$

  6652. \end_inset

  6653. 

  6654.  is Hermitian Toeplitz, the Levinson-Durbin

  6655. \begin_inset Index

  6656. status collapsed

  6657. 

  6658. \begin_layout Plain Layout

  6659. Levinson-Durbin

  6660. \end_layout

  6661. 

  6662. \end_inset

  6663. 

  6664.  algorithm can be used, making the solution to the problem 

  6665. \begin_inset Formula $\mathcal{O}\left(N^{2}\right)$

  6666. \end_inset

  6667. 

  6668.  instead of 

  6669. \begin_inset Formula $\mathcal{O}\left(N^{3}\right)$

  6670. \end_inset

  6671. 

  6672. .

  6673.  Also, it can be proven that all the roots of 

  6674. \begin_inset Formula $A(z)$

  6675. \end_inset

  6676. 

  6677.  are within the unit circle, which means that 

  6678. \begin_inset Formula $1/A(z)$

  6679. \end_inset

  6680. 

  6681.  is always stable.

  6682.  This is in theory; in practice because of finite precision, there are two

  6683.  commonly used techniques to make sure we have a stable filter.

  6684.  First, we multiply 

  6685. \begin_inset Formula $R(0)$

  6686. \end_inset

  6687. 

  6688.  by a number slightly above one (such as 1.0001), which is equivalent to

  6689.  adding noise to the signal.

  6690.  Also, we can apply a window to the auto-correlation, which is equivalent

  6691.  to filtering in the frequency domain, reducing sharp resonances.

  6692. \end_layout

  6693. 

  6694. \begin_layout Section

  6695. Pitch Prediction

  6696. \begin_inset Index

  6697. status collapsed

  6698. 

  6699. \begin_layout Plain Layout

  6700. pitch

  6701. \end_layout

  6702. 

  6703. \end_inset

  6704. 

  6705. 

  6706. \end_layout

  6707. 

  6708. \begin_layout Standard

  6709. During voiced segments, the speech signal is periodic, so it is possible

  6710.  to take advantage of that property by approximating the excitation signal

  6711.  

  6712. \begin_inset Formula $e[n]$

  6713. \end_inset

  6714. 

  6715.  by a gain times the past of the excitation:

  6716. \end_layout

  6717. 

  6718. \begin_layout Standard

  6719. \begin_inset Formula \[

  6720. e[n]\simeq p[n]=\beta e[n-T]\ ,\]

  6721. 

  6722. \end_inset

  6723. 

  6724. where 

  6725. \begin_inset Formula $T$

  6726. \end_inset

  6727. 

  6728.  is the pitch period, 

  6729. \begin_inset Formula $\beta$

  6730. \end_inset

  6731. 

  6732.  is the pitch gain.

  6733.  We call that long-term prediction since the excitation is predicted from

  6734.  

  6735. \begin_inset Formula $e[n-T]$

  6736. \end_inset

  6737. 

  6738.  with 

  6739. \begin_inset Formula $T\gg N$

  6740. \end_inset

  6741. 

  6742. .

  6743. \end_layout

  6744. 

  6745. \begin_layout Section

  6746. Innovation Codebook

  6747. \end_layout

  6748. 

  6749. \begin_layout Standard

  6750. The final excitation 

  6751. \begin_inset Formula $e[n]$

  6752. \end_inset

  6753. 

  6754.  will be the sum of the pitch prediction and an 

  6755. \emph on

  6756. innovation

  6757. \emph default

  6758.  signal 

  6759. \begin_inset Formula $c[n]$

  6760. \end_inset

  6761. 

  6762.  taken from a fixed codebook, hence the name 

  6763. \emph on

  6764. Code

  6765. \emph default

  6766.  Excited Linear Prediction.

  6767.  The final excitation is given by

  6768. \end_layout

  6769. 

  6770. \begin_layout Standard

  6771. \begin_inset Formula \[

  6772. e[n]=p[n]+c[n]=\beta e[n-T]+c[n]\ .\]

  6773. 

  6774. \end_inset

  6775. 

  6776. The quantization of 

  6777. \begin_inset Formula $c[n]$

  6778. \end_inset

  6779. 

  6780.  is where most of the bits in a CELP codec are allocated.

  6781.  It represents the information that couldn't be obtained either from linear

  6782.  prediction or pitch prediction.

  6783.  In the 

  6784. \emph on

  6785. z

  6786. \emph default

  6787. -domain we can represent the final signal 

  6788. \begin_inset Formula $X(z)$

  6789. \end_inset

  6790. 

  6791.  as

  6792. \begin_inset Formula \[

  6793. X(z)=\frac{C(z)}{A(z)\left(1-\beta z^{-T}\right)}\]

  6794. 

  6795. \end_inset

  6796. 

  6797. 

  6798. \end_layout

  6799. 

  6800. \begin_layout Section

  6801. Noise Weighting

  6802. \begin_inset Index

  6803. status collapsed

  6804. 

  6805. \begin_layout Plain Layout

  6806. error weighting

  6807. \end_layout

  6808. 

  6809. \end_inset

  6810. 

  6811. 

  6812. \begin_inset Index

  6813. status collapsed

  6814. 

  6815. \begin_layout Plain Layout

  6816. analysis-by-synthesis

  6817. \end_layout

  6818. 

  6819. \end_inset

  6820. 

  6821. 

  6822. \end_layout

  6823. 

  6824. \begin_layout Standard

  6825. Most (if not all) modern audio codecs attempt to 

  6826. \begin_inset Quotes eld

  6827. \end_inset

  6828. 

  6829. shape

  6830. \begin_inset Quotes erd

  6831. \end_inset

  6832. 

  6833.  the noise so that it appears mostly in the frequency regions where the

  6834.  ear cannot detect it.

  6835.  For example, the ear is more tolerant to noise in parts of the spectrum

  6836.  that are louder and 

  6837. \emph on

  6838. vice versa

  6839. \emph default

  6840. .

  6841.  In order to maximize speech quality, CELP codecs minimize the mean square

  6842.  of the error (noise) in the perceptually weighted domain.

  6843.  This means that a perceptual noise weighting filter 

  6844. \begin_inset Formula $W(z)$

  6845. \end_inset

  6846. 

  6847.  is applied to the error signal in the encoder.

  6848.  In most CELP codecs, 

  6849. \begin_inset Formula $W(z)$

  6850. \end_inset

  6851. 

  6852.  is a pole-zero weighting filter derived from the linear prediction coefficients

  6853.  (LPC), generally using bandwidth expansion.

  6854.  Let the spectral envelope be represented by the synthesis filter 

  6855. \begin_inset Formula $1/A(z)$

  6856. \end_inset

  6857. 

  6858. , CELP codecs typically derive the noise weighting filter as 

  6859. \begin_inset Formula \begin{equation}

  6860. W(z)=\frac{A(z/\gamma_{1})}{A(z/\gamma_{2})}\ ,\label{eq:gamma-weighting}\end{equation}

  6861. 

  6862. \end_inset

  6863. 

  6864. where 

  6865. \begin_inset Formula $\gamma_{1}=0.9$

  6866. \end_inset

  6867. 

  6868.  and 

  6869. \begin_inset Formula $\gamma_{2}=0.6$

  6870. \end_inset

  6871. 

  6872.  in the Speex reference implementation.

  6873.  If a filter 

  6874. \begin_inset Formula $A(z)$

  6875. \end_inset

  6876. 

  6877.  has (complex) poles at 

  6878. \begin_inset Formula $p_{i}$

  6879. \end_inset

  6880. 

  6881.  in the 

  6882. \begin_inset Formula $z$

  6883. \end_inset

  6884. 

  6885. -plane, the filter 

  6886. \begin_inset Formula $A(z/\gamma)$

  6887. \end_inset

  6888. 

  6889.  will have its poles at 

  6890. \begin_inset Formula $p'_{i}=\gamma p_{i}$

  6891. \end_inset

  6892. 

  6893. , making it a flatter version of 

  6894. \begin_inset Formula $A(z)$

  6895. \end_inset

  6896. 

  6897. .

  6898. \end_layout

  6899. 

  6900. \begin_layout Standard

  6901. The weighting filter is applied to the error signal used to optimize the

  6902.  codebook search through analysis-by-synthesis (AbS).

  6903.  This results in a spectral shape of the noise that tends towards 

  6904. \begin_inset Formula $1/W(z)$

  6905. \end_inset

  6906. 

  6907. .

  6908.  While the simplicity of the model has been an important reason for the

  6909.  success of CELP, it remains that 

  6910. \begin_inset Formula $W(z)$

  6911. \end_inset

  6912. 

  6913.  is a very rough approximation for the perceptually optimal noise weighting

  6914.  function.

  6915.  Fig.

  6916.  

  6917. \begin_inset CommandInset ref

  6918. LatexCommand ref

  6919. reference "cap:Standard-noise-shaping"

  6920. 

  6921. \end_inset

  6922. 

  6923.  illustrates the noise shaping that results from Eq.

  6924.  

  6925. \begin_inset CommandInset ref

  6926. LatexCommand ref

  6927. reference "eq:gamma-weighting"

  6928. 

  6929. \end_inset

  6930. 

  6931. .

  6932.  Throughout this paper, we refer to 

  6933. \begin_inset Formula $W(z)$

  6934. \end_inset

  6935. 

  6936.  as the noise weighting filter and to 

  6937. \begin_inset Formula $1/W(z)$

  6938. \end_inset

  6939. 

  6940.  as the noise shaping filter (or curve).

  6941. \end_layout

  6942. 

  6943. \begin_layout Standard

  6944. \begin_inset Float figure

  6945. wide false

  6946. sideways false

  6947. status open

  6948. 

  6949. \begin_layout Plain Layout

  6950. \begin_inset ERT

  6951. status collapsed

  6952. 

  6953. \begin_layout Plain Layout

  6954. 

  6955. 

  6956. \backslash

  6957. begin{center}

  6958. \end_layout

  6959. 

  6960. \end_inset

  6961. 

  6962. 

  6963. \begin_inset Graphics

  6964. 	filename ref_shaping.eps

  6965. 	width 45page%

  6966. 	keepAspectRatio

  6967. 

  6968. \end_inset

  6969. 

  6970. 

  6971. \begin_inset ERT

  6972. status collapsed

  6973. 

  6974. \begin_layout Plain Layout

  6975. 

  6976. 

  6977. \backslash

  6978. end{center}

  6979. \end_layout

  6980. 

  6981. \end_inset

  6982. 

  6983. 

  6984. \end_layout

  6985. 

  6986. \begin_layout Plain Layout

  6987. \begin_inset Caption

  6988. 

  6989. \begin_layout Plain Layout

  6990. Standard noise shaping in CELP.

  6991.  Arbitrary y-axis offset.

  6992. \begin_inset CommandInset label

  6993. LatexCommand label

  6994. name "cap:Standard-noise-shaping"

  6995. 

  6996. \end_inset

  6997. 

  6998. 

  6999. \end_layout

  7000. 

  7001. \end_inset

  7002. 

  7003. 

  7004. \end_layout

  7005. 

  7006. \end_inset

  7007. 

  7008. 

  7009. \end_layout

  7010. 

  7011. \begin_layout Section

  7012. Analysis-by-Synthesis

  7013. \end_layout

  7014. 

  7015. \begin_layout Standard

  7016. One of the main principles behind CELP is called Analysis-by-Synthesis (AbS),

  7017.  meaning that the encoding (analysis) is performed by perceptually optimising

  7018.  the decoded (synthesis) signal in a closed loop.

  7019.  In theory, the best CELP stream would be produced by trying all possible

  7020.  bit combinations and selecting the one that produces the best-sounding

  7021.  decoded signal.

  7022.  This is obviously not possible in practice for two reasons: the required

  7023.  complexity is beyond any currently available hardware and the 

  7024. \begin_inset Quotes eld

  7025. \end_inset

  7026. 

  7027. best sounding

  7028. \begin_inset Quotes erd

  7029. \end_inset

  7030. 

  7031.  selection criterion implies a human listener.

  7032.  

  7033. \end_layout

  7034. 

  7035. \begin_layout Standard

  7036. In order to achieve real-time encoding using limited computing resources,

  7037.  the CELP optimisation is broken down into smaller, more manageable, sequential

  7038.  searches using the perceptual weighting function described earlier.

  7039. \end_layout

  7040. 

  7041. \begin_layout Standard

  7042. \begin_inset Newpage newpage

  7043. \end_inset

  7044. 

  7045. 

  7046. \end_layout

  7047. 

  7048. \begin_layout Chapter

  7049. The Speex Decoder Specification

  7050. \end_layout

  7051. 

  7052. \begin_layout Section

  7053. Narrowband decoder

  7054. \end_layout

  7055. 

  7056. \begin_layout Standard

  7057. <Insert decoder figure here>

  7058. \end_layout

  7059. 

  7060. \begin_layout Subsection

  7061. Narrowband modes

  7062. \end_layout

  7063. 

  7064. \begin_layout Standard

  7065. There are 7 different narrowband bit-rates defined for Speex, ranging from

  7066.  250 bps to 24.6 kbps, although the modes below 5.9 kbps should not be used

  7067.  for speech.

  7068.  The bit-allocation for each mode is detailed in table 

  7069. \begin_inset CommandInset ref

  7070. LatexCommand ref

  7071. reference "cap:bits-narrowband"

  7072. 

  7073. \end_inset

  7074. 

  7075. .

  7076.  Each frame starts with the mode ID encoded with 4 bits which allows a range

  7077.  from 0 to 15, though only the first 7 values are used (the others are reserved).

  7078.  The parameters are listed in the table in the order they are packed in

  7079.  the bit-stream.

  7080.  All frame-based parameters are packed before sub-frame parameters.

  7081.  The parameters for a certain sub-frame are all packed before the following

  7082.  sub-frame is packed.

  7083.  The 

  7084. \begin_inset Quotes eld

  7085. \end_inset

  7086. 

  7087. OL

  7088. \begin_inset Quotes erd

  7089. \end_inset

  7090. 

  7091.  in the parameter description means that the parameter is an open loop estimatio

  7092. n based on the whole frame.

  7093. \end_layout

  7094. 

  7095. \begin_layout Standard

  7096. \begin_inset Float table

  7097. placement h

  7098. wide true

  7099. sideways false

  7100. status open

  7101. 

  7102. \begin_layout Plain Layout

  7103. \begin_inset ERT

  7104. status collapsed

  7105. 

  7106. \begin_layout Plain Layout

  7107. 

  7108. 

  7109. \backslash

  7110. begin{center}

  7111. \end_layout

  7112. 

  7113. \end_inset

  7114. 

  7115. 

  7116. \begin_inset Tabular

  7117. <lyxtabular version="3" rows="12" columns="11">

  7118. <features>

  7119. <column alignment="center" valignment="top" width="0pt">

  7120. <column alignment="center" valignment="top" width="0pt">

  7121. <column alignment="center" valignment="top" width="0pt">

  7122. <column alignment="center" valignment="top" width="0pt">

  7123. <column alignment="center" valignment="top" width="0pt">

  7124. <column alignment="center" valignment="top" width="0pt">

  7125. <column alignment="center" valignment="top" width="0pt">

  7126. <column alignment="center" valignment="top" width="0pt">

  7127. <column alignment="center" valignment="top" width="0pt">

  7128. <column alignment="center" valignment="top" width="0pt">

  7129. <column alignment="center" valignment="top" width="0pt">

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  7136. \end_layout

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  7234. 

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  7279. 

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  7306. 

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  7308. 1

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  7315. 

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  7323. \begin_inset Text

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  8267. \end_inset

  8268. </cell>

  8269. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8270. \begin_inset Text

  8271. 

  8272. \begin_layout Plain Layout

  8273. 43

  8274. \end_layout

  8275. 

  8276. \end_inset

  8277. </cell>

  8278. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8279. \begin_inset Text

  8280. 

  8281. \begin_layout Plain Layout

  8282. 119

  8283. \end_layout

  8284. 

  8285. \end_inset

  8286. </cell>

  8287. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8288. \begin_inset Text

  8289. 

  8290. \begin_layout Plain Layout

  8291. 160

  8292. \end_layout

  8293. 

  8294. \end_inset

  8295. </cell>

  8296. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8297. \begin_inset Text

  8298. 

  8299. \begin_layout Plain Layout

  8300. 220

  8301. \end_layout

  8302. 

  8303. \end_inset

  8304. </cell>

  8305. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8306. \begin_inset Text

  8307. 

  8308. \begin_layout Plain Layout

  8309. 300

  8310. \end_layout

  8311. 

  8312. \end_inset

  8313. </cell>

  8314. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8315. \begin_inset Text

  8316. 

  8317. \begin_layout Plain Layout

  8318. 364

  8319. \end_layout

  8320. 

  8321. \end_inset

  8322. </cell>

  8323. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8324. \begin_inset Text

  8325. 

  8326. \begin_layout Plain Layout

  8327. 492

  8328. \end_layout

  8329. 

  8330. \end_inset

  8331. </cell>

  8332. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">

  8333. \begin_inset Text

  8334. 

  8335. \begin_layout Plain Layout

  8336. 79

  8337. \end_layout

  8338. 

  8339. \end_inset

  8340. </cell>

  8341. </row>

  8342. </lyxtabular>

  8343. 

  8344. \end_inset

  8345. 

  8346. 

  8347. \begin_inset ERT

  8348. status collapsed

  8349. 

  8350. \begin_layout Plain Layout

  8351. 

  8352. 

  8353. \backslash

  8354. end{center}

  8355. \end_layout

  8356. 

  8357. \end_inset

  8358. 

  8359. 

  8360. \end_layout

  8361. 

  8362. \begin_layout Plain Layout

  8363. \begin_inset Caption

  8364. 

  8365. \begin_layout Plain Layout

  8366. Bit allocation for narrowband modes

  8367. \begin_inset CommandInset label

  8368. LatexCommand label

  8369. name "cap:bits-narrowband"

  8370. 

  8371. \end_inset

  8372. 

  8373. 

  8374. \end_layout

  8375. 

  8376. \end_inset

  8377. 

  8378. 

  8379. \end_layout

  8380. 

  8381. \end_inset

  8382. 

  8383. 

  8384. \end_layout

  8385. 

  8386. \begin_layout Subsection

  8387. LSP decoding

  8388. \end_layout

  8389. 

  8390. \begin_layout Standard

  8391. Depending on the mode, LSP parameters are encoded using either 18 bits or

  8392.  30 bits.

  8393. \end_layout

  8394. 

  8395. \begin_layout Standard

  8396. Interpolation

  8397. \end_layout

  8398. 

  8399. \begin_layout Standard

  8400. Safe margin

  8401. \end_layout

  8402. 

  8403. \begin_layout Subsection

  8404. Adaptive codebook

  8405. \end_layout

  8406. 

  8407. \begin_layout Standard

  8408. For rates of 8 kbit/s and above, the pitch period is encoded for each subframe.

  8409.  The real period is 

  8410. \begin_inset Formula $T=p_{i}+17$

  8411. \end_inset

  8412. 

  8413.  where 

  8414. \begin_inset Formula $p_{i}$

  8415. \end_inset

  8416. 

  8417.  is a value encoded with 7 bits and 17 corresponds to the minimum pitch.

  8418.  The maximum period is 144.

  8419.  At 5.95 kbit/s (mode 2), the pitch period is similarly encoded, but only

  8420.  once for the frame.

  8421.  Each sub-frame then has a 2-bit offset that is added to the pitch value

  8422.  of the frame.

  8423.  In that case, the pitch for each sub-frame is equal to 

  8424. \begin_inset Formula $T-1+offset$

  8425. \end_inset

  8426. 

  8427. .

  8428.  For rates below 5.95 kbit/s, only the per-frame pitch is used and the pitch

  8429.  is constant for all sub-frames.

  8430. \end_layout

  8431. 

  8432. \begin_layout Standard

  8433. Speex uses a 3-tap predictor for rates of 5.95 kbit/s and above.

  8434.  The three gain values are obtained from a 5-bit or a 7-bit codebook, depending

  8435.  on the mode.

  8436.   

  8437. \end_layout

  8438. 

  8439. \begin_layout Subsection

  8440. Innovation codebook

  8441. \end_layout

  8442. 

  8443. \begin_layout Standard

  8444. Split codebook, size and entries depend on bit-rate

  8445. \end_layout

  8446. 

  8447. \begin_layout Standard

  8448. a 5-bit gain is encoder on a per-frame basis

  8449. \end_layout

  8450. 

  8451. \begin_layout Standard

  8452. Depending on the mode, higher resolution per sub-frame

  8453. \end_layout

  8454. 

  8455. \begin_layout Standard

  8456. innovation sub-vectors concatenated, gain applied

  8457. \end_layout

  8458. 

  8459. \begin_layout Subsection

  8460. Perceptual enhancement

  8461. \end_layout

  8462. 

  8463. \begin_layout Standard

  8464. Optional, implementation-defined.

  8465.  

  8466. \end_layout

  8467. 

  8468. \begin_layout Subsection

  8469. Bit-stream definition

  8470. \end_layout

  8471. 

  8472. \begin_layout Standard

  8473. This section defines the bit-stream that is transmitted on the wire.

  8474.  One speex packet consist of 1 frame header and 4 sub-frames:

  8475. \end_layout

  8476. 

  8477. \begin_layout Standard

  8478. \begin_inset Tabular

  8479. <lyxtabular version="3" rows="1" columns="5">

  8480. <features>

  8481. <column alignment="center" valignment="top" width="0">

  8482. <column alignment="center" valignment="top" width="0">

  8483. <column alignment="center" valignment="top" width="0">

  8484. <column alignment="center" valignment="top" width="0">

  8485. <column alignment="center" valignment="top" width="0">

  8486. <row>

  8487. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8488. \begin_inset Text

  8489. 

  8490. \begin_layout Plain Layout

  8491. Frame Header

  8492. \end_layout

  8493. 

  8494. \end_inset

  8495. </cell>

  8496. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8497. \begin_inset Text

  8498. 

  8499. \begin_layout Plain Layout

  8500. Subframe 1

  8501. \end_layout

  8502. 

  8503. \end_inset

  8504. </cell>

  8505. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8506. \begin_inset Text

  8507. 

  8508. \begin_layout Plain Layout

  8509. Subframe2

  8510. \end_layout

  8511. 

  8512. \end_inset

  8513. </cell>

  8514. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8515. \begin_inset Text

  8516. 

  8517. \begin_layout Plain Layout

  8518. Subframe 3

  8519. \end_layout

  8520. 

  8521. \end_inset

  8522. </cell>

  8523. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">

  8524. \begin_inset Text

  8525. 

  8526. \begin_layout Plain Layout

  8527. Subframe 4

  8528. \end_layout

  8529. 

  8530. \end_inset

  8531. </cell>

  8532. </row>

  8533. </lyxtabular>

  8534. 

  8535. \end_inset

  8536. 

  8537. 

  8538. \end_layout

  8539. 

  8540. \begin_layout Standard

  8541. The frame header is variable length, depending on decoding mode and submode.

  8542.  The narrowband frame header is defined as follows:

  8543. \end_layout

  8544. 

  8545. \begin_layout Standard

  8546. \begin_inset Tabular

  8547. <lyxtabular version="3" rows="1" columns="6">

  8548. <features>

  8549. <column alignment="center" valignment="top" width="0">

  8550. <column alignment="center" valignment="top" width="0">

  8551. <column alignment="center" valignment="top" width="0">

  8552. <column alignment="center" valignment="top" width="0">

  8553. <column alignment="center" valignment="top" width="0">

  8554. <column alignment="center" valignment="top" width="0">

  8555. <row>

  8556. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8557. \begin_inset Text

  8558. 

  8559. \begin_layout Plain Layout

  8560. wb bit

  8561. \end_layout

  8562. 

  8563. \end_inset

  8564. </cell>

  8565. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8566. \begin_inset Text

  8567. 

  8568. \begin_layout Plain Layout

  8569. modeid

  8570. \end_layout

  8571. 

  8572. \end_inset

  8573. </cell>

  8574. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8575. \begin_inset Text

  8576. 

  8577. \begin_layout Plain Layout

  8578. LSP

  8579. \end_layout

  8580. 

  8581. \end_inset

  8582. </cell>

  8583. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8584. \begin_inset Text

  8585. 

  8586. \begin_layout Plain Layout

  8587. OL-pitch

  8588. \end_layout

  8589. 

  8590. \end_inset

  8591. </cell>

  8592. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8593. \begin_inset Text

  8594. 

  8595. \begin_layout Plain Layout

  8596. OL-pitchgain

  8597. \end_layout

  8598. 

  8599. \end_inset

  8600. </cell>

  8601. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">

  8602. \begin_inset Text

  8603. 

  8604. \begin_layout Plain Layout

  8605. OL ExcGain

  8606. \end_layout

  8607. 

  8608. \end_inset

  8609. </cell>

  8610. </row>

  8611. </lyxtabular>

  8612. 

  8613. \end_inset

  8614. 

  8615. 

  8616. \end_layout

  8617. 

  8618. \begin_layout Standard

  8619. wb-bit: Wideband bit (1 bit) 0=narrowband, 1=wideband

  8620. \end_layout

  8621. 

  8622. \begin_layout Standard

  8623. modeid: Mode identifier (4 bits)

  8624. \end_layout

  8625. 

  8626. \begin_layout Standard

  8627. LSP: Line Spectral Pairs (0, 18 or 30 bits)

  8628. \end_layout

  8629. 

  8630. \begin_layout Standard

  8631. OL-pitch: Open Loop Pitch (0 or 7 bits)

  8632. \end_layout

  8633. 

  8634. \begin_layout Standard

  8635. OL-pitchgain: Open Loop Pitch Gain (0 or 4 bits)

  8636. \end_layout

  8637. 

  8638. \begin_layout Standard

  8639. OL-ExcGain: Open Loop Excitation Gain (0 or 5 bits)

  8640. \end_layout

  8641. 

  8642. \begin_layout Standard

  8643. ...

  8644. \end_layout

  8645. 

  8646. \begin_layout Standard

  8647. Each subframe is defined as follows:

  8648. \end_layout

  8649. 

  8650. \begin_layout Standard

  8651. \begin_inset Tabular

  8652. <lyxtabular version="3" rows="1" columns="4">

  8653. <features>

  8654. <column alignment="center" valignment="top" width="0">

  8655. <column alignment="center" valignment="top" width="0">

  8656. <column alignment="center" valignment="top" width="0">

  8657. <column alignment="center" valignment="top" width="0">

  8658. <row>

  8659. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8660. \begin_inset Text

  8661. 

  8662. \begin_layout Plain Layout

  8663. FinePitch

  8664. \end_layout

  8665. 

  8666. \end_inset

  8667. </cell>

  8668. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8669. \begin_inset Text

  8670. 

  8671. \begin_layout Plain Layout

  8672. PitchGain

  8673. \end_layout

  8674. 

  8675. \end_inset

  8676. </cell>

  8677. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  8678. \begin_inset Text

  8679. 

  8680. \begin_layout Plain Layout

  8681. InnovationGain

  8682. \end_layout

  8683. 

  8684. \end_inset

  8685. </cell>

  8686. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">

  8687. \begin_inset Text

  8688. 

  8689. \begin_layout Plain Layout

  8690. Innovation VQ

  8691. \end_layout

  8692. 

  8693. \end_inset

  8694. </cell>

  8695. </row>

  8696. </lyxtabular>

  8697. 

  8698. \end_inset

  8699. 

  8700. 

  8701. \end_layout

  8702. 

  8703. \begin_layout Standard

  8704. FinePitch: (0 or 7 bits)

  8705. \end_layout

  8706. 

  8707. \begin_layout Standard

  8708. PitchGain: (0, 5, or 7 bits)

  8709. \end_layout

  8710. 

  8711. \begin_layout Standard

  8712. Innovation Gain: (0, 1, 3 bits)

  8713. \end_layout

  8714. 

  8715. \begin_layout Standard

  8716. Innovation VQ: (0-96 bits)

  8717. \end_layout

  8718. 

  8719. \begin_layout Standard

  8720. ...

  8721. \end_layout

  8722. 

  8723. \begin_layout Subsection

  8724. Sample decoder

  8725. \end_layout

  8726. 

  8727. \begin_layout Standard

  8728. This section contains some sample source code, showing how a basic Speex

  8729.  decoder can be implemented.

  8730.  The sample decoder is narrowband submode 3 only, and with no advanced features

  8731.  like enhancement, vbr etc.

  8732. \end_layout

  8733. 

  8734. \begin_layout Standard

  8735. ...

  8736. \end_layout

  8737. 

  8738. \begin_layout Subsection

  8739. Lookup tables

  8740. \end_layout

  8741. 

  8742. \begin_layout Standard

  8743. The Speex decoder includes a set of lookup tables and codebooks, which are

  8744.  used to convert between values of different domains.

  8745.  This includes:

  8746. \end_layout

  8747. 

  8748. \begin_layout Standard

  8749. - Excitation 10x16 (3200 bps)

  8750. \end_layout

  8751. 

  8752. \begin_layout Standard

  8753. - Excitation 10x32 (4000 bps)

  8754. \end_layout

  8755. 

  8756. \begin_layout Standard

  8757. - Excitation 20x32 (2000 bps)

  8758. \end_layout

  8759. 

  8760. \begin_layout Standard

  8761. - Excitation 5x256 (12800 bps)

  8762. \end_layout

  8763. 

  8764. \begin_layout Standard

  8765. - Excitation 5x64 (9600 bps)

  8766. \end_layout

  8767. 

  8768. \begin_layout Standard

  8769. - Excitation 8x128 (7000 bps)

  8770. \end_layout

  8771. 

  8772. \begin_layout Standard

  8773. - Codebook for 3-tap pitch prediction gain (Normal and Low Bitrate)

  8774. \end_layout

  8775. 

  8776. \begin_layout Standard

  8777. - Codebook for LSPs in narrowband CELP mode

  8778. \end_layout

  8779. 

  8780. \begin_layout Standard

  8781. ...

  8782. \end_layout

  8783. 

  8784. \begin_layout Standard

  8785. The exact lookup tables are included here for reference.

  8786. \end_layout

  8787. 

  8788. \begin_layout Section

  8789. Wideband embedded decoder

  8790. \end_layout

  8791. 

  8792. \begin_layout Standard

  8793. QMF filter.

  8794.  Narrowband signal decoded using narrowband decoder

  8795. \end_layout

  8796. 

  8797. \begin_layout Standard

  8798. For the high band, the decoder is similar to the narrowband decoder, with

  8799.  the main difference being that there is no adaptive codebook.

  8800. \end_layout

  8801. 

  8802. \begin_layout Standard

  8803. Gain is per-subframe

  8804. \end_layout

  8805. 

  8806. \begin_layout Chapter

  8807. Speex narrowband mode

  8808. \begin_inset CommandInset label

  8809. LatexCommand label

  8810. name "sec:Speex-narrowband-mode"

  8811. 

  8812. \end_inset

  8813. 

  8814. 

  8815. \begin_inset Index

  8816. status collapsed

  8817. 

  8818. \begin_layout Plain Layout

  8819. narrowband

  8820. \end_layout

  8821. 

  8822. \end_inset

  8823. 

  8824. 

  8825. \end_layout

  8826. 

  8827. \begin_layout Standard

  8828. This section looks at how Speex works for narrowband (

  8829. \begin_inset Formula $8\:\mathrm{kHz}$

  8830. \end_inset

  8831. 

  8832.  sampling rate) operation.

  8833.  The frame size for this mode is 

  8834. \begin_inset Formula $20\:\mathrm{ms}$

  8835. \end_inset

  8836. 

  8837. , corresponding to 160 samples.

  8838.  Each frame is also subdivided into 4 sub-frames of 40 samples each.

  8839. \end_layout

  8840. 

  8841. \begin_layout Standard

  8842. Also many design decisions were based on the original goals and assumptions:

  8843. \end_layout

  8844. 

  8845. \begin_layout Itemize

  8846. Minimizing the amount of information extracted from past frames (for robustness

  8847.  to packet loss)

  8848. \end_layout

  8849. 

  8850. \begin_layout Itemize

  8851. Dynamically-selectable codebooks (LSP, pitch and innovation)

  8852. \end_layout

  8853. 

  8854. \begin_layout Itemize

  8855. sub-vector fixed (innovation) codebooks

  8856. \end_layout

  8857. 

  8858. \begin_layout Section

  8859. Whole-Frame Analysis

  8860. \begin_inset Index

  8861. status collapsed

  8862. 

  8863. \begin_layout Plain Layout

  8864. linear prediction

  8865. \end_layout

  8866. 

  8867. \end_inset

  8868. 

  8869. 

  8870. \end_layout

  8871. 

  8872. \begin_layout Standard

  8873. In narrowband, Speex frames are 20 ms long (160 samples) and are subdivided

  8874.  in 4 sub-frames of 5 ms each (40 samples).

  8875.  For most narrowband bit-rates (8 kbps and above), the only parameters encoded

  8876.  at the frame level are the Line Spectral Pairs (LSP) and a global excitation

  8877.  gain 

  8878. \begin_inset Formula $g_{frame}$

  8879. \end_inset

  8880. 

  8881. , as shown in Fig.

  8882.  

  8883. \begin_inset CommandInset ref

  8884. LatexCommand ref

  8885. reference "cap:Frame-open-loop-analysis"

  8886. 

  8887. \end_inset

  8888. 

  8889. .

  8890.  All other parameters are encoded at the sub-frame level.

  8891. \end_layout

  8892. 

  8893. \begin_layout Standard

  8894. Linear prediction analysis is performed once per frame using an asymmetric

  8895.  Hamming window centered on the fourth sub-frame.

  8896.  Because linear prediction coefficients (LPC) are not robust to quantization,

  8897.  they are first converted to line spectral pairs (LSP)

  8898. \begin_inset Index

  8899. status collapsed

  8900. 

  8901. \begin_layout Plain Layout

  8902. line spectral pair

  8903. \end_layout

  8904. 

  8905. \end_inset

  8906. 

  8907. .

  8908.  The LSP's are considered to be associated to the 

  8909. \begin_inset Formula $4^{th}$

  8910. \end_inset

  8911. 

  8912.  sub-frames and the LSP's associated to the first 3 sub-frames are linearly

  8913.  interpolated using the current and previous LSP coefficients.

  8914.  The LSP coefficients and converted back to the LPC filter 

  8915. \begin_inset Formula $\hat{A}(z)$

  8916. \end_inset

  8917. 

  8918. .

  8919.  The non-quantized interpolated filter is denoted 

  8920. \begin_inset Formula $A(z)$

  8921. \end_inset

  8922. 

  8923.  and can be used for the weighting filter 

  8924. \begin_inset Formula $W(z)$

  8925. \end_inset

  8926. 

  8927.  because it does not need to be available to the decoder.

  8928.  

  8929. \end_layout

  8930. 

  8931. \begin_layout Standard

  8932. To make Speex more robust to packet loss, no prediction is applied on the

  8933.  LSP coefficients prior to quantization.

  8934.  The LSPs are encoded using vector quantization (VQ) with 30 bits for higher

  8935.  quality modes and 18 bits for lower quality.

  8936. \end_layout

  8937. 

  8938. \begin_layout Standard

  8939. \begin_inset Float figure

  8940. wide false

  8941. sideways false

  8942. status open

  8943. 

  8944. \begin_layout Plain Layout

  8945. \begin_inset ERT

  8946. status collapsed

  8947. 

  8948. \begin_layout Plain Layout

  8949. 

  8950. 

  8951. \backslash

  8952. begin{center}

  8953. \end_layout

  8954. 

  8955. \end_inset

  8956. 

  8957. 

  8958. \begin_inset Graphics

  8959. 	filename speex_analysis.eps

  8960. 	width 35page%

  8961. 

  8962. \end_inset

  8963. 

  8964. 

  8965. \begin_inset ERT

  8966. status collapsed

  8967. 

  8968. \begin_layout Plain Layout

  8969. 

  8970. 

  8971. \backslash

  8972. end{center}

  8973. \end_layout

  8974. 

  8975. \end_inset

  8976. 

  8977. 

  8978. \end_layout

  8979. 

  8980. \begin_layout Plain Layout

  8981. \begin_inset Caption

  8982. 

  8983. \begin_layout Plain Layout

  8984. Frame open-loop analysis

  8985. \begin_inset CommandInset label

  8986. LatexCommand label

  8987. name "cap:Frame-open-loop-analysis"

  8988. 

  8989. \end_inset

  8990. 

  8991. 

  8992. \end_layout

  8993. 

  8994. \end_inset

  8995. 

  8996. 

  8997. \end_layout

  8998. 

  8999. \end_inset

  9000. 

  9001. 

  9002. \end_layout

  9003. 

  9004. \begin_layout Section

  9005. Sub-Frame Analysis-by-Synthesis

  9006. \end_layout

  9007. 

  9008. \begin_layout Standard

  9009. \begin_inset Float figure

  9010. wide false

  9011. sideways false

  9012. status open

  9013. 

  9014. \begin_layout Plain Layout

  9015. \begin_inset ERT

  9016. status collapsed

  9017. 

  9018. \begin_layout Plain Layout

  9019. 

  9020. 

  9021. \backslash

  9022. begin{center}

  9023. \end_layout

  9024. 

  9025. \end_inset

  9026. 

  9027. 

  9028. \begin_inset Graphics

  9029. 	filename speex_abs.eps

  9030. 	lyxscale 75

  9031. 	width 40page%

  9032. 

  9033. \end_inset

  9034. 

  9035. 

  9036. \begin_inset ERT

  9037. status collapsed

  9038. 

  9039. \begin_layout Plain Layout

  9040. 

  9041. 

  9042. \backslash

  9043. end{center}

  9044. \end_layout

  9045. 

  9046. \end_inset

  9047. 

  9048. 

  9049. \end_layout

  9050. 

  9051. \begin_layout Plain Layout

  9052. \begin_inset Caption

  9053. 

  9054. \begin_layout Plain Layout

  9055. Analysis-by-synthesis closed-loop optimization on a sub-frame.

  9056. \begin_inset CommandInset label

  9057. LatexCommand label

  9058. name "cap:Sub-frame-AbS"

  9059. 

  9060. \end_inset

  9061. 

  9062. 

  9063. \end_layout

  9064. 

  9065. \end_inset

  9066. 

  9067. 

  9068. \end_layout

  9069. 

  9070. \end_inset

  9071. 

  9072. 

  9073. \end_layout

  9074. 

  9075. \begin_layout Standard

  9076. The analysis-by-synthesis (AbS) encoder loop is described in Fig.

  9077.  

  9078. \begin_inset CommandInset ref

  9079. LatexCommand ref

  9080. reference "cap:Sub-frame-AbS"

  9081. 

  9082. \end_inset

  9083. 

  9084. .

  9085.  There are three main aspects where Speex significantly differs from most

  9086.  other CELP codecs.

  9087.  First, while most recent CELP codecs make use of fractional pitch estimation

  9088.  with a single gain, Speex uses an integer to encode the pitch period, but

  9089.  uses a 3-tap predictor (3 gains).

  9090.  The adaptive codebook contribution 

  9091. \begin_inset Formula $e_{a}[n]$

  9092. \end_inset

  9093. 

  9094.  can thus be expressed as:

  9095. \begin_inset Formula \begin{equation}

  9096. e_{a}[n]=g_{0}e[n-T-1]+g_{1}e[n-T]+g_{2}e[n-T+1]\label{eq:adaptive-3tap}\end{equation}

  9097. 

  9098. \end_inset

  9099. 

  9100. where 

  9101. \begin_inset Formula $g_{0}$

  9102. \end_inset

  9103. 

  9104. , 

  9105. \begin_inset Formula $g_{1}$

  9106. \end_inset

  9107. 

  9108.  and 

  9109. \begin_inset Formula $g_{2}$

  9110. \end_inset

  9111. 

  9112.  are the jointly quantized pitch gains and 

  9113. \begin_inset Formula $e[n]$

  9114. \end_inset

  9115. 

  9116.  is the codec excitation memory.

  9117.  It is worth noting that when the pitch is smaller than the sub-frame size,

  9118.  we repeat the excitation at a period 

  9119. \begin_inset Formula $T$

  9120. \end_inset

  9121. 

  9122. .

  9123.  For example, when 

  9124. \begin_inset Formula $n-T+1\geq0$

  9125. \end_inset

  9126. 

  9127. , we use 

  9128. \begin_inset Formula $n-2T+1$

  9129. \end_inset

  9130. 

  9131.  instead.

  9132.  In most modes, the pitch period is encoded with 7 bits in the 

  9133. \begin_inset Formula $\left[17,144\right]$

  9134. \end_inset

  9135. 

  9136.  range and the 

  9137. \begin_inset Formula $\beta_{i}$

  9138. \end_inset

  9139. 

  9140.  coefficients are vector-quantized using 7 bits at higher bit-rates (15

  9141.  kbps narrowband and above) and 5 bits at lower bit-rates (11 kbps narrowband

  9142.  and below).

  9143. \end_layout

  9144. 

  9145. \begin_layout Standard

  9146. Many current CELP codecs use moving average (MA) prediction to encode the

  9147.  fixed codebook gain.

  9148.  This provides slightly better coding at the expense of introducing a dependency

  9149.  on previously encoded frames.

  9150.  A second difference is that Speex encodes the fixed codebook gain as the

  9151.  product of the global excitation gain 

  9152. \begin_inset Formula $g_{frame}$

  9153. \end_inset

  9154. 

  9155.  with a sub-frame gain corrections 

  9156. \begin_inset Formula $g_{subf}$

  9157. \end_inset

  9158. 

  9159. .

  9160.  This increases robustness to packet loss by eliminating the inter-frame

  9161.  dependency.

  9162.  The sub-frame gain correction is encoded before the fixed codebook is searched

  9163.  (not closed-loop optimized) and uses between 0 and 3 bits per sub-frame,

  9164.  depending on the bit-rate.

  9165. \end_layout

  9166. 

  9167. \begin_layout Standard

  9168. The third difference is that Speex uses sub-vector quantization of the innovatio

  9169. n (fixed codebook) signal instead of an algebraic codebook.

  9170.  Each sub-frame is divided into sub-vectors of lengths ranging between 5

  9171.  and 20 samples.

  9172.  Each sub-vector is chosen from a bitrate-dependent codebook and all sub-vectors

  9173.  are concatenated to form a sub-frame.

  9174.  As an example, the 3.95 kbps mode uses a sub-vector size of 20 samples with

  9175.  32 entries in the codebook (5 bits).

  9176.  This means that the innovation is encoded with 10 bits per sub-frame, or

  9177.  2000 bps.

  9178.  On the other hand, the 18.2 kbps mode uses a sub-vector size of 5 samples

  9179.  with 256 entries in the codebook (8 bits), so the innovation uses 64 bits

  9180.  per sub-frame, or 12800 bps.

  9181.  

  9182. \end_layout

  9183. 

  9184. \begin_layout Section

  9185. Bit-rates

  9186. \end_layout

  9187. 

  9188. \begin_layout Standard

  9189. So far, no MOS (Mean Opinion Score

  9190. \begin_inset Index

  9191. status collapsed

  9192. 

  9193. \begin_layout Plain Layout

  9194. mean opinion score

  9195. \end_layout

  9196. 

  9197. \end_inset

  9198. 

  9199. ) subjective evaluation has been performed for Speex.

  9200.  In order to give an idea of the quality achievable with it, table 

  9201. \begin_inset CommandInset ref

  9202. LatexCommand ref

  9203. reference "cap:quality_vs_bps"

  9204. 

  9205. \end_inset

  9206. 

  9207.  presents my own subjective opinion on it.

  9208.  It should be noted that different people will perceive the quality differently

  9209.  and that the person that designed the codec often has a bias (one way or

  9210.  another) when it comes to subjective evaluation.

  9211.  Last thing, it should be noted that for most codecs (including Speex) encoding

  9212.  quality sometimes varies depending on the input.

  9213.  Note that the complexity is only approximate (within 0.5 mflops and using

  9214.  the lowest complexity setting).

  9215.  Decoding requires approximately 0.5 mflops

  9216. \begin_inset Index

  9217. status collapsed

  9218. 

  9219. \begin_layout Plain Layout

  9220. complexity

  9221. \end_layout

  9222. 

  9223. \end_inset

  9224. 

  9225.  in most modes (1 mflops with perceptual enhancement).

  9226. \end_layout

  9227. 

  9228. \begin_layout Standard

  9229. \begin_inset Float table

  9230. placement h

  9231. wide true

  9232. sideways false

  9233. status open

  9234. 

  9235. \begin_layout Plain Layout

  9236. \begin_inset ERT

  9237. status collapsed

  9238. 

  9239. \begin_layout Plain Layout

  9240. 

  9241. 

  9242. \backslash

  9243. begin{center}

  9244. \end_layout

  9245. 

  9246. \end_inset

  9247. 

  9248. 

  9249. \begin_inset Tabular

  9250. <lyxtabular version="3" rows="17" columns="5">

  9251. <features>

  9252. <column alignment="center" valignment="top" width="0pt">

  9253. <column alignment="center" valignment="top" width="0pt">

  9254. <column alignment="center" valignment="top" width="0pt">

  9255. <column alignment="center" valignment="top" width="0pt">

  9256. <column alignment="center" valignment="top" width="0pt">

  9257. <row>

  9258. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  9259. \begin_inset Text

  9260. 

  9261. \begin_layout Plain Layout

  9262. Mode

  9263. \end_layout

  9264. 

  9265. \end_inset

  9266. </cell>

  9267. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  9268. \begin_inset Text

  9269. 

  9270. \begin_layout Plain Layout

  9271. Quality

  9272. \end_layout

  9273. 

  9274. \end_inset

  9275. </cell>

  9276. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  9277. \begin_inset Text

  9278. 

  9279. \begin_layout Plain Layout

  9280. Bit-rate

  9281. \begin_inset Index

  9282. status collapsed

  9283. 

  9284. \begin_layout Plain Layout

  9285. bit-rate

  9286. \end_layout

  9287. 

  9288. \end_inset

  9289. 

  9290.  (bps)

  9291. \end_layout

  9292. 

  9293. \end_inset

  9294. </cell>

  9295. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  9296. \begin_inset Text

  9297. 

  9298. \begin_layout Plain Layout

  9299. mflops

  9300. \begin_inset Index

  9301. status collapsed

  9302. 

  9303. \begin_layout Plain Layout

  9304. complexity

  9305. \end_layout

  9306. 

  9307. \end_inset

  9308. 

  9309. 

  9310. \end_layout

  9311. 

  9312. \end_inset

  9313. </cell>

  9314. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">

  9315. \begin_inset Text

  9316. 

  9317. \begin_layout Plain Layout

  9318. Quality/description

  9319. \end_layout

  9320. 

  9321. \end_inset

  9322. </cell>

  9323. </row>

  9324. <row>

  9325. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9326. \begin_inset Text

  9327. 

  9328. \begin_layout Plain Layout

  9329. 0

  9330. \end_layout

  9331. 

  9332. \end_inset

  9333. </cell>

  9334. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9335. \begin_inset Text

  9336. 

  9337. \begin_layout Plain Layout

  9338. -

  9339. \end_layout

  9340. 

  9341. \end_inset

  9342. </cell>

  9343. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9344. \begin_inset Text

  9345. 

  9346. \begin_layout Plain Layout

  9347. 250

  9348. \end_layout

  9349. 

  9350. \end_inset

  9351. </cell>

  9352. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9353. \begin_inset Text

  9354. 

  9355. \begin_layout Plain Layout

  9356. 0

  9357. \end_layout

  9358. 

  9359. \end_inset

  9360. </cell>

  9361. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  9362. \begin_inset Text

  9363. 

  9364. \begin_layout Plain Layout

  9365. No transmission (DTX)

  9366. \end_layout

  9367. 

  9368. \end_inset

  9369. </cell>

  9370. </row>

  9371. <row>

  9372. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9373. \begin_inset Text

  9374. 

  9375. \begin_layout Plain Layout

  9376. 1

  9377. \end_layout

  9378. 

  9379. \end_inset

  9380. </cell>

  9381. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9382. \begin_inset Text

  9383. 

  9384. \begin_layout Plain Layout

  9385. 0

  9386. \end_layout

  9387. 

  9388. \end_inset

  9389. </cell>

  9390. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9391. \begin_inset Text

  9392. 

  9393. \begin_layout Plain Layout

  9394. 2,150

  9395. \end_layout

  9396. 

  9397. \end_inset

  9398. </cell>

  9399. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9400. \begin_inset Text

  9401. 

  9402. \begin_layout Plain Layout

  9403. 6

  9404. \end_layout

  9405. 

  9406. \end_inset

  9407. </cell>

  9408. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  9409. \begin_inset Text

  9410. 

  9411. \begin_layout Plain Layout

  9412. Vocoder (mostly for comfort noise)

  9413. \end_layout

  9414. 

  9415. \end_inset

  9416. </cell>

  9417. </row>

  9418. <row>

  9419. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9420. \begin_inset Text

  9421. 

  9422. \begin_layout Plain Layout

  9423. 2

  9424. \end_layout

  9425. 

  9426. \end_inset

  9427. </cell>

  9428. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9429. \begin_inset Text

  9430. 

  9431. \begin_layout Plain Layout

  9432. 2

  9433. \end_layout

  9434. 

  9435. \end_inset

  9436. </cell>

  9437. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9438. \begin_inset Text

  9439. 

  9440. \begin_layout Plain Layout

  9441. 5,950

  9442. \end_layout

  9443. 

  9444. \end_inset

  9445. </cell>

  9446. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9447. \begin_inset Text

  9448. 

  9449. \begin_layout Plain Layout

  9450. 9

  9451. \end_layout

  9452. 

  9453. \end_inset

  9454. </cell>

  9455. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  9456. \begin_inset Text

  9457. 

  9458. \begin_layout Plain Layout

  9459. Very noticeable artifacts/noise, good intelligibility

  9460. \end_layout

  9461. 

  9462. \end_inset

  9463. </cell>

  9464. </row>

  9465. <row>

  9466. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9467. \begin_inset Text

  9468. 

  9469. \begin_layout Plain Layout

  9470. 3

  9471. \end_layout

  9472. 

  9473. \end_inset

  9474. </cell>

  9475. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9476. \begin_inset Text

  9477. 

  9478. \begin_layout Plain Layout

  9479. 3-4

  9480. \end_layout

  9481. 

  9482. \end_inset

  9483. </cell>

  9484. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9485. \begin_inset Text

  9486. 

  9487. \begin_layout Plain Layout

  9488. 8,000

  9489. \end_layout

  9490. 

  9491. \end_inset

  9492. </cell>

  9493. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9494. \begin_inset Text

  9495. 

  9496. \begin_layout Plain Layout

  9497. 10

  9498. \end_layout

  9499. 

  9500. \end_inset

  9501. </cell>

  9502. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  9503. \begin_inset Text

  9504. 

  9505. \begin_layout Plain Layout

  9506. Artifacts/noise sometimes noticeable

  9507. \end_layout

  9508. 

  9509. \end_inset

  9510. </cell>

  9511. </row>

  9512. <row>

  9513. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9514. \begin_inset Text

  9515. 

  9516. \begin_layout Plain Layout

  9517. 4

  9518. \end_layout

  9519. 

  9520. \end_inset

  9521. </cell>

  9522. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9523. \begin_inset Text

  9524. 

  9525. \begin_layout Plain Layout

  9526. 5-6

  9527. \end_layout

  9528. 

  9529. \end_inset

  9530. </cell>

  9531. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9532. \begin_inset Text

  9533. 

  9534. \begin_layout Plain Layout

  9535. 11,000

  9536. \end_layout

  9537. 

  9538. \end_inset

  9539. </cell>

  9540. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9541. \begin_inset Text

  9542. 

  9543. \begin_layout Plain Layout

  9544. 14

  9545. \end_layout

  9546. 

  9547. \end_inset

  9548. </cell>

  9549. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  9550. \begin_inset Text

  9551. 

  9552. \begin_layout Plain Layout

  9553. Artifacts usually noticeable only with headphones

  9554. \end_layout

  9555. 

  9556. \end_inset

  9557. </cell>

  9558. </row>

  9559. <row>

  9560. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9561. \begin_inset Text

  9562. 

  9563. \begin_layout Plain Layout

  9564. 5

  9565. \end_layout

  9566. 

  9567. \end_inset

  9568. </cell>

  9569. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9570. \begin_inset Text

  9571. 

  9572. \begin_layout Plain Layout

  9573. 7-8

  9574. \end_layout

  9575. 

  9576. \end_inset

  9577. </cell>

  9578. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9579. \begin_inset Text

  9580. 

  9581. \begin_layout Plain Layout

  9582. 15,000

  9583. \end_layout

  9584. 

  9585. \end_inset

  9586. </cell>

  9587. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9588. \begin_inset Text

  9589. 

  9590. \begin_layout Plain Layout

  9591. 11

  9592. \end_layout

  9593. 

  9594. \end_inset

  9595. </cell>

  9596. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  9597. \begin_inset Text

  9598. 

  9599. \begin_layout Plain Layout

  9600. Need good headphones to tell the difference

  9601. \end_layout

  9602. 

  9603. \end_inset

  9604. </cell>

  9605. </row>

  9606. <row>

  9607. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9608. \begin_inset Text

  9609. 

  9610. \begin_layout Plain Layout

  9611. 6

  9612. \end_layout

  9613. 

  9614. \end_inset

  9615. </cell>

  9616. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9617. \begin_inset Text

  9618. 

  9619. \begin_layout Plain Layout

  9620. 9

  9621. \end_layout

  9622. 

  9623. \end_inset

  9624. </cell>

  9625. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9626. \begin_inset Text

  9627. 

  9628. \begin_layout Plain Layout

  9629. 18,200

  9630. \end_layout

  9631. 

  9632. \end_inset

  9633. </cell>

  9634. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9635. \begin_inset Text

  9636. 

  9637. \begin_layout Plain Layout

  9638. 17.5

  9639. \end_layout

  9640. 

  9641. \end_inset

  9642. </cell>

  9643. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  9644. \begin_inset Text

  9645. 

  9646. \begin_layout Plain Layout

  9647. Hard to tell the difference even with good headphones

  9648. \end_layout

  9649. 

  9650. \end_inset

  9651. </cell>

  9652. </row>

  9653. <row>

  9654. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9655. \begin_inset Text

  9656. 

  9657. \begin_layout Plain Layout

  9658. 7

  9659. \end_layout

  9660. 

  9661. \end_inset

  9662. </cell>

  9663. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9664. \begin_inset Text

  9665. 

  9666. \begin_layout Plain Layout

  9667. 10

  9668. \end_layout

  9669. 

  9670. \end_inset

  9671. </cell>

  9672. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9673. \begin_inset Text

  9674. 

  9675. \begin_layout Plain Layout

  9676. 24,600

  9677. \end_layout

  9678. 

  9679. \end_inset

  9680. </cell>

  9681. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9682. \begin_inset Text

  9683. 

  9684. \begin_layout Plain Layout

  9685. 14.5

  9686. \end_layout

  9687. 

  9688. \end_inset

  9689. </cell>

  9690. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  9691. \begin_inset Text

  9692. 

  9693. \begin_layout Plain Layout

  9694. Completely transparent for voice, good quality music

  9695. \end_layout

  9696. 

  9697. \end_inset

  9698. </cell>

  9699. </row>

  9700. <row>

  9701. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

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  9717. \end_inset

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  9720. \begin_inset Text

  9721. 

  9722. \begin_layout Plain Layout

  9723. 3,950

  9724. \end_layout

  9725. 

  9726. \end_inset

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  9730. 

  9731. \begin_layout Plain Layout

  9732. 10.5

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  9735. \end_inset

  9736. </cell>

  9737. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  9738. \begin_inset Text

  9739. 

  9740. \begin_layout Plain Layout

  9741. Very noticeable artifacts/noise, good intelligibility

  9742. \end_layout

  9743. 

  9744. \end_inset

  9745. </cell>

  9746. </row>

  9747. <row>

  9748. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9749. \begin_inset Text

  9750. 

  9751. \begin_layout Plain Layout

  9752. 9

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  9755. \end_inset

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  9757. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9758. \begin_inset Text

  9759. 

  9760. \begin_layout Plain Layout

  9761. -

  9762. \end_layout

  9763. 

  9764. \end_inset

  9765. </cell>

  9766. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9767. \begin_inset Text

  9768. 

  9769. \begin_layout Plain Layout

  9770. -

  9771. \end_layout

  9772. 

  9773. \end_inset

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  9775. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9776. \begin_inset Text

  9777. 

  9778. \begin_layout Plain Layout

  9779. -

  9780. \end_layout

  9781. 

  9782. \end_inset

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  9852. \begin_inset Text

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  9854. \begin_layout Plain Layout

  9855. -

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  9861. \begin_inset Text

  9862. 

  9863. \begin_layout Plain Layout

  9864. -

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  9872. \begin_layout Plain Layout

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  9900. 

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  9908. \begin_inset Text

  9909. 

  9910. \begin_layout Plain Layout

  9911. -

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  9917. \begin_inset Text

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  9919. \begin_layout Plain Layout

  9920. -

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  9938. 

  9939. \begin_layout Plain Layout

  9940. 13

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  9946. \begin_inset Text

  9947. 

  9948. \begin_layout Plain Layout

  9949. -

  9950. \end_layout

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  9955. \begin_inset Text

  9956. 

  9957. \begin_layout Plain Layout

  9958. -

  9959. \end_layout

  9960. 

  9961. \end_inset

  9962. </cell>

  9963. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9964. \begin_inset Text

  9965. 

  9966. \begin_layout Plain Layout

  9967. -

  9968. \end_layout

  9969. 

  9970. \end_inset

  9971. </cell>

  9972. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  9973. \begin_inset Text

  9974. 

  9975. \begin_layout Plain Layout

  9976. Application-defined, interpreted by callback or skipped

  9977. \end_layout

  9978. 

  9979. \end_inset

  9980. </cell>

  9981. </row>

  9982. <row>

  9983. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9984. \begin_inset Text

  9985. 

  9986. \begin_layout Plain Layout

  9987. 14

  9988. \end_layout

  9989. 

  9990. \end_inset

  9991. </cell>

  9992. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  9993. \begin_inset Text

  9994. 

  9995. \begin_layout Plain Layout

  9996. -

  9997. \end_layout

  9998. 

  9999. \end_inset

  10000. </cell>

  10001. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  10002. \begin_inset Text

  10003. 

  10004. \begin_layout Plain Layout

  10005. -

  10006. \end_layout

  10007. 

  10008. \end_inset

  10009. </cell>

  10010. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  10011. \begin_inset Text

  10012. 

  10013. \begin_layout Plain Layout

  10014. -

  10015. \end_layout

  10016. 

  10017. \end_inset

  10018. </cell>

  10019. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  10020. \begin_inset Text

  10021. 

  10022. \begin_layout Plain Layout

  10023. Speex in-band signaling

  10024. \end_layout

  10025. 

  10026. \end_inset

  10027. </cell>

  10028. </row>

  10029. <row>

  10030. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  10031. \begin_inset Text

  10032. 

  10033. \begin_layout Plain Layout

  10034. 15

  10035. \end_layout

  10036. 

  10037. \end_inset

  10038. </cell>

  10039. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  10040. \begin_inset Text

  10041. 

  10042. \begin_layout Plain Layout

  10043. -

  10044. \end_layout

  10045. 

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  10047. </cell>

  10048. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  10049. \begin_inset Text

  10050. 

  10051. \begin_layout Plain Layout

  10052. -

  10053. \end_layout

  10054. 

  10055. \end_inset

  10056. </cell>

  10057. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  10058. \begin_inset Text

  10059. 

  10060. \begin_layout Plain Layout

  10061. -

  10062. \end_layout

  10063. 

  10064. \end_inset

  10065. </cell>

  10066. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">

  10067. \begin_inset Text

  10068. 

  10069. \begin_layout Plain Layout

  10070. Terminator code

  10071. \end_layout

  10072. 

  10073. \end_inset

  10074. </cell>

  10075. </row>

  10076. </lyxtabular>

  10077. 

  10078. \end_inset

  10079. 

  10080. 

  10081. \begin_inset ERT

  10082. status collapsed

  10083. 

  10084. \begin_layout Plain Layout

  10085. 

  10086. 

  10087. \backslash

  10088. end{center}

  10089. \end_layout

  10090. 

  10091. \end_inset

  10092. 

  10093. 

  10094. \end_layout

  10095. 

  10096. \begin_layout Plain Layout

  10097. \begin_inset Caption

  10098. 

  10099. \begin_layout Plain Layout

  10100. Quality versus bit-rate

  10101. \begin_inset CommandInset label

  10102. LatexCommand label

  10103. name "cap:quality_vs_bps"

  10104. 

  10105. \end_inset

  10106. 

  10107. 

  10108. \end_layout

  10109. 

  10110. \end_inset

  10111. 

  10112. 

  10113. \end_layout

  10114. 

  10115. \end_inset

  10116. 

  10117. 

  10118. \end_layout

  10119. 

  10120. \begin_layout Section

  10121. Perceptual enhancement

  10122. \begin_inset Index

  10123. status collapsed

  10124. 

  10125. \begin_layout Plain Layout

  10126. perceptual enhancement

  10127. \end_layout

  10128. 

  10129. \end_inset

  10130. 

  10131. 

  10132. \end_layout

  10133. 

  10134. \begin_layout Standard

  10135. 

  10136. \series bold

  10137. This section was only valid for version 1.1.12 and earlier.

  10138.  It does not apply to version 1.2-beta1 (and later), for which the new perceptual

  10139.  enhancement is not yet documented.

  10140. \end_layout

  10141. 

  10142. \begin_layout Standard

  10143. This part of the codec only applies to the decoder and can even be changed

  10144.  without affecting inter-operability.

  10145.  For that reason, the implementation provided and described here should

  10146.  only be considered as a reference implementation.

  10147.  The enhancement system is divided into two parts.

  10148.  First, the synthesis filter 

  10149. \begin_inset Formula $S(z)=1/A(z)$

  10150. \end_inset

  10151. 

  10152.  is replaced by an enhanced filter:

  10153. \begin_inset Formula \[

  10154. S'(z)=\frac{A\left(z/a_{2}\right)A\left(z/a_{3}\right)}{A\left(z\right)A\left(z/a_{1}\right)}\]

  10155. 

  10156. \end_inset

  10157. 

  10158. where 

  10159. \begin_inset Formula $a_{1}$

  10160. \end_inset

  10161. 

  10162.  and 

  10163. \begin_inset Formula $a_{2}$

  10164. \end_inset

  10165. 

  10166.  depend on the mode in use and 

  10167. \begin_inset Formula $a_{3}=\frac{1}{r}\left(1-\frac{1-ra_{1}}{1-ra_{2}}\right)$

  10168. \end_inset

  10169. 

  10170.  with 

  10171. \begin_inset Formula $r=.9$

  10172. \end_inset

  10173. 

  10174. .

  10175.  The second part of the enhancement consists of using a comb filter to enhance

  10176.  the pitch in the excitation domain.

  10177.  

  10178. \end_layout

  10179. 

  10180. \begin_layout Standard

  10181. \begin_inset Newpage newpage

  10182. \end_inset

  10183. 

  10184. 

  10185. \end_layout

  10186. 

  10187. \begin_layout Chapter

  10188. Speex wideband mode (sub-band CELP)

  10189. \begin_inset Index

  10190. status collapsed

  10191. 

  10192. \begin_layout Plain Layout

  10193. wideband

  10194. \end_layout

  10195. 

  10196. \end_inset

  10197. 

  10198. 

  10199. \begin_inset CommandInset label

  10200. LatexCommand label

  10201. name "sec:Speex-wideband-mode"

  10202. 

  10203. \end_inset

  10204. 

  10205. 

  10206. \end_layout

  10207. 

  10208. \begin_layout Standard

  10209. For wideband, the Speex approach uses a 

  10210. \emph on

  10211. q

  10212. \emph default

  10213. uadrature 

  10214. \emph on

  10215. m

  10216. \emph default

  10217. irror 

  10218. \emph on

  10219. f

  10220. \emph default

  10221. ilter

  10222. \begin_inset Index

  10223. status collapsed

  10224. 

  10225. \begin_layout Plain Layout

  10226. quadrature mirror filter

  10227. \end_layout

  10228. 

  10229. \end_inset

  10230. 

  10231.  (QMF) to split the band in two.

  10232.  The 16 kHz signal is thus divided into two 8 kHz signals, one representing

  10233.  the low band (0-4 kHz), the other the high band (4-8 kHz).

  10234.  The low band is encoded with the narrowband mode described in section 

  10235. \begin_inset CommandInset ref

  10236. LatexCommand ref

  10237. reference "sec:Speex-narrowband-mode"

  10238. 

  10239. \end_inset

  10240. 

  10241.  in such a way that the resulting 

  10242. \begin_inset Quotes eld

  10243. \end_inset

  10244. 

  10245. embedded narrowband bit-stream

  10246. \begin_inset Quotes erd

  10247. \end_inset

  10248. 

  10249.  can also be decoded with the narrowband decoder.

  10250.  Since the low band encoding has already been described, only the high band

  10251.  encoding is described in this section.

  10252. \end_layout

  10253. 

  10254. \begin_layout Section

  10255. Linear Prediction

  10256. \end_layout

  10257. 

  10258. \begin_layout Standard

  10259. The linear prediction part used for the high-band is very similar to what

  10260.  is done for narrowband.

  10261.  The only difference is that we use only 12 bits to encode the high-band

  10262.  LSP's using a multi-stage vector quantizer (MSVQ).

  10263.  The first level quantizes the 10 coefficients with 6 bits and the error

  10264.  is then quantized using 6 bits, too.

  10265. \end_layout

  10266. 

  10267. \begin_layout Section

  10268. Pitch Prediction

  10269. \end_layout

  10270. 

  10271. \begin_layout Standard

  10272. That part is easy: there's no pitch prediction for the high-band.

  10273.  There are two reasons for that.

  10274.  First, there is usually little harmonic structure in this band (above 4

  10275.  kHz).

  10276.  Second, it would be very hard to implement since the QMF folds the 4-8

  10277.  kHz band into 4-0 kHz (reversing the frequency axis), which means that

  10278.  the location of the harmonics is no longer at multiples of the fundamental

  10279.  (pitch).

  10280. \end_layout

  10281. 

  10282. \begin_layout Section

  10283. Excitation Quantization

  10284. \end_layout

  10285. 

  10286. \begin_layout Standard

  10287. The high-band excitation is coded in the same way as for narrowband.

  10288.  

  10289. \end_layout

  10290. 

  10291. \begin_layout Section

  10292. Bit allocation

  10293. \end_layout

  10294. 

  10295. \begin_layout Standard

  10296. For the wideband mode, the entire narrowband frame is packed before the

  10297.  high-band is encoded.

  10298.  The narrowband part of the bit-stream is as defined in table 

  10299. \begin_inset CommandInset ref

  10300. LatexCommand ref

  10301. reference "cap:bits-narrowband"

  10302. 

  10303. \end_inset

  10304. 

  10305. .

  10306.  The high-band follows, as described in table 

  10307. \begin_inset CommandInset ref

  10308. LatexCommand ref

  10309. reference "cap:bits-wideband"

  10310. 

  10311. \end_inset

  10312. 

  10313. .

  10314.  For wideband, the mode ID is the same as the Speex quality setting and

  10315.  is defined in table 

  10316. \begin_inset CommandInset ref

  10317. LatexCommand ref

  10318. reference "tab:wideband-quality"

  10319. 

  10320. \end_inset

  10321. 

  10322. .

  10323.  This also means that a wideband frame may be correctly decoded by a narrowband

  10324.  decoder with the only caveat that if more than one frame is packed in the

  10325.  same packet, the decoder will need to skip the high-band parts in order

  10326.  to sync with the bit-stream.

  10327. \end_layout

  10328. 

  10329. \begin_layout Standard

  10330. \begin_inset Float table

  10331. placement h

  10332. wide true

  10333. sideways false

  10334. status open

  10335. 

  10336. \begin_layout Plain Layout

  10337. \begin_inset ERT

  10338. status collapsed

  10339. 

  10340. \begin_layout Plain Layout

  10341. 

  10342. 

  10343. \backslash

  10344. begin{center}

  10345. \end_layout

  10346. 

  10347. \end_inset

  10348. 

  10349. 

  10350. \begin_inset Tabular

  10351. <lyxtabular version="3" rows="7" columns="7">

  10352. <features>

  10353. <column alignment="center" valignment="top" width="0pt">

  10354. <column alignment="center" valignment="top" width="0pt">

  10355. <column alignment="center" valignment="top" width="0pt">

  10356. <column alignment="center" valignment="top" width="0pt">

  10357. <column alignment="center" valignment="top" width="0pt">

  10358. <column alignment="center" valignment="top" width="0pt">

  10359. <column alignment="center" valignment="top" width="0pt">

  10360. <row>

  10361. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  10362. \begin_inset Text

  10363. 

  10364. \begin_layout Plain Layout

  10365. Parameter

  10366. \end_layout

  10367. 

  10368. \end_inset

  10369. </cell>

  10370. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  10371. \begin_inset Text

  10372. 

  10373. \begin_layout Plain Layout

  10374. Update rate

  10375. \end_layout

  10376. 

  10377. \end_inset

  10378. </cell>

  10379. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  10380. \begin_inset Text

  10381. 

  10382. \begin_layout Plain Layout

  10383. 0

  10384. \end_layout

  10385. 

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  10524. 

  10525. \end_inset

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  10672. 

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  10676. \begin_inset Text

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  10689. \begin_layout Plain Layout

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  10705. \begin_inset Text

  10706. 

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  10715. 

  10716. \begin_layout Plain Layout

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  10724. 

  10725. \begin_layout Plain Layout

  10726. 20

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  10728. 

  10729. \end_inset

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  10732. \begin_inset Text

  10733. 

  10734. \begin_layout Plain Layout

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  10737. 

  10738. \end_inset

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  10742. 

  10743. \begin_layout Plain Layout

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  10746. 

  10747. \end_inset

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  10753. 

  10754. \begin_layout Plain Layout

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  10770. \begin_inset Text

  10771. 

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  10780. 

  10781. \begin_layout Plain Layout

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  10789. 

  10790. \begin_layout Plain Layout

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  10793. 

  10794. \end_inset

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  10798. 

  10799. \begin_layout Plain Layout

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  10802. 

  10803. \end_inset

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  10807. 

  10808. \begin_layout Plain Layout

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  10811. 

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  10816. 

  10817. \end_inset

  10818. 

  10819. 

  10820. \begin_inset ERT

  10821. status collapsed

  10822. 

  10823. \begin_layout Plain Layout

  10824. 

  10825. 

  10826. \backslash

  10827. end{center}

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  10830. \end_inset

  10831. 

  10832. 

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  10837. 

  10838. \begin_layout Plain Layout

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  10841. LatexCommand label

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  10843. 

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  10845. 

  10846. 

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  10848. 

  10849. \end_inset

  10850. 

  10851. 

  10852. \end_layout

  10853. 

  10854. \end_inset

  10855. 

  10856. 

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  10859. \begin_layout Standard

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  10862. wide true

  10863. sideways false

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  10865. 

  10866. \begin_layout Plain Layout

  10867. \begin_inset ERT

  10868. status collapsed

  10869. 

  10870. \begin_layout Plain Layout

  10871. 

  10872. 

  10873. \backslash

  10874. begin{center}

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  10876. 

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  10879. 

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  10889. 

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  10946. 

  10947. \begin_layout Plain Layout

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  10958. \begin_layout Plain Layout

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  10962. \end_inset

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  10966. 

  10967. \begin_layout Plain Layout

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  10975. 

  10976. \begin_layout Plain Layout

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  10979. 

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  11004. 

  11005. \begin_layout Plain Layout

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  11008. 

  11009. \end_inset

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  11015. 

  11016. \begin_layout Plain Layout

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  11018. \end_layout

  11019. 

  11020. \end_inset

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  11024. 

  11025. \begin_layout Plain Layout

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  11027. \end_layout

  11028. 

  11029. \end_inset

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  11033. 

  11034. \begin_layout Plain Layout

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  11037. 

  11038. \end_inset

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  11049. \end_inset

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  11053. 

  11054. \begin_layout Plain Layout

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  11056. \end_layout

  11057. 

  11058. \end_inset

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  11061. \begin_inset Text

  11062. 

  11063. \begin_layout Plain Layout

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  11066. 

  11067. \end_inset

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  11073. 

  11074. \begin_layout Plain Layout

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  11076. \end_layout

  11077. 

  11078. \end_inset

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  11082. 

  11083. \begin_layout Plain Layout

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  11085. \end_layout

  11086. 

  11087. \end_inset

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  11090. \begin_inset Text

  11091. 

  11092. \begin_layout Plain Layout

  11093. Artifacts/noise sometimes noticeable

  11094. \end_layout

  11095. 

  11096. \end_inset

  11097. </cell>

  11098. </row>

  11099. <row>

  11100. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  11101. \begin_inset Text

  11102. 

  11103. \begin_layout Plain Layout

  11104. 6

  11105. \end_layout

  11106. 

  11107. \end_inset

  11108. </cell>

  11109. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  11110. \begin_inset Text

  11111. 

  11112. \begin_layout Plain Layout

  11113. 20,600

  11114. \end_layout

  11115. 

  11116. \end_inset

  11117. </cell>

  11118. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  11119. \begin_inset Text

  11120. 

  11121. \begin_layout Plain Layout

  11122. Need good headphones to tell the difference

  11123. \end_layout

  11124. 

  11125. \end_inset

  11126. </cell>

  11127. </row>

  11128. <row>

  11129. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  11130. \begin_inset Text

  11131. 

  11132. \begin_layout Plain Layout

  11133. 7

  11134. \end_layout

  11135. 

  11136. \end_inset

  11137. </cell>

  11138. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  11139. \begin_inset Text

  11140. 

  11141. \begin_layout Plain Layout

  11142. 23,800

  11143. \end_layout

  11144. 

  11145. \end_inset

  11146. </cell>

  11147. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  11148. \begin_inset Text

  11149. 

  11150. \begin_layout Plain Layout

  11151. Need good headphones to tell the difference

  11152. \end_layout

  11153. 

  11154. \end_inset

  11155. </cell>

  11156. </row>

  11157. <row>

  11158. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  11159. \begin_inset Text

  11160. 

  11161. \begin_layout Plain Layout

  11162. 8

  11163. \end_layout

  11164. 

  11165. \end_inset

  11166. </cell>

  11167. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  11168. \begin_inset Text

  11169. 

  11170. \begin_layout Plain Layout

  11171. 27,800

  11172. \end_layout

  11173. 

  11174. \end_inset

  11175. </cell>

  11176. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  11177. \begin_inset Text

  11178. 

  11179. \begin_layout Plain Layout

  11180. Hard to tell the difference even with good headphones

  11181. \end_layout

  11182. 

  11183. \end_inset

  11184. </cell>

  11185. </row>

  11186. <row>

  11187. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  11188. \begin_inset Text

  11189. 

  11190. \begin_layout Plain Layout

  11191. 9

  11192. \end_layout

  11193. 

  11194. \end_inset

  11195. </cell>

  11196. <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">

  11197. \begin_inset Text

  11198. 

  11199. \begin_layout Plain Layout

  11200. 34,200

  11201. \end_layout

  11202. 

  11203. \end_inset

  11204. </cell>

  11205. <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">

  11206. \begin_inset Text

  11207. 

  11208. \begin_layout Plain Layout

  11209. Hard to tell the difference even with good headphones

  11210. \end_layout

  11211. 

  11212. \end_inset

  11213. </cell>

  11214. </row>

  11215. <row>

  11216. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  11217. \begin_inset Text

  11218. 

  11219. \begin_layout Plain Layout

  11220. 10

  11221. \end_layout

  11222. 

  11223. \end_inset

  11224. </cell>

  11225. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">

  11226. \begin_inset Text

  11227. 

  11228. \begin_layout Plain Layout

  11229. 42,200

  11230. \end_layout

  11231. 

  11232. \end_inset

  11233. </cell>

  11234. <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">

  11235. \begin_inset Text

  11236. 

  11237. \begin_layout Plain Layout

  11238. Completely transparent for voice, good quality music

  11239. \end_layout

  11240. 

  11241. \end_inset

  11242. </cell>

  11243. </row>

  11244. </lyxtabular>

  11245. 

  11246. \end_inset

  11247. 

  11248. 

  11249. \begin_inset ERT

  11250. status collapsed

  11251. 

  11252. \begin_layout Plain Layout

  11253. 

  11254. 

  11255. \backslash

  11256. end{center}

  11257. \end_layout

  11258. 

  11259. \end_inset

  11260. 

  11261. 

  11262. \end_layout

  11263. 

  11264. \begin_layout Plain Layout

  11265. \begin_inset Caption

  11266. 

  11267. \begin_layout Plain Layout

  11268. Quality versus bit-rate for the wideband encoder

  11269. \begin_inset CommandInset label

  11270. LatexCommand label

  11271. name "tab:wideband-quality"

  11272. 

  11273. \end_inset

  11274. 

  11275. 

  11276. \end_layout

  11277. 

  11278. \end_inset

  11279. 

  11280. 

  11281. \end_layout

  11282. 

  11283. \end_inset

  11284. 

  11285. 

  11286. \end_layout

  11287. 

  11288. \begin_layout Standard

  11289. \begin_inset ERT

  11290. status open

  11291. 

  11292. \begin_layout Plain Layout

  11293. 

  11294. 

  11295. \backslash

  11296. clearpage

  11297. \end_layout

  11298. 

  11299. \end_inset

  11300. 

  11301. 

  11302. \end_layout

  11303. 

  11304. \begin_layout Standard

  11305. \begin_inset ERT

  11306. status collapsed

  11307. 

  11308. \begin_layout Plain Layout

  11309. 

  11310. 

  11311. \backslash

  11312. clearpage

  11313. \end_layout

  11314. 

  11315. \end_inset

  11316. 

  11317. 

  11318. \end_layout

  11319. 

  11320. \begin_layout Chapter

  11321. \start_of_appendix

  11322. Sample code

  11323. \begin_inset CommandInset label

  11324. LatexCommand label

  11325. name "sec:Sample-code"

  11326. 

  11327. \end_inset

  11328. 

  11329. 

  11330. \end_layout

  11331. 

  11332. \begin_layout Standard

  11333. This section shows sample code for encoding and decoding speech using the

  11334.  Speex API.

  11335.  The commands can be used to encode and decode a file by calling:

  11336. \family typewriter

  11337. 

  11338. \begin_inset Newline newline

  11339. \end_inset

  11340. 

  11341. % sampleenc in_file.sw | sampledec out_file.sw

  11342. \family default

  11343. 

  11344. \begin_inset Newline newline

  11345. \end_inset

  11346. 

  11347. where both files are raw (no header) files encoded at 16 bits per sample

  11348.  (in the machine natural endianness).

  11349. \end_layout

  11350. 

  11351. \begin_layout Section

  11352. sampleenc.c

  11353. \end_layout

  11354. 

  11355. \begin_layout Standard

  11356. sampleenc takes a raw 16 bits/sample file, encodes it and outputs a Speex

  11357.  stream to stdout.

  11358.  Note that the packing used is 

  11359. \series bold

  11360. not

  11361. \series default

  11362.  compatible with that of speexenc/speexdec.

  11363. \end_layout

  11364. 

  11365. \begin_layout Standard

  11366. \begin_inset CommandInset include

  11367. LatexCommand lstinputlisting

  11368. filename "sampleenc.c"

  11369. lstparams "caption={Source code for sampleenc},label={sampleenc-source-code},numbers=left,numberstyle={\\footnotesize}"

  11370. 

  11371. \end_inset

  11372. 

  11373. 

  11374. \end_layout

  11375. 

  11376. \begin_layout Section

  11377. sampledec.c

  11378. \end_layout

  11379. 

  11380. \begin_layout Standard

  11381. sampledec reads a Speex stream from stdin, decodes it and outputs it to

  11382.  a raw 16 bits/sample file.

  11383.  Note that the packing used is 

  11384. \series bold

  11385. not

  11386. \series default

  11387.  compatible with that of speexenc/speexdec.

  11388. \end_layout

  11389. 

  11390. \begin_layout Standard

  11391. \begin_inset CommandInset include

  11392. LatexCommand lstinputlisting

  11393. filename "sampledec.c"

  11394. lstparams "caption={Source code for sampledec},label={sampledec-source-code},numbers=left,numberstyle={\\footnotesize}"

  11395. 

  11396. \end_inset

  11397. 

  11398. 

  11399. \end_layout

  11400. 

  11401. \begin_layout Standard

  11402. \begin_inset Newpage newpage

  11403. \end_inset

  11404. 

  11405. 

  11406. \end_layout

  11407. 

  11408. \begin_layout Chapter

  11409. Jitter Buffer for Speex

  11410. \end_layout

  11411. 

  11412. \begin_layout Standard

  11413. \begin_inset CommandInset include

  11414. LatexCommand lstinputlisting

  11415. filename "../speexclient/speex_jitter_buffer.c"

  11416. lstparams "caption={Example of using the jitter buffer for Speex packets},label={example-speex-jitter},numbers=left,numberstyle={\\footnotesize}"

  11417. 

  11418. \end_inset

  11419. 

  11420. 

  11421. \end_layout

  11422. 

  11423. \begin_layout Standard

  11424. \begin_inset Newpage newpage

  11425. \end_inset

  11426. 

  11427. 

  11428. \end_layout

  11429. 

  11430. \begin_layout Chapter

  11431. IETF RTP Profile

  11432. \begin_inset CommandInset label

  11433. LatexCommand label

  11434. name "sec:IETF-draft"

  11435. 

  11436. \end_inset

  11437. 

  11438. 

  11439. \end_layout

  11440. 

  11441. \begin_layout Standard

  11442. \begin_inset CommandInset include

  11443. LatexCommand verbatiminput

  11444. filename "draft-ietf-avt-rtp-speex-05-tmp.txt"

  11445. 

  11446. \end_inset

  11447. 

  11448. 

  11449. \end_layout

  11450. 

  11451. \begin_layout Standard

  11452. \begin_inset Newpage newpage

  11453. \end_inset

  11454. 

  11455. 

  11456. \end_layout

  11457. 

  11458. \begin_layout Chapter

  11459. Speex License

  11460. \begin_inset CommandInset label

  11461. LatexCommand label

  11462. name "sec:Speex-License"

  11463. 

  11464. \end_inset

  11465. 

  11466. 

  11467. \end_layout

  11468. 

  11469. \begin_layout Standard

  11470. \begin_inset CommandInset include

  11471. LatexCommand verbatiminput

  11472. filename "../COPYING"

  11473. 

  11474. \end_inset

  11475. 

  11476. 

  11477. \end_layout

  11478. 

  11479. \begin_layout Standard

  11480. \begin_inset Newpage newpage

  11481. \end_inset

  11482. 

  11483. 

  11484. \end_layout

  11485. 

  11486. \begin_layout Chapter

  11487. GNU Free Documentation License

  11488. \end_layout

  11489. 

  11490. \begin_layout Standard

  11491. Version 1.1, March 2000

  11492. \end_layout

  11493. 

  11494. \begin_layout Standard

  11495. Copyright (C) 2000 Free Software Foundation, Inc.

  11496.  59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Everyone is permitted

  11497.  to copy and distribute verbatim copies of this license document, but changing

  11498.  it is not allowed.

  11499.  

  11500. \end_layout

  11501. 

  11502. \begin_layout Section*

  11503. 0.

  11504.  PREAMBLE

  11505. \end_layout

  11506. 

  11507. \begin_layout Standard

  11508. The purpose of this License is to make a manual, textbook, or other written

  11509.  document "free" in the sense of freedom: to assure everyone the effective

  11510.  freedom to copy and redistribute it, with or without modifying it, either

  11511.  commercially or noncommercially.

  11512.  Secondarily, this License preserves for the author and publisher a way

  11513.  to get credit for their work, while not being considered responsible for

  11514.  modifications made by others.

  11515. \end_layout

  11516. 

  11517. \begin_layout Standard

  11518. This License is a kind of "copyleft", which means that derivative works

  11519.  of the document must themselves be free in the same sense.

  11520.  It complements the GNU General Public License, which is a copyleft license

  11521.  designed for free software.

  11522. \end_layout

  11523. 

  11524. \begin_layout Standard

  11525. We have designed this License in order to use it for manuals for free software,

  11526.  because free software needs free documentation: a free program should come

  11527.  with manuals providing the same freedoms that the software does.

  11528.  But this License is not limited to software manuals; it can be used for

  11529.  any textual work, regardless of subject matter or whether it is published

  11530.  as a printed book.

  11531.  We recommend this License principally for works whose purpose is instruction

  11532.  or reference.

  11533.  

  11534. \end_layout

  11535. 

  11536. \begin_layout Section*

  11537. 1.

  11538.  APPLICABILITY AND DEFINITIONS

  11539. \end_layout

  11540. 

  11541. \begin_layout Standard

  11542. This License applies to any manual or other work that contains a notice

  11543.  placed by the copyright holder saying it can be distributed under the terms

  11544.  of this License.

  11545.  The "Document", below, refers to any such manual or work.

  11546.  Any member of the public is a licensee, and is addressed as "you".

  11547. \end_layout

  11548. 

  11549. \begin_layout Standard

  11550. A "Modified Version" of the Document means any work containing the Document

  11551.  or a portion of it, either copied verbatim, or with modifications and/or

  11552.  translated into another language.

  11553. \end_layout

  11554. 

  11555. \begin_layout Standard

  11556. A "Secondary Section" is a named appendix or a front-matter section of the

  11557.  Document that deals exclusively with the relationship of the publishers

  11558.  or authors of the Document to the Document's overall subject (or to related

  11559.  matters) and contains nothing that could fall directly within that overall

  11560.  subject.

  11561.  (For example, if the Document is in part a textbook of mathematics, a Secondary

  11562.  Section may not explain any mathematics.) The relationship could be a matter

  11563.  of historical connection with the subject or with related matters, or of

  11564.  legal, commercial, philosophical, ethical or political position regarding

  11565.  them.

  11566. \end_layout

  11567. 

  11568. \begin_layout Standard

  11569. The "Invariant Sections" are certain Secondary Sections whose titles are

  11570.  designated, as being those of Invariant Sections, in the notice that says

  11571.  that the Document is released under this License.

  11572. \end_layout

  11573. 

  11574. \begin_layout Standard

  11575. The "Cover Texts" are certain short passages of text that are listed, as

  11576.  Front-Cover Texts or Back-Cover Texts, in the notice that says that the

  11577.  Document is released under this License.

  11578. \end_layout

  11579. 

  11580. \begin_layout Standard

  11581. A "Transparent" copy of the Document means a machine-readable copy, represented

  11582.  in a format whose specification is available to the general public, whose

  11583.  contents can be viewed and edited directly and straightforwardly with generic

  11584.  text editors or (for images composed of pixels) generic paint programs

  11585.  or (for drawings) some widely available drawing editor, and that is suitable

  11586.  for input to text formatters or for automatic translation to a variety

  11587.  of formats suitable for input to text formatters.

  11588.  A copy made in an otherwise Transparent file format whose markup has been

  11589.  designed to thwart or discourage subsequent modification by readers is

  11590.  not Transparent.

  11591.  A copy that is not "Transparent" is called "Opaque".

  11592. \end_layout

  11593. 

  11594. \begin_layout Standard

  11595. Examples of suitable formats for Transparent copies include plain ASCII

  11596.  without markup, Texinfo input format, LaTeX input format, SGML or XML using

  11597.  a publicly available DTD, and standard-conforming simple HTML designed

  11598.  for human modification.

  11599.  Opaque formats include PostScript, PDF, proprietary formats that can be

  11600.  read and edited only by proprietary word processors, SGML or XML for which

  11601.  the DTD and/or processing tools are not generally available, and the machine-ge

  11602. nerated HTML produced by some word processors for output purposes only.

  11603. \end_layout

  11604. 

  11605. \begin_layout Standard

  11606. The "Title Page" means, for a printed book, the title page itself, plus

  11607.  such following pages as are needed to hold, legibly, the material this

  11608.  License requires to appear in the title page.

  11609.  For works in formats which do not have any title page as such, "Title Page"

  11610.  means the text near the most prominent appearance of the work's title,

  11611.  preceding the beginning of the body of the text.

  11612. \end_layout

  11613. 

  11614. \begin_layout Section*

  11615. 2.

  11616.  VERBATIM COPYING

  11617. \end_layout

  11618. 

  11619. \begin_layout Standard

  11620. You may copy and distribute the Document in any medium, either commercially

  11621.  or noncommercially, provided that this License, the copyright notices,

  11622.  and the license notice saying this License applies to the Document are

  11623.  reproduced in all copies, and that you add no other conditions whatsoever

  11624.  to those of this License.

  11625.  You may not use technical measures to obstruct or control the reading or

  11626.  further copying of the copies you make or distribute.

  11627.  However, you may accept compensation in exchange for copies.

  11628.  If you distribute a large enough number of copies you must also follow

  11629.  the conditions in section 3.

  11630. \end_layout

  11631. 

  11632. \begin_layout Standard

  11633. You may also lend copies, under the same conditions stated above, and you

  11634.  may publicly display copies.

  11635. \end_layout

  11636. 

  11637. \begin_layout Section*

  11638. 3.

  11639.  COPYING IN QUANTITY

  11640. \end_layout

  11641. 

  11642. \begin_layout Standard

  11643. If you publish printed copies of the Document numbering more than 100, and

  11644.  the Document's license notice requires Cover Texts, you must enclose the

  11645.  copies in covers that carry, clearly and legibly, all these Cover Texts:

  11646.  Front-Cover Texts on the front cover, and Back-Cover Texts on the back

  11647.  cover.

  11648.  Both covers must also clearly and legibly identify you as the publisher

  11649.  of these copies.

  11650.  The front cover must present the full title with all words of the title

  11651.  equally prominent and visible.

  11652.  You may add other material on the covers in addition.

  11653.  Copying with changes limited to the covers, as long as they preserve the

  11654.  title of the Document and satisfy these conditions, can be treated as verbatim

  11655.  copying in other respects.

  11656. \end_layout

  11657. 

  11658. \begin_layout Standard

  11659. If the required texts for either cover are too voluminous to fit legibly,

  11660.  you should put the first ones listed (as many as fit reasonably) on the

  11661.  actual cover, and continue the rest onto adjacent pages.

  11662. \end_layout

  11663. 

  11664. \begin_layout Standard

  11665. If you publish or distribute Opaque copies of the Document numbering more

  11666.  than 100, you must either include a machine-readable Transparent copy along

  11667.  with each Opaque copy, or state in or with each Opaque copy a publicly-accessib

  11668. le computer-network location containing a complete Transparent copy of the

  11669.  Document, free of added material, which the general network-using public

  11670.  has access to download anonymously at no charge using public-standard network

  11671.  protocols.

  11672.  If you use the latter option, you must take reasonably prudent steps, when

  11673.  you begin distribution of Opaque copies in quantity, to ensure that this

  11674.  Transparent copy will remain thus accessible at the stated location until

  11675.  at least one year after the last time you distribute an Opaque copy (directly

  11676.  or through your agents or retailers) of that edition to the public.

  11677. \end_layout

  11678. 

  11679. \begin_layout Standard

  11680. It is requested, but not required, that you contact the authors of the Document

  11681.  well before redistributing any large number of copies, to give them a chance

  11682.  to provide you with an updated version of the Document.

  11683.  

  11684. \end_layout

  11685. 

  11686. \begin_layout Section*

  11687. 4.

  11688.  MODIFICATIONS

  11689. \end_layout

  11690. 

  11691. \begin_layout Standard

  11692. You may copy and distribute a Modified Version of the Document under the

  11693.  conditions of sections 2 and 3 above, provided that you release the Modified

  11694.  Version under precisely this License, with the Modified Version filling

  11695.  the role of the Document, thus licensing distribution and modification

  11696.  of the Modified Version to whoever possesses a copy of it.

  11697.  In addition, you must do these things in the Modified Version: 

  11698. \end_layout

  11699. 

  11700. \begin_layout Itemize

  11701. A.

  11702.  Use in the Title Page (and on the covers, if any) a title distinct from

  11703.  that of the Document, and from those of previous versions (which should,

  11704.  if there were any, be listed in the History section of the Document).

  11705.  You may use the same title as a previous version if the original publisher

  11706.  of that version gives permission.

  11707. \end_layout

  11708. 

  11709. \begin_layout Itemize

  11710. B.

  11711.  List on the Title Page, as authors, one or more persons or entities responsible

  11712.  for authorship of the modifications in the Modified Version, together with

  11713.  at least five of the principal authors of the Document (all of its principal

  11714.  authors, if it has less than five).

  11715. \end_layout

  11716. 

  11717. \begin_layout Itemize

  11718. C.

  11719.  State on the Title page the name of the publisher of the Modified Version,

  11720.  as the publisher.

  11721. \end_layout

  11722. 

  11723. \begin_layout Itemize

  11724. D.

  11725.  Preserve all the copyright notices of the Document.

  11726. \end_layout

  11727. 

  11728. \begin_layout Itemize

  11729. E.

  11730.  Add an appropriate copyright notice for your modifications adjacent to

  11731.  the other copyright notices.

  11732. \end_layout

  11733. 

  11734. \begin_layout Itemize

  11735. F.

  11736.  Include, immediately after the copyright notices, a license notice giving

  11737.  the public permission to use the Modified Version under the terms of this

  11738.  License, in the form shown in the Addendum below.

  11739. \end_layout

  11740. 

  11741. \begin_layout Itemize

  11742. G.

  11743.  Preserve in that license notice the full lists of Invariant Sections and

  11744.  required Cover Texts given in the Document's license notice.

  11745. \end_layout

  11746. 

  11747. \begin_layout Itemize

  11748. H.

  11749.  Include an unaltered copy of this License.

  11750. \end_layout

  11751. 

  11752. \begin_layout Itemize

  11753. I.

  11754.  Preserve the section entitled "History", and its title, and add to it an

  11755.  item stating at least the title, year, new authors, and publisher of the

  11756.  Modified Version as given on the Title Page.

  11757.  If there is no section entitled "History" in the Document, create one stating

  11758.  the title, year, authors, and publisher of the Document as given on its

  11759.  Title Page, then add an item describing the Modified Version as stated

  11760.  in the previous sentence.

  11761. \end_layout

  11762. 

  11763. \begin_layout Itemize

  11764. J.

  11765.  Preserve the network location, if any, given in the Document for public

  11766.  access to a Transparent copy of the Document, and likewise the network

  11767.  locations given in the Document for previous versions it was based on.

  11768.  These may be placed in the "History" section.

  11769.  You may omit a network location for a work that was published at least

  11770.  four years before the Document itself, or if the original publisher of

  11771.  the version it refers to gives permission.

  11772. \end_layout

  11773. 

  11774. \begin_layout Itemize

  11775. K.

  11776.  In any section entitled "Acknowledgements" or "Dedications", preserve the

  11777.  section's title, and preserve in the section all the substance and tone

  11778.  of each of the contributor acknowledgements and/or dedications given therein.

  11779. \end_layout

  11780. 

  11781. \begin_layout Itemize

  11782. L.

  11783.  Preserve all the Invariant Sections of the Document, unaltered in their

  11784.  text and in their titles.

  11785.  Section numbers or the equivalent are not considered part of the section

  11786.  titles.

  11787. \end_layout

  11788. 

  11789. \begin_layout Itemize

  11790. M.

  11791.  Delete any section entitled "Endorsements".

  11792.  Such a section may not be included in the Modified Version.

  11793. \end_layout

  11794. 

  11795. \begin_layout Itemize

  11796. N.

  11797.  Do not retitle any existing section as "Endorsements" or to conflict in

  11798.  title with any Invariant Section.

  11799.  

  11800. \end_layout

  11801. 

  11802. \begin_layout Standard

  11803. If the Modified Version includes new front-matter sections or appendices

  11804.  that qualify as Secondary Sections and contain no material copied from

  11805.  the Document, you may at your option designate some or all of these sections

  11806.  as invariant.

  11807.  To do this, add their titles to the list of Invariant Sections in the Modified

  11808.  Version's license notice.

  11809.  These titles must be distinct from any other section titles.

  11810. \end_layout

  11811. 

  11812. \begin_layout Standard

  11813. You may add a section entitled "Endorsements", provided it contains nothing

  11814.  but endorsements of your Modified Version by various parties--for example,

  11815.  statements of peer review or that the text has been approved by an organization

  11816.  as the authoritative definition of a standard.

  11817. \end_layout

  11818. 

  11819. \begin_layout Standard

  11820. You may add a passage of up to five words as a Front-Cover Text, and a passage

  11821.  of up to 25 words as a Back-Cover Text, to the end of the list of Cover

  11822.  Texts in the Modified Version.

  11823.  Only one passage of Front-Cover Text and one of Back-Cover Text may be

  11824.  added by (or through arrangements made by) any one entity.

  11825.  If the Document already includes a cover text for the same cover, previously

  11826.  added by you or by arrangement made by the same entity you are acting on

  11827.  behalf of, you may not add another; but you may replace the old one, on

  11828.  explicit permission from the previous publisher that added the old one.

  11829. \end_layout

  11830. 

  11831. \begin_layout Standard

  11832. The author(s) and publisher(s) of the Document do not by this License give

  11833.  permission to use their names for publicity for or to assert or imply endorseme

  11834. nt of any Modified Version.

  11835.  

  11836. \end_layout

  11837. 

  11838. \begin_layout Section*

  11839. 5.

  11840.  COMBINING DOCUMENTS

  11841. \end_layout

  11842. 

  11843. \begin_layout Standard

  11844. You may combine the Document with other documents released under this License,

  11845.  under the terms defined in section 4 above for modified versions, provided

  11846.  that you include in the combination all of the Invariant Sections of all

  11847.  of the original documents, unmodified, and list them all as Invariant Sections

  11848.  of your combined work in its license notice.

  11849. \end_layout

  11850. 

  11851. \begin_layout Standard

  11852. The combined work need only contain one copy of this License, and multiple

  11853.  identical Invariant Sections may be replaced with a single copy.

  11854.  If there are multiple Invariant Sections with the same name but different

  11855.  contents, make the title of each such section unique by adding at the end

  11856.  of it, in parentheses, the name of the original author or publisher of

  11857.  that section if known, or else a unique number.

  11858.  Make the same adjustment to the section titles in the list of Invariant

  11859.  Sections in the license notice of the combined work.

  11860. \end_layout

  11861. 

  11862. \begin_layout Standard

  11863. In the combination, you must combine any sections entitled "History" in

  11864.  the various original documents, forming one section entitled "History";

  11865.  likewise combine any sections entitled "Acknowledgements", and any sections

  11866.  entitled "Dedications".

  11867.  You must delete all sections entitled "Endorsements."

  11868. \end_layout

  11869. 

  11870. \begin_layout Section*

  11871. 6.

  11872.  COLLECTIONS OF DOCUMENTS

  11873. \end_layout

  11874. 

  11875. \begin_layout Standard

  11876. You may make a collection consisting of the Document and other documents

  11877.  released under this License, and replace the individual copies of this

  11878.  License in the various documents with a single copy that is included in

  11879.  the collection, provided that you follow the rules of this License for

  11880.  verbatim copying of each of the documents in all other respects.

  11881. \end_layout

  11882. 

  11883. \begin_layout Standard

  11884. You may extract a single document from such a collection, and distribute

  11885.  it individually under this License, provided you insert a copy of this

  11886.  License into the extracted document, and follow this License in all other

  11887.  respects regarding verbatim copying of that document.

  11888.  

  11889. \end_layout

  11890. 

  11891. \begin_layout Section*

  11892. 7.

  11893.  AGGREGATION WITH INDEPENDENT WORKS

  11894. \end_layout

  11895. 

  11896. \begin_layout Standard

  11897. A compilation of the Document or its derivatives with other separate and

  11898.  independent documents or works, in or on a volume of a storage or distribution

  11899.  medium, does not as a whole count as a Modified Version of the Document,

  11900.  provided no compilation copyright is claimed for the compilation.

  11901.  Such a compilation is called an "aggregate", and this License does not

  11902.  apply to the other self-contained works thus compiled with the Document,

  11903.  on account of their being thus compiled, if they are not themselves derivative

  11904.  works of the Document.

  11905. \end_layout

  11906. 

  11907. \begin_layout Standard

  11908. If the Cover Text requirement of section 3 is applicable to these copies

  11909.  of the Document, then if the Document is less than one quarter of the entire

  11910.  aggregate, the Document's Cover Texts may be placed on covers that surround

  11911.  only the Document within the aggregate.

  11912.  Otherwise they must appear on covers around the whole aggregate.

  11913. \end_layout

  11914. 

  11915. \begin_layout Section*

  11916. 8.

  11917.  TRANSLATION

  11918. \end_layout

  11919. 

  11920. \begin_layout Standard

  11921. Translation is considered a kind of modification, so you may distribute

  11922.  translations of the Document under the terms of section 4.

  11923.  Replacing Invariant Sections with translations requires special permission

  11924.  from their copyright holders, but you may include translations of some

  11925.  or all Invariant Sections in addition to the original versions of these

  11926.  Invariant Sections.

  11927.  You may include a translation of this License provided that you also include

  11928.  the original English version of this License.

  11929.  In case of a disagreement between the translation and the original English

  11930.  version of this License, the original English version will prevail.

  11931. \end_layout

  11932. 

  11933. \begin_layout Section*

  11934. 9.

  11935.  TERMINATION

  11936. \end_layout

  11937. 

  11938. \begin_layout Standard

  11939. You may not copy, modify, sublicense, or distribute the Document except

  11940.  as expressly provided for under this License.

  11941.  Any other attempt to copy, modify, sublicense or distribute the Document

  11942.  is void, and will automatically terminate your rights under this License.

  11943.  However, parties who have received copies, or rights, from you under this

  11944.  License will not have their licenses terminated so long as such parties

  11945.  remain in full compliance.

  11946.  

  11947. \end_layout

  11948. 

  11949. \begin_layout Section*

  11950. 10.

  11951.  FUTURE REVISIONS OF THIS LICENSE

  11952. \end_layout

  11953. 

  11954. \begin_layout Standard

  11955. The Free Software Foundation may publish new, revised versions of the GNU

  11956.  Free Documentation License from time to time.

  11957.  Such new versions will be similar in spirit to the present version, but

  11958.  may differ in detail to address new problems or concerns.

  11959.  See http://www.gnu.org/copyleft/.

  11960. \end_layout

  11961. 

  11962. \begin_layout Standard

  11963. Each version of the License is given a distinguishing version number.

  11964.  If the Document specifies that a particular numbered version of this License

  11965.  "or any later version" applies to it, you have the option of following

  11966.  the terms and conditions either of that specified version or of any later

  11967.  version that has been published (not as a draft) by the Free Software Foundatio

  11968. n.

  11969.  If the Document does not specify a version number of this License, you

  11970.  may choose any version ever published (not as a draft) by the Free Software

  11971.  Foundation.

  11972. \end_layout

  11973. 

  11974. \begin_layout Standard

  11975. \begin_inset CommandInset index_print

  11976. LatexCommand printindex

  11977. 

  11978. \end_inset

  11979. 

  11980. 

  11981. \end_layout

  11982. 

  11983. \end_body

  11984. \end_document