Carla/source/modules/juce_audio_basics/sources/juce_ResamplingAudioSource.h

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2017 - ROLI Ltd.

   JUCE is an open source library subject to commercial or open-source
   licensing.

   The code included in this file is provided under the terms of the ISC license
   http://www.isc.org/downloads/software-support-policy/isc-license. Permission
   To use, copy, modify, and/or distribute this software for any purpose with or
   without fee is hereby granted provided that the above copyright notice and
   this permission notice appear in all copies.

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{

//==============================================================================
/**
    A type of AudioSource that takes an input source and changes its sample rate.

    @see AudioSource, LagrangeInterpolator, CatmullRomInterpolator
*/
class JUCE_API  ResamplingAudioSource  : public AudioSource
{
public:
    //==============================================================================
    /** Creates a ResamplingAudioSource for a given input source.

        @param inputSource              the input source to read from
        @param deleteInputWhenDeleted   if true, the input source will be deleted when
                                        this object is deleted
        @param numChannels              the number of channels to process
    */
    ResamplingAudioSource (AudioSource* inputSource,
                           bool deleteInputWhenDeleted,
                           int numChannels = 2);

    /** Destructor. */
    ~ResamplingAudioSource();

    /** Changes the resampling ratio.

        (This value can be changed at any time, even while the source is running).

        @param samplesInPerOutputSample     if set to 1.0, the input is passed through; higher
                                            values will speed it up; lower values will slow it
                                            down. The ratio must be greater than 0
    */
    void setResamplingRatio (double samplesInPerOutputSample);

    /** Returns the current resampling ratio.

        This is the value that was set by setResamplingRatio().
    */
    double getResamplingRatio() const noexcept                  { return ratio; }

    /** Clears any buffers and filters that the resampler is using. */
    void flushBuffers();

    //==============================================================================
    void prepareToPlay (int samplesPerBlockExpected, double sampleRate) override;
    void releaseResources() override;
    void getNextAudioBlock (const AudioSourceChannelInfo&) override;

private:
    //==============================================================================
    OptionalScopedPointer<AudioSource> input;
    double ratio, lastRatio;
    AudioSampleBuffer buffer;
    int bufferPos, sampsInBuffer;
    double subSampleOffset;
    double coefficients[6];
    SpinLock ratioLock;
    const int numChannels;
    HeapBlock<float*> destBuffers;
    HeapBlock<const float*> srcBuffers;

    void setFilterCoefficients (double c1, double c2, double c3, double c4, double c5, double c6);
    void createLowPass (double proportionalRate);

    struct FilterState
    {
        double x1, x2, y1, y2;
    };

    HeapBlock<FilterState> filterStates;
    void resetFilters();

    void applyFilter (float* samples, int num, FilterState& fs);

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (ResamplingAudioSource)
};

} // namespace juce