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This document describes the differences between Rack Pro plugin and Cardinal.
It is not possible to know all the internal details of the official plugin due to it not being open-source, so more technical details are best-guesses based on its behaviour.

The obvious big difference is that the official plugin is a commercial, closed-source product while Cardinal is free and open-source.

Also, the official plugin works pretty much like the free standalone where you login and download modules.
This is intentionally not allowed/enabled in Cardinal, as the target is to make a self-contained plugin binary. Online access is also not allowed.

Bellow follows a list of features comparing the official plugin to Cardinal.

Feature Rack Pro Cardinal Additional notes
Open-Source No Yes
Free (of cost) No Yes
Officially supported Yes, if you pay No, but you can fix it yourself
Contains internal modules Core only Everything is internal
Loads external modules Yes No
Supports closed-source modules Yes No
Supports physical devices Yes No Audio + MIDI only through the DAW/Host or via JACK in standalone
Plugin in AU format No Yes
Plugin in LV2 format No Yes
Plugin in VST2 format Yes Yes
Plugin in VST3 format No WIP
Plugin inside itself No, will crash Yes Technical limitations prevent Rack Pro from loading inside itself
Multi-threaded engine Yes No, uses host audio thread Intentional in Cardinal, for removing jitter
Supports ARM systems No Yes This means Apple M1 too, yes
Supports BSD systems No Yes Available as FreeBSD port
Synth plugin variant 16 ins, 16 outs 2 ins, 2 outs
FX plugin variant 16 ins, 16 outs 2 ins, 2 outs
Raw-CV plugin variant Unsupported 8 audio IO + 10 CV IO Available in JACK, LV2 and VST3 formats, not possible in AU and VST2
Arbitrary parameter automation Yes No Unsupported in Cardinal, tricky to do for many plugin formats at once
Integrated plugin host No, Host payed separately Yes, using Carla or Ildaeil
Host sync/timing Using MIDI signals Using dedicated module
Linux/X11 event handling Runs on 2nd thread Runs on main/GUI thread
v1 module compatibility No No, but with less restrictions Module widgets can load resources at any point
Online phone-home Yes No Online access is strictly forbidden in Cardinal
Proper dark theme No, only room brightness Yes All dark panel variants have explicit permission when required
Proper Linux headless mode No, always requires X11 Yes

Additionally, Cardinal contains the following built-in modules not present in the official plugin or standalone:

  • Aria Salvatrice modules (except Arcane related modules, due to their online requirement)
  • Mog (never updated to v2)
  • mscHack (never updated to v2)
  • rackwindows
  • Audio File
  • Audio to CV Pitch converter
  • Carla Plugin Host
  • Ildaeil Host
  • glBars (OpenGL bars visualization, as seen in XMMS and XBMC/Kodi)
  • Text Editor (resizable and with syntax highlight)
  • Host Parameters (24 host-exposed parameters as CV sources)
  • Host Time (play, reset, bar, beat, tick, bar-phase and beat-phase CV sources)
  • Host CV (for the Raw-CV plugin variant, allows direct CV access to/from the DAW)