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DSP prototyping in Faust for VCV Rack

Screenshot of ProtoFaust


These are the instructions for Linux, but it should be relatively simple to modify them for use on Windows or MacOS:

  1. clone this repository: git clone
  2. download and install the latest VCV Rack SDK – the Makefile defaults to ../Rack-SDK but respects the RACK_DIR shell variable
  3. install Faust (I recommend using a recent version)
  4. make run will compile and install your module; Rack is run if it is found in your path

Prototype your own DSP

The default Faust process is a simple three-oscillator synth with resonant filter. Simply edit src/faust/main.dsp to change this. The main process is

process(in1 , in2 , in3 , in4 , in5 , in6 , in7 , in8) = internal_processor
     internal_processor = ... ;

You can simply put your mono DSP process in there:

    internal_processor = (in1 : gui_attacher) :
                         your_mono_process :
                         _ , in2 , in3 , in4 , in5 , in6 , in7 , in8 :

Or in stereo:

    internal_processor = (in1 : gui_attacher) , in2 :
                         your_stereo_process :
                         _ , _ , in3 , in4 , in5 , in6 , in7 , in8 :

Just make sure that you add gui_attacher somewhere -- this will attach the GUI parameters and simply copy any mono input signal to its output. If you fail to do so, the ProtoFaust module will not find any of the knobs, buttons and LEDs (they will be thought as superfluous and optimized out) and probably crash.


Signal ranges

Input signals from VCV Rack are divided by 5.0. Conversely, output signals are multiplied by 5.0 to bring them back in range. This keeps values in the usual range of DSP processing (-1.0 .. +1.0) and should help when porting algorithms to VCV Rack. All signals are full-range, so you have to apply any input or output saturation yourself.

Knobs have a range of 0.0 .. 1.0; the center position is located at 0.5. Toggle switches take on values of 0.0 and 1.0, whereas three-way switches add a third state of 0.5.

Ideas and bug fixes

This module is very new and experimental. So please send problems, bug reports, fixes and any ideas that come to your mind. Thanks!


Code of conduct

Please read the code of conduct before asking for help, filing bug reports or contributing to this project. Thanks!


Copyright (c) 2019-2020 Martin Zuther and contributors

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see

Thank you for using free software!