# Using Faust DSP language in VCV Prototype

The [Faust audio DSP language](https://faust.grame.fr) can be used in VCV Prototype. The compiler can be embedded in applications or plugins using [libfaust](https://faustdoc.grame.fr/manual/embedding/), and DSP code can be edited and JIT compiled on the fly.

Note that to facilitate compilation and deployement, the interpreter backend (slower produced DSP code) is used instead of the faster [LLVM IR](https://llvm.org) backend.

## Compilation

- type `make && make install` to build it
- you can now add a Faust aware VCV Prototype in your Rack session and start coding in Faust

## Loading/editing/compiling .dsp files

Faust DSP files have to be loaded in VCV Prototype and edited in a external editor (Visual Studio Code, Atom...). Each time the file is saved, it will be recompiled and executed. To possibly save compilation time, the DSP machine code is saved in a cache, and possibly restored the next time the session will be loaded.

The 6 *switches*, *knobs* as well as the *lights* and *switchLights* can be connected to UI controllers using metadata:

- `[switch:N]` (with N from 1 to 6) has to be used in a `button` or `checkbox` item to connect it to the prototype interface switch number N. Pushed buttons will become red  when on, and checkboxes will become white when on.
- `[knob:N]` (with N from 1 to 6) has to be used in a `vslider`, `hslider`  or `nentry` item to connect it to the prototype interface knob number N. The knob [0..1] range will be mapped to the slider/nentry [min..max] range.
- `[light_red|green|red:N]` (with N from 1 to 6) has to be used in a `vbargraph` or `hbargraph` item to connect it to the prototype interface light number N.
- `[switchlight_red|green|red:N]` (with N from 1 to 6) has to be used in a `vbargraph` or `hbargraph` to connect it to the prototype interface switchLight number N.

Other metadata:
- `[scale:lin|log|exp]` metadata is implemented.

The [faust_libraries/rack.lib](https://github.com/sletz/VCV-Prototype/blob/master/faust_libraries/rack.lib) Faust library contains useful functions to convert VC signals, and can be enriched if needed.

## DSP examples

Here is a simple example showing how oscillators can be controlled by UI items:

```
import("stdfaust.lib");

// UI controllers connected using metadata
freq = hslider("freq [knob:1]", 200, 50, 5000, 0.01);
gain = hslider("gain [knob:2]", 0.5, 0, 1, 0.01);
gate = button("gate [switch:1]");

// DSP processor
process = os.osc(freq) * gain, os.sawtooth(freq) * gain * gate;
```

Some additional files can be seen in the examples folder:

- [synth.dsp](https://github.com/VCV-Prototype/blob/master/examples/synth.dsp) demonstrates how to use all different VCV Prototype UI items
- [organ.dsp](https://github.com/VCV-Prototype/blob/master/examples/organ.dsp) demonstrates a MIDI controllable additive synthesis based organ
- [physicalmodel.dsp](https://github.com/VCV-Prototype/blob/master/examples/physicalmodel.dsp) demonstrates a modal synthesis based bell connected to a reverb