nih-faust-jit

A plugin to load Faust dsp files and JIT-compile them with LLVM. Limited to stereo audio (DSP scripts with more than 2 input/ouput chans will be refused). The selected DSP script is saved as part of the plugin state and therefore is saved with your DAW project. A two-part GUI is provided:

• Select which script to load and where to look for the Faust libraries that this script may import
• Tweak the parameters described in the script (shown as various egui widgets)

Both effect and instrument DSPs are supported, with MIDI notes and CCs in both cases. The DSP script type is normally detected from its metadata. E.g. if the script contains a line like:

declare options "[midi:on][nvoices:12]";

then the script will be considered to be an instrument with 12 voices of polyphony. But you can override this via the GUI to force the DSP script type and number of voices: this is notably useful for scripts that describe instruments but do not contain a [nvoices:xxx] metadata.

UI

• DSP widgets are shown in a two-directional scrollable panel (you can also left-click on empty space and drag to pan around)
• v/h/tgroups are implemented as foldable containers
• double-click on any slider's label to reset it to its default value
• hover a bargraph to see its current value

Building

First install Rust and Faust.

For now, Faust paths need to be provided through environment variables at build time. The build time environment variables are:

• FAUST_LIB: which libfaustXXX to link with. By default it statically links with libfaustwithllvm in order to generate a self-contained plugin (which is more convenient if you are on Windows, as else you would need extra setup so the plugin can find Faust and llvm DLLs at runtime). Just set it to "faust" if you are on OSX or Linux and want to dynamically link with a regular system installation of Faust and llvm (dynamic linking is cargo's default, and shouldn't be a problem there)
• FAUST_LIB_PATH: where to look for the faust static/dynamic library
• FAUST_HEADERS_PATH: where to look for the Faust C/CPP headers
• DSP_LIBS_PATH: where the plugin should look by default for the Faust DSP libraries, so your script can import e.g. "stdfaust.lib". This can then be overriden at runtime with the plugin's GUI
• LLVM_CACHE_FOLDER: where to cache the llvm bytecode of the scripts, for shorter reload times. This variable must be set, but can be an empty string if you do not want to use caching. This folder will be created if it doesn't exist, so you can just delete it to flush the cache. Caching is based only on the contents of the script itself, not on what it may import.

You can set these env vars via command line, or edit the .cargo/config.toml before building. You may need to run cargo clean after changing them so new values are taken into account. Check .github/workflows/rust.yml to see e.g. how these are overriden for building on Ubuntu.

Then, you can compile and package the VST3 and CLAP plugins with:

cargo xtask bundle nih_faust_jit --release

Running the standalone version of the plugin is just:

cargo run --release

Known shortcomings

• Scripts are reloaded only when clicking on the Set or reload DSP script button. Therefore, anytime you modify something in the top panel (ie. things related to how the DSP should be loaded), don't forget to manually reload the script (just re-select the same file in the file picker).
• Volume can get high quickly when using polyphonic DSPs, because Faust voices are just summed together. The plugin exposes a Gain parameter to the host. Don't forget to use it if your instrument script doesn't perform some volume reduction already.
• Parameters changed via the GUI widgets are not saved in the plugin's state. They will return to the default value they have in the script when the plugin is reloaded.
• Keyboard input is not supported (you cannot directly type a value in numeric entry). This comes from a bug in baseview.

Faust features not yet supported

• Soundfiles
• Some style (knob and led) and scale (exp for sliders/bargraphs, and log for bargraphs) metadata are not taken into account in the GUI

Crates

The main crate containing the plugin is nih_faust_jit. Parts of its logic are exposed as lower-level crates, that could be reused in other projects:

faust_jit defines the SingletonDsp type. It wraps the part of the libfaust API that is needed to:

• load an effect or instrument DSP from a script,
• process audio buffers with it,
• extract the information needed to build a GUI that can tweak the DSP's internal parameters (represented as the DspWidget type).

faust_jit is related to rust-faust, but rust-faust deals only with static compilation of DSP scripts to Rust code. The faust_jit crate is not limited to stereo DSP scripts (only the plugin is).

faust_jit_egui draws an egui GUI from the DspWidgets.