rudel

Rudel is a native Rust fork of Strudel (itself the JS port of TidalCycles): live-coded, algorithmic music patterns with a Koto scripting layer, native audio, MIDI out, and SuperDirt-compatible OSC out.

Licensed under AGPL-3.0-or-later, the same as Strudel. Sound bank licensing follows the source samples you load.

Workspace

Crate	Role
rudel-core	Pure pattern engine: Pattern = State -> Vec<Hap>, exact rational time, combinators, controls, signals, sample transforms, tonal helpers, and scheduler-neutral event extraction.
rudel-mini	pest mini-notation parser ported from Strudel's krill.pegjs: sequences, groups, rests, alternation, stacks, choices, Euclidean rhythms, ranges, polymeter, degradation, and sample indices.
rudel-dsp	Offline-testable voices: synth oscillators, noise, built-in drums, sampler playback, filters, envelopes, panning, and per-voice post effects.
rudel-audio	Real-time audio engine: lookahead scheduler, cpal output, sample bank loading, mixer, delay, and fundsp reverb.
rudel-lang	Koto bindings for Rudel patterns, controls, signals, factories, higher-order callbacks, sample transforms, and tonal operations.
rudel-midi	MIDI output: control-map to note/CC/program messages, timed windows, port wrapper, and real-time scheduler.
rudel-osc	SuperDirt OSC output: hand-rolled OSC 1.0 encoding, /dirt/play messages, UDP sender, and real-time scheduler.
rudel-app	Native egui editor with Koto live evaluation, audio/MIDI/OSC output selection, sample loading, and a one-cycle visualizer grouped by orbit.

Run the app

cargo run --release -p rudel-app

Type a pattern in the editor, press Ctrl+Enter to evaluate, then press Play:

stack(
  s("bd ~ bd bd").gain(0.9),
  s("~ sd ~ sd"),
  s("hh*8").gain(0.5),
  note("c4 e4 g4 b4").s("triangle").room(0.5),
  note("c2 ~ g2 ~").s("saw").lpf("400 1600").gain(0.6).delay(0.3)
)

The app starts with native audio. Use the output selector for MIDI or OSC; OSC defaults to 127.0.0.1:57120 for local SuperDirt.

Mondo Notation

Mondo Notation is Strudel's Lisp-like way of writing the same patterns, and Rudel speaks it. Put // mondo on the first line and the whole script is read as mondo:

// mondo
$ s [bd rim [~ bd] rim] # bank tr707
$ n <0 2 4 [3 1] -1>*4 # scale C4:minor # jux rev # dec .2 # delay .5

Round parens call a function, # chains one call onto the last, and $ separates patterns into a stack. That is this, in Koto:

stack(
  s("bd rim [~ bd] rim").bank("tr707"),
  n("<0 2 4 [3 1] -1>*4").scale("C4:minor").jux(rev).dec(0.2).delay(0.5)
)

To reach for mondo inside an otherwise-Koto script, tag a single pattern with it instead: mondo`s hh*8`.

Mondo is compiled to Koto rather than interpreted, so every control, transform and signal Rudel exposes is reachable from it. Its two limits — :/.. want literal operands, and def binds values rather than functions — are in docs/UNSUPPORTED.md.

Csound

Rudel can play a pattern on a Csound instrument instead of one of its own voices, the way @strudel/csound does — loadCsound, loadOrc, and the csound / csoundm outputs.

This is the one feature with an outside dependency. There is no pure-Rust Csound, and the WebAssembly build Strudel loads in the browser needs a browser to run, so Rudel uses the native library. Nothing links against it: Rudel builds and runs exactly as before without Csound, the library is opened only when a script first asks for it, and a script that asks when it is not there gets an error saying so while the rest of the pattern keeps playing.

To get started, install Csound (downloads; the 64-bit build, which is what the installers give you), then paste this in and press Play:

loadCsound`
instr Beep
    asig = vco2(p5, p4)
    asig *= linsegr:a(0, .01, 1, p3, 1, .1, 0)
    out(asig, asig)
endin`

note("c3 e3 g3 c4").csound('Beep')

loadOrc('github:user/repo/branch/some.orc') loads an orchestra from a URL instead. An orchestra that will not compile reports Csound's own message — the line number and the offending source — in the app's error panel.

Rudel looks for csound64.dll / libcsound64.so / libcsound64.dylib on the usual library path, then in the default install locations. Set RUDEL_CSOUND_LIB to a full path to override that, which is also all an unpacked build needs. Details, including how Csound is mixed in, are in docs/UNSUPPORTED.md.

Examples

cargo run -p rudel-audio --example play
cargo run -p rudel-audio --example live -- 'note("c e g").fast(2).room(0.4)'
cargo run -p rudel-audio --example samples -- path/to/samples

For sample folders, immediate subdirectories become sound names and files inside them become sample indices.

Using the library

use rudel_core::*;

let pat = note(seq([60, 64, 67, 71]))
    .s("triangle")
    .jux(|p| p.rev())
    .every(4, |p| p.fast(2))
    .gain(0.8);

Install mini-notation when you want strings to parse like Strudel patterns. As in Strudel, double-quoted strings are mini-notation and single-quoted strings are plain strings:

rudel_mini::install();

let pat = note("c3 [e3 g3] <c4 e4>")
    .s("saw")
    .chop(4)
    .room(0.4);

Current Status

Rudel has a usable native live-coding path today: pattern engine, mini-notation, synth/drum/sample audio, effects, Koto live evaluation, an egui app, MIDI out, and SuperDirt-compatible OSC out. The core, mini parser, transforms, audio event scheduling, MIDI, OSC, and Koto bindings are covered by unit, integration, and Strudel parity tests.

Still evolving: richer synth families, more Strudel sample-bank loading modes, MIDI input/clock-in, per-pattern routing helpers, deeper editor ergonomics, and the long tail of Strudel/Tidal compatibility.

Some Strudel packages bridge to browser-only platform APIs, and one — the experimental TidalCycles interpreter — is an alternative source language rather than a notation over the one Rudel has; these are intentionally not ported. See docs/UNSUPPORTED.md for the authoritative list of unsupported and intentionally different features.

Tests

cargo test --workspace
cargo clippy --workspace --all-targets -- -D warnings
cargo bench -p rudel-lang   # performance benchmarks over representative patterns

CI (.github/workflows/ci.yml) runs the test + clippy checks on every push and PR; the suite includes the parity drift guards (reference surface, per-package API inventory, and mini/tonal goldens).

Parity oracle notes live in tools/oracle/README.md.

Contributing

See CONTRIBUTING.md for setup, check commands, parity oracle guidance, and contribution conventions.