strudel-compose

name	strudel-compose
description	Write a new Strudel track or extend an existing one from a brief. Use when the user wants to compose, draft, sketch, or add a track to the album in this repo, or asks for a Strudel pattern in a given vibe/genre/reference.

The user wants a Strudel pattern written or extended. Strudel is a JS-based live-coding music language (strudel.cc, docs at strudel.cc/learn).

Before composing

Get clear on:

1. Brief — vibe, genre, references, mood, energy arc.
2. Length — single pattern (one cycle that loops), or a track with sections?
3. Section — new file in tracks/ (give it a name) or extending an existing one?

If the brief is one word ("ambient"), ask one targeted follow-up. Don't ask three.

How to write a good Strudel pattern

• Start with the rhythmic foundation. Tempo (setcps) and the simplest pulse first. Layer on top.
• Use stack() to layer voices. Each voice does one job (bass, pad, melody, percussion, texture).
• Modulate with sine.range(a, b).slow(N) instead of static numbers — that's where movement comes from. Apply to lpf, gain, pan, etc.
• Use mini-notation idioms: <a b c> for one-per-cycle, [a b] for subdivisions, *N for repeats, (3,8) for Euclidean rhythms, ? for random drop.
• Reverb and delay are cheap drama. .room(0.9).delay(0.5).delaytime(0.5) turns a thin pattern into a wash. Use sparingly on drums.
• Don't over-write. A good ambient track can be 6 lines. If it's 80 lines and you can't hear the structure, you wrote a forest.

Output structure for a track file

// XX — Title
// One-line vibe description.
// Reference vibe: 1-2 artists/albums.

setcps(N)

stack(
  // voice 1: foundation (bass / drone)
  ...,
  // voice 2: rhythm
  ...,
  // voice 3: melody / texture
  ...,
)

After writing

Always test before declaring done. Invoke the strudel-test skill (or do it manually): open strudel.cc in agent-browser, paste, play, screenshot, listen for errors.

A pattern that doesn't parse is worse than no pattern.

For a sectioned track, also run the structural gates — they're static (no render) and catch flat dynamics or a missing build/strip arc before anyone listens:

make eval ARGS="v2-gen/<track-id>"     # contrast / arc / baseline assertions
make eval ARGS="--update"              # record the new track's baseline once it passes

A track that fails contrast or arc isn't done — fix the section gains/voices (quiet intro and outro, a real climax, a strip-back section), don't lower the bar. An intentionally-flat ambient piece can declare that in its manifest: "eval": { "allow_flat": true }.

Common pitfalls

• s("bd") SILENTLY DROPS without a bank. The drum pack we load (tidal-drum-machines.json) prefixes every sample with its drum-machine name — AkaiLinn_bd, RolandTR909_bd, etc. Bare "bd" / "sd" / "hh" resolve to nothing and you hear nothing. Always chain .bank("AkaiLinn") (or another bank with the kit you want) on percussion. Synth oscillators (sine, sawtooth, triangle, square, white) need no bank.
• setcps(120) is wrong — cps is cycles per second, not BPM. setcps(0.5) ≈ 30 bpm in 4/4, setcps(2) ≈ 120 bpm.
• .note() and note() both exist — the standalone note("...") is the usual entry point.
• Don't chain .s() after .note() and expect both to apply — note(...).s("piano") works because Strudel maps notes to the sample's playback rate.
• See [[strudel-conduct]] for the full list of gotchas we hit while building live (Pattern.onTrigger semantics, hap.context.locations shape, etc.).