8.12.19. STRUDEL-19 — One-Shots: Fire-and-Forget Stings on Events

A strudel pattern is normally an endless loop. daStrudel adds the piece a game or tool needs for event audio: a pattern that plays once and then stops and dies. This is what lets a pattern be used as a sound effect — a win sting, a pickup chime, an impact — fired from host state, with no baked or shipped audio asset.

There are two halves:

• stop — once(pat) / playFor(pat, n) gate a pattern to its first cycle (or first n cycles) and emit silence forever after. These are pure Pattern combinators; they compose with everything.

• die — strudel_one_shot(pat, gain, quant_cycles, len_cycles) fires pat as a self-retiring track: it plays, goes silent, and the track removes itself from the mix once every voice has finished ringing (so the release tail is never clipped).

8.12.19.1. Part A: once / playFor — the stop half

You can see the stop without listening: query the gated pattern and watch the onsets vanish past the window. once keeps cycle 0; playFor(pat, n) keeps the first n cycles:

let phrase <- once(note("c5 e5 g5 c6", "triangle"))
var c0 <- phrase(TimeSpan(start = 0.0lf, stop = 1.0lf))   // 4 onsets — plays
var c1 <- phrase(TimeSpan(start = 1.0lf, stop = 2.0lf))   // 0 onsets — silent forever

Because they are ordinary combinators, the gate composes with the rest of the pattern algebra (fast, stack, the fluent setters, …) before you ever turn it into a one-shot.

8.12.19.2. Part B: strudel_one_shot — the die half

Fire a sting from the host loop. The track is live while it sounds, then auto-removes once its voices stop ringing — you never call strudel_remove_track. strudel_active_tracks() reports how many tracks are live, so the host (or a test) can ask “is the sting still ringing?”:

let sting <- (note("c5 e5 g5 c6", "triangle")
    |> gain(0.8) |> room(0.5) |> orbit(2) |> attack(0.005) |> release(0.4))
strudel_one_shot(sting, 1.0, 0.0, 0.5)   // gain 1.0, immediate, half a cycle long
// ... keep calling strudel_tick() in the host loop; the track retires itself

Compose orbit / room / gain into pat to give the sting its own reverb bus, independent of the music tracks.

8.12.19.3. Part C: Quantize to the beat

quant_cycles > 0 snaps the start to the global beat grid: 0 is immediate, 0.25 is the next quarter-cycle beat. A sting triggered at an arbitrary instant then waits a few milliseconds so it lands musically in time instead of on the exact frame of the event:

strudel_one_shot(sting, 1.0, 0.25, 0.5)   // snap to the next 1/4-cycle beat

8.12.19.4. Part D: Parametric SFX — a different sting per event

Each one-shot is a fresh, independent track, so the pattern can vary per event. Fire a higher sting as “events” intensify — pitch by impact, instrument by surface — all without a single audio file:

let phrases <- ["c4 e4 g4", "e4 g4 c5", "g4 c5 e5", "c5 e5 g5"]
// on event i:
let sting <- (note(phrases[i], "triangle")
    |> gain(0.7) |> room(0.4) |> orbit(2) |> attack(0.005) |> release(0.3))
strudel_one_shot(sting, 1.0, 0.0, 0.5)

This is the discrete-event complement to the continuous adaptive control (signal + orbit fades) covered in the comparison page: sustained layers crossfade with signals and orbit levels; momentary events fire one-shots.

See also

Full source: tutorials/daStrudel/daStrudel_19_one_shots.das

Previous tutorial: STRUDEL-18 — SFX Lab: a procedural sound-effect workbench

How daStrudel differs from strudel.cc (one-shots are a daStrudel extension): daslang strudel vs strudel.cc — Feature Comparison

Full daStrudel reference: Strudel (Live Coding)