Sound

No files. A table of ten-number recipes becomes the whole sound of a game, and there is no AudioContext until the player touches something.

Two rules before anything else:

• No sound comes out until a user gesture unlocks the audio. Browsers refuse otherwise. This package installs no listener of its own — you call unlock() from your own handler.
• play() returns accepted, not audible. The throttle, the ladder and the voice ceiling all run with no device present; only the rendering does not. That is what makes the policy layer testable in Node.

---

A game's whole sound

import { createAudio, createBed, validateSounds } from '@latticekit/audio';
import type { SoundDef } from '@latticekit/audio';

const SOUNDS = {
  tap:     { bus: 'ui',  minGapMs: 40,
             layers: [{ wave: 'sine', hz: 1180, gain: 0.05, hold: 0.03, cutoff: 2400 }] },
  place:   { bus: 'sfx', minGapMs: 60,
             layers: [{ wave: 'triangle', hz: 180, toHz: 90, gain: 0.22, hold: 0.14, cutoff: 1200 },
                      { wave: 'noise', hz: 0, gain: 0.10, hold: 0.05, cutoff: 3000 }] },
  collect: { bus: 'sfx', minGapMs: 45, ladder: { steps: 5, windowMs: 900 },
             layers: [{ wave: 'triangle', hz: 660, toHz: 880, gain: 0.16, hold: 0.1, cutoff: 3200 }] },
  deny:    { bus: 'ui',  minGapMs: 120,
             layers: [{ wave: 'square', hz: 140, gain: 0.08, hold: 0.09, cutoff: 900 }] },
} satisfies Record<string, SoundDef>;

export const audio = createAudio({ sounds: SOUNDS });

/** Assert this is empty in your own test. `validateSounds` returns problems rather than
 *  throwing, because a shipped game must not refuse to start because a sound is 0.03 too loud. */
export const problems = validateSounds(SOUNDS);

/** From YOUR handler. This package installs no listener — a listener at import time is exactly
 *  the boot-time side effect the determinism rule exists to prevent. */
export function onFirstTouch(): void {
  audio.unlock();
}

/** The ambience. One continuous bed, driven by numbers the game already has. */
export const bed = createBed(audio, [
  { wave: 'sine',  hz: 50, gain: 0.16, cutoff: 220, cutoffAtFull: 1.2 },
  { wave: 'noise', hz: 0,  gain: 0.10, cutoff: 320, cutoffAtFull: 4.2, band: [0, 0.55] },
  { wave: 'sine',  hz: 88, gain: 0.07, cutoff: 400, cutoffAtFull: 2.0, band: [0.45, 1] },
]);

/** Every frame, with the SAME number that lerps the palette — so the world cannot look warm
 *  and sound cold, and a mismatch cannot get reported as a lighting bug. */
export function everyFrame(activity: number, daylight: number): void {
  bed.set(activity, daylight);
}

export function collect(): void {
  audio.play('collect');    // twenty of these in one tap is one chord, never twenty blips
}

audio.play('colect') does not compile — the argument type is inferred from the table's keys. There is no SoundId type to maintain.

---

A sound is ten numbers, not a node graph

One fixed signal chain per layer:

source → [highpass] → [lowpass] → gain envelope → [pan] → bus

What you may vary: which of five sources (sine, triangle, square, sawtooth, noise), one starting pitch, one exponential sweep target, one peak gain, one decay length, one start delay, one attack override, one low-pass corner, one high-pass corner, one pan. What you may not vary: the order of the chain, the envelope's shape, the number of filters, whether anything modulates anything else.

That is enough for a pitch-swept sine that is a kick drum, two detuned saws that beat against each other, and noise through a high-pass that is a hi-hat. It is not enough for an FM bell, and that is the trade.

The refusal that matters most is routing. The moment routing is author-defined the clipping ceiling can no longer be validated statically — a feedback delay at 0.9 turns a 0.16 chord into a runaway and no static check can see it.

import { validateSounds } from '@latticekit/audio';

export const clipping = validateSounds({
  chord: { minGapMs: 100, layers: [
    { wave: 'sine', hz: 440, gain: 0.60, hold: 0.4 },
    { wave: 'sine', hz: 550, gain: 0.64, hold: 0.4 },
  ] },
});
// [{ sound: 'chord', code: 'clips',
//    message: 'chord peaks at 1.24, ceiling is 0.95 — WebAudio sums and hard-clips above 1.0…' }]

It sums only the layers alive at the same instant, so an arpeggio of three 0.5 layers 90 ms apart is not reported as a 1.5 chord. The other codes: no-layers, no-throttle, ladder-shorter-than-gap, ladder-too-short, inaudible, sub-audio-frequency, zero-hold.

Set the master by arithmetic, not by the meter. One exhibit's worst case summed to 1.455 across strings, gate tones and bed, so its master had to sit at or below 0.65 for the total to stay under the 0.95 ceiling; the measured peak was 0.253 because unrelated frequencies never align. WebAudio hard-clips instantaneously, and the point of this package is a ceiling that is provable rather than probable.

---

Bursts must not stack — two defences, because they fail differently

minGapMs handles the repeat of one sound. It is required, not optional, because the author who most needs it is exactly the author who would omit it.

MAX_VOICES (24) handles twenty different sounds in the same millisecond, which no per-sound gap can see. Past the ceiling, play drops rather than queues: a queued burst arrives after the moment that caused it and reads as lag.

Voices are counted by scheduled end time, never by an onended callback. A counter driven by onended leaks — the bed's oscillators never end, so their callback never fires, and a game that runs for an hour ends up permanently at the ceiling and goes silent.

import type { Audio } from '@latticekit/audio';

export function settings(audio: Audio<'tap'>): void {
  audio.setMaxVoices(12);     // a SETTER. Never rebuild the engine for this
  audio.setMaxPan(0);         // a mono switch, for an accessibility setting
}

Why those are setters and not a rebuild. dispose() closes the AudioContext and a document gets about six of them, ever. A voice-ceiling slider that rebuilt the engine on every drag — which is the only thing a construction-time ceiling allows — permanently silences the page in about a second. The ceiling is one integer in one comparison: nothing is allocated from it, no handle derives from it, and no save or log records it.

Two consequences before you drag one: lowering the ceiling refuses new plays and does not cut live voices short, so audio.voices may read above audio.maxVoices until the release tails pass. And at a ceiling of 2, mashing gives a burst with holes in it — and which holes changes with the order things were struck.

---

The traps that cost real sessions

A chord cannot be one sound. minGapMs is keyed on the sound id, so six strings sharing an id are six plays of the same sound in the same instant and five of them are thrown away. That is exactly right for a "collect all" button and exactly wrong for a chord, and the package has no way to tell them apart. Spell a chord as n different ids — twelve rows where two would do — or arpeggiate with per-layer delay.

A suspended context freezes the clock, and then the throttle refuses everything for ever. In a tab that has never had a real user gesture, available reports true (a context object exists) while currentTime stays at 0 — so the second play of any id is refused permanently. The symptom is "the first sound works and nothing after it does", and it points nowhere near the cause. Call unlock() from a real gesture handler and check that audio.now() advances.

Never use Math.pow for intervals. SEMITONE is exported for exactly this — the twelfth root of two, written out — because pow is not required by the language spec to be correctly rounded. Walk the interval one multiply at a time and use exact small-integer ratios for partials. A gate that hums a minor third and opens for something merely near it is a game failing silently: a player hears two pitches that are close, cannot say why one is wrong, and blames their ear.

attack is the whole difference between an instrument and a notification. The default is about 6 ms and at 6 ms a note is struck. Raise it to 30 ms — still fast by UI standards — and the onset moves past the point where it reads as caused by the press; it becomes a notification about the press. Below about 6 ms the leading-edge click comes back, because a gain stepping from 0 to 0.3 in one sample is a click whatever the recipe asked for.

Mixer.setGain takes no ramp length. It always approaches over about 15 ms, which is right for a duck down and far too fast for the recovery — so a recovery has to be driven frame by frame from your own envelope, and because an approach re-anchored sixty times a second never arrives, quantize the write to about a hundredth so it only fires when the number actually moves. Wire a duck on the mixer, from onScheduled, rather than at each call site: there is then exactly one place it can be forgotten.

A bed that must duck cannot be on the ducking bus. createBed defaults to sfx, correctly, because a player muting music should not silence the world — but a bed that ducks under gameplay sounds must be on a bus those sounds are not, which ties the ambience to the music switch. Both defaults are right on their own and they conflict; pick deliberately.

createBed's sagTo default is too deep for a low-pitched bed, and validateSounds does not check bed layers. At the 0.55 default a 41 Hz layer sags to 22.7 Hz — under the audible floor the validator enforces for one-shots. Use about 0.8 for anything pitched that low.

---

The bed — the half that survives twenty minutes

A loop is annoying at twenty minutes because it is the same twenty minutes regardless of what the player did. What wears out is melody; texture does not. Nobody has ever been annoyed by rain.

• level scales gain and opens the filters — an empty world is silent, not quiet.
• tone sags the pitch, closes the top end and crossfades band layers. A plant losing power winds down: a drop in level alone reads as a mixing change, a drop in pitch reads as machinery stopping.
• band: [0, 0.55] on crickets and band: [0.45, 1] on coil whine gives a day↔night crossfade as two layers trading places. One filter sweep sounds like a filter sweep; two layers trading places sounds like evening. Overlap the bands, or keep one unbanded layer — a bed that is silent at some middle value of tone is a hole the player walks into.

set is safe to call every frame: it ramps toward the figures, allocates nothing, creates no nodes after the first, and does not re-issue an unchanged target.

A bed built before unlock() stands its nodes up on the first unlock, at whatever level it has been driven to in the meantime.

---

Testing it with no speaker

import { createAudio } from '@latticekit/audio';
import type { SoundDef, VoicePlan } from '@latticekit/audio';

const SOUNDS = {
  collect: { bus: 'sfx', minGapMs: 45,
             layers: [{ wave: 'triangle', hz: 660, gain: 0.16, hold: 0.1 }] },
} satisfies Record<string, SoundDef>;

export function throttleTest(): number {
  let now = 0;
  const audio = createAudio({ sounds: SOUNDS, context: () => null, now: () => now });
  const plans: VoicePlan[] = [];
  audio.onScheduled((plan) => plans.push({ ...plan }));   // COPY: the object is reused

  audio.play('collect');
  audio.play('collect');       // inside the 45 ms gap
  return plans.length;         // 1 — the gap, asserted with no mock at all
}

context: () => null is a headless run. onScheduled is not only a test hook: a HUD can flash a meter on the beat from it, with no analyser and no real context.

The test every game built on this needs, because validateSounds cannot see a sound that is declared and never played — a defect that is silent, and is a game that is simply quiet at the one moment it should not be:

/** In a test: read your own `src/**` with `node:fs`, join it, and pass it here. */
export function unplayed(sourceText: string, ids: readonly string[]): readonly string[] {
  return ids.filter((id) => !sourceText.includes(`play('${id}')`));
}

That grep fails on any table indexed by an integer — one exhibit reported twelve of fifteen sounds "unplayed" because they were played through STRING_IDS[i]. Know that before you trust it.

---

Buses, and what you persist

Three buses — music, sfx, ui — plus master. Fixed and closed, because the reason buses exist is a player who wants the music off and the alerts on, and that player needs the same three switches in every game.

This package stores nothing. mixer.snapshot() returns a small versioned value and restore() takes one back; hand it to the save layer as a device-scoped preference, not as save state — a player who hits START OVER must not get their sound turned back on.

Screen-x → pan is not computed here. That needs a camera, and this package does not know the camera exists. Four lines in the game; PlayOptions.pan takes the result.

---

If the game ships silent, say why

Four exhibits in this kit deliberately make no sound, and they all give the same reason: a page that starts making noise before a visitor has touched it is worse than a silent one. If you are not going to wire an unlock gesture, do not declare sounds. And if audio is genuinely refused, say so plainly in the HUD rather than pretending — pretending is a worse lie than the notice.

---

What this skill does not cover

you want	read
where unlock() gets called from	input
the one number that should drive both the light and the bed	art
storing a player's volume settings	saving
a meter or a beat indicator on screen	hud

Long form, on disk: node_modules/@latticekit/audio/README.md.