Concept

Bus

A named mix bucket with its own gain stage, FX chain, voice limit, and (optional) sidechain key.

TL;DR

A Bus is the routing target for one or more sounds. You declare it once in createEngine, then talk to it by name. Level changes and mutes ramp over 10ms internally so you never get a click. fadeTo accepts a curve for longer transitions.

Mental model

A bus has three nodes: input → fxInput (FX chain head) → output. Voices target input; master takes output.

API surface

Bus — public interface ts

class Bus {
  readonly name: string;
  readonly input: GainNode;          // connect voices/sources here
  readonly output: GainNode;         // connected to master

  level: number;                     // setter ramps over 10ms (click-free)
  muted: boolean;                    // setter ramps over 10ms

  fadeTo(target: number, ms: number, curve?: FadeCurve): Promise<void>;

  voiceCount: number;
  voices(): readonly Voice[];

  concurrency: ConcurrencyConfig | null;
  setConcurrency(c: ConcurrencyConfig | null): void;

  addFx(fx: FxInsert): void;
  removeFx(fx: FxInsert): void;
  fx(): readonly FxInsert[];
}

Live demo

Slam the slider — no click. Try the fade buttons for curve-based transitions.

Recipes

Direct level vs. fadeTo

ts ts

// Smooth fade — won't pop because of the 10ms internal ramp on direct writes,
// or use fadeTo() with a curve for longer transitions.
engine.bus('music').level = 0.5;
await engine.bus('music').fadeTo(0, 1200, 'equal-power');

Enumerate active voices on a bus

ts ts

const bus = engine.bus('sfx');
console.log('voices on this bus:', bus.voiceCount);
for (const v of bus.voices()) v.fade({ to: 0, ms: 200 });

Pitfalls

Don't write to output.gain.value directly.

The Bus class wraps that with a 10ms ramp. Bypassing it produces audible clicks in Chrome and Firefox.

Don't share an FxInsert between buses.

Each FX node has its own internal connections. Construct one per bus, dispose when removed.

Concurrency — voice-limit policies.
Mixer — the wider bus graph.
Ducking — sidechain a bus from another.

Bus