# polyphony

> Chords on an instrument whose engine plays one voice: a note takes the voice that holds it, else a free one, else the one held longest, whose note is let go first. No sound and no engine of its own: it plays the engines it is given.

```bash
npx shadcn@latest add @audio-ui/polyphony
```

```ts
import { createPolyphony } from "@/lib/polyphony";
```

- Files: `lib/polyphony.ts`
- Depends on: nothing; npm: `@audio-ui/engine`
- Used by: `use-polyphony`, `voice-pool`

| Export | Kind | What it is |
| --- | --- | --- |
| `VoiceEngine` | interface | What a voice plays a note on: the engine of an instrument, which holds one note at a time. |
| `Polyphony` | interface | Notes played as chords on engines that hold one note each, every note by an id its note off gives again. |
| `createPolyphony` | function | Plays chords on `engines`, one note each: what turns an instrument whose engine plays one voice into a polyphonic one. |

## Usage

Plays chords on engines that hold one note each. A note takes the voice that holds it already, else a free one, else the one held longest, whose note is let go first. It makes no sound and no engine: it takes engines you made and connected, so it schedules ahead on the audio clock as well as it plays live.

```ts
import { createPolyphony } from "@/lib/polyphony";

const voices = createPolyphony(engines);
voices.noteOn({ frequency: 440, velocity: 0.8 }, "a4", time);
voices.noteOff("a4", time + 0.5);
voices.release(stopTime); // every note held, as a stop does
```

Notes are ordered by when they came, not by a clock. On a page, [`usePolyphony`](/docs/hooks/use-polyphony) makes the engines and gives you `noteOn` and `noteOff`; for a device of the library, [`voice-pool`](/docs/lib/voice-pool) plays on it.