# instrument-rack

> Instrument racks: an instrument whose chains each start with an instrument of the library, then effects, all played by every note in layers and summed as a rack with its macros; the engine that plays one on a MIDI track.

```bash
npx shadcn@latest add @audio-ui/instrument-rack
```

```ts
import { chainInstrument, createInstrumentRackEngine } from "@/lib/instrument-rack";
```

- Files: `lib/instrument-rack.ts`
- Depends on: `arrangement`, `device-library`, `rack`, `voice-pool`; npm: `@audio-ui/engine`
- Used by: `arrangement-engine`, `drum-rack`

| Export | Kind | What it is |
| --- | --- | --- |
| `chainInstrument` | function | The instrument a chain of an instrument rack plays: its first device, when it is an instrument of the library. |
| `InstrumentRackEngine` | interface | An instrument rack playing on a context: a note player, its sound out at `output`. |
| `createInstrumentRackEngine` | function | Plays instrument racks on `ctx`: each chain's instrument with `voices` voices into the chain, its effects in series after it, the chains summed as any rack's. |

## Usage

An instrument whose chains each start with an instrument of the library, then effects, played by every note whose key and velocity fall in a chain's zone, in layers, and summed as a rack with its macros: a split, or soft and hard layers.

```ts
import { createInstrumentRackEngine } from "@/lib/instrument-rack";

const instrument = createInstrumentRackEngine(ctx, libraryDevice, 8); // 8 voices a chain
instrument.output.connect(destination);
instrument.update(rack, { tempo });
```

`chainInstrument` finds the instrument at the head of a chain. Zones come from `inZone` and `FULL_ZONE` in [`arrangement`](/docs/lib/arrangement); the [arrangement engine](/docs/lib/arrangement-engine) plays it on a MIDI track.