---
title: useSoundTransitions
description: "Plays sounds when observed state changes match rules."
---

```tsx
import { useSoundTransitions } from 'filedom/sound';

useSoundTransitions(score, [
  { when: (prev, next) => prev !== undefined && next > prev, sound: 'merge' },
]);
```

After each change to `state`, every rule whose `when(prev, next)` returns true plays its sound. If your state lives in a store that emits domain events, use [useEmittedSounds](/docs/reference/hooks/use-emitted-sounds) instead.

## Parameters

```ts
useSoundTransitions<TState>(
  state: TState,
  rules: readonly SoundTransition<TState>[],
  opts?: { playOnMount?: boolean; scheme?: SoundScheme<SoundEvent>; backend?: SoundBackend; }
)
```

`state`: value to observe. Rules run when its identity changes, so replace object state instead of mutating it.

`rules`: each rule has `when(prev, next)`, `sound`, and optional playback `options`. `sound` and `options` may also be functions of `prev` and `next`; a `sound` function can return null to play nothing. `prev` is undefined on the first run.

`opts`: `playOnMount` (default false) also checks the rules on mount. `scheme` and `backend` are optional.

## Returns

Nothing (`void`).