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# start()

Starts the audio engine.

```
func start() throws
```

## Discussion

This method calls the [`prepare()`](/documentation/AVFAudio/AVAudioEngine/prepare()) method if you don’t call it after invoking [`stop()`](/documentation/AVFAudio/AVAudioEngine/stop()). It then starts the audio hardware through the [`AVAudioInputNode`](/documentation/AVFAudio/AVAudioInputNode) and [`AVAudioOutputNode`](/documentation/AVFAudio/AVAudioOutputNode) instances in the audio engine. This method throws an error when:

- There’s a problem in the structure of the graph, such as the input can’t route to an output or to a recording tap through converter nodes.
- An [`AVAudioSession`](/documentation/AVFAudio/AVAudioSession) error occurs.
- The driver fails to start the hardware.

---

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