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# mainMixerNode

The audio engine’s optional singleton main mixer node.

```
var mainMixerNode: AVAudioMixerNode { get }
```

## Discussion

The audio engine constructs a singleton main mixer and connects it to the [`outputNode`](/documentation/AVFAudio/AVAudioEngine/outputNode) when first accessing this property. You can then connect additional audio nodes to the mixer.

If the client never sets the connection format between the `mainMixerNode` and the `outputNode`, the engine always updates the format to track the format of the `outputNode` on startup or restart, even after an [`AVAudioEngineConfigurationChangeNotification`](/documentation/AVFAudio/AVAudioEngineConfigurationChangeNotification). Otherwise, it’s the client’s responsibility to update the connection format after an [`AVAudioEngineConfigurationChangeNotification`](/documentation/AVFAudio/AVAudioEngineConfigurationChangeNotification).

By default, the mixer’s output format (sample rate and channel count) tracks the format of the output node.

---

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