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# Audio Unit Voice I/O

Configure system voice processing and respond to speech events.

## Topics

### Observing muted speech

[`kAUVoiceIOProperty_MutedSpeechActivityEventListener`](/documentation/AudioToolbox/kAUVoiceIOProperty_MutedSpeechActivityEventListener)

A property to register a listener that the system calls when it detects speech while the user has the microphone muted.

[`AUVoiceIOMutedSpeechActivityEventListener`](/documentation/AudioToolbox/AUVoiceIOMutedSpeechActivityEventListener)

A block that the system calls to indicate speech activity while the user has the microphone muted.

[`AUVoiceIOSpeechActivityEvent`](/documentation/AudioToolbox/AUVoiceIOSpeechActivityEvent)

Constants that indicate the state of muted speech.

### Configuring voice processing

[`kAUVoiceIOProperty_BypassVoiceProcessing`](/documentation/AudioToolbox/kAUVoiceIOProperty_BypassVoiceProcessing)

A property that bypasses all processing for microphone uplink done by the voice processing unit.

[`kAUVoiceIOProperty_VoiceProcessingEnableAGC`](/documentation/AudioToolbox/kAUVoiceIOProperty_VoiceProcessingEnableAGC)

A property to enable automatic gain control on the processed microphone uplink.

[`kAUVoiceIOProperty_MuteOutput`](/documentation/AudioToolbox/kAUVoiceIOProperty_MuteOutput)

A property to mute the output of the processed microphone uplink.

### Configuring ducking of other audio

[`AUVoiceIOOtherAudioDuckingConfiguration`](/documentation/AudioToolbox/AUVoiceIOOtherAudioDuckingConfiguration)

A structure that you use to configure ducking of other non-voice audio in a voice chat.

### Inspecting errors

[`kAUVoiceIOErr_UnexpectedNumberOfInputChannels`](/documentation/AudioToolbox/kAUVoiceIOErr_UnexpectedNumberOfInputChannels)

An error that indicates that the audio unit encountered an unexpected number of input channels during initialization.


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