iOS 5/6: low volume after first usage of CoreAudio

Question

I work on a VoIP app. The AudioSession's mode is set to kAudioSessionMode_VoiceChat.

For a call, I open a CoreAudio AudioUnit with subtype kAudioUnitSubType_VoiceProcessingIO . Everything works fine. After the first call, I close the AudioUnit with AudioUnitUninitialize() and I deactivate the audio session.

Now, however, it seems as if the audio device is not correctly released: the ringer volume is very low, the media player's volume is lower than usual. And for a subsequent call, I cannot activate kAudioUnitSubType_VoiceProcessingIO anymore. It works to create an AudioUnit with kAudioUnitSubType_RemoteIO instead, but also the call's volume is very low (both receiver and speaker).

This first occured on iOS 5. With the iPhone 5 on iOS 6, it is even worse (even lower volume).

Has anyone seen this? Do I need to do more than AudioUnitUninitialize() to release the Voice Processing unit?

Answer 1

I've found the solution: I've incorrectly used AudioUnitUninitialize() to free the audio component retrieved with AudioComponentInstanceNew(). Correct is to use AudioComponentInstanceDispose().

Answer 2

Yes, you need to dispose the audioUnit when using voiceProcessingIO. For some reason there is no problem when using RemoteIO subtype. So whenever you get OSStatus -66635 (kAudioQueueErr_MultipleVoiceProcessors), check for missing AudioComponentInstanceDispose() calls.