I'm using a VoiceProcessingIO (kAudioUnitSubType_VoiceProcessingIO) audio unit in my VoIP application to record and play audio while also making use of system-provided signal processing. Everything works fine except when the unit is initialized, if anything else is playing audio, that audio becomes significantly quieter whereas whatever I output is heard at full volume. When the unit is uninitialized, the volume of the other audio changes back to what it was.
Some users apparently don't like this behavior so I'm looking for a way to control this, if at all possible, but I can't seem to find anything related to this; the information related to the VoiceProcessingIO unit on OS X is generally extremely scarce as opposed to iOS.
The only thing I've found that comes close is the kAUVoiceIOProperty_DuckNonVoiceAudio property which seems to be exactly what I need but it's only available on iOS and is also marked deprecated.