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I have created an aggregated device containing multiple audio devices. I would like to enable/disable input or output channels from an aggregate CoreAudio device. When calling core audio to receive the number of streams (using kAudioDevicePropertyStreams) the return value is always 1. I have also tried the implementation in CoreAudio Utility classes: CAHALAudioDevice::GetIOProcStreamUsage. Still I could not see how to access sub-streams and disable/enable them. What needs to be done to accomplish disable/enable of sub-streams? Here is CAHALAudioDevice::GetIOProcStreamUsage for reference: void // make an AudioHardwareIOProcStreamUsage the right size UInt32 theNumberStreams = GetNumberStreams(inIsInput); UInt32 theSize = SizeOf32(void*) + SizeOf32(UInt32) + (theNumberStreams * SizeOf32(UInt32)); CAAutoFree<AudioHardwareIOProcStreamUsage> theStreamUsage(theSize); // set it up theStreamUsage->mIOProc = reinterpret_cast<void*>(inIOProcID); theStreamUsage->mNumberStreams = theNumberStreams; // get the property CAPropertyAddress theAddress(kAudioDevicePropertyIOProcStreamUsage, inIsInput ? kAudioDevicePropertyScopeInput : kAudioDevicePropertyScopeOutput); GetPropertyData(theAddress, 0, NULL, theSize, theStreamUsage); // fill out the return value for(UInt32 theIndex = 0; theIndex < theNumberStreams; ++theIndex) { outStreamUsage[theIndex] = (theStreamUsage->mStreamIsOn[theIndex] != 0); } } kAudioDevicePropertyIOProcStreamUsage always returns one stream regardless of the amount of sub devices in the aggregated audio device