Using iOS 3d Mixer

I have a AUGraph setup fairly simply with a multichannel mixer connected to an I/O unit. The playback is accessed through a callback function and everything works nicely.

I am trying to switch over to the 3D Mixer instead of the Multichannel mixer. So I switched the parameter from kAudioUnitSubType_MultiChannelMixer to kAudioUnitSubType_AU3DMixerEmbedded and left all the other setup the same.

The result was sort of a high pitched whine that seemed开发者_StackOverflow to start sounding like something then became just whine-ish. I have gone through each of the 3D Mixer unit's parameters and set them to their defaults but there was no change. Flipping on and off the k3DMixerParam_Enable parameter did work at muting and unmuting the playback though.

What setup I might have missed? or know where to find an example of a working 3d Mixer?

As already pointed out the 3d mixer needs mono inputs. But you also have to use UInt16 as the input sample data type. This is a working AudioStreamBasicDescription:

AudioStreamBasicDescription streamFormat = {0};
size_t bytesPerSample = sizeof (UInt16);

streamFormat.mFormatID          = kAudioFormatLinearPCM;
streamFormat.mFormatFlags       = kAudioFormatFlagsCanonical;
streamFormat.mBytesPerPacket    = bytesPerSample;
streamFormat.mFramesPerPacket   = 1;
streamFormat.mBytesPerFrame     = bytesPerSample;
streamFormat.mChannelsPerFrame  = 1;
streamFormat.mBitsPerChannel    = 8 * bytesPerSample;
streamFormat.mSampleRate        = graphSampleRate;

// Set the input stream format of the desired 3D mixer unit audio bus
AudioUnitSetProperty (
                      mixerUnit,
                      kAudioUnitProperty_StreamFormat,
                      kAudioUnitScope_Input,
                      audioBus,
                      &streamFormat,
                      sizeof (streamFormat)
                      );

As all answers already mention: the 3D Mixer on iOS needs mono inputs.

On iOS 8 / Xcode 6, the concept of canonical formats is deprecated and I found this (and only this) mono stream format description working as 3D Mixer input bus stream format description:

AudioStreamBasicDescription monoStreamFormat = {0};
monoStreamFormat.mSampleRate        = sampleRate;
monoStreamFormat.mFormatID          = kAudioFormatLinearPCM;
monoStreamFormat.mFormatFlags       = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
monoStreamFormat.mBitsPerChannel    = 16;
monoStreamFormat.mChannelsPerFrame  = 1;
monoStreamFormat.mFramesPerPacket   = 1;
monoStreamFormat.mBytesPerPacket    = 2;
monoStreamFormat.mBytesPerFrame     = 2;

The sample rate should be set and then obtained from the AVAudioSession.

Set this format on the output of the Audio Unit connected to the 3D Mixer input. Which is probably a AUConverter Unit...

Note however, this hasn't been tested for < iOS 8.

The 3d Mixer needed mono inputs.

http://lists.apple.com/archives/coreaudio-api/2010/Sep/msg00144.html