How to Use AUMatrixMixer in iOS

Question

I've been trying for a few days to use the kAudioUnitSubType_MatrixMixer on iOS.

For testing purposes I tried to port the MatrixMixerTest sample code from MacOSX. But I don't have any sound (there is no error reported).

here is what I do :

• Create AUGraph
• Add RemoteIO Node to graph
• Add MatrixMixer Node to graph
• Connect MatrixMixer to RemoteIO.
• Open AUGraph
• Getting the Mixer AudioUnit from MatrixMixer Node
• Setting 2 Input Bus to Mixer AudioUnit
• Setting 1 Output Bus to Mixer AudioUnit
• Setting Rendering Callback to both Inputs
• Setting Correct StreamFormat to each input bus
• Setting Correct StreamFormat to output bus
• AuGraph Initialize
• Setting All volumes of the matrixmixer to 1.0

And when I start the graph no sound, and no error. And when I show the matrix Mixer with PrintMatrixMixerVolumes (from Core Audio Utility by Apple) everything looks normal.

One of my question is : Is the AUMatrixMixer really works on iOS ? And the other is : Is there something specific to do with this Audio Unit ?

Thank You

EDIT : When I print the matrix it shows :

Input Channels = 4, Output Channels = 2 Input Elements: 0:[2, T] 1:[2, T]
Output Elements: 0:[2, T]
Global Volume: 1.000 1.000 (1.000) (1.000) 1.000 (1.000) (1.000) 1.000 (1.000) (1.000) 1.000 (1.000) (1.000) 1.000 1.000

Answer 1

I had the same issue, everything seemed ok but no sound. I solved with this line to set the Master Volume for the Matrix Mixer:

AudioUnitSetParameter(matrixMixer, kMatrixMixerParam_Volume, kAudioUnitScope_Global, 0xFFFFFFFF, 1.0, 0);