About using kAudioUnitSubType_MatrixMixer with AVAudioEngine

Question

var mixerUnitDescription = AudioComponentDescription()
 mixerUnitDescription.componentType = kAudioUnitType_Mixer;
 mixerUnitDescription.componentSubType = kAudioUnitSubType_MatrixMixer;
 mixerUnitDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
 mixerUnitDescription.componentFlags = 0;
 mixerUnitDescription.componentFlagsMask = 0;
 
 AVAudioUnit.instantiate(with: mixerUnitDescription) { [self] mixerUnit, error in
 var status = AudioUnitSetParameter(avAudioUnit!.audioUnit, kMatrixMixerParam_Volume, kAudioUnitScope_Global, 0xFFFFFFFF, 1.0, 0)
 
 var numInputBuses:UInt32 = 2
 var numOutputBuses:UInt32 = 1
 // Input bus config
 status = AudioUnitSetProperty(avAudioUnit!.audioUnit,
 AudioUnitPropertyID(kAudioUnitProperty_ElementCount),
 AudioUnitScope(kAudioUnitScope_Input),
 0,
 &numInputBuses,
 UInt32(MemoryLayout<UInt32>.size))
 }

When I set the volume, I get the error -10867 kAudioUnitErr_Uninitialized. However, I can successfully set the number of input and output bus. Why is that?

• Gordon Childs: The question title mentions an AVAudioEngine but there's no sign of one in your question. Can you show how you're configuring the engine? AVAudioEngine will eventually initialize your mixer, at which point you should be able to set volumes. Maybe it will initialize if you call prepare. Anyhow, show more code.