Managing the Matrix Mixer + multichannel audio

Connections.cpp

// This is how I did the connections in my test (after setting the stream format, of course)

for(size_t i = 0; i < filePlayers.size(); ++i) {
  filePlayers[i].setFile(ofFilePath::getAbsolutePath("hats.wav"));
  filePlayers[i].loop();
  filePlayers[i].connectTo(mixer, i); // connect file player 0 to mixer input bus 0, etc 
}

mixer.connectTo(output);

DebugOutput.cpp

// This demonstrates how to use the MatrixMixerVolumes utility
// You'll need to #include "MatrixMixerVolumes.h" in files where you want to use it

FILE * debugFile = fopen("/Users/Adam/Desktop/MatrixMixerVolumes.txt", "w");
PrintMatrixMixerVolumes(debugFile, mixer);
fclose(debugFile);

// It's probably easiest to try this at first with a minimal matrix mixer setup,
// or else it'll produce a HUUUUGE file

// I used a setup with 4 file players and one 16 channel output and found that
// easy enough to understand

SettingLevels.cpp

// Example of how to set matrix mixer levels

Float32 levels[NUMBER_OF_FILE_PLAYERS * 2 + 1][NUMBER_OF_CHANNELS + 1] = {0};

levels[0][NUMBER_OF_CHANNELS] = 0.777; // set the input volume of file player 0 to 0.777

levels[0][5] = 0.999; // set the level of file player 0 in channel 5 to 0.999
levels[NUMBER_OF_FILE_PLAYERS * 2][5] = 0.888; // set the output volume of channel 5 to 0.888

levels[0][3] = 0.666; // set the level of file player 0 in channel 3 to 0.666
levels[NUMBER_OF_FILE_PLAYERS * 2][3] = 0.555; // set the output volume of channel 3 to 0.555 

levels[NUMBER_OF_FILE_PLAYERS * 2][NUMBER_OF_CHANNELS] = 1; // setting the global volume to 1

OFXAU_PRINT(AudioUnitSetProperty(mixer,
                                 kAudioUnitProperty_MatrixLevels,
                                 kAudioUnitScope_Global,
                                 0,
                                 levels,
                                 sizeof(levels)),
			"setting matrix volume levels");
			
// Note: I've been trying to get the file player to produce mono audio, to no avail.
// It seems to refuse any attempt to set the channel count to 1. So, we'll need to keep the "* 2"
// going on in the levels array. So, setting file player 3's level on channel 8 would be:

levels[3 * 2][8] = 0.1234;

StreamFormat.cpp

// Setting the output unit and the matrix mixer to use the same stream format (in this case, 16 channel audio) 

output.setDevice("Soundflower (16ch)"); // <- should set the device before the stream format

AudioStreamBasicDescription ASBD = {
	.mSampleRate       = 44100,
	.mFormatID         = kAudioFormatLinearPCM,
	.mFormatFlags      = kAudioFormatFlagsAudioUnitCanonical,
	
	.mChannelsPerFrame = 16, // <- change this to 24 in your case
	.mFramesPerPacket  = 1,
	
	.mBitsPerChannel   = sizeof(AudioUnitSampleType) * 8,
	.mBytesPerPacket   = sizeof(AudioUnitSampleType),
	.mBytesPerFrame    = sizeof(AudioUnitSampleType)
};
	
OFXAU_PRINT(AudioUnitSetProperty(output,
                                 kAudioUnitProperty_StreamFormat,
                                 kAudioUnitScope_Input,
                                 0,
                                 &ASBD,
                                 sizeof(ASBD)),
			"setting output unit's input ASBD");
	
// setting mixer to have 960 input busses, 1 output bus and use the
// 16 channel stream format on its output bus
mixer.setChannelLayout(NUMBER_OF_FILE_PLAYERS, 1, NULL, &ASBD);