Apple

I am having endless issues with MusicTrack. I am trying to create a drum machine.

1) Looping (MusicTrackLoopInfo): is broken as far as I can tell, if you wish to try and change notes on the fly whilst looping (unless someone can tell me different or has a workaround?).

2) With the code below I use MusicTrackNewMIDINoteEvent to insert notes at regular interval (0.25, 0.5 etc). But due to the above, this is useless. So instead I tried using MusicTrackNewUserEvent to try and trigger note events from that.

The plan was to pass a timestamp, and fire UserEvent's on every 16th note, and check with an Array if to play a drum sound or not.

However, when played, it is totally out of time and absolutely unusable for triggering drum noises.

Am I right in saying user UserEvent's are not as accurate timing wise as NoteEvent's?

The whole method (midiTest) is called on a separate thread with...

[NSThread detachNewThreadSelector:@selector(midiTest) toTarget:audioEngine withObject:nil];

I am exasperated by it all! Any ideas?

-(void) midiTest {

OSStatus result = noErr;

[self createAUGraph];

[self configureAndStartAudioProcessingGraph: self.processingGraph];

// Create a client

MIDIClientRef virtualMidi;

result = MIDIClientCreate(CFSTR("Virtual Client"),

MyMIDINotifyProc,

NULL,

&virtualMidi);

// Create an endpoint

MIDIEndpointRef virtualEndpoint;

result = MIDIDestinationCreate(virtualMidi, (CFStringRef)@"Virtual Destination", MyMIDIReadProc, (__bridge void *)(self), &virtualEndpoint);

MusicSequence s;

NewMusicSequence(&s);

MusicTrack sequenceTrack;

MusicSequenceNewTrack(s, &sequenceTrack);

NSValue * sequenceStruct = [NSValue value:&s withObjCType:@encode(MusicSequence)];

[self.musicSequenceArray addObject: sequenceStruct];

MusicSequenceSetUserCallback(s, UserCallback, NULL);

MusicPlayer p;

NewMusicPlayer(&p);

MusicSequenceSetMIDIEndpoint(s, virtualEndpoint);

[self loadPreset];

MusicPlayerSetSequence(p, s);

result = MusicSequenceGetIndTrack(s, 0, &sequenceTrack);

MIDINoteMessage noteMessage;

noteMessage.channel = 0;

noteMessage.note = 60;

noteMessage.velocity = 100;

noteMessage.releaseVelocity = 0;

noteMessage.duration = 0.0;

int ticksPerBar = 4;

for (int i = 0; i<(8 *ticksPerBar); i++) {

UserEvent event;

event.length = 0;

event.length = sizeof(UserEvent);

event.playedNote = noteMessage.note;

event.tStamp = (float)i/ticksPerBar;

event.message = noteMessage;

event.player = _samplerUnit;

event.midiStatus = 144;

result = MusicTrackNewMIDINoteEvent(sequenceTrack, (float)i/ticksPerBar, &noteMessage);

//MusicTrackNewUserEvent( sequenceTrack, (float)i/ticksPerBar, (MusicEventUserData *)&event);

}

MusicTrackLoopInfo loopInfo = { 8.0f, 0 };

result = MusicTrackSetProperty(sequenceTrack, kSequenceTrackProperty_LoopInfo, &loopInfo, sizeof(MusicTrackLoopInfo));

MusicPlayerPreroll(p);

MusicPlayerStart(p);

}

References:
	>Handling App Interruptions - AudioUnit fails to restart (From: Joe White <email@hidden>)