Apple

On Apr 4, 2013, at 1:20 AM, Ben wrote:

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);

}
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References:
	>Handling App Interruptions - AudioUnit fails to restart (From: Joe White <email@hidden>)
	>MusicTrack timing and looping issues. (From: Ben <email@hidden>)
	>Re: MusicTrack timing and looping issues. (From: Douglas Scott <email@hidden>)