Take a midi packet with 3 bytes in hexadecimal notation such as 99 3C 64. This stream encapsulates the following instructions:

Play middle C on channel 10 at velocity 100. Now lets strip it down to nibbles & bits.

9 -> Note on message. (Examples of other status messages are: 0xB for controller change, 0x C for program change & 0xE for pitch-bend)

9 -> Middle channel 10. (Range 0 -15)

3C ->Middle C -> Note 60

64 -> 100 in decimal

Determining if a stream begins with a status byte.

A set high-bit on the first byte identifies the byte as a status message. This can be accomplished visually by converting 99 from hex to binary 10011001,  and seeing if the first bit is 1. This can be tested mathematically with the following condtion:

0×99 > 0x7F

Once you have determined that the byte actually sets a status, you need to identify the actual status that is set. Some examples of status messages are: 0xB for controller change, 0xC for program change & 0xE for pitch-bend. To get the value of the left nibble, you can use the following expression.

0×99 >> 4 (Shift the 4 places) or 0×99 / 0×10

Determining the midi transmission channel.

The second nibble (99) of the first byte in the stream, represents the midi transmission channel. Channels are 0 indexed so they range from 0-F in hex or 0-15 in decimal. So we can tell quite easily that the transmission channel in our stream is 10 just by adding 1 to the second nibble. We can extract the 2nd nibble using the following expression:

0×99 % 0×10 (% = modulo)

and get the midi channel by adding 1 to the result

(0×99 % 0×10) + 1

Determining the note number and velocity.

These are pretty simple. Just convert the Hex values to a decimal values

0x3c = 60

0×64 = 100

I’ll post my parser here when I’m done with it this weekend.

After perusing MIDIService.h, I gathered that I had to ultimately use the MIDISend().

extern OSStatus MIDISend(
    MIDIPortRef port,
    MIDIEndpointRef dest,
    const MIDIPacketList *pktlist);

When it was time to create a MIDIEndpointRef, I was presented with numerous paths. My initial instinct was to traverse some hierachy to get to the Blofeld MIDI Out but it turns out that each MIDIEntity can be reference using a unique id. I was hoping that this info would be available in the Audio MIDI Setup utility but it turns out you can only get at it via code. So I created a foundation tool with the following code.

#import <Foundation/Foundation.h>

#import <CoreMIDI/CoreMIDI.h>

int main (int argc, const char * argv[]) {

    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

	MIDIDeviceRef midiDevice;

	int numOfDevices = MIDIGetNumberOfDevices();

	int numOfBlofeldEntities;

	for(int i=0; i< numOfDevices; i++ ){

		midiDevice = MIDIGetDevice(i);

		NSDictionary *midiDeviceProperties;

		MIDIObjectGetProperties(midiDevice, (CFPropertyListRef *)&midiDeviceProperties, YES);

		NSLog(@"midiDeviceProperties:%@", midiDeviceProperties);

	}

    [pool drain];

    return 0;

}

After running the tool, I get the ff output. I need to run this on multiple Macs to verify that the uniqueID is actually the same regardless of which machine I run it on.

2009-01-11 23:24:31.273 MidiProperties[4198:10b] midiDeviceProperties-5:{

    SerialNumber = "8290071532-023547011532";

    USBLocationID = -46923776;

    USBVendorProduct = 317063187;

    "apple.midi.audiomidisetup.widget.xPosition" = 385;

    "apple.midi.audiomidisetup.widget.yPosition" = 203;

    driver = "com.apple.AppleMIDIUSBDriver";

    entities =     (

                {

            destinations =             (

                                {

                    name = "Blofeld MIDI out";

                    uniqueID = -934632258;

                }

            );

            embedded = 0;

            maxSysExSpeed = 3125;

            name = "Waldorf Blofeld";

            sources =             (

                                {

                    name = "Blofeld MIDI in";

                    uniqueID = 1439776402;

                }

            );

            uniqueID = -1524681845;

        }

    );

    image = "/Library/Audio/MIDI Devices/Access Music/Images/Virus TI Snow.tiff";

    manufacturer = "Waldorf Music GmbH";

    model = "Waldorf Blofeld";

    name = Blofeld;

    offline = 0;

    "receives MTC" = 0;

    "receives clock" = 0;

    "supports General MIDI" = 0;

    "supports MMC" = 0;

    "transmits MTC" = 0;

    "transmits clock" = 0;

    uniqueID = 1111148707;

}

Finally armed with the blofeld’s MIDI Out uniqueID, the rest was cake. Here is the code I used to send the note on message.

#import <Foundation/Foundation.h>

#import <CoreMIDI/CoreMIDI.h>

MIDIEndpointRef getEndpointWithUniqueID(MIDIUniqueID id){

	MIDIObjectRef endPoint;

	MIDIObjectType foundObj;

	MIDIObjectFindByUniqueID(id, &endPoint, &foundObj);

	return (MIDIEndpointRef) endPoint;

}

MIDIClientRef getMidiClient(){

	MIDIClientRef midiClient;

	NSString *outPortName =@"blofeldOut";

	MIDIClientCreate((CFStringRef)outPortName, NULL, NULL, &midiClient);

	return midiClient;

}

MIDIPortRef getOutPutPort(){

	MIDIPortRef outPort;

	NSString *outPortName =@"blofeldOut";

	MIDIOutputPortCreate(getMidiClient(), (CFStringRef)outPortName, &outPort);

	return outPort;

}

MIDIPacketList getMidiPacketList(){

	MIDIPacketList packetList;

	packetList.numPackets = 1;

	MIDIPacket* firstPacket = &packetList.packet[0];

	firstPacket->timeStamp = 0;	// send immediately

	firstPacket->length = 3;

	firstPacket->data[0] = 0x90;

	firstPacket->data[1] = 60;

	firstPacket->data[2] = 64;

	// TODO: add end note sequence

	return packetList;

}

void play_note(void) {

	NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; 

	MIDIPacketList packetList=getMidiPacketList();

	MIDIUniqueID blofeldEndpointID = -934632258;

	MIDIEndpointRef blofeldEndpoint = getEndpointWithUniqueID(blofeldEndpointID);

	MIDISend(getOutPutPort(), blofeldEndpoint, &packetList);

	MIDIEndpointDispose(blofeldEndpoint);

	[pool drain];

}

int main (int argc, const char * argv[]) {

    play_note();

    return 0;

}