MIDI Time Code is a synchronization technique widely used in the audio and music industry, often in conjunction with SMPTE time code. In fact, MIDI Time Code (MTC) is simply a MIDI implementation of SMPTE time code. A typical use of MTC is as follows: A musician records himself playing an acoustic instrument (e.g. violin) on one track of a multi-track tape recorder. He records SMPTE time code on another track, using one of the commercially available hardware SMPTE generators, such as the OpCode Studio-3. Next, he synchronizes a sequencer to the time code, using a SMPTE-to-MIDI converter, and plays along with it on a MIDI keyboard. The MIDI is recorded in the sequencer. He continues, building up a number of "tracks" in this manner. Finally, he records the entire MIDI performance to tape. The sequencer begins playing in exactly the right place, thanks to the SMPTE. He can even begin the tape in the middle and the sequencer finds the correct location in the sequence and begins playing from that spot.
MTC is organized in hours:minutes:seconds:frames, where there are either 24, 25, or 30 frames per second, depending on the MTC format. Additionally, there is a 30-frame drop-frame format used for color television. MTC consists of occassional full-frame messages and a large number of quarter-frame messages. MTC normally runs forward, but can run backwards as well. For further details of MTC, see the MIDI Detailed Specification, available from the The International MIDI Association. Their address at the time of this writing is 5316 W. 57th St., Los Angeles, CA. 90056.
The MusicKit accepts MIDI Time Code (MTC) through any MIDI device (either of the serial ports on NeXT hardware) and provides a way of synchronizing a MKConductor's performance to the incoming time code. It can also generate MTC and send it out any MIDI device. It can even receive MTC and generate it at the same time, through the same or different MIDI devices. Finally, it can receive and transmit ordinary MIDI through any MIDI device while receiving or generating time code.