MIDI Time Code and MIDI Clock Explained
When you try to synchronize two devices using MIDI timing messages, you’re met with several choices. One is between MIDI Time Code (MTC) and MIDI Clock. The other is frame rates and tempo map or synch track.
MIDI Time Code uses absolute time in its messages (the actual time on the clock from the beginning of the song or reference point in hours, minutes, seconds, frames, and subframes). This data can then be translated into SMPTE messages (the kind of synchronization data used in film and television).
If you choose MTC, you also have to decide the frame rate for the time code. Several frame rates are available, and each is associated with certain mediums. They are as follows:
24 fps (frames per second): This rate is mainly used for films.
25 fps: This is for audio, video, and film equipment used in Europe and other places that use the SECAM or PAL formats.
29.97 fps: This is for color televisions used in the United States, Japan, and other places that use the NTSC format.
30 fps: This rate is used for black-and-white television or used working with audio only in the United States (Europe’s black-and-white TVs use the 25-fps rate).
If this isn’t confusing enough, both the 29.97- and 30-fps rates also have either drop frame or nondrop frame formats. This gets pretty technical, but drop frame formats basically drop two frames every minute, except for the tenth minute, so that the timing data matches the clock exactly. These are generally used for live video feeds.
MIDI Clock is different from MTC in that it tracks the time of a song in beats and measures rather than in minutes and seconds. MIDI Clock messages are generally sent every 1/24 of a beat, but you can set most sequencer programs to much higher resolutions than that. Cubase VST version 5 can be set as high as, get this, 1,920 PPQ (pulses per quarter note).
When you choose MIDI Clock, you need to choose between using tempo map or synch track, as follows:
Tempo map: This is basically a layout of the tempos and time signatures used in a song. To use a tempo map to synchronize your SIAB system and sequencer, you need to create the map itself.
Synch track: A synch track is a track (at least was a track on analog recorders) that follows along with the tempo and measures of a song. To use a synch track, you need to first record one. If you have a digital recorder, you most likely don’t need to take up an actual track to do this.
So which do you choose? Unfortunately, that question doesn’t have a clear answer. The equipment that you have dictates part of your answer. (For instance, the Roland VS-1680 SIAB system can send MIDI Clock and MTC messages, but it doesn’t always effectively respond to those messages.)
The goals you have for your music dictate the other part. If you’re composing music for film or TV, your choice is clear (24 fps and 29.97 fps, respectively).
If your equipment and musical goals don’t limit your choice, choose what you like. Just make sure that both machines have the same settings.