It is the digital equivalent of the SMPTE, in that it travels from machine to machine without being memorized on a physical support system. The SMPTE code can be converted into MTC in order to synchronize MIDI machines [The Midi Protocol ] with the SMPTE time code.
There are 4 types of messages in MTC's:
Full Frame Messages: contains timing messages. Namely:
hour : minute : second : frame
It is composed of 4 bytes and for every frame one of these bytes gets sent. For example if we were to send the following frame:
05 : 12 : 19 : 10
the following byte-sequence would be sent (the numerical information is contained in the last 5 bits of each byte):
0 0 1 0 0 1 0 1 (hour)
0 0 0 0 1 1 0 0 (minute)
0 0 0 1 0 0 1 1 (second)
0 0 0 0 1 0 1 0 (frame)
The second and third bits in the first byte specify the number of frames per second, as illustrated in the following table:
Table 17.2. Binary Codes for the MTC's fps
Binary Code Frames per second (fps) 00 24 01 25 10 29.97 11 30
The table shows that the example message has an fps value of 25.
1/4 frame message: this message gets sent each quarter of a frame. Four of these messages are inserted in the bit sequence that corresponds to 1 frame. Their function is to constantly provide the reference rhythm.
Cueing messages: messages used for automation and for the MIDI Machine Control.
User bits: their role is to transport information inserted by the user.