Musical Instrument Digital Interface.

Originally developed in the early 1980s to control one digital synthesizer from another. Today MIDI is used to transmit almost every aspect of a musical performance. However, it must be understood that MIDI data is all about how a sound will be produced, not the actual sound itself. So data sent from one device to another could find itself being played with a piano sound while the original information was actually a drum sequence. General MIDI was in part introduced to alleviate this problem, except that the subset was really a consumer format and of not much use to the professional community. Amongst the command sets of MIDI are note-on, note-off, key velocity and pitch, modulation such as pitch bend, program changes, timing and many more. Its use has moved outside of strictly music and is used for lighting cues amongst other applications. The one great advantage of MIDI, apart from its ubiquity, is that file sizes are relatively small compared to what an actual audio file would be. The MIDI protocol uses eight-bit serial transmission with one start bit and one stop bit, has a 31.25 KBPS data rate, and is asynchronous. Connection is made through a five-pin DIN plug, of which only three of the pins are generally used.
(See General MIDI)