MIDI (Musical Instrument Digital Interface) is a protocol designed for recording and playing back music on digital synthesizers that is supported by many makes of personal computer sound cards. Originally intended to control one keyboard from another, it was quickly adopted for the personal computer. Rather than representing musical sound directly, it transmits information about how music is produced. The command set includes note-ons, note-offs, key velocity, pitch bend and other methods of controlling a synthesizer. The sound waves produced are those already stored in a wavetable in the receiving instrument or sound card.
Since a MIDI file only represents player information, it is far more concise than formats that the sound directly. An advantage is very small file size. A disadvantage is the lack of specific sound control.
With a program that provides this interface, you can create music using a standard keyboard or other input device. You or others can then play your MIDI-conforming creation with the same or another program and a sound card as a music synthesizer. The MIDI program may come with a graphical user interface that looks like a sound studio control room. Many sound cards come as a package with MIDI software (for example, Media Vision's Pro Audio Studio 16).
The MIDI protocol uses eight-bit serial transmission with one start bit and one stop bit, has a 31.25 Kbs data rate, and is asynchronous. Connection is made through a five-pin DIN plug, of which three pins are used.