MIDI (Musical Instrument Digital Interface) is an industry-standard protocol defined in 1982 that enables electronic musical instruments such as keyboard controllers, computers, and other electronic equipment to communicate, control, and synchronize with each other. MIDI allows computers, synthesizers, MIDI controllers, sound cards, samplers and drum machines to control one another, and to exchange system data (acting as a raw data encapsulation method for sysex commands). MIDI does not transmit an audio signal or media — it transmits “event messages” such as the pitch and intensity of musical notes to play, control signals for parameters such as volume, vibrato and panning, cues, and clock signals to set the tempo. As an electronic protocol, it is notable for its widespread adoption throughout the industry.
Note names and MIDI note numbers.All MIDI compatible controllers, musical instruments, and MIDI-compatible software follow the same MIDI 1.0 specification, and thus interpret any given MIDI message the same way, and so can communicate with and understand each other. MIDI composition and arrangement takes advantage of MIDI 1.0 and General MIDI (GM) technology to allow musical data files to be shared among many different files due to some incompatibility with various electronic instruments by using a standard, portable set of commands and parameters. Because the music is simply data rather than recorded audio waveforms, the data size of the files is quite small by comparison.
MIDI 1.0 is also used as a control protocol in applications other than music, including:
show control theatre lighting special effects sound design VJ-ing recording system synchronization audio processor control Digital DJing otherwise known as Controllerism computer networking, as demonstrated by the early first-person shooter game MIDI Maze, 1987 animatronic figure control animation parameter control, as demonstrated by Apple Motion v2 Such non-musical applications of the MIDI 1.0 protocol (sometimes over MIDI-DIN, sometimes using other transports) are possible because of its general-purpose nature. Any device built with a standard MIDI Out connector should in theory be able to control any other device with a MIDI In port, just as long as the developers of both devices have the same understanding about the semantic meaning of all the MIDI messages the sending device emits. This agreement can come either because both follow the official MIDI standard specifications, or else in the case of any non-standard functionality, because the message meanings are directly agreed upon by the two manufacturers.
(Sourced from Wikipedia Musical_Instrument_Digital_Interface)