MIDI

MIDI is an acronym for “Musical Instrument Digital Interface,” a standard that defines how musical synthesizers and instruments connect and interface with computers and with one another. The standard defines both the hardware, such as the input and output ports used to connect equipment, and the manner in which information is stored and used to control the equipment.

Although the MIDI acronym was originated by Roland Corporation, a company best known for making electronic keyboards, the actual protocol was a product of the joint efforts of musicians and musical manufacturers interested in synchronizing keyboards and synthesizers. During the early 1980s, no standard had yet been defined to allow instruments created by different manufacturers to communicate with each other. Existing protocols were manufacturer-specific, so they did not allow an instrument from one maker to interface with one from another.

The movement toward a MIDI standard began with the efforts of Roland to produce instruments that could be connected to computers. At the time, the Commodore 64 home computer—equipped with a crude analog synthesizer chip—had been introduced, as had the first IBM PC, which lacked a sound chip of [Page 315]any kind. Concentrating on the latter, Roland worked to develop a digital sequencer that would be compatible with its entire line of musical equipment. The result was a PC card that could be inserted into an available expansion slot; the card, known as the MPU-401 (Musical Processing Unit, model 401), was the first MIDI interface created exclusively for a computer. More importantly, accompanying the card was a digital language designed to allow computers to communicate with instruments; this language became known as MIDI, and was eventually adopted by other companies as the standard for the industry.

The widespread adoption of the MIDI standard led to the creation of the MIDI Manufacturer's Association (MMA), an organization composed of musical-instrument manufacturers that would be responsible for documenting and circulating existing and new standards.

In its most basic form, the MIDI standard determines when a synthesizer, for example, should begin or stop playing a note or sequence of notes. MIDI files do not contain actual sounds; rather, they contain information about how to create the sounds. MIDI files store data in the form of electronic information transmitted to and used by instruments to control, for example, which, when, and how notes are played, as well as any adjustments that need to be made to the instrument (e.g., volume). The data is in binary form, a series of codes composed of different sequences of 1s and 0s.

MIDI files are general files that follow a standard format used to describe how to create whatever music is encoded; they are decoded by sequencers, which use the directions stored in binary to play back or recreate the musical performance. In everyday language, MIDI files contain a series of messages. When MIDI files are created, each message receives a timestamp indicating when it was created. These timestamps are then used by the sequencer to determine when to “play” each message and in what sequence (hence the name “sequencer”) relative to the other messages.

...