What Is MIDI?

MIDI (or Musical Instrument Digital Interface) is an industry-standard interface used on electronic musical keyboards and PCs for computer control of musical instruments and devices.

MIDI was born in 1983 when a group of major electronic-instrument manufacturers realized the need for such a standard and developed one. Before MIDI, it was very difficult or impossible to interface equipment made by different manufactures. Therefore, it was quite common to see keyboardists playing several keyboards at the same time, since no one keyboard was the "overall best" in everything.

Physically, MIDI consists of three wires with a five-pin DIN type connector at each end (two pins are not used).

MIDI data is not the same as sound data. What is transmitted over the wire is information on how to play a song, not the physical sound data itself. MIDI can be thought of better as a player-piano roll than a compact disk: just as the piano-roll instructs the player-piano to create the sounds, MIDI data tells a MIDI device which notes to play, patches (instruments) to use, and other information to help the instrument recreate the song. When you listen to a MIDI file, you're hearing an actual 'performance' by the instrument, not a 'recording' of a past performance.

MIDI was not designed to be used with personal computers, but since it is a digital interface, they actually work very well together. Combining at least one MIDI instrument with a personal computer and a MIDI interface (a device that allows the computer to "speak" MIDI) allows for many interesting applications. With a music notation software, music can be played on a music keyboard or other MIDI instrument, and immediately be displayed on the computer screen. Mistakes can be corrected, and other musical symbols, such as dynamic markings, tempo changes, and even lyrics, can be entered to make a complete score. In effect, you have a music "word processor", and the advantages parallel those of using a word processor over a typewriter. Another very popular piece of software is the MIDI sequencer. This software allows musicians to create songs one "track" at a time, similar to a multi-track tape player, using a MIDI device. The difference is the sequencer doesn't record the sound but the actual "notes" and other MIDI information. Therefore, if a performer makes a few mistakes in an otherwise great performance, s/he can correct the wrong notes via the computer and all is well!

Technically, there is no such thing as a "MIDI file", but you'll hear the term all the time. What is really meant is a Standard MIDI File, or SMF. This file is a computer-independent standard for storing MIDI data in a computer file. Although most MIDI programs have their own formats for storing things, virtually all of them can speak SMF, allowing basic MIDI data to be transferred from program to program (at the risk of losing some specialized data from the individual program).

Recently, General MIDI has appeared as a new addition to the MIDI standard. General MIDI adds standards on the order of patches (instruments), such as Acoustic Piano being #1, etc. It also standardizes drum kits, that is, which notes play which drums. Non General-MIDI keyboards can do what they want with these orderings, making it difficult to play sequences done on one instrument on another one (a "remapping" is required. Most of the files you'll see on the Internet are General MIDI.