MIDI is an acronym that stands for Musical Instrument Digital Interface. It’s a way to connect devices that make and control sound — such as synthesizers, samplers, and computers — so that they can communicate with each other using MIDI messages.
This lets one keyboard trigger sounds on another synthesizer, and it makes it possible to record music in a form that allows for easy note editing, flexible orchestration, and song arrangement.
Virtual instruments — computer programs that simulate hardware synthesizers and samplers — also communicate with computer sequencing software running on the same computer using MIDI messages.
History
MIDI evolved as a standard to enable communication between the more compact and affordable synthesizers that were available in the early 1980s, after the era of large, expensive modular analog synthesizers. MIDI was meant to allow someone to control multiple synthesizers from a single keyboard, so as to generate, for example, the massive layered sounds popular in some ’80s pop music.
Formerly, such connections between instruments were not standardized, so incompatibilities were common. The MIDI standard was completed in 1983 by a consortium of musical equipment manufacturers (including Korg, Oberheim, Roland, Sequential Circuits, and Yamaha). Products featuring the standard, such as the popular Yamaha DX7, were on the market soon after.
Before long, sequencing software for personal computers could take advantage of the MIDI communications protocol to let users record, store, and edit music, as well as manage large collections of synthesizer sounds.