MIDI
Maintained by the MIDI Manufacturers Association
MIDI (Musical Instrument Digital Interface) is a technical standard and communication protocol that lets electronic musical instruments, computers, and other audio devices exchange performance data such as which notes are played, how hard,…
Definition
MIDI (Musical Instrument Digital Interface) is a technical standard and communication protocol that lets electronic musical instruments, computers, and other audio devices exchange performance data such as which notes are played, how hard, and for how long. Rather than transmitting actual audio, MIDI sends compact messages describing musical events, which a receiving synthesizer or software instrument interprets to produce sound. It also defines a standard file format for storing sequences of these messages.
Overview
MIDI was introduced in the early 1980s through collaboration among electronic instrument manufacturers who wanted a common way for synthesizers and controllers from different companies to communicate, replacing a landscape of incompatible proprietary interfaces. Before MIDI, connecting a keyboard from one manufacturer to a synthesizer from another was often impossible; the standard's adoption effectively unified the electronic music industry around a single low-level communication format that persists largely unchanged in its core design decades later. Mechanically, MIDI represents musical events as short, discrete messages, such as "note on" (which key, how hard it was struck, called velocity), "note off", pitch bend, and control changes (like sustain pedal or modulation), each identified by a channel number so up to sixteen independent instrument parts can share one connection. These messages traveled originally over a dedicated serial connection at a fixed baud rate through 5-pin DIN connectors, though modern systems commonly carry MIDI over USB or network protocols instead. Because MIDI data is just instructions, not audio, the same MIDI file or performance can sound completely different depending on which synthesizer or sound font renders it, and file sizes are tiny compared to recorded audio. MIDI differs fundamentally from audio formats like WAV or MP3: it is a symbolic, instruction-based representation of a performance rather than a recording of actual sound waves, similar to how a musical score differs from a recording of a performance. This makes MIDI easy to edit note-by-note, transpose, or reassign to different instrument sounds after the fact, something not possible with recorded audio without complex processing. It complements rather than competes with digital audio workstations, which typically handle both MIDI sequencing and audio recording side by side, and it has been extended over time by companion specifications like General MIDI, standardizing instrument sound assignments across devices, and more recently MIDI 2.0, adding higher resolution and bidirectional device communication. In practice, MIDI is used to connect keyboard controllers, drum machines, and synthesizers to computers for music production, to sequence and edit compositions in digital audio workstations, and to control non-musical equipment like stage lighting that has adopted MIDI as a convenient control protocol. Film scoring, video game audio, and electronic music production rely heavily on MIDI for its editability and the flexibility to swap virtual instrument sounds without re-recording a performance. Musicians and educators also use MIDI-enabled instruments and software for practice, arranging, and notation software that converts played performances directly into sheet music. The main limitation of MIDI is that it carries no audio itself, so playback quality entirely depends on the receiving synthesizer or sound library, meaning a MIDI file can sound dramatically different across devices, unlike a fixed audio recording. Classic MIDI's fixed data rate and limited resolution for parameters like velocity and pitch bend were also long-standing constraints, which MIDI 2.0 aims to address but has not yet fully replaced. When exact, device-independent playback fidelity matters more than editability, a recorded audio format is the appropriate choice instead of MIDI.
Specification
- Transmits symbolic performance data, not recorded audio
- Supports sixteen independent channels over one connection
- Encodes note-on, note-off, velocity, and control-change messages
- Originally used 5-pin DIN serial connectors, now often carried over USB
- Defines a standard file format for storing musical sequences
- Extended by General MIDI for consistent instrument sound mapping
- Enables note-level editing and instrument reassignment after recording
- Also used to control non-musical equipment like stage lighting