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MIDI (Musical Instrument Digital Interface) is a technical standard that enables electronic musical instruments, computers, and other audio devices to communicate with and synchronize one another. It is a protocol for sending performance instructions, not audio signals. For instance, a MIDI keyboard sends data messages to a computer or sound module about which notes are played, how forcefully they are struck, and how long they are held.

Key components

MIDI message format: A set of commands that devices use to describe musical actions. A message is a small packet of data that includes a status byte and one or more data bytes.

Status byte: The first byte of a message that indicates its type (e.g., "Note On" or "Program Change") and which of 16 channels it applies to.

Data bytes: The subsequent bytes that provide the parameters for the message. For example, a "Note On" message's data bytes would contain the note's pitch and velocity (volume).

Standard MIDI File (SMF): A file format (.mid or .midi) that stores sequences of MIDI data. Because these files contain instructions instead of raw audio, they are very small and easy to edit. A MIDI file can contain multiple tracks, tempo information, and other musical data.

Physical connectors: The original MIDI 1.0 standard used 5-pin DIN cables for one-way serial communication. Modern MIDI communication is often handled over a USB cable, which can carry MIDI data in both directions simultaneously.

MIDI channels: Each physical MIDI connection can carry 16 independent channels of data. This allows for multi-timbral performance, where a single controller can send data to up to 16 different instruments or sound modules at once.