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Musical Instrument Digital Interface (MIDI) is a hardware specification and protocol standardized in 1983 to communicate note and effect information between synthesizers, computers, music keyboards, controllers, and other electronic music devices. It is basically a high-speed serial connection with separate connections for MIDI in, MIDI out and MIDI through (to allow devices to be daisy-chained).


The basic unit of information is a "note on/off" event which includes a note number (pitch) and key velocity (loudness). There are many other message types for events such as pitch bend, patch changes and synthesizer-specific events for loading new patches.[1]

There is a file format for expressing MIDI data which is like a dump of data sent over a MIDI port. The MIME type "audio/midi" isn't actually registered so it should be "audio/x-midi".[1]


Basic MIDI support was added through a QuickTime Musical Instruments extension for QuickTime 2.0. A Macintosh MIDI Manager had also been in development for QuickTime 2.1, but was never released for classic Mac OS.[2] MIDI support was updated in QuickTime 2.5, which was released on July 22, 1996.[3]

Support for MIDI in Mac OS X (now macOS), iPadOS, and iOS 4.2 or later is managed through the Core MIDI framework.[4]


  1. 1.0 1.1 Musical Instrument Digital Interface at the Free On-Line Dictionary Of Computing. 1998-06-27.
  2. Apple Easter Eggs: QuickTime by David K. Every & Daniel Fanton, MacKido. 2002-11-09.
  3. Apple finally released QuickTime 2.5! by Judith L. Stern and Robert Lettieri, Little QuickTime Page. 1996-07-22.
  4. Core MIDI, Apple Developer. Accessed 2021-10-11.

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