What is MIDI?
MIDI is a language that musical devices and apps use to tell each other what to play. A MIDI message says things like this key went down, this hard, and now it came up. It carries no sound. Something at the other end, a synthesizer or an instrument inside a music app, turns those messages into sound. The name stands for Musical Instrument Digital Interface, and the standard dates from 1983.
I make InputConfig, a free Mac app that reads and sends MIDI, and this site has free tools for trying everything on this page in a browser.
On this page: 9 sections
Think of it as instructions, not sound
A recording captures what something sounded like. MIDI captures what was done: which keys, how hard, for how long, and which knobs were turned. Play the same MIDI through a piano sound and it is a piano. Play it through strings and it is strings. MIDI is sheet music that machines can read and play back at once. That is also why a MIDI file is tiny next to an audio file, and why one can be moved to another key without any loss.
InputConfig is free on the Mac App Store. macOS 14 or later, no account, no tracking, open source.
Meet the messages
| Message | What it says | More |
|---|---|---|
| Note On and Note Off | A key went down, this hard, and came back up | Note numbers, velocity |
| Control Change | A knob, fader or pedal moved to this value | MIDI CC list |
| Program Change | Switch to this sound | Program Change |
| Pitch Bend | The pitch wheel moved | Pitch bend |
| Clock, Start and Stop | Keep in time, and run now | MIDI clock |
Most messages are two or three numbers, and the values in them run from 0 to 127. Nearly everything a player does is a note, a Control Change or a pitch bend. The MIDI message decoder shows the numbers inside any message.
Know what a MIDI controller is
A MIDI controller is anything that sends MIDI and makes no sound itself: a keyboard, a pad grid, a box of knobs, a foot pedal. It needs something to play, which is usually a music app on a computer. A MIDI keyboard with no computer attached is silent, and that surprises most people once. The controller sends the instructions, and the instrument makes the sound. How to connect a MIDI keyboard to a Mac gets one working.
Know how MIDI travels
- USB. The usual way now. One cable carries MIDI both ways and powers a small keyboard.
- Five-pin cables. The original round plugs, still on synthesizers and interfaces. In, Out and Thru explains the three sockets.
- Bluetooth and networks. Bluetooth MIDI cuts the cable, and network MIDI joins computers.
- Inside one computer. A virtual MIDI port passes MIDI from one app to another.
Sixteen channels share any one of these connections, so one cable can carry sixteen separate parts. However it travels, the messages are the same.
Know what a MIDI file is
A MIDI file, ending in .mid, is the same messages written down with a time on each one: a whole song as instructions. A music app can open it, change any note, swap the instruments and export audio. A MIDI file is a performance you can still edit. The MIDI file viewer and player opens one in the browser, and how to play a MIDI file on a Mac covers GarageBand.
Try it without buying anything
- Play notes. The virtual MIDI keyboard plays from the letter keys of a computer.
- Watch them. The MIDI visualizer draws each note over a piano.
- Record them. The MIDI recorder saves what you played as a MIDI file.
- Make a beat. The drum machine is a grid of drum hits that can export MIDI.
A browser and a computer keyboard are enough to learn what MIDI does. On a Mac, GarageBand is free and plays MIDI with real instrument sounds.
See what else MIDI can do
MIDI is not only for music. Because a pad or a knob is just a message, it can be turned into anything. InputConfig maps MIDI pads, knobs and pedals to keyboard shortcuts, mouse clicks and the Mac's volume, which makes a cheap pad controller a shortcut deck for any app. It goes the other way too: a game controller's buttons and sticks can send MIDI notes and Control Change into a music app. A MIDI message is a button press that any app can be taught to understand. MIDI on a Mac is the guide to all of it.
The short version
- What it is. A language of instructions between musical devices and apps.
- What it is not. Sound. Something else turns the instructions into sound.
- Why it matters. Any controller can play any instrument, and every note can be edited later.
MIDI says what to play, and leaves how it sounds to whatever is listening.
Questions
What does MIDI stand for?
Musical Instrument Digital Interface. It is a standard, first published in 1983, that lets instruments, controllers and computers from any maker talk to each other.
Is MIDI audio?
No. MIDI carries instructions such as which note and how hard. An instrument or a music app turns those instructions into audio.
What is a MIDI controller?
A device that sends MIDI and makes no sound of its own, such as a keyboard, a pad controller, a knob box or a pedal. It plays the sounds of whatever it is connected to.
Do I need a MIDI keyboard to use MIDI?
No. A computer keyboard can play notes in GarageBand and Logic Pro with Musical Typing, and a virtual MIDI keyboard in a browser does the same.
What is a MIDI file?
A file, ending in .mid, that stores a performance as timed MIDI messages. It holds no sound, so it is small, and every note in it can be edited.
What is the difference between MIDI and audio?
Audio is a recording of sound. MIDI is a record of what was played. Audio always sounds the same, and MIDI can be played back with any instrument, at any tempo, in any key.
Related
Free. macOS 14 or later. No account, nothing leaves your Mac. Open source on GitHub.
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