What is MIDI? Notes, velocity, controllers and the MIDI note number chart

MIDI (Musical Instrument Digital Interface) is the standard that lets keyboards, computers, drum machines and other instruments talk to each other. It was standardized in 1983. A MIDI message does not carry sound: it carries instructions, such as which note to play, how hard and when to stop, and the instrument that receives them makes the sound. MIDI notes are numbered from 0 to 127, and middle C is note 60.

What does MIDI send?

Every key you press, and every knob, button or slider you move on a MIDI controller, becomes a MIDI event. The main messages are:

• Note-on: the note number (which pitch), the velocity (how hard it was played) and the channel.
• Note-off: ends the note.
• Control change (CC): sends the moves of a wheel, fader, knob or pedal, such as the modulation wheel, volume or the sustain pedal.
• Pitch bend: bends the pitch, for example from a keyboard's pitch wheel.
• Aftertouch: how hard you keep pressing a key after it is down.
• Program change: switches the receiving device to another patch.

Note and controller messages go out on one of 16 channels, so one MIDI cable or port can play up to 16 separate instruments; a device with several ports has 16 channels on each. MIDI started on five-pin DIN cables and also runs over 3.5 mm minijacks on smaller gear, USB and Bluetooth. A MIDI file (.mid) is also a set of instructions, not audio, which is why it is so small.

MIDI vs audio

Audio is a recording of the sound itself. MIDI is a recording of the performance: the notes, their timing and how hard they were played. Because MIDI stores the notes and not the sound, the same keyboard performance can be played back as a piano, a synth, a guitar or a whole orchestra, just by changing the instrument it goes to. In a DAW you can also move notes, fix timing and change velocities after you record.

MIDI keyboards and controllers

Keyboards are by far the most common kind of MIDI controller. A controller keyboard sends notes; a software instrument in your DAW, or a hardware synth, makes the sound. Most connect over USB, and macOS, Windows, Linux and iOS include standard drivers for class-compliant USB MIDI devices. Turn the keyboard on as a MIDI input in your DAW's MIDI settings, then play a track that holds an instrument. A keyboard with only five-pin MIDI ports needs a MIDI interface to reach a computer.

MIDI note number chart

Notes run from 0 (C-1, about 8.18 Hz) to 127 (G9, about 12,544 Hz), well beyond the 88 keys of a piano, which run from A0 (note 21) to C8 (note 108). Middle C is note 60, and General MIDI specifies that note 69 plays A440. The note number is 12 times (octave + 1), plus the note's position from C (C is 0, C# is 1, up to B at 11).

Why your DAW names the octaves differently

The note name is only a label, and DAWs number the octaves differently. This chart calls note 60 C4. Ableton Live and Logic Pro call it C3, so their range runs from C-2 to G8; FL Studio calls it C5. So in Ableton Live or Logic Pro, take one off this chart's octave numbers, and in FL Studio add one. Logic Pro can show C4 instead, under Logic Pro, Settings, Display, Display Middle C As. Note 60 is the same key either way.

These are the notes of the octave from middle C, with their frequencies in standard tuning (A4 = 440 Hz, equal temperament):

Each octave up doubles the frequency. To find the note of a sound you already have, use the pitch detector, which also names middle C as C4.

What is MIDI velocity?

Velocity is how hard a key or pad was struck. In Logic Pro, for example, note velocities run from 1 to 127, with 127 the loudest; in MIDI 1.0 a note-on with velocity 0 acts as a note-off, which is why note velocities start at 1. Velocity usually sets loudness, and it can also change the tone, for example by opening a filter. In the piano roll you can edit each note's velocity to make a programmed part sound less mechanical.

MIDI CC numbers

Control change messages are numbered, and each sends a value from 0 to 127. General MIDI instruments must respond to these, among others:

General MIDI also puts drums on channel 10, with each note number mapped to a drum sound. An instrument can map other CC numbers to its own controls; its manual lists them.

MPE and MIDI 2.0

MIDI Polyphonic Expression (MPE) gives each note its own MIDI channel, so pitch bend and other expression can change one note in a chord without moving the others. Kiln Synthesizer supports MPE with per-note bend over the standard 48-semitone range, pressure and slide, and has 28 MPE patches in its library. In 2020 the MIDI Association introduced MIDI 2.0, an update to MIDI 1.0 with higher resolution and up to 256 channels (16 groups of 16).

Questions

What does MIDI stand for?

Musical Instrument Digital Interface.

Is MIDI audio?

No. MIDI carries instructions, such as notes, velocity and controller moves. An instrument, hardware or software, turns them into sound.

What MIDI note is middle C?

Note 60. This chart calls it C4; Ableton Live and Logic Pro call it C3, and FL Studio calls it C5.

What MIDI note is A440?

Note 69: A4 in this chart, A3 in Ableton Live and Logic Pro, A5 in FL Studio.

How many MIDI channels are there?

Sixteen per MIDI 1.0 cable or port. A device can have several ports, and MIDI 2.0 allows up to 256 channels (16 groups of 16).