MIDI Explained: What It Is, How It Works, and Why It Matters for Every Musician

MIDI — Musical Instrument Digital Interface — is the reason a keyboard you buy today can play a string section, a brass ensemble or a drumkit inside your computer, and why a wrong note you played last Tuesday can be fixed without re-recording anything. The standard was finalized in 1983, and the same bytes still travel between instruments and computers today. Understanding what MIDI is and what it is not will make you a more confident composer, arranger and producer.

MIDI is not audio

This is the single most important thing to know. When you play a MIDI keyboard, the cable does not carry sound. It carries a stream of small instructions: which note was pressed, how hard, and for how long. The MIDI Association puts it plainly: "MIDI is not audio." The sound itself is created by whatever receives those instructions — a software instrument inside a DAW, a hardware synthesizer, or a sampler — and it can be changed at any point without touching the original performance.

Think of a player-piano roll: the holes in the paper tell the piano which keys to press and when, but the paper itself makes no sound. A MIDI signal works the same way.

MIDI data (left arrow) carries instructions, not sound. The computer's software instrument generates the audio (right arrow). Swapping the instrument changes the sound without changing the performance.

A short history: 1983

Before 1983 every synthesizer manufacturer used its own proprietary system for connecting instruments. Roland's Ikutaro Kakehashi and Sequential Circuits' Dave Smith proposed a common standard, with Yamaha, Korg and Kawai joining the effort. The MIDI specification was published in August 1983. That year the Roland Jupiter-6 and Sequential Circuits Prophet-600 became the first instruments to demonstrate MIDI compatibility live at the Winter NAMM Show. Within a few years, MIDI was built into nearly every keyboard, drum machine and sequencer sold. It has since connected hardware instruments across five decades without changing its core byte format.

The anatomy of a MIDI message

Every MIDI instruction is a short packet of one to three bytes. The first byte is the status byte: it names the type of message and the channel (1–16). The bytes that follow are the data bytes. Here is what the most common messages look like.

A Note On message: three bytes that say which note to play, how hard, and on which of the 16 channels.

Note On and Note Off. When you press a key, the keyboard sends a Note On message. When you release it, it sends a Note Off. Each includes a note number and a velocity value. A Note On with velocity 0 acts as a Note Off — that convention lets a device use the same status byte for both and is part of the original MIDI 1.0 standard.

Note numbers: 0 to 127. MIDI numbers every pitch from 0 (a very low C, C−1) up to 127 (a high G, G9). Middle C — the C in the middle of the standard 88-key piano — is note number 60. The Piano Keyboard worksheet shows you where every note sits; once you know the note names, counting up or down from middle C (60) gives you any MIDI number. The note number tells the instrument which pitch to play; the instrument's tuning does the rest.

MIDI note numbers across two octaves centered on middle C (note 60). Each white key is two or one number above its neighbor; each black key sits between the white keys on either side.

Velocity: 0 to 127. The velocity byte measures how quickly the key was depressed — in practice, how hard you played. A value of 1 is the softest touch a Note On can carry; 127 is the hardest. Because velocity 0 functions as Note Off, working note velocities run from 1 to 127 in practice. A software instrument converts velocity into volume, brightness or both: a sampled piano plays a different sample at velocity 20 than at velocity 100, reproducing the acoustic reality that harder keystrokes sound brighter and louder.

The velocity range 1–127. At velocity 1 a sampled piano plays its quietest layer; at 127 it plays the hardest strike. Most DAWs show velocity as bar height in the lane below the piano roll.

16 channels. One MIDI cable or USB port carries up to 16 independent channels, numbered 1–16. Each channel is a separate "conversation": you can assign your keyboard to channel 1 and control a bass synth on channel 2 while a drum machine runs on channel 10 — all down the same wire simultaneously. By convention, General MIDI (see below) reserves channel 10 for percussion.

One MIDI port carries 16 independent channels. Each channel can drive a different software instrument or hardware device.

Control Change messages

Beyond notes, a keyboard or sequencer can send Control Change (CC) messages to adjust how the sound behaves in real time. Each CC message names a controller number (0–127) and a value (0–127). Three CC numbers you will meet constantly:

• CC 1 — Modulation wheel. Moving the left-hand mod wheel sends CC 1 values. Most synths and samplers route it to vibrato depth, though the patch decides the exact effect.
• CC 7 — Channel volume. The main volume fader on a MIDI keyboard or mixing template.
• CC 64 — Sustain pedal. Values 64–127 say the pedal is down; 0–63 say it is up. When you use a sustain pedal on a MIDI controller, every press and release sends a CC 64 message.

Three of the most common Control Change numbers. The value byte (0–127) sets the amount or state.

Program Change: choosing the instrument

A Program Change message (status byte 0xCn, one data byte) tells the receiving device to switch to a different sound. MIDI 1.0 supports 128 patches per channel (numbered 0–127 internally, though most devices label them 1–128). That 128-patch limit gave rise to General MIDI.

General MIDI: 128 standard sounds

Developed by the MIDI Manufacturers Association and published in 1991, General MIDI (GM) assigns a specific instrument to each of the 128 program numbers so that a MIDI file made on one device plays back roughly the same on another. Program 1 (internal number 0) is always Acoustic Grand Piano; program 41 is Violin; program 57 is Trumpet; program 115 is Steel Drum. Percussion sounds are fixed to channel 10, where MIDI note number 35 is an Acoustic Bass Drum and note 38 is a Snare.

Before GM, a file composed on a Roland synthesizer might play clarinet parts on a guitar patch when opened on a Yamaha. GM made the first fully portable MIDI files possible.

General MIDI (1991) assigns a fixed instrument to each of the 128 program numbers so that a MIDI file plays back consistently on any GM device. Program 1 is always Acoustic Grand Piano.

Pitch bend

The pitch-bend wheel sends a 14-bit value (two data bytes combined) that smoothly raises or lowers pitch above or below the current note. The range is set by the patch — most default to two semitones up or down, though it can be widened. Because the value is continuous, pitch bend lets you replicate guitar bends, brass scoops and slide-guitar effects on a keyboard.

Pitch bend uses a 14-bit value. The default range on most devices is two semitones up and two semitones down; patch settings can widen it.

MIDI timing: clock and sync

A MIDI Clock message fires 24 times per quarter note. Devices that share the same clock — a drum machine, a sequencer and a DAW — stay locked in tempo no matter what tempo you choose. A related message, MIDI Timecode (MTC), derives from SMPTE and synchronizes music to video frame by frame.

MIDI Clock fires 24 pulses per quarter note, locking every device that follows it to the same tempo.

From controller to DAW: how it all fits together

The most common MIDI setup today is a keyboard controller connected by USB to a computer running a DAW. The keyboard sends MIDI messages; the DAW records them on a MIDI track; a software instrument (a VST plugin or a built-in instrument) receives those messages and renders audio in real time.

The modern MIDI production chain. The keyboard never makes sound on its own; the software instrument does the job.

Because the DAW records instructions rather than audio, every parameter is editable after the fact. You can:

• Fix a wrong note without replaying the whole take.
• Change the tempo of the entire piece without changing pitch.
• Swap the software instrument — turn a piano part into a marimba or strings — without re-recording.
• Copy a MIDI pattern and transpose it to a new key with two clicks.

This is why MIDI has become the foundation of computer-based composition and production. For a full walkthrough of a home production setup — gear, DAW choices and the six stages of a track — see How to Start Producing Music at Home.

The piano roll

The piano roll view is the standard way a DAW displays recorded MIDI data. Horizontal bars represent notes: their left edge is when the note starts, their right edge is when it ends, their vertical position is the pitch (a full keyboard runs up the left side), and their color or shade encodes velocity. You can click and drag individual notes, draw new ones, or erase them.

The piano roll in a typical DAW. Pitch runs vertically, time runs left to right. The velocity lane below shows how hard each note was played.

For a guide to relating what you see in the piano roll to what appears on a staff, Tissimo's article From Piano Roll to Staff Notation goes through the connection step by step.

Quantize

When you record a MIDI performance, the timing is rarely perfect. Quantize aligns each note's start time to the nearest grid division — quarter note, eighth note, sixteenth note, or a swing grid. A 100 % quantize snaps notes to the exact grid; most DAWs also offer partial quantize (e.g., 50 %) that moves notes only halfway to the grid, keeping some of the human feel.

Quantize is non-destructive in most DAWs: the original timing is stored, and you can remove quantize to restore the performance. The Tempo & the Metronome worksheet builds the internal pulse that makes quantize decisions easier — the more solidly you internalize a beat, the less correction you need.

Quantize moves each note's start to the nearest grid line. Here, eighth-note quantize tidies a slightly uneven recording.

MIDI files (.mid)

A MIDI file stores a complete sequence of MIDI messages with timing information. Because it contains only instructions — not audio — a standard .mid file for a full three-minute song is typically just a few kilobytes, far smaller than an audio recording. MIDI files are cross-platform: you can open a .mid file in any DAW, any notation program, or any software instrument. Many free sheet-music archives distribute .mid files alongside PDFs.

The file holds one or more tracks, each with its own channel assignments, tempo map and time signature data. Opening a .mid in a notation editor — such as Sibelius, Finale or MuseScore — will generate a staff representation that you can edit and print. The Time Signatures I: Simple Time worksheet and the Major Scale worksheet both give you the reading skills that let you check a staff printout against what you intended to play.

The hardware: 5-pin DIN, USB and Bluetooth

The original MIDI connector is the 5-pin DIN plug (DIN 180°), which became a fixture on synthesizers, drum machines and keyboards in the 1980s. Each device has three sockets: MIDI In (receives data), MIDI Out (sends data) and MIDI Thru (passes the In signal through unchanged to the next device in the chain). The DIN connector carries the signal as a 31,250 baud serial stream — a data rate chosen to be reliably achievable with the microprocessors of 1983.

USB-MIDI emerged as computers adopted USB in the late 1990s and early 2000s. A USB-MIDI cable or a keyboard with a built-in USB connection presents itself to the computer as a MIDI device without a separate driver on most modern operating systems. Bluetooth MIDI, introduced in the iOS MIDI spec around 2014, allows wireless controllers — though it adds a few milliseconds of latency that can matter in live performance.

Three ways to send MIDI. USB-MIDI is standard for keyboard controllers; 5-pin DIN is still common on hardware synths; Bluetooth suits wireless controllers where a few milliseconds of extra latency is acceptable.

MIDI 2.0

The MIDI Association released MIDI 2.0 in January 2020, the first major revision of the standard in nearly four decades. It keeps full backward compatibility with MIDI 1.0: devices negotiate which protocol to use through MIDI Capability Inquiry (MIDI-CI), so a 2.0 device connected to a 1.0 device falls back to the original protocol automatically.

MIDI 2.0 raises resolution dramatically. Velocity and control values in MIDI 1.0 fit in 7 bits (0–127); MIDI 2.0 uses 16-bit velocity and 32-bit controllers, which means thousands of steps instead of 128. This finer resolution makes subtle dynamics — a barely audible pianissimo, a gradual crescendo — far more accurate. MIDI 2.0 also restructures addressing to support 16 groups of 16 channels each (256 channels per cable vs. the original 16), introduces per-note controllers for polyphonic expression, and adds Jitter Reduction Timestamps for tighter synchronization.

MIDI 2.0 hardware and software support began appearing in 2022–2023. For most beginners, MIDI 1.0 is what every DAW, keyboard and plugin you use speaks; MIDI 2.0 is the direction the standard is heading.

MIDI 2.0 (January 2020) raises resolution from 7-bit (128 steps) to 16–32-bit, multiplies channel count, and adds bidirectional negotiation — while remaining backward-compatible with every MIDI 1.0 device.

Why MIDI matters for learning music

MIDI is a practice tool as much as a production tool. Because it records exactly when and how hard you played each note, a teacher or student can see rhythm precision and dynamics at a glance in the piano roll, without needing to record audio. You can record a scale, zoom into the velocity lane, and immediately see which finger landed soft or which beat was rushed.

MIDI also separates pitch practice from rhythm practice: set quantize to 100 %, and you can listen to the pitch choices you made without rhythm errors getting in the way. Remove quantize, and you hear the rhythm accurately. Ear Training: Rhythm Dictation — the Ear Training: Rhythm Dictation worksheet — builds the same subdivision awareness you need to judge and correct your MIDI timing.

For reading notation, the bridge between the piano roll and the staff is worth building. Every note in the piano roll has a staff equivalent. The Note Names: Treble Clef worksheet makes the mapping automatic; once note names are fluent, moving between piano roll and staff notation takes seconds instead of minutes.

If you want a teacher to watch you play and give feedback in real time, Tissimo's one-on-one lessons let a teacher hear your MIDI instrument directly — whether you are working on rhythm, phrasing or ear training.

Free worksheets for MIDI-connected skills

• The Piano Keyboard — Learn the note names and the layout of the 88 keys; the foundation for reading MIDI note numbers.
• Note Names: Treble Clef — Map staff positions to the note names MIDI uses, so the piano roll and the staff connect.
• Tempo & the Metronome — Build a steady internal pulse; the skill that makes quantize decisions easier and performances tighter.
• Major Scale — The scale underlying most MIDI compositions; understand it and transposing a MIDI part to a new key makes immediate sense.
• Ear Training: Rhythm Dictation — Transcribe rhythms by ear; pairs with MIDI's velocity and timing data to sharpen what you hear and what you play.
• Time Signatures I: Simple Time — 4/4, 3/4 and 2/4; knowing the meter helps you set the DAW grid correctly before you record.

Sources

• About MIDI — The MIDI Association — Foundational overview: MIDI is not audio; the standard connects instruments across devices.
• What is MIDI? Notes, velocity, controllers and the MIDI note number chart — Vitric Audio — Velocity range (1–127 working range; 0 acts as Note Off), CC 1/7/64, 16 channels, MIDI 2.0 year, .mid file format.
• MIDI — Wikipedia — Historical record: Kakehashi and Smith collaboration, August 1983 publication, 5-pin DIN, USB-MIDI timeline, General MIDI 1991, MIDI 2.0 January 2020.
• General MIDI — Wikipedia — 128 program numbers, percussion channel 10, instrument-family layout, GM published 1991.
• MIDI Note Numbers — StudioCode — Note number 0–127, middle C = 60, DAW labeling conventions.
• Details about MIDI 2.0 — The MIDI Association — Resolution (16-bit velocity, 32-bit CC), backward compatibility via MIDI-CI, MIDI 2.0 release date.
• MIDI 2.0 Unveiled at 2020 Winter NAMM Show — ProSoundWeb — January 2020 public unveiling and specification adoption.
• MIDI Note On message — Recording Blogs — Three-byte structure, channel in status nibble, velocity 0 as Note Off convention.