One cable, 16 lanes of traffic — here's what's actually moving through it.

01What MIDI Actually Sends

MIDI doesn't transmit audio. It transmits instructions — small data packets called MIDI messages that tell a receiving device what to play, how loud, and when to stop. Every message rides on one of 16 channels, numbered 1 through 16. Think of it like a 16-lane highway inside a single 5-pin DIN cable: your keyboard can live on channel 1, a drum machine on channel 10, a bass synth on channel 3, and none of them interfere. One physical connection, one whole rack under control.

Channel 10 has a specific legacy: General MIDI reserves it for drums, so GM-compatible gear still expects percussion there by default. You can override that on most modern hardware, but it's worth knowing why your synth defaults to a kick drum on that channel.

DAW MIDI piano-roll showing CC automation lane alongside note data
DAW piano-roll showing a CC automation lane running alongside note data in the same MIDI track

02The Messages That Actually Matter

Note On / Note Off are the foundation. Note On fires when you press a key — it carries the pitch (0–127) and velocity (how hard you hit, also 0–127). Note Off fires on release. That's 128 possible pitches, 128 velocity levels, per channel.

Control Change (CC) messages handle everything continuous: mod wheel, expression pedal, filter cutoff, reverb depth. Each CC has a number (0–127) and a value (0–127). CC 1 is conventionally modulation; CC 7 is channel volume; CC 11 is expression. Hardware knobs and faders generate these in real time, and your DAW can record every twist.

Program Change messages tell the receiving device to swap to a different patch or preset — switch from a piano to a string ensemble mid-song without touching the hardware. Program Changes carry a number from 0 to 127, giving you 128 reachable patches per channel. Bank Select (CC 0 and CC 32 in combination) unlocks deeper preset libraries beyond those first 128.

Pitch Bend is its own message type, with higher resolution than a standard CC — 14-bit rather than 7-bit — so the slide sounds smooth rather than stepped.

03Putting It Together

These three or four message types account for nearly everything in a typical live or studio rig. Understanding them means you can troubleshoot a silent synth (wrong channel?), a runaway volume swell (CC 7 stuck open?), or a patch that won't switch (Program Change blocked in your DAW?). The protocol is older than most of the people reading this, but it's lean by design — and that's exactly why it still works.