MIDI Messages: Notes, Velocity & Control

MIDI is not audio. It is a system for sending musical and control information as messages: play this note, release it, move this controller, bend the pitch, change a parameter…

You already know MIDI note numbers: C4 = 60, E4 = 64, G4 = 67. Now we look at the messages that carry those instructions.

1. Note On and Note Off

NOTE ON: channel + note number + velocity
NOTE OFF: channel + note number + release velocity/value

Press a key below. The monitor shows the event, its MIDI channel, note name/number and velocity. Release it and a Note Off message appears.

Live MIDI event monitor

TIMEMESSAGECHNOTE / CONTROLVALUE

2. Velocity is data — not inherently volume

Velocity normally represents how quickly/hard a key was played and is commonly mapped to loudness, but a synthesizer can map it to other parameters such as filter cutoff, timbre, envelope amount or sample selection.

C4 at velocity 30   ≠   C4 at velocity 120    — same pitch, different performance data

3. Control Change (CC) and Pitch Bend

Most MIDI 1.0 CC values use 7-bit data: 0–127. Pitch Bend uses higher resolution and is normally centred at 0 in software displays.

4. MIDI channels

Traditional MIDI provides 16 logical channels. Messages on the same physical MIDI connection can therefore address different instruments or parts.

Channel 1 → synth    Channel 2 → bass    Channel 10 → GM percussion convention
Channel 10 is not inherently “the drum channel” in MIDI. Using Channel 10 for percussion is a General MIDI convention.

5. General MIDI — useful legacy knowledge

General MIDI standardised instrument/program behaviour and a percussion map so compatible MIDI files could play with broadly predictable instrumentation on different devices. You do not need to memorise the whole GM map.

Core drum notes worth recognising

35Acoustic Bass Drum
36Bass Drum 1
38Acoustic Snare
40Electric Snare
42Closed Hi-Hat
44Pedal Hi-Hat
46Open Hi-Hat
49 / 51Crash / Ride
Key idea: with a drum instrument, MIDI note number can select a sound rather than simply representing chromatic musical pitch. This idea remains useful far beyond General MIDI.

6. MIDI 1.0 DIN is serial

Classic 5-pin DIN MIDI transmits data sequentially at 31.25 kbit/s. Messages therefore occupy time on the wire; they do not all physically arrive at exactly the same instant.

Why it matters: a dense stream of note and controller messages can create small timing offsets. We exaggerate the animation so you can see the ordering; the real transmission is much faster.

7. What is actually inside a basic message?

A common MIDI 1.0 channel-voice message uses a status byte followed by one or two data bytes. A typical Note On is three bytes.

STATUS: Note On + ChannelDATA 1: Note Number 0–127DATA 2: Velocity 0–127

At classic DIN speed, a three-byte MIDI message takes roughly 0.96 ms to transmit on the wire.

31,250 bits/s → 320 µs per transmitted byte → ~0.96 ms for 3 bytes

That includes MIDI's serial framing around each 8-bit byte. You do not need to memorise the calculation — the point is that serial messages take a finite amount of time.

8. MIDI is not a sound

MIDI

Instructions and performance/control data: note numbers, velocity, controllers, channels, pitch bend and more.

Audio

The actual changing electrical/digital representation of sound that we hear and process.

MIDI Note On 60 → synthesizer receives instruction → synthesizer generates audio

Next: use these note-trigger ideas to build our own kick, snare and hi-hat sounds from synthesis components.