Glossary · MIDI Field Guide

0–9

14-bit controller: A controller value split across two Control Change messages, an MSB on CC 0–31 and an LSB on CC 32–63, giving 16,384 steps. See 14-bit pairs.

A

Active Sensing: System real-time message FE. Once a receiver has seen one, it expects another at least every 300 ms and silences its voices if the stream stops. See Timing.
Aftertouch: Pressure applied to keys after they are down. Channel pressure (Dn) sends one value for the whole channel; polyphonic key pressure (An) sends one per note.
AMEI: Association of Musical Electronics Industry, the Japanese body that co-develops and co-publishes the MIDI specifications with the MIDI Association. It grew out of the Japan MIDI Standards Committee (JMSC).

B

Bank Select: CC 0 (MSB) and CC 32 (LSB), sent before a Program Change to reach more than 128 sounds. The new bank takes effect on the next Program Change. See GM2 banks.
Basic channel: The channel on which a device receives channel mode messages (Omni, Mono, Poly). In Mono mode, the device uses consecutive channels starting from it.
BLE-MIDI: MIDI over Bluetooth Low Energy. Messages travel in GATT notifications with a header byte and 13-bit millisecond timestamps. See Transports.

C

Channel: One of 16 logical streams on a MIDI 1.0 connection, carried in the low nibble of a channel message status byte. People count channels 1–16; the nibble holds 0–F. See Channels.
Channel mode message: Control Change numbers 120–127, which set receiver state rather than a sound parameter: All Sound Off, Reset All Controllers, Local Control, All Notes Off, and the Omni/Mono/Poly switches. See Channel mode.
Channel voice message: A message that controls sound on one channel: Note Off/On, Poly Pressure, Control Change, Program Change, Channel Pressure, and Pitch Bend. See Channel voice.
Control Change (CC): Status Bn followed by a controller number and a value. Used for knobs, pedals, volume, pan, and many other parameters. See Control Change.

D

Daisy chain: Connecting devices in series, MIDI OUT or THRU to the next device's IN. Each opto-isolated hop adds a little edge distortion, so long chains can become unreliable.
Data byte: A byte with bit 7 clear (00–7F) that carries a value for the preceding status byte. See Status and data bytes.
Delta time: In a Standard MIDI File, the number of ticks between one event and the previous one in the same track, stored as a variable-length quantity. See Track chunks.
DIN: The 5-pin, 180° circular connector used for classic MIDI. A current loop runs over pins 4 and 5, and pin 2 is the shield. See 5-pin DIN.
Division: The timing field in a Standard MIDI File header. It is either ticks per quarter note or an SMPTE frame rate with ticks per frame. See Division.
Drop frame: The 29.97 fps timecode format that skips frame numbers 0 and 1 at the start of each minute, except every tenth minute, so the timecode stays aligned with wall-clock time. See Drop frame.

E

Endpoint: In MIDI 2.0, a device or application that exchanges Universal MIDI Packets in both directions. Its name, protocol, and Function Blocks can be discovered with UMP Stream messages. See UMP Stream.
EOX: End of Exclusive, status byte F7, which terminates a System Exclusive message. Any other non-real-time status byte also ends SysEx.

F

Function Block: A MIDI 2.0 description of a functional part of an Endpoint, such as a synth engine, and the UMP Groups it uses. Hosts use Function Blocks to name and route ports.

G

General MIDI (GM): A 1991 specification that standardizes 128 program sounds, a percussion key map on channel 10, and minimum polyphony and controller support, so files play back recognizably on any GM device. See General MIDI.
GM2: General MIDI Level 2 (1999). It extends GM with bank-selected variation sounds, more drum kits, more controllers and RPNs, and Universal SysEx for effects and tuning. See Extensions.
Group: In the Universal MIDI Packet, a 4-bit field that selects one of 16 groups, each with its own 16 channels, giving 256 channels per UMP Endpoint. See UMP.
GS: Roland's extension of General MIDI, introduced with the Sound Canvas line. It adds variation banks, drum kits, and SysEx-addressable parameters. See Extensions.

I

IAC Driver: The Inter-Application Communication driver in macOS. It provides virtual MIDI buses for routing MIDI between applications.
Identity Request: The Universal Non-Real Time SysEx message F0 7E <dev> 06 01 F7. Devices answer with their manufacturer, family, model, and version. See Identity.
Interface (MIDI interface): Hardware that connects a computer to DIN MIDI ports, usually over USB. Multi-port interfaces expose several independent 16-channel ports.

J

JR Timestamp: Jitter Reduction timestamp: a UMP Utility message that records when a message was sent, so a receiver can rebuild the original timing despite transport jitter. See JR timestamps.

L

Local Control: CC 122. Local Off disconnects an instrument's keyboard from its own sound engine, so a sequencer can echo the notes back without doubling them.
LSB / MSB: Least and most significant byte. MIDI splits values wider than 7 bits into a 7-bit MSB and a 7-bit LSB; pitch bend sends the LSB first.

M

Manufacturer ID: The first byte(s) after F0 in a SysEx message, identifying who defined the rest. IDs are one byte (01–7C) or three bytes beginning with 00. See Manufacturer IDs.
Merge: Combining two or more MIDI streams into one. A merger must interleave complete messages and must not split SysEx, which may require buffering.
Meta event: A Standard MIDI File event, FF type length data, that carries file-only information such as tempo, time signature, track name, and End of Track. It is never sent over a MIDI cable. See Meta events.
MIDI 1.0 Protocol: The original byte-stream message format from 1983: 7-bit data values, 16 channels per port, and status bytes with bit 7 set.
MIDI 2.0: The 2020 extension of MIDI. It adds the Universal MIDI Packet, higher-resolution messages, per-note controllers, and bidirectional capability negotiation, while staying compatible with MIDI 1.0. See MIDI 2.0 & UMP.
MIDI Association: The global organization, formerly the MIDI Manufacturers Association (MMA), that publishes MIDI specifications together with AMEI. Specifications are free to download from midi.org.
MIDI beat: A sixteenth note, equal to six MIDI clocks. Song Position Pointer counts in MIDI beats. See Song Position Pointer.
MIDI clock: System real-time message F8, sent 24 times per quarter note, which a follower can use to track the leader's tempo. See MIDI clock.
MIDI-CI: MIDI Capability Inquiry: Universal SysEx messages for discovery, Profile Configuration, Property Exchange, and Process Inquiry between two devices. See MIDI-CI.
MMA: MIDI Manufacturers Association, the US standards body for MIDI. It now operates as the MIDI Association.
Mono mode: Channel mode (CC 126) in which each channel plays one note at a time. Used by guitar controllers, and the basis for one-note-per-channel schemes such as MPE.
MPE: MIDI Polyphonic Expression. Each sounding note gets its own channel, so pitch bend, pressure, and CC 74 can be applied per note. See MPE.
MTC: MIDI Time Code: SMPTE hours, minutes, seconds, and frames sent as eight quarter-frame messages (F1) or as a SysEx full frame. See MIDI Time Code.
MUID: MIDI Unique Identifier, a random 28-bit number that a MIDI-CI device picks to address and identify itself in CI messages. See MUID.
Multitimbral: Able to play different sounds on different channels at the same time. A 16-part multitimbral synth can be a whole band on one port.

N

Note number: The 7-bit pitch value (0–127) in note messages. Note 60 is middle C and note 69 is A440. See Note numbers.
NRPN: Non-Registered Parameter Number: CC 99 (MSB) and CC 98 (LSB) select a manufacturer-defined parameter, which Data Entry then sets. See RPN & NRPN.
Null RPN: Selecting RPN 127/127 (7F 7F), which deselects any parameter so a stray Data Entry message has no effect. See Null RPN.

O

Omni mode: A receive mode in which a device responds to channel messages on all 16 channels. Omni On is CC 125 and Omni Off is CC 124.
Opto-isolator: The optocoupler at every DIN MIDI IN. It electrically separates devices, which prevents ground loops. See Electrical.

P

Patch: An informal word for a stored sound or preset, selected with Program Change. The name comes from patch cables on modular synths.
Per-note controller: A MIDI 2.0 message that changes a controller for a single note, rather than a whole channel. Both registered and assignable kinds exist.
Pitch bend: Status En with a 14-bit value, LSB first, where 8192 means no bend. The range in semitones is set by RPN 0. See Pitch bend.
Poly mode: Channel mode (CC 127) in which a channel can play several notes at once. Almost all keyboard instruments use it.
Port: One 16-channel MIDI connection, such as a physical DIN socket, a USB cable number, or a virtual bus. Software usually names ports, not devices.
PPQ / PPQN: Pulses (ticks) per quarter note. It is the time resolution of a sequencer or MIDI file; MIDI clock is fixed at 24 PPQN. See Ticks and PPQ.
Profile: In MIDI-CI, a standardized set of behaviors and controller mappings, such as a Drawbar Organ or Orchestral Articulation profile, that two devices can agree to turn on. See Profiles.
Program Change: Status Cn plus one data byte that selects a sound. Wire values 0–127 are usually shown as programs 1–128. See Program Change.
Property Exchange: The MIDI-CI mechanism for getting and setting device data, such as program lists and device info, as JSON resources carried in SysEx. See Property Exchange.

Q

Quarter frame: An MTC message (F1) that carries one nibble of timecode. Eight quarter frames, spread over two frames, carry the full time. See Quarter frames.

R

Real-time message: A one-byte system message (F8–FF), such as clock, Start, Stop, or Active Sensing. It can appear anywhere in the stream, even inside another message. See System real-time.
RPN: Registered Parameter Number: CC 101 (MSB) and CC 100 (LSB) select a standardized parameter, such as pitch bend sensitivity or tuning, which Data Entry then sets. See RPN list.
RTP-MIDI: MIDI over IP networks, defined in RFC 6295 and also called AppleMIDI or Network MIDI. It runs on UDP with a session protocol and journaling for recovery from packet loss. See RTP-MIDI.
Running status: Leaving out a repeated channel status byte. The receiver reuses the last one, which saves up to a third of the bandwidth for dense note data. See Running status.

S

SMF: Standard MIDI File (.mid): an MThd header chunk plus one or more MTrk track chunks of timestamped events. See Standard MIDI Files.
SMPTE timecode: Hours:minutes:seconds:frames timecode from film and video, at 24, 25, 29.97 drop-frame, or 30 fps. MTC carries it over MIDI.
Song Position Pointer: System common message F2 with a 14-bit count of MIDI beats (sixteenths) from the start of the song, used to cue a follower before Continue. See SPP.
Status byte: A byte with bit 7 set (80–FF) that starts a message and says what kind it is. For channel messages, it also gives the channel. See Status and data bytes.
SysEx (System Exclusive): A variable-length message framed by F0 … F7, used for manufacturer-specific data and Universal SysEx. See System Exclusive.
System common message: A system message that is not real-time: MTC quarter frame, Song Position Pointer, Song Select, Tune Request, and EOX. Receiving one cancels running status. See System common.

T

Tempo: Playback speed. In MIDI files it is stored as microseconds per quarter note (500,000 = 120 BPM) by the Set Tempo meta event. See Set Tempo.
THRU: A DIN port that repeats whatever arrives at the device's IN, used to daisy-chain several receivers from one source.
Tick: The smallest unit of time in a sequencer or MIDI file. Its length in seconds depends on the division and the current tempo.
Track: In an SMF, one MTrk chunk. Format 0 files have a single track; format 1 files have several tracks that play at the same time. See Tracks.
TRS MIDI: MIDI over 3.5 mm or 2.5 mm stereo jacks. The MIDI Association's CA-033 standardizes the Type A wiring; Type B swaps tip and ring. See TRS.

U

UMP: Universal MIDI Packet: the 32-to-128-bit packet format that carries both MIDI 1.0 and MIDI 2.0 messages, with message type and group fields. See UMP.
Universal SysEx: SysEx with ID 7E (non-real-time) or 7F (real-time), defined by the MIDI specification itself. Examples are Identity Request, GM System On, Master Volume, MTC Full Frame, and MIDI-CI. See Universal SysEx.
USB-MIDI: The USB device class for MIDI. Version 1.0 carries 32-bit event packets with a cable number and Code Index Number; version 2.0 carries UMP. See USB.

V

Velocity: How hard (in practice, how fast) a key was struck, 1–127 in Note On. In MIDI 1.0, Note On with velocity 0 means Note Off. See Velocity.
VLQ: Variable-length quantity: the Standard MIDI File encoding for delta times and lengths, 7 bits per byte with bit 7 as a continuation flag, up to 4 bytes. See VLQ.

W

Web MIDI API: The W3C browser API (navigator.requestMIDIAccess) that lets web pages list MIDI ports and send and receive messages. Try it on the Try it page.

X

XG: Yamaha's extended General MIDI format, introduced in 1994. It adds many voices, effects, and NRPN- and SysEx-addressable parameters. See Extensions.

Z

Zone: In MPE, a master channel plus a range of member channels. The Lower Zone uses channel 1 as master; the Upper Zone uses channel 16. See Zones.