MIDI beat clock, or simply MIDI clock, is a clock signal that is broadcast via
MIDI
Musical Instrument Digital Interface (; MIDI) is an American-Japanese technical standard that describes a communication protocol, digital interface, and electrical connectors that connect a wide variety of electronic musical instruments, ...
to ensure that several MIDI-enabled devices such as a
synthesizer
A synthesizer (also synthesiser or synth) is an electronic musical instrument that generates audio signals. Synthesizers typically create sounds by generating waveforms through methods including subtractive synthesis, additive synthesis a ...
or
music sequencer
A music sequencer (or audio sequencer or simply sequencer) is a device or application software that can record, edit, or play back music, by handling Musical note, note and performance information in several forms, typically CV/Gate, MIDI, or Open ...
stay in synchronization. Clock events are sent at a rate of 24 pulses per quarter note. Those pulses are used to maintain a synchronized tempo for synthesizers that have
beats-per-minute-dependent voices and also for
arpeggiator
A synthesizer (also synthesiser or synth) is an electronic musical instrument that generates audio signals. Synthesizers typically create sounds by generating waveforms through methods including subtractive synthesis, additive synthesis an ...
synchronization.
The clock is presented as a stream of single-byte MIDI messages. Playback at the tempo presented by the beat clock can be started, stopped and resumed with other single-byte MIDI messages. Location information can be specified using Song Position Pointer messages.
MIDI beat clock differs from
MIDI timecode
MIDI time code (MTC) embeds the same timing information as standard SMPTE timecode as a series of small 'quarter-frame' MIDI messages. There is no provision for the user bits in the standard MIDI time code messages, and SysEx messages are use ...
in that MIDI beat clock is
tempo
In musical terminology, tempo (Italian for 'time'; plural 'tempos', or from the Italian plural), measured in beats per minute, is the speed or pace of a given musical composition, composition, and is often also an indication of the composition ...
-dependent.
Messages
MIDI beat clock defines the following real-time messages:
* clock (decimal 248, hex 0xF8)
* start (decimal 250, hex 0xFA)
* continue (decimal 251, hex 0xFB)
* stop (decimal 252, hex 0xFC)
MIDI also specifies a System Common message called Song Position Pointer (SPP). SPP can be used in conjunction with the above real-time messages for complete transport control. This message consists of 3 bytes; a status byte (decimal 242, hex 0xF2), followed by two 7-bit data bytes (least significant byte first) forming a 14-bit value that specifies the number of ''MIDI beats'' (1 MIDI beat = a 16th note = 6 clock pulses) since the start of the song. This message only needs to be sent once if a jump to a different position in the song is needed. Thereafter, only real-time clock messages need to be sent to advance the song position one clock tick at a time.
Pulses per quarter note
Pulses per quarter note (PPQN), also known as pulses per quarter (PPQ), and ticks per quarter note (TPQN), is the smallest unit of time used for sequencing note and automation events.
The number of pulses per quarter note is sometimes referred to as the ''resolution'' of a MIDI device, and affects the timing of notes that can be achieved by a sequencer. If the resolution is too low (too few PPQN), the performance recorded into the sequencer may sound artificial (being quantized by the pulse rate), losing subtle variations in timing that give the music a ''human'' feeling. Purposefully quantized music can have resolutions as low as 24 (the standard for
Sync24 and MIDI, which allows triplets and swinging by counting alternate numbers of clock ticks) or even 4 PPQN (which has only one clock pulse per 16th note). At the other end of the spectrum, modern computer-based MIDI sequencers designed to capture more nuance may use 960 PPQN and beyond. This resolution is a measure of time relative to
tempo
In musical terminology, tempo (Italian for 'time'; plural 'tempos', or from the Italian plural), measured in beats per minute, is the speed or pace of a given musical composition, composition, and is often also an indication of the composition ...
since the tempo defines the length of a
quarter note
A quarter note ( AmE) or crotchet ( BrE) () is a musical note played for one quarter of the duration of a whole note (or semibreve). Quarter notes are notated with a filled-in oval note head and a straight, flagless stem. The stem usually ...
and so the duration of each pulse.
See also
*
DIN sync
DIN sync, also called Sync24, is a synchronization interface for electronic musical instruments. It was introduced in 1980 by Roland Corporation and has been superseded by MIDI.
Definition and history
DIN sync was introduced in 1980 by Ro ...
*
Word clock
In digital audio electronics, a word clock or wordclock (sometimes sample clock, which can have a broader meaning) is a clock signal used to synchronise other devices, such as digital audio tape machines and compact disc players, which inter ...
References
External links
Freeware to measure a midiclock beat signalMIDI specificationSummary of MIDI messages{{Webarchive, url=https://web.archive.org/web/20160112192415/http://www.midi.org/techspecs/midimessages.php , date=2016-01-12
Song Position Pointer (SPP)
PPQN Timing CalculatorExplanation on Sweetwater''Information Retrieval for Music and Motion'', Meinard Müller, Springer Science & Business Media, 09.09.2007 - 318 pages
Encodings
MIDI standards
Synchronization