MIDI beat clock
Encyclopedia
MIDI beat clock is a clock signal that is broadcast via MIDI to ensure that several MIDI-enabled devices such as a synthesizer
or music sequencer
stay in synchronization. It is not MIDI timecode
.
Unlike MIDI timecode, the MIDI beat clock is tempo
-dependent. Clock events are sent at a rate of 24 ppqn (pulses per quarter note). Those pulses are used to maintain a synchronized tempo for synthesizers that have BPM-dependent voices and also for arpeggiator synchronization. It does not transmit any location information (bar number or time code) and so must be used in conjunction with a positional reference (such as timecode) for complete sync.
Because of limitations in MIDI and synthesizers, devices driven by MIDI beatclock are often subject to clock drift
. For this reason, it is a common practice on equipment that supports another clock source such as ADAT
or wordclock to use both that source and MIDI beatclock.
MIDI beat clock defines the following real time messages:
Synthesizer
A synthesizer is an electronic instrument capable of producing sounds by generating electrical signals of different frequencies. These electrical signals are played through a loudspeaker or set of headphones...
or music sequencer
Music sequencer
The music sequencer is a device or computer software to record, edit, play back the music, by handling note and performance information in several forms, typically :...
stay in synchronization. It is not MIDI timecode
MIDI timecode
MIDI time code , or MIDI time division, 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 used to carry this information instead...
.
Unlike MIDI timecode, the MIDI beat clock is tempo
Tempo
In musical terminology, tempo is the speed or pace of a given piece. Tempo is a crucial element of any musical composition, as it can affect the mood and difficulty of a piece.-Measuring tempo:...
-dependent. Clock events are sent at a rate of 24 ppqn (pulses per quarter note). Those pulses are used to maintain a synchronized tempo for synthesizers that have BPM-dependent voices and also for arpeggiator synchronization. It does not transmit any location information (bar number or time code) and so must be used in conjunction with a positional reference (such as timecode) for complete sync.
Because of limitations in MIDI and synthesizers, devices driven by MIDI beatclock are often subject to clock drift
Clock drift
Clock drift refers to several related phenomena where a clock does not run at the exact right speed compared to another clock. That is, after some time the clock "drifts apart" from the other clock. This phenomenon is also used for instance in computers to build random number generators...
. For this reason, it is a common practice on equipment that supports another clock source such as ADAT
ADAT
Alesis Digital Audio Tape or ADAT is a magnetic tape format used for the simultaneous digital recording of eight analog audio or digital audio tracks at once, onto a Super VHS tape that is used by consumer VCRs.- History :...
or wordclock to use both that source and MIDI beatclock.
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)