MIDI beat clock
MIDI beat clock (also known as MIDI timing clock or simply MIDI 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:
- clock (decimal 248, hex 0xF8)
- start (decimal 250, hex 0xFA)
- continue (decimal 251, hex 0xFB)
- stop (decimal 252, hex 0xFC)