Clock Sources
Once the position is established, the next essential factor for synchronization is the playback speed. Once 2 devices start playing from the same position, they must run at exactly the same speed in order to remain in sync. Therefore, a single speed reference must be used, and all devices in the system must follow that reference. For digital audio, the speed is determined by the audio clock rate. For video, the speed is determined by the video sync signal.
Audio clock
Audio clock signals run at the speed of the sample rate used by a digital audio device and are transmitted in several ways:
- Word clock
Word clock is a dedicated signal running at the current sample rate that is fed over BNC coaxial cables between devices. It is the most reliable form of audio clock, and is relatively easy to connect and use.
- AES/SPDIF Digital Audio
An audio clock source is embedded within AES and SPDIF digital audio signals. This clock source can be used as a speed reference. Preferably, the signal itself does not contain any actual audio (digital black), but any digital audio source can be used if necessary.
- ADAT Lightpipe
ADAT Lightpipe, the 8-channel digital audio protocol developed by Alesis, also contains audio clock and can be used as a speed reference. It is transmitted between devices via optical cables.
Do not confuse the audio clock embedded in the Lightpipe protocol with ADAT Sync, which uses a proprietary DIN plug connection for timecode transmission and machine control.
MIDI clock
MIDI clock is a signal that uses position and timing data based on musical bars and beats to determine location and speed (tempo). It can perform the same function as a positional reference and a speed reference for other MIDI devices. Cubase supports sending MIDI clock to external devices but cannot slave to incoming MIDI clock.
MIDI clock cannot be used to synchronize digital audio. It is only used for MIDI devices to play in musical sync with one another. Cubase cannot be used as a MIDI clock slave.