What is "Sample Accurate Clock"?

"Sample Accurate" is a general term that has taken on a specific meaning for timing and clock found in musical devices.  It has become the term to describe the use of audio pulses that are locked into a relationship with a Digital Audio Sample Rate and provide a much higher degree of reliability and precision when coming from a DAW instead of MIDI Clock.

An example of this is when audio pulses (square waves) are placed on a dedicated audio track and aligned to the grid within a Digital Audio Workstation (DAW).  The DAW, which specializes in mixing streams of audio together, cannot allow any of the audio tracks to drift apart, including the square waves that make up the audio clock stream.

Certain external devices can receive those audio pulses and use them as a reliable clock source.  Some devices can even act as a hub that translate that audio into clock protocols that other devices can use (more on that further down).

Contrast that to MIDI Clock coming from a DAW.  MIDI Clock is not audio, it's packets of serial data that move over DIN or USB ports.  There's no low-level linkage between the audio that's being played on the computer and MIDI Clock, so there's nothing that will prevent the MIDI data stream from either drifting away from the audio stream or introducing jitter, especially if the computer resources are taxed.

The idea for "Sample Accurate Clock" actually comes from a time before the digital revolution in music fully took hold.  For a time, almost every studio was a mix of Analog Tape Recorders and Digital Sequencers that needed to be kept in sync.  One of the ways this could happen was by striping a dedicated track on the Tape Recorder with audio information representing clock pulses.  So then, no matter what was going on with the Tape Machine (ie: wobble and speed), every track on the tape passes over the Tape Heads at the same rate, including the track containing the pulses.  And just as I described above, an external device could receive these audio pulses from the tape and use them as a clock source.  The pulses would be locked onto the tape and in turn, the external devices would be locked onto the pulses.  Simple and very effective.

The type of external device that can lock onto to these pulses could be anything, but usually it's a specialized kind of device that reads those pulses and then outputs clock in other formats, compatible with many other machines.  Such a device becomes a hub or bridge for translating clock from one protocol to another.  One such device is CLOCKstep:MULTI.

Here's a video of CLOCKstep:MULTI being demonstrated using Sample Accurate Clock with Ableton Live 11, and another video showing how it could even be used with Analog Tape like the days of old.

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