Clocking and Sync

Digital devices that keep their own time will drift apart. One master clock, everyone else follows.

Related

Sample RateLatencyOrgan

The problem

When several digital devices keep their own time, their samples land in different places. The first symptom is a slightly gritty top end; the next is a click every few seconds. One master clock, everything else following.

Signal chain

The master can be a converter, an interface or a dedicated clock, distributed over word clock, ADAT or an embedded digital stream. Once each slave locks, its samples fall on the same time grid.

Placement and settings

Choose the most stable device as master and set the rest to external sync. Every device must run the same rate; do not leave a 44.1 kHz unit in a 48 kHz session. Keep clock cables short, avoid long daisy chains, and wait for lock before recording.

What to listen for

Play a sustained chord or an organ note and listen for a rough top end or periodic soft ticks. Swap the master and slave roles and hear it again; when lock is unstable, the low end also sounds loose.

Common misconceptions

• Each device is more accurate on its own clock → each may be accurate, the sum is not.
• Clock only affects digital connections → it sets every sampling instant.
• Nothing is wrong until you hear a click → a gritty top end is already a symptom.

Sources

• Watkinson, The Art of Digital Audio, clocking and interfacing chapters
• AES Convention paper on word clock distribution and jitter

Used for fact-checking only; all prose is original.