Word clock

A word clock or wordclock (sometimes sample clock, which can have a broader meaning) is a clock signal used to synchronise other devices, such as digital audio tape machines and compact disc players, which interconnect via digital audio. S/PDIF, AES/EBU, ADAT, and TDIF are some of the formats that use a word clock. Various audio over Ethernet systems use broadcast packets to distribute the word clock. The device which generates the word clock - usually with multiple output connectors - is the only master clock source for all the slave audio devices.

Word clock is so named because it clocks each sample. Samples are represented in data words.

Word clock should not be confused with timecode; word clock is used entirely to keep a perfectly timed and constant bitrate to avoid data errors. Timecode is actual data (technically metadata) about the media being transmitted, and is optional, being sent in a higher layer. Time code can be used as an initial phase reference for jam sync using the word clock as the frequency reference.

Professional digital audio equipment may have a word clock input or output to synchronize timing between multiple devices. Although the electrical characteristics of the word clock signal have not been completely standardized, some characteristics should always apply. Things that should remain consistent are TTL level, a 75ohm output impedance, 75ohm cables and a 75ohm terminating resistor at the end of a chain or cable.

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