Word Clock Synchronization; Understanding Word Clock - M-Audio ProFire Lightbridge User Manual

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M-Audio ProFire Lightbridge User Guide 14

Word Clock Synchronization

11

Understanding Word Clock

Your computer-based DAW stores and manipulates music as digital samples. Those samples are sent to and from
your DAW as "snapshots" of data. These snapshots are all the same size—16- or 24-bit, depending on your selected
resolution—with a beginning and an end, and are sent one after the other as a stream of data. Think of this data
stream as a sentence, made up of a series of words of identical length.
Precise, accurate timing in sending and receiving those words is critical. Each device in your interconnected digital
world must share the same timing in order to communicate correctly—that is, their clocks must be synchronized.
This synchronization is achieved by designating one device as the timing "master," and all other connected devices
as "slaves," locking the slaves to the master. Only one device in the chain can be the master, and all other devices
must slave to that master. All devices must be running at the same sample rate as well. For example, if the master is
running at 44.1kHz, no other device can be set to 48kHz.
Word clock is an important part of digital studios but is often overlooked by engineers new to digital recording. It
is crucial to set up word clock correctly because without precise synchronization between your digital devices, your
digital audio signal will be filled with clicks and pops, (if, in fact, it plays at all).
Scenario 1: ProFire Lightbridge as Word Clock Master
By selecting "internal" in the control panel, you designate ProFire Lightbridge as the word clock master. You will
then need to select "slave" mode on each of your other digital devices (this is usually an internal menu setting on
that device).
In Figure 1 below, digital multitracks are connected to optical ports 1 and 2 of the ProFire Lightbridge, and a DAT
machine to the S/PDIF I/O. ProFire Lightbridge is selected as the master, and each of the other devices set to
slave.
Master
S/PDIF
(RCA)
Slave Slave Slave
Figure 1 – ProFire Lightbridge as clock master