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HARDWARE INSTALLATION
41
Synchronization is critical for clean digital I/O
Synchronization is critical in any audio system, but
it is especially important when you are transferring
audio between digital audio devices. Your success
in using the digital I/O features on your MOTU
device depends almost entirely on proper synchro-
nization. The following sections guide you through
several recommended scenarios.
Be sure to choose a digital audio clock master
When you transfer digital audio between two
devices, their audio clocks must be in phase with
one another — or phase-locked. Otherwise, you’ll
hear clicks, pops, and distortion in the audio — or
perhaps no audio at all.
Figure 4-6: When transferring audio, two devices must have phase-
locked audio clocks to prevent clicks, pops or other artifacts.
There are two ways to achieve phase lock: slave one
device to the other, or slave both devices to a third
master clock. If you have three or more digital
audio devices, you need to slave them all to a single
master audio clock.
Figure 4-7: To keep the your MOTU interface phased-locked with
other digital audio devices connected to it, choose a clock master.
Also remember that audio phase lock can be
achieved independently of timecode (location).
For example, one device can be the timecode
master while another is the audio clock master. But
only one device can be the audio clock master. If
you set things up with this rule in mind, you’ll have
trouble-free audio transfers with your MOTU
hardware.
SYNCING WORD CLOCK DEVICES
The word clock connectors on your MOTU device
allow you to synchronize it with a wide variety of
other word clock-equipped devices.
For standard word clock sync, you need to choose
an audio clock master (as explained in “Be sure to
choose a digital audio clock master” on page 41).
In the simplest case, you have two devices and one
is the word clock master and the other is the slave
as shown below in Figure 4-8 and Figure 4-9.
Figure 4-8: Slaving another digital audio device to your MOTU device
(a 24Ai in this example) via word clock. For the 24Ai clock source,
choose any source besides word clock, as it is not advisable to chain
word clock.
Figure 4-9: Slaving your MOTU device (a 24Ai in this example) to word
clock. For the 24Ai clock source, choose ‘Word Clock In’.
Daisy-chaining word clock
If necessary, you can daisy-chain several word
clock devices together. When doing so, connect
WORD CLOCK OUT from the first (master)
device to the WORD CLOCK IN on the second
device. Then connect its WORD CLOCK THRU
port to the next device’s WORD CLOCK IN port,
and so on. On your MOTU interface, use its
Not phase-locked Phase-locked
Device A
Device B
Master
Slave
Master
Slave Slave
Master
Slave
Word clock OUT
Word clock IN
Other device
24Ai
Audio
clock
Master
Slave
Word clock master device
Word clock OUT
Word clock IN
24Ai
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