Syncing Word Clock Devices - MOTU 828 User Manual

SYNCING WORD CLOCK DEVICES

The word clock connectors on the 828 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 29).
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 4-11 and Figure 4-12.
Master
Word clock OUT
Word clock IN
Slave
Figure 4-11: Slaving another digital audio device to the 828 via word
clock. For the 828 clock source, choose Internal (or any source other
than Word Clock, as daisy-chaining word clock is not recommended).
Word clock master device
Audio
clock
Master
Word clock OUT
Word clock IN
Slave
Figure 4-12: Slaving the 828 to word clock. For the 828 clock source,
choose 'Word Clock In' .
The 828 word clock input provides proper 75 ohm
termination, but only when the BNC jack is
configured to operate as a word clock output.
Alternately, the word clock output can be
configured as a word clock thru, which connects
the input clock signal directly to the output, with
no termination on the input. See the "Daisy-
chaining word clock" below.
H A R D W A R E I N S T A L L A T I O N
Resolving to a word clock signal that matches the
828 base clock rate
The 828 can resolve to a word clock signal running
at an even multiple of the current system clock
setting (the base clock rate). For example, the 828
could be running at 96 kHz while resolving to a
48 kHz word clock signal from another device.
Similarly, the 828 could run at 88.2 kHz and
resolve to 44.1 kHz word clock signal. Conversely,
the 828 could run at 48 kHz and resolve to a 96
kHz word clock signal. However, if the 828 is
running at 96 kHz, it cannot resolve to a word
clock signal running at 44.1 kHz.
828
In summary, the word clock signal must be one of
the following:
the same as the current 828 clock rate
Other device
2x or 4x the current 828 clock rate
half or quarter of the current 828 clock rate
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,
828
and so on. If the 828 is in the middle of the chain,
use its WORD CLOCK OUT port and change its
operation from OUT to THRU (using item #7 on
page 43 or from the front panel menu). If the 828
is the first device in the chain (to generate word
clock for the other devices), do not enable WORD
CLOCK THRU mode.
Make sure that the last device in the word clock
chain has 75 ohm termination on its input.
If you have more than four word clock devices that
you need to synchronize, try to avoid chaining
their word clock connections. Instead, use a word
clock distribution device of some kind.
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