User Manual

HARDWARE INSTALLATION
53
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
WORD CLOCK OUT port and change its
operation from OUT to THRU in the Device tab of
the MOTU AVB Control web app (item #15 on 18).
If you have more than four word clock devices that
you need to synchronize, avoid chaining their word
clock connections. Instead, use a word clock
distribution device of some kind.
Word clock is not needed for AVB networking
When working with multiple MOTU AVB
interfaces on an AVB network, synchronization is
handled by AVB, so no word clock connections are
necessary. See the next section for details.
SYNCING AN AVB NETWORK
The AVB protocol provides sophisticated and
accurate timing, synchronization, and clocking
features for AVB device networks of any size as
shown on pages 40-41, including:
■ Low latency
■ Network-wide time base
■ Better-than-sample-accurate phase lock across
all connected devices
■ Timing accuracy down to the nanosecond
Choosing a master clock
The web app provides an easy way to choose one
device as the master clock for your whole MOTU
AVB network.
1 Go to the Devices tab (page 18).
2 In the device list (item #1 on page 18), choose
the MOTU interface you wish to use as the clock
master.
3 Click the Become Clock Master button below the
Clock Mode menu.
Now, all other MOTU AVB devices on the network
are resolved to this device.
Figure 4-13: Choosing a clock master.
Alternately, you can go to the clock mode menu for
each individual device separately and choose the
master clock device by hand. For example, you may
be in a situation where at least one MOTU device
on the network must remain resolved to its own
clock (or another clock source). Just know that in
this case, audio cannot be streamed between
MOTU AVB devices that don’t share the same
master clock.
Resolving the master clock device to an
external clock source
The MOTU device you’ve specified as the AVB
network clock master can itself be resolved to an
external time base such as word clock or optical.
Just choose the desired clock source from its Clock