User Manual

HARDWARE INSTALLATION
42
Figure 4-9: Slaving your MOTU device (a 24Ai in this example) to word
clock. For the 24Ai clock source, choose ‘Word Clock In’.
Follow system clock / Force 1x clock
When operating the 24Ai or 24Ao at high sample
rates (88.2 kHz or higher), the Word Clock Out can
either match the interface’s operational sample rate
or its corresponding 1x sample rate. For example, if
the 24Ao is operating at 192kHz, you can choose to
generate a word out rate of 48kHz using the Force
1x Clock setting in the Device tab of the MOTU
AVB Control web app (item #15 on page 14).
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 35-36, 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 14).
2 In the device list (item #1 on page 14), 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 4-10: 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
Mode menu (in the Device tab). Doing so
effectively resolves the entire AVB network to the
external clock source.
Audio
clock
Master
Slave
Word clock master device
Word clock OUT
Word clock IN
24Ai