User Manual-Mac

INSTALLING THE PCI-424 HARDWARE
49
SYNCING WORD CLOCK DEVICES
All MOTU PCI audio interfaces provide a word
clock input and/or output that allows you to
synchronize the PCI-424 system clock with other
word clock devices.
The HD192 interface has two word clock inputs:
System Word and AES Word In. Use the System
Word Input for general purpose word clock sync.
For details about the AES Word In, see “Clocking
scenarios for AES/EBU input” on page 32.
the 24I/O interface provides one BNC Word C lock
jack that can be switched via software between
input or output. For details, see “24I/O interface
options” on page 72.
For standard word clock sync, you need to choose
an audio clock master (as explained in “Choosing a
digital audio clock master” on page 35). 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 3-31 and Figure 3-32.
Figure 3-31: Slaving another digital audio device to the PCI-424
system via the word clock of the PCI interface (an HD192 in this
example). For the PCI-424 system clock source, choose any source
besides word clock, as it is not advisable to chain word clock.
Figure 3-32: Slaving the PCI-424 system to word clock. For the
PCI-424 system clock source, choose the word clock input of the inter-
face receiving the word clock.
Don’t chain word clock
If you have three or more digital audio devices that
you need to synchronize, avoid chaining their word
clock connections (OUT to IN, OUT to IN, etc.), as
this causes problems. Instead, use a dedicated
synchronizer like the Digital Timepiece or a word
clock distribution device of some kind.
Slaving to 2x and 1/2x word clock
All MOTU PCI interfaces that support 96 kHz
operation (see “Sample rate” on page 66 for a
summary) have the ability to slave to a word clock
signal running at either twice or half the current
PCI-424 system clock. For example, the PCI-424
system could be running at 96 kHz while slaving to
a 48 kHz word clock signal from a MOTU Digital
Timepiece. Similarly, the PCI-424 system could
run at 88.2 kHz and slave to 44.1 kHz word clock.
Conversely, the PCI-424 system could run at
48 kHz and slave to a 96 kHz word clock signal. In
all of these cases, the front panel clock LEDs flash
both sample rates to indicate that the PCI-424
system is slaving to word clock at either twice or
half its system clock rate. But if the PCI-424 system
is running at 96 kHz, it cannot slave to word clock
running at 44.1 kHz.
Remember, the word clock signal must be one of
the following:
■ the same as the PCI-424 system clock
■ twice the PCI-424 system clock
■ half of the PCI-424 system clock
Master
Slave
Word clock OUT
Word clock IN
Other device
Audio
clock
Master
Slave
MOTU Digital Timepiece universal synchronizer
Word clock OUT
Word clock IN