User Manual-Windows

INSTALLING THE PCI-424 HARDWARE
34
■ Transfer digital audio into or out of the HD192 at
a sample rate that is completely different than the
HD192 system clock rate.
■ Transfer digital audio into the HD192 without
the need for any external synchronization
arrangements.
■ Receive AES/EBU input at one sample rate, run
the HD192 system clock at a second sample rate,
and send AES/EBU output at yet a third sample
rate.
Rate conversion does not add any appreciable noise
to the audio signal (under -120 dB).
Digital I/O without sample rate conversion
Without sample rate conversion, when you transfer
digital audio between two devices, their audio
clocks must be in phase with one another — or
phase-locked, as discussed in “Choosing a digital
audio clock master” on page 37.
Figure 4-8: With the HD192’s sample rate conversion turned off, you
need to keep it phased-locked with the other AES/EBU device by
choosing a clock master.
Digital I/O with sample rate conversion
With sample rate conversion (SRC), an extra level
of master/slave clocking is added to the equation,
as demonstrated below in Figure 4-9, which shows
the clocking going on when you transfer digital
audio from the HD192 (AES/EBU OUT) to a DAT
deck (AES/EBU IN) using SRC. Notice that with
SRC, the DAT deck is not slaved to the HD192’s
system clock. Instead, their clocks are running
completely independently of one another. But also
notice that the DAT deck must still slave to the
sample-rate-converted output from the HD192 for
a clean digital audio transfer (unless it has its own
rate converter on its AES/EBU input).
Figure 4-9: Clock relationships when sending audio from the HD192
to a DAT deck using sample rate conversion. The DAT deck needs to be
slaving to its AES/EBU input. *Note: the HD192 AES/EBU output can
actually be clocked from a number of different sources. In this
example, it is running under its own crystal. For details about other
possible clock sources, see “HD192 interface options” on page 71.
System clock, AES clock & rate convert settings
When you are setting up AES/EBU input and
output with the HD192, pay careful attention to the
following settings in the MOTU PCI Audio
Console window:
■ System clock
■ AES input options (Interface options button)
■ AES output options (Interface options button)
Clocking scenarios for AES/EBU input
There are three possible clocking scenarios for the
HD192 AES/EBU input:
1. Simple transfer (slave the HD192 system clock to
the AES/EBU input signal — no sample rate
conversion).
2. Sample rate convert the AES/EBU input.
Master
Slave
Master
Slave Slave
HD192 master clock
Input
clock
Output
clock
HD192 Sample
Rate converter
(slaves to HD192 SRC output clock)
(master)
(slaves to HD192 master clock)
DAT deck
(master*)