MOTU V4HD User Manual page 32

V4HD master clock
Input
clock
V4HD Sample
Rate converter
Output
clock
Video deck
Figure 3-20: Clock relationships when sending audio from the V4HD
to a video deck using sample rate conversion. The video deck needs to
be slaving to its AES/EBU input. *Note: the V4HD AES/EBU output can
be clocked from a number of different sources. In this example, it is
resolved to the V4HD system clock. For details about other possible
clock sources, see "Rate convert options for digital audio output"
below.
Here are a few examples:
Master
AES/EBU OUT
AES/EBU IN
Slave
Figure 3-21: Rate-converting AES/EBU input.
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(master)
(slaves to V4HD master clock)
(master*)
(slaves to V4HD SRC output clock)
Other device
V4HD clock source
setting: Internal
V4HD
V4HD Sample Rate
Conversion setting:
AES In
Camera
Video out
Video in
ADAT optical in
ADAT optical out
Figure 3-22: Capturing digital audio from a device that is not resolved
with the V4HD. In this case, sample rate conversion is used.
A caution about using rate conversion
Rate conversion can be a life saver in situations
where resolving digital audio clocks is difficult or
impossible. However, when you do so, you run the
risk of the audio drifting apart from picture over
time. If the audio clip being captured is short, this
may not be an issue. But for longer record/playback
passes (more than a few minutes), you are much
better off resolving the V4HD to picture during the
digital audio transfer.
Most devices employ a clock crystal that has an
accuracy of ±50 parts per million, which produces
drift that amounts to approximately one frame
every five minutes at 60 fps.
Rate convert options for digital audio output
The V4HD digital audio output banks can also
employ sample rate conversion. For details see
"Sample Rate Convert" on page 75.
I N S T A L L I N G T H E V 4 H D H A R D W A R E
V4HD clock source
setting: Video Clock
V4HD Sample Rate
Conversion setting:
ADAT Optical in
Digital mixer running under
its own digital audio clock