Avid Technology Digidesign USD, User Manual, Page: 71 / 96

Appendix A: Additional Synchronization Information 67
appendix a
Additional Synchronization Information
Video and VITC Signals
Black Burst and House Sync
A black burst signal is essentially a “posi-
tion-less” video signal. As with any
“shared” video signal, you’ll want to en-
sure that your video feed comes from a
properly buffered and distributed source,
such as a video distribution amplifier, or
the video reference/black burst output of
another device in the house sync chain.
Resolving to video instead of house/black
There are several reasons why you would
resolve the USD to a video signal rather
than house sync.
When House Sync is Unavailable
Resolve to
a video signal whenever you are synchro-
nizing Pro Tools (or other device) to video,
and you either:
• do not have a black burst generator
– or –
• your setup includes equipment that lacks
house sync/black burst input and syn-
chronization capability (including con-
sumer grade VCR, or some entry-level
PC-based editing systems).
Simple Setups
In a modest setting with one
or two VTRs, Pro Tools and the USD, using
the video signal as the clock reference is of-
ten satisfactory. In these situations, proper
sync can be achieved using the video signal
as clock reference.
Why VITC is Unavailable for Clock Reference
VITC itself does not provide clock informa-
tion directly as part of its time code infor-
mation, only positional information. How-
ever, since VITC is always embedded into a
video signal, that video signal can be used
as a clock reference by selecting Video In-
put as the clock reference (or Video Ref In if
your facility has house sync).
LTC Signals
Because it’s an analog audio signal, LTC can
sometimes be susceptible to either tape
dropouts (tape shedding), or to level mis-
matches between the LTC source and the
LTC input. The USD’s freewheeling feature
allows you to compensate for brief time
code dropouts. However, if you have seri-
ous dropouts, you may not be able to sus-
tain accurate synchronization.