Avid Technology Digidesign USD, User Manual, Page: 54 / 96

Universal Slave Driver 50
To pause or stop VITC from the front panel:
■
Press and release the Run/Stop/Clear
switch when you want to pause or stop the
generating process.
To generate VITC Internally using USD Setup:
1
Ensure that the USD is connected in-line
with a video source and video destination.
2
Ensure that VITC Insertion Enabled is se-
lected in the USD Setup window, and that
you have selected the appropriate format
(NTSC or PAL).
3
If necessary, select onto which line pair
you’ll be generating VITC using the VITC
Generate Lines pop-up menu.
4
Select the appropriate clock reference, us-
ing USD Setup’s Clock Ref selector.
5
From the Positional Ref selector, select
Generate.
6
In the Generator/Bi-Phase Preset win-
dow, type in the desired time code start
time, in Hrs:Min:Sec:Frm. To reset to
00:00:00:00, click Zero.
7
Click Set. Typically, at this point you
would arm the destination VTR to record
video, so that VITC can be inserted into the
video signal, and be recorded on the desti-
nation videotape. Make sure that your cho-
sen clock reference is actually present and
running, and that it is synchronized with
the incoming video signal
8
Click Run to start. The time code ad-
dresses will begin to increment.
9
Click Stop when you want to pause or
stop the generating process.
✽ Regardless of whether you are generating or
regenerating, an active video signal will need
to be present at one of the USD’s video inputs.
If in doubt, always check if the machine is
paused, stopped or unlaced.
VITC Timing Rule
The following rule is in effect whenever
you are generating or regenerating VITC.
◆
Inserted VITC should be monotonic, re-
gardless of whether it is being regenerated
or generated.
By monotonic, we mean that the VITC
should be smoothly ascending or descend-
ing, with no repeated or skipped frame ad-
dresses. In order to achieve monotonicity,
the external positional reference (while re-
generating) or the clock source (in Genera-
tor Preset Mode) must be synchronous
with the video signal onto which the VITC
is being inserted.
Example of VITC Timing Rule
As an example, if you are using LTC as a po-
sitional reference from a 3/4-inch U-Matic
VTR, then that VTR should be referenced to
the same video signal that you are applying
to the USD. As another example, in Gener-
ator Preset Mode (Positional Reference =
Generate), a clock reference of Internal is
not a good choice, simply because the
USD’s internal crystal runs asynchronously
with respect to the supplied video signal,
and thus repeated or skipped frame ad-
dresses are sure to eventually occur.