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OPERATION
being displayed. Each time it is pressed, the display alternates between
the time and user bits. The colons of the display are blanked when user
bits are displayed.
3.9.1
Understanding Time Code 'Add One' Compensation
- How it Affects the Accuracy of the Timecode and Burn-ins
Most time code readers assume that the user bit information is not
changing, and hence make no provision to compensate the user bits for the
delays involved with reading the numbers. Timecode generators that are
built in to the VTR's also suffer from this problem when they are 'slaving' to
external timecode.
transfer this information to the generator, with one or two fields of delay.
The time numbers are compensated for the reading delays, so this problem
affects only the user bits. This phenomena applies to the timecode being
recorded on tape using the 're-gen' mode of the VTR's generator and to the
character generator outputs from the VTR's build in readers.
The following precautions should be taken to ensure that the numbers
being laid down on tape and window dubs of them are accurate:
1.
Record VITC from the 4025TR onto all your transfer tapes, even
if the client does not specify them specifically.
2
When recording timecode from the 4025TR, the timecode
generator in your VTR should either be turned off, or set to an
'external direct' mode. In this mode, the VTR's generator does
not attempt to read the incoming code, but merely passes the
4025TR's
intervention.
3.
When making window burn-ins of the 4025TR data, use the
4025TR Character inserter, which accurately compensates for
the film pulldown. Separate video paths are provided for the
4025TR VITC and Character generators, so you can make one
tape without burn-ins, and a simultaneous tape with a burn-in.
4.
The Afterburner reader can be used to make a frame accurate
window dub from a previously transferred tape. In order for the
Afterburner to recover the 'Key Info' part of the keykode
number, make sure that the 4025TR's VITC generator is on and
use one of the 4025TR's + KEYKODE or 3-line VITC modes.
Model 4025TR Film Footage Encoder Manual
Specifically, they read the incoming user bits and
code
through
the
signal
amplifiers
without
Page 3-37
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