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Re: [TIG] What is Legal?



In analog formats, there is certainly a rationale for sticking with "legal"
limits for video.  Even if the material is never broadcast, it is still
possible to over-deviate an analog tape machine, with unfortunate results for
the material, and sometimes the tape and machine as well.  Since most analog
machines are designed to match "legal" limits--more or less--a PROC set up to
FCC transmission specs gives good recordings too.

In digital formats, you simply run out of digits if you go beyond the
machine's limits.  The tape doesn't oversaturate, needles don't pin, and
smoke doesn't come out.  (The signals still get trashed, however, since any
bits that end up beyond the range of the machine are lost).   Most digital
machines have more range than the analog ones did, so it is possible to
create perfectly acceptable digital signals that turn into a mess if directly
dubbed to an analog format, or if they hit the clipper stage in a
transmitter.

But not all digital video is transmitted now, or ever.  We do a number of
projects every year where D-1 video is shot out on film.  For these efforts,
it is neither necessary nor desirable to stick to the limits of composite
analog transmission systems.

The way we approach this issue at DuArt is to give our colorists standard
analog waveform monitors and vectorscopes, fed from precision encoders that
look at the 601 signals as they go to tape.  The colorists can also look at
the composite analog signal on their picture monitors if they wish.  If the
job is going to be broadcast down the road (or merely converted to analog),
it's already correct and there are no nasty surprises.  Like yours, our
philosophy is that any tape we make should play back properly (within
proscribed limits) on any correctly functioning machine.  What the client
sees in the transfer is what they get when the program goes out, which means,
for the time being, that it must "fit" into NTSC or PAL limits.  Needless to
say, when digital broadcast standards are finalized, we'll "calibrate" for
them as well.

On the other hand, we don't intentionally limit the 601 signals inside of
their range, so if a job comes along that is going to be re-shot on film, and
it is desirable to use the full  capabilities of our equipment for that
purpose, we can do it.  In such case, if any tapes are made (instead of
taking it straight to disk), it is with the understanding that they are only
serving as intermediate "digital" storage and are not be used for anything
else.

Christopher Bacon
DuArt Film & Video