Re: [Avid-L2] Rookie TC question

On Oct 21, 2009, at 7:27 PM, David Dawkins wrote:

> IIRC there reasoning had to do with backwards compatibility.
> D(please don't make me dig out those manuals from the 70s)D

I say:

No need to do that, David. ;)
Though it is correct that that's why the Intercarrier Frequency Offset
of 4.5MHz was maintained, it's now known that there were other options.
It was found that the ICFO did not have to be absolutely 4.5MHz, any
more than the frame rate had to be exactly 30fps. The fear was that
considering the RF electronics of the time, it was better to be safe
and keep the ICFO firmly at 4.5MHz. Since the FCC's concern was to
prevent RF interference with other channels, they chose to make sure
that the aural carrier not be allowed to move upward in frequency,
which might interfere with the next channel above. Of course, the
aural bandwidth COULD have been narrowed a bit to take this into
consideration, but that was not how the FCC chose to go.
Again, that goes back to the origin of our NTSC compatible color TV
system, not the (much later) need for Drop-Frame TC.

Dennis Degan, Video Editor-Consultant-Knowledge Bank
NBC Today Show, New York

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