Re: OT: Processing video signals as audio?

[Catilyne <catilyne@icicle.net>]

At 08:30 PM 6/1/2004, Suit & Tie Guy wrote:

>i used to work at a television station, and tried to pay attention to the 
>techs when they were maintaining the video stuff. something that's 
>important to keep in mind about video signals is that they are very 
>similar to audio signals, but at a much higher frequency range.

Ditto: another ex-Radio/Television major here, as well as having worked in 
a few TV stations myself.  Wish I'd paid more attention in my video 
engineering classes, however...  ;)

Back in the 80's, we actually tried to do a very similar thing -- record 
video signal to hard disk and edit/mutilate it -- after Digidesign first 
released Sound Tools on the Atari ST (later to become Pro Tools, and to be 
ported over to Mac when the bastards left all of us Atari users stranded 
high-&-dry; bitter still? who, me...?).  To be fair, we baffled the hell 
out of the Digidesign Support techs for about two weeks until we were able 
to collect some research from them.

What we were finally told (and all standard disclaimers apply) was that 
the 
problem was not only the frequency range, but also the bias of the 
signal.  Audio waveforms, as we all know, usually start at a zero crossing 
then go positive (compression) for a length of time before falling, 
crossing zero and going negative (rarefaction).  They then return to the 
zero crossing before another cycle.

Video, on the other hand, behaves much more like a digital signal: instead 
of zero being the "midpoint" of the wave's vertical axis, zero is the 
floor; the signal starts moving positive, moves up and down, then falls 
back to zero before going positive again.

Thus, audio is a bi-polar signal, while video is mono-polar.  Or at least 
that's the answer we finally got back from Digidesign.

Now, it wasn't unheard of for those guys to lie through their teeth just 
to 
get rid of us.  In fact, I'm kind of interested to hear from others with 
more video experience whether that explanation is really the straight dope.

         -c-

_____
"i want to reach my hand into the dark and *feel* what reaches back"
                                                 -recoil