Re: Laser Disc Rambling

[nrc@cbema.att.com (Neal R Caldwell, Ii)]

>From article <m0k2GLL-0002zPC@chinet.chi.il.us>, by katefans@chinet.chi.il.us (Chris Williams):
> Chris here,
> 
>> Color is another interesting issue.  VHS video tape has no built in
>> time base correction which leads errors in color reproduction.
> 
>   Richard Caldwell is wrong about the function and purpose of a time base
> corrector. 

I wasn't explaining the function and purpose of a time base corrector.
I was discussing the differences between the video tape and laser disc
of _The Whole Story_.  One of the differences is in the color reproduction
which is an area were laser disc has an advantage because of it's time
base correction.

Chris's explanation of time base correction is correct in so far as
it deals with the problem of horizontal line jitter.  Horizontal line
jitter is another important reason that video tape is inferior to laser 
disc.  There was nothing specific about that feature of time base 
correction that bore upon my comparison so I did not discuss it.  This 
is, after all, Love-Hounds, not rec.video.  As I said, anyone who wants 
to learn about the advantages of laser disc in that level of detail 
should request Bob Niland's excellent series of articles on the subject.

>    A reference color signal is used to correct the timing of each line to
> the ideal standard by delaying the video signal varying amounts. The T.B.C.
> in a LD player corrects for speed variations of the rotating platter. 

The phase and amplitude of the 3.58 MHz color subcarrier is referenced to 
that of the 3.58 MHz sinewave colorburst transmitted after every
horizontal sync pulse.  When the tape speed does not remain constant
across a scan line the resulting time base error skews the phase
relationships and the color will not be correct.  The time base
correction in laser video prevents this problem.

>   Sorry to cast aspersions on Richard's omniscience.

Don't be ridiculous!  If I were gifted with omniscience I certainly
wouldn't be mucking about with phase relationships, time base errors 
and color subcarriers; I'd be cataloging Kate's lingerie by color, style 
and fabric.


"Don't drive too slowly."                 Richard Caldwell
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