From: duvall@eagle.sangamon.edu (Mike Duvall)
Subject: Re: TBC use
X-Newsreader: TIN [version 1.1 PL6]
Organization: Sangamon State University
Date: Thu, 31 Dec 1992 01:50:52 GMT

I have run a production company full time for seven years and part time
for the last seven years. I have seen a lot of changes and have some
good hints for you.  FIRST be careful using the term broadcast quality.
It is generally accept that SVHS cannot be used to edit for commercials.
I have seem some people shoot commercials on SVHS and then edit to
another format. Some engineers do not consider 3/4" broadcast quality.
The FCC has rules but as long as the picture quality is very good you
usually don't have problems. Lighting is very important!!! Toasters are
also not broadcast quality or some might say full-broadcast quality but
many people still use them. You will not have trouble if the picture
quality looks good and the station will accept a SVHS tape. REMEMBER
BROADCAST QUALITY CANNOT BE MADE FROM CHEAP GEAR. You cannot take a home
camcorder and turn the low resolution, noisy picture into broadcast
quality. It still looks like home video. VCRs range from $300 to
$100,000 mainly because of picture quality. If you are using SVHS or any
cheap format you are at the bottom of the quality barrell but not out in
the cold. 
GENLOCK and TBC...genlock is generated lock and is really very simple.
In the old days of TV, even as far back as 1980s you had a sync
generator and it sent signals such as H, V, SC, and Sync to each piece
of gear ie cmaeras, switchers, TBC and so on. Then sync generators
became cheaper to build and so cameras and other gear came with sync
generators. Every piece of stand alone gear has a sync gen in it. What
gen lock does is locks the internal sync gen to an incoming video
signal. the incoming signal can be any composite video signal (a signal
with sync on it) such as color bars, black, even program. usually your
sync gen or switcher has black burst which is a composite video signal
without any picture except black, and 
BB is sent to all the gear ( to the genlock input)
The piec of gear must have horizontal phase and subcarrier phase
adusted. (another article needed. )
TBCs...A recorded video signal has nearly undetectable problems with
timing. A video signal has 525 lines each line recorded on tape. If you
grabbed hold of a tape and stretched it the lines would be farther apart
and then would not come up at the right time. The lines would always be
behind the head when the head looks for it (highly exaggerated) A tbc
will store several lines in memory and in it detects a missing line (not
a frame, 525lines 30 times a second) it will repeat the line before it
because it has it in memory. Ten years ago I had a TBC that was +/- 4
lines or 2 lines of memory. I had a tape that got out by three lines
after it played for 50 minutes. The result was the picture jumped up and
down by one line. The client didn't even notice. With improved storage
techniques some TBC gained an entire frame of memory. A device that
holds a frame in memory is a FRAME SYNC. A frame sync is often confused
with a TBC. They are not the same. A frame sync will delay an entire
frame until it matches a reference signal. This device is used to sync
incoming microwaves from network feeds or remote vans. TBC/Framesync
both correct time base errors and  frame sync. 

So gen lock has nothing to do with broadcast output. You cannot clean up
a crummy video signal. It is only as good as what you first record. TBCs
help keep a video signal stable and don't help the look of the picture.
If it is not broadcastable you can't make it. Garbage in and garbage out
no matter the TBC. 

LAST.. no offense but I would suggest that you find someplace to learn
these things before you take any money for a commercial. you will be
competing with people who are experience and there are a lot of peopl
who will stick it to you. Research you market, who is your competition.
What can you offer potential clients. Some client will go to you because
you contacted them others will ask tough questions like Lets see a
program like your trying to sell me or what commericials have you done
that Ive seen? You can make good money if you are good and know your stuff!
--
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||               ||                    J. Michael Duvall             
|| TTTTT  V    V ||             Associate Professor Communication
||   T     V  V  ||                 Sangamon State University
||   T      V    ||                Springfield, Illinois 62704  
||_______________||                 duvall@eagle.sangamon.edu
||   *       *   ||
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Newsgroups: rec.video.production,rec.video