[QuadList] What to do with 1/2 inch tapes and proc amps

[Chill315 at aol.com]

This is a good discussion regarding 1/2 inch tapes.  I hope I do  not get 
too verbose with this answer.
 
The EIA-J tapes may be a real problem.  The first step is to look at  the 
raw video on a waveform monitor.
 
Is the sync even interlaced?  Some of the early cameras were just free  
running horizontal oscillators and vertical locked to power line.
Is it industrial or RS-170?  Look for equalizing pulses in the  vertical 
interval.  If not, then many professional proc amps and TBC's will  have 
problems.
What is the level that you are dealing with?  Hopefully 100 over 40  but 
don't count on it with the early AGC circuits for video.  
 
If you get past this first step, then it is see what works.  For non  
RS-170 video, you are in never, never land.  It is try, try, and try  again.  The 
3M unit may help.  Also there are other very early proc  amps out there.  
Even a video DA to adjust sync to a 40 IRE level may  help.
 
There are video DA's that have sync stretch in them, that may be something  
to try.
 
What will the proc Amp do for you?
 
It will allow you to adjust the video levels prior to Analog to  Digital 
conversion to give you best range in that process.  It will clean  up the sync 
pulses to allow proper write clock operation.  
 
What will be the bad things it will do?
 
If used before a TBC, it may put a lot of jitter in your final  picture.  
This is because the Proc Amp has replaced the sync and the video  is not 
always coherent with the video anymore.  You sometimes see this as  high 
frequency jitter or Venetian blinds.  
 
If not RS-170 sync it will burp a lot if it only works with RS-170  sync.  
Again never, never land.
 
If heterodyne color we are into never, never land again.  Each  manufacture 
treated this in different ways.  Grass Valley was not designed  for this.  
Now if used before the TBC, again it is never, never land.   You have to 
experiment to see what you can do.
 
Where do you put it in the chain?
 
The TBC has a proc amp on the output.  It is required in the design of  any 
TBC to function.  Since the Horizontal interval is not digitized, it  has 
to be re-generated and inserted in the output of the TBC.  Along with  the 
other handles that we expect.  Manufactures have a couple of choices on  where 
to put the video gain in a TBC.  Most do it at the output.  It  is possible 
to put it before the A-D converter.  This gives you better  dynamic range.  
It is an engineering trade off.
 
There is one method that works almost every time.  It requires some of  the 
most sophisticated equipment known to man.  A black magic cloth, a good  
monitor and a camera.  Use an under scan monitor and point a camera at it  to 
just fill the scans of the camera.  Drape it so light does not get in  and 
start the transfer.  The fast time constant of the monitor serves as  the 
TBC.  If you have access to ramp or stair steps, then set up the  monitor and 
camera to give as good a transfer as possible.  Monitor for  correct 
brightness and contrast.  Camera for correct white and black plus  gamma.
 
Chris Hill
WA8IGN
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