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

[David Dean]

Hi List

Here is a trick I have used with half inch tapes, I have a dual standard Panasonic DVD recorder which acts as one of the best TBCs I have seen, put in any old signal, and it outputs broadcast PAL or NTSC, (depends on which standard is selected). It is useful to have a variable attenuator on the input. Dont forget to pass the sound through it as well to keep it in sync !

Jobs a goodun

  
David Dean
Westpoint Television
Archiving Services 
2" Quad , 1" B, 1"C, D1, D2, D3, D5, HDCam and HDV 
.5", EIAJ, In Various Standards where supported
Alchemist Ph.C conversions with Clean Cut
Snell and Wilcox Ukon for HD frame rate conversions and Up and Down conversions
Digital Vision DVNR with scratch  and dropout concealment
Tel 020 8742 3400 
  ----- Original Message ----- 
  From: Chill315 at aol.com 
  To: quadlist at quadvideotapegroup.com 
  Sent: Tuesday, December 13, 2011 1:35 PM
  Subject: [QuadList] What to do with 1/2 inch tapes and proc amps


  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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