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<DIV>We have had a lively discussion of a proc amp. so here is a little
background information that most of us probably know. Please feel free to
add anything you can.</DIV>
<DIV> </DIV>
<DIV>A Processing Amplifier is a device that is used in the video chain to
adjust levels and do other corrections to the signal. RCA originally
called it a Stabilizing Amplifier. </DIV>
<DIV> </DIV>
<DIV>The unit takes an incoming video signal and strips sync off. This is
regenerated to provide clean pulses with the proper rise times, levels,
etc. This can be done via a gen-lock technique with a very fast time
constant or just strip, stretch, reshape and reinsert method. (The cheaper
ones do the latter.)</DIV>
<DIV> </DIV>
<DIV>The video is treated as a separate signal. Video is usually clamped
during the horizontal interval to remove any DC variations or AC hum. It
is then adjusted for correct levels, black, white, and Chroma. After this,
the sync portion of the signal is reinserted back into the video with
adjustments for levels, burst phase, and timing of sync to video. Some of
these are internal so you can not do it without the green screwdriver.
</DIV>
<DIV> </DIV>
<DIV>For a transmitter, the processor must do several additional steps.
First is White clip to prevent negative modulation of the transmitter.
This is usually done about 105 IREs. Because Chroma can exceed that level,
the white clip is done in two ways. The hard clip is done in the separated
luminance channel. Luminance was separated to allow individual adjustment
of Chroma and Luminance.) Soft clip does it to both luminance and
Chroma. Soft clip is set higher. Then the linearity corrector is
added to allow for correct of the transmitter gamma cure to make it a linear
system. </DIV>
<DIV> </DIV>
<DIV>In addition we use a Proc Amp at the output of an edit suite to do a couple
of things. Fist is to provide a way to reinsert house sync directly from
the sync generator so that the SCH phase remains constant. Also it keeps
the quad machine from having H shifts upon the camera or source switch in the
studio. We also use it to provide a white clip to prevent the over
deviation of the modulator in the quad.</DIV>
<DIV> </DIV>
<DIV>This is the simplest definition of a proc amp. I hope it helps.</DIV>
<DIV> </DIV>
<DIV>Chris Hill</DIV>
<DIV>WA8IGN</DIV></FONT></BODY></HTML>