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RE: Clippers


Hope this helps enlighten your understanding of TV broadcasting.

Jim Mendrala
Real Image Technology, Inc.

You wrote:

I am looking for some feedback as to how everyone is handling the 
CCIR-601 component standard (SMPTE-259M) with references to signal 
levels (clipping).

In the NTSC composite world, we found ourselves pushing the envelope 
by adjusting the whites to 104 / 106 and the blacks down to between 7.5 to
3 units.
In the component world these levels equate to signal levels of up to 725 / 
730 mV and as low as 0 to -40mV.  What I get out of the SMPTE 
standard appears to suggest that video should stay between the 0 to 
700mV range.  What happened to the headroom we used to play with?  Is 
everyone following these guidelines?  Is everyone with the daVinci's 
using the hard clips or have the HP units been set up to chop it all off.

Any feedback would be appreciated

Tony Meerakker
Magnetic North

A telecine operator controls indirectly the modulation of the TV
transmitter so he must understand what he is doing to the transmitter.
Running 104  to 106 ire units should never happen as the pipe is set for
100 ire units (714 mv). Go to more than 100 ire units and you might make
the sound buzz as the transmitter amplitude modulation of the visual
carrier goes to zero. Setup of 7.5 ire units can be anywhere from 5 to 10
ire units and be acceptable for NTSC transmission. The networks however
call out 7.5 ire [(10+5)/2=setup] Check the FCC rules. I believe that as
long as we "simulcast" NTSC with DTV we will have a problem. DTV from
component is not required to have setup and doesn't need it. Setup was put
into the TV signal to reduce the vertical retrace lines seen on the old
1940s TV sets before color, vidicons, saticons, and CCDs. It should be done
away with giving an extra 7.5% contrast.

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