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Old April 17th, 2003, 08:04 AM   #1
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Unsafe Broadcast IREs

This is more a curiosity than something that I have yet to do.

The term "Safe" Broadcast levels. What happens if you do deliver unsafe footage for broadcast and if they didn't know it, and viewed it. Does it blow monitors? Does it clip the colors, whites, blacks etc? What exactly happens when its not "safe"?

What are the levels(IRE) for suitable "Safe" broadcast?

Curiosity thang...

Thanks for posting!

Cheers!

Derrick
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Old April 17th, 2003, 09:26 AM   #2
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Luma and chroma ( in a slightly different way) will automatically be clipped just before it enters the transmitter, resulting in washed out areas. These signals does'nt blow anything...they just would introduce video rattle in the audio chain of consumer (intercarrier) TV receivers.
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Old April 17th, 2003, 09:42 AM   #3
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Andre,

So the clip would appear/sound choppy in the instances of blown whites etc. I was was curious about that for sometime.

Thanks for your reply.
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Old April 17th, 2003, 02:03 PM   #4
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Correct Derrick. The official name for this sound artifact is "intercarrier buzz". The minimum value for video carrier in NTSC transmission is 12.5 +/-2.5 % of the peak carrier value (sync tip). This corresponds to 100 IRE video levels. Chroma and luma together which come summed up at the transmission stage, can be tolerated to generate signal levels slightly beyond this 100IRE levels for moving pictures (in NTSC) resulting in sporadic zero carrier situations which are generally no recognized as sound problems.Test patterns (fixed images) however are not allowed to go beyond the 100IRE. That's why broadcasters use 75% (instead of 100%) color bar test patterns.
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Old April 17th, 2003, 02:18 PM   #5
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Nice! Very informative...

I am doing some color correction within Avid Xpress and I have +/- levels in my sequence. I'm balancing them out.

It makes more sense to me now.

Thanks, Andre, for the details. The why? Has been answered...

Cheers!

Derrick
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