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Old 09-14-2010, 11:50 AM
Postman Postman is offline
Join Date: Dec 1999
Location: Metropolis
Posts: 2,370
Default Re: Broadcast levels of Prologic Downmix from 5.1

Based on what I've see it is not dealt with very gracefully. Either there will be a limiter somewhere or more likely the signal will simply clip. If the consumer's set does the downmix, which is the usual situation for a surround broadcast watched on a typical receiver, there is little you can do beyond trying to prevent the downmix from exceeding 0dbfs. Since your surround mix is being constrained to -6dbfs, the downmix probably will be okay. There may be some limiting built into the Dolby chip in the consumer's device, I'm not sure if having one is standard practice or not, but you certainly cannot rely on it.

If the downmix is being handled by the broadcaster, to feed standard def/stereo outlets, you can be sure there is a big honkin' limiter in line that will take care of those peaks and most of your other dynamics too.

There are things you can do during the mix to lessen the possiblility of problems. For one thing, you can resist a temptation to spread loud sounds, like bass or singers or voice over, across many surround channels at once. Like, put the kick drum into L+R, or Center, but not all three.
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