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Old 01-28-2007, 04:55 PM   #16
leviramsey
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The only statements [I've read/heard/etc.] that Sirius doesn't use dynamic bitrate allocation have been from various board posters (many of whom, based on posting history, are advocates for XM, which has been proven to use static bitrate allocations).

OTOH, there is evidence that Sirius has the ability now to dynamically allocate bits between channels (essentially statistical multiplexing). There's a patent issued to Lucent from the mid-to-late-'90s, prior to when the encode/decode system would reasonably have been finalized, that covers how to do it with the PAC codec (with certain indications from the patent documentation that, at least to my reading, indicate that dynamic allocation was a major selling point of the PAC codec for digital audio broadcasting applications). There's also a Crutchfield article from 2003 or 2004, a tour of Sirius' equipment and facilities, that includes a photo of hardware that's described as performing the dynamic allocations.

It could be that Sirius is not taking advantage of dynamic allocations now. For instance, they may have been using it and found that the allocation algorithms (which fundamentally rest on determining the relative compressibility of each channel which is not that trivial) weren't at a point to where they were giving appreciably better SQ. It's also possible that some of the enhancements that Sirius made to the PAC codec removed the possibility of dynamic allocation.
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