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Old 11th January 2011, 00:32   #14  |  Link
A.Fenderson
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Join Date: Mar 2009
Posts: 230
Quote:
Originally Posted by TinTime View Post
I also would agree with what others have said - if there's a 640 AC3 or full rate DTS track available then just use them.

As rik1138 said there are some rare examples where this isn't the case (LPCM / TrueHD with <640 AC3 or DTS-HD with a half rate core) but they're so few and far between that (IMO) it's not worth shelling out money in order to transcode. I'd just live with the lower rate, or if you do transcode then use a free solution such as Aften. No point in worrying about it anyway until you actually find a disk where this is the case
I had incorrectly assumed that the DTS core+extension model wouldn't bother to accomodate anything other than a full-rate core, but according to this DTS document (.pdf), they can be half-rate, or, under certain circumstances, several other rates between half and full. Kinda counter-intuitive, IMO, since you're presumably just shifting the quality you're trying to achieve/surpass from the core to the extension, but then again maybe the extension codecs are that much more efficient than the core that it saves overall space at the same perceptual quality level when decoding the HD stream--I just wish it weren't done at the expense of the quality of the more compatible core stream.

Quote:
Originally Posted by 7ekno View Post
Not sure if you have stumbled across this link or not, but it's an interesting study done by European broadcasters (the pretty graphs start on page 21!):
http://tech.ebu.ch/webdav/site/tech/...h/tech3324.pdf

For those too lazy to click the link, basically the "Original ANC", "DTS 1500" and "DD+ 448" (AC3 640kbps) tracks all score 92-95% on the perceived quality score (so the lossless formats should score the same as "ANC_Original"!) ...

7ek
Thanks for the link, that's good info. Unfortunately, they didn't seem to use actual standard AC3 @ 640kbps, and I'm not sure you can equate DD+ @ 448 with AC3 @ 640. It would have been cool if they'd tested 768 kbps DTS in the mix as well.

A few more questions come to mind:

* Has anyone here bothered using Aften/eac3to to reencode to AC3@640 for similar reasons, and if so did the resulting file sound more transparent to the high-def/lossless source than did the (presumably) low-bitrate compatibility track that had been used alongside/within the HD/lossless?

* Has anyone ever had any compatibility problem with Aften-encoded AC3 tracks (via BD-RB/eac3to etc) on hardware decoders (BD player, HT receiver)?

* Are BD players set to bitstream via SPDIF actually streaming 640kbps AC3 tracks at full bitrate, or stripping it down to 448 somehow for compatibility with older receivers, seeing as how until BD/HD-DVD, no consumer devices I'm aware of really output 640 kbps AC3? Has anyone ever happened across an older DD/AC3 receiver that didn't support/function with bitstreamed 640 kbps AC3?
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