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Old 16 April 2006, 12:49 am   #1
isurf
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Default How does MPC work with Dolby Prologic II?

Hello, I just came across MPC being a further development of the MPEG I Layer II (mp2) codec. Since mp2 is highly estimated by me I wonder how well MPC works with Dolby Prologic II.

Until now I was relying on OGG at quality 6 or higher which resulted in files of at least 192kbit/s.

Now the main point is that the suround code in Dolby Prologic II is encoded in a way that the human ear doesn't hear it. That's why mp3 just sucks on it.

I would be most thankful for any further information.
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Old 16 April 2006, 07:45 am   #2
Shy
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To clarify, there is Dolby Pro Logic II decoding that "extracts" the directional cues in stereo content to the rear, center and subwoofer channels, and there is Dolby Pro Logic II "encoding" that mixes all 6 channels of a surround source into stereo in a way that makes the audio optimal for decoding/playback with Dolby Pro Logic II.
And it does it all poorly. Its success of actually extracting content not specially encoded with that method into surround channels is minimal, with the cost of ruining the frequncy balance and the overall sound. Its success of decoding audio encoded in the same method is better, but the sound is greatly degraded as well.

Codecs cope badly with such audio data because it is unnatural and ruins the codecs' ability to deal with stereo efficiently as they normally do, which causes high bitrates. It's a "hack" by Dolby, which only their own technology handles "properly."

That said, according to my own tests, like everything, Musepack handles audio encoded with Dolby Pro Logic II far better than MP3, and better than AAC and Vorbis as well with what I tested.

I would suggest you not to use Dolby Pro Logic II encoded files. Keeping the original surround tracks is a far more sensible solution if you're concerned with quality.
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Old 16 April 2006, 05:11 pm   #3
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well,
though I cannot talk much about DPL2,
I can about Logic7, which was the original technics and even reported to work better than the later built DPL2 decoding.

Oppositely to the old simple DPL decoding,
Logic7(dpl2) decoding can make audiophile fun.

MPC performs quite ok, especially at q7, q8 (which use --ms 13 by default), and really well, if you add --ms 15 as switch to the q setting, even --quality 5 --ms 15 was reported to sound very well with clearly lower bitrates than eg. plain q6.

mp3, even lame versions, perform inconsistant in Logic7 decoding, it depends to much on the version and setting, as the mp3 developers change too much from version to version and logic7/dpl2 decoding is obviously not on the standard test list.

the free available "dpl2" encoding, which means encoding surround channels (eg. rear left and rear right) to a stereo stream, should be named DS2, the term & technics DS2 was invented by Dark Avenger, the one who is also author of HeadAC3he. iirc, Dolby has no patent or somewhat on the encoding site, as Logic7 as decoder was earlier on the market by far.
Headac3he (and later BeSweet by DSPGuru) contained DS2 to encode eg. 5.1 movie soundtracks to stereo with keeping the surround as close as possible.
And you don't find (or very rarely) especially "DPL2/Logic7 encoded" marked CDs (though you find sometimes "Dolby Surround" labelled albums, which had so a Dolby certificate for the old normal Dolby Surround and those old decoders).
There was one CD once, when dpl2 was introduced, though that CD contained "normal" songs, from various artists, eg. Sara K., Erich Kunzel & Cincinnati Orchestra etc. Even that CD had not a label like "patented dpl2 mix". The sound engineers knew howto mix the sound even before Dolby came up with the dpl2.
And sometimes you get excellent effects even with very old recordings from the 60s and 70s
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