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Old 1st August, 2004, 10:13 PM
cadaveca cadaveca is offline
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Originally Posted by Áedán

The AC3 specification clearly defines both the packet structure and the compression used. The compression technique used is based around psychoacoustic analysis, and works by throwing away parts of the sound that the encoder believes humans will not be able to hear. That's exactly the same technique used by MP3, OGG, ATRAC, DCC, MPEG2 and a whole host of others. That's nothing new, as psychoacoustics has been an expanding field for a good number of years now.

AC3 is definately not a 'container format'. That is, an AC3 stream can only handle AC3 encoding. It cannot handle DTS, MPEG2 or any other varient. Re-encoding DTS, MPEG2 or other compressed source material leads to a loss in sound quality, as the different psychoaccoustic engines regard different things are 'important'. This loss is noticable on high end systems.
Although ac-3's current applications are only 5.1/4.1 sound, there ARE other uses...and like you say, re-encoding anything to ac-3 will cause a loss of quality ON HIGH END SYSTEMS. Just because this is the case, just not mean that the only application is what is used currently. AC-3 WAS DESIGNED TO BE A CONTAINER FORMAT. It's just not used that way. Remember, Dolby wanted to be THE SOLE SOUND PROVIDER to satelitte braodcasts. This would be a unsurrmountable edge for them that DTS, THX, MP3, OGG, ACTRAC or anything else could have. It's the loss of quality in these other areas that let these other standards break ground.
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