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:-( MP3 destroys Surround Sound encoding
post Dec 3 2002, 00:18
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I've been experimenting with MP3 and converting my CDs to MP3-320 compressed files. Unfortunately, I've discovered that the MP3 encoding process destroys the Rear Channel Sound. In a few cases I can still hear music in the rear, but for most songs the rear speaker just produces garbage sound... rather disappointing compared to the rich sound produced from the original CD!

I suppose MP3 considers the rear channel information to be "inaudible" which it would be in a standard 2-speaker stereo arrangement, but the addition of the rear speaker makes these types of sounds *very* audible. It's basically an echo effect that is audible when listening to the CD and places the listener *inside* the music, but sadly lacking on the MP3 rip. The stripping of that rear channel echo dramatically diminishes the experience.


P.S. I'm using CDex for ripping and LAME for encoding with the following settings: q=0;Very High Quality, Stereo, 320kbps.
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post Dec 20 2002, 03:36
Post #2

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Joined: 28-October 02
From: London, UK
Member No.: 3644

Hi Mgz

This is (unfortunately) not a hardware malfunction. Dolby Pro-logic was developed as a mechanism for encoding a front center and surround channel into a standard stereo stream (i.e. four channels from a standard two-channel stereo stream.)

The mechanism relies heavily on stereo imaging (as described here and here.)

The same effect (sound from the center and surround channels) may occur on non-DPL tracks if there are sufficiently out-of-phase stereo sounds, such as heavy reverb or recording the audience in stereo on live shows.

Lossy encoders tend to sacrifice stereo information at lower bitrates, since this leaves more bandwidth for removing more apparent artifacts. Any deviation from the original recording could result in unusual sounds from the center and surround channels.

DPL and DPL-II are discribed in-depth on the Dolby Web Site.
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