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Subject: Re: AW: Question about CD-Quality and MP3

Re: AW: Question about CD-Quality and MP3

From: Frej Bjon <fbjon_at_abo.fi>
Date: 2006-02-02

On Thu, 02 Feb 2006 16:37:29 +0200, Michael E. DiFebbo <medifebbo@rcn.com>
wrote:

> This is a common misperception, but at best it is only partially true.
> The term "joint stereo" has two different meanings when used with
> respect to encoding MP3s.
>
> The joint stereo method that you refer to is "intensity stereo."
> Intensity stereo is only used by modern MP3 encoders for very low
> bitrate files (lower than 96kbps if I remember correctly). For higher
> bitrates, "joint stereo" refers to M/S stereo.

Ah, how wonderfully unambiguous. Well, in that case, it used to be that
you should use stereo encoding, but these days the encoders are smarter
than that :).

Now that you mention it, I do recall that encoders can decide
frame-by-frame which method to use (M/S or separate channels), but I
wonder how it's decided which is better. Encoding with both and picking
the one with smaller size is trivial, but inefficient. Also, you say M/S
is more efficient to encode when much of the source is centered and mono,
but does the opposite apply? Is it less efficient if the stereo field is
really wide?

-Frej
Received on Thu Feb 2 16:25:45 2006


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