[vorbis] mp3-wav-cd-audio "acoustically equivalent" to wav-cd-audio ?

Gian-Carlo Pascutto gcp at sjeng.org
Fri Aug 31 02:57:52 PDT 2001

----- Original Message -----
From: "Yusuf Goolamabbas" <yusufg at outblaze.com>
To: <vorbis at xiph.org>
Sent: Friday, August 31, 2001 9:54 AM
Subject: [vorbis] mp3-wav-cd-audio "acoustically equivalent" to wav-cd-audio

> regarding WAV, we used to store the masters on the disk, but moved them
> offline due to space concerns. If a user downloads the MP3 and creates a
> from it, that is going to be precisely equivalent on the audio CD in
> quality.

An MP3 will _never_ reach the precise equivalent of an audio CD
in quality (for normal music).

> I have tested it myself in MATLAB using spectral and phase analysis
> (I am a physics guy, after all).

A pretty bad one I guess. You should know that looking at the graphs
is NOT going to tell you much about the subjective audio quality.

> 5. listen to the CD in a standard player. You will hear zero differrence
> sound quality.

Many of us have done the same and the conclusion is:

a) there are always _audible_ differences in _some_ samples
b) how many people will be able to tell the difference depends vastly
on the used MP3 encoder, used settings, and listener experience

> And that they will not
> be able to improve upon the sound quality , though it is quite possible
> may degrade it, during their own post-processing stages.

Here is something to think about. What if I want to equalize the
sound before listening? With the WAV that would be no problem.
But if I try to equalize the WAV produced by the decoded MP3 I
am going to violate some of the assumptions the MP3 encoder made
and suddenly some artifacts may become very audible.

What if I someone gets a CD made from the MP3 and tries to rip it
and encode to Vorbis? It will sound like shit. If the CD had been
made from the original WAV it would have been no problem.


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