Re: ogg to mp3 audio (also via 8233a question)
Steve Lamb wrote:
> On Fri, 7 Feb 2003 11:28:53 -0800 (PST)
> Jack Pistachio <jackpistachio@yahoo.com> wrote:
> > Encoding to either ogg or mp3 is lossy, but when converting
> > back to wav the information in the mp3 or ogg audio should
> > be retained completely.
>
> Erm, no. These two statements are mutually exclusive. The very
> definition of lossy compression is that information is lost. Hence, lossy.
> Lossless compression loses no information.
Hmm. One of you is misunderstanding something; either Jack
misunderstands audio compression, or Steve misunderstands what Jack said.
I'm not sure which is the case.
Let's be quite clear here.
Compressing audio with MP3 or Vorbis will reduce audio quality by
discarding allegedly inaudible signal components and introducing some
degree of compression artifacts. (Vorbis's artifacts are much milder
than MP3's, but there are still some, especially at high compression
ratios.)
Decoding from either MP3 or Vorbis back to .wav does not lose any
_additional_ quality. It won't restore quality that was lost in
compression, but quality won't get any worse. (Unless you go out of your
way to make it worse, such as by reducing a stereo signal to mono, or
reducing the sample rate.)
When audio data has been decompressed back to .wav, encoding it again
with Vorbis or MP3 will tend to reduce quality still further, especially
if the previous encoding had been done with the other encoder. Lossy
audio compressors tend to deal poorly with artifacts introduced by
previous rounds of compression. Again, Vorbis does a better job of this
than MP3, but the effect is still noticeable.
That help?
Craig
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