[vorbis-dev] Serious, inacceptable artefacts with Ogg Vorbis

Monty xiphmont at xiph.org
Tue Sep 17 15:44:57 PDT 2002

On Wed, Sep 18, 2002 at 12:21:12AM +0200, Michael Noisternig wrote:
> I was really surprised when I got the results seeing that Ogg Vorbis got 
> last place in my ranking. Not only that, but it even was ranked 2nd 
> place by the other people in average. (Though that doesn't mean too much 
> seeing that many people couldn't even pick out the uncompressed wav.)
> So what made me rank it that bad? I noticed strange artefacts in the 
> entire Ogg Vorbis encoded sample already when I got through the list the 
> first time. But when I listened to it with headphones the artefacts got 
> really *inacceptable*. I don't know how to describe them, maybe echoing 
> or bubbling. They made me rank MP3 and Real even better than Ogg Vorbis 
> although they had cut away all the high frequencies!

This sounds like a possibly buggy *decoder*, or something seriously
wrong with playback (eg, accidentally mixing down to mono with L-R

I assume c't sent .wav files pre-decompressed?  Are you using any
playback postprocessing (like a 'spatial expander')?  The last time we
got a report like this, it turned out that the person involved
accidentally turned on 'stereo enhancement' on their amplifier, and it
mangled the decompressed playback (as Vorbis pulls stereo tricks that
badly confused the strereo 'enhancement' algorithm).

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