Vorbis dev - Sep 2002 - Serious, inacceptable artefacts with Ogg Vorbis

Hello developers,

I recently participated in a public listening test that was held by 
German magazine c't. They had two categories, 64 kbps and 128 kbps.
I only participated in the 64 kbps test where there were 7 .wav files, 
with 1 of them the original one and the other 6 being encoded with 
different encoders. Without knowing which file was encoded with which 
encoder you had to give each one a place in your ranking.
The samples were 20 secs long with a pop, a (sort of) jazz and a 
classical piece.

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!

Still surprised (and disappointed) by Ogg Vorbis' bad quality I compared 
  the actual 1.0 with an old RC2. And surprisingly again the artefacts 
in the old RC2 were much less then in the actual one, though there was a 
lot more noise.

Hoping and to make sure my complaints are taken serious I have encluded 
my personal ranking for the listening test:

Platz 1: unkomprimiert (WAV)
Platz 2: Windows Media Audio
Platz 3: MP3Pro
Platz 4: AAC
Platz 5: RealAudio
Platz 6: MP3
Platz 7: Ogg Vorbis

I still have the samples so I can send them to you if you want.
But anyway, I can reproduce the artefacts with any audio data and Ogg 
Vorbis encoder.

I don't know, am I the only one who hears those artefacts (it seems a 
bit like this)? Anyway, I'm hoping to get some comments.

Michael Noisternig

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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
mixing).

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).

Monty
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Hi:

Just curious.  Do you know if this was 64kbps managed bitrate or quality 0?

Geoff.

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