Vorbis - Apr 2001 - questions about artifacts in low bitrate streams

Hello-
 I recently downloaded Verbs and started playing with the encoder.  The
quality was great when I encoded a few samples at medium and high bitrates,
but when trying to encode the same clips at 16 kbps, artifacts are audible
during playback- short bursts of screeching noise, not just distortion.  I'm
using oggenc 1.0 beta 4 to encode, sonique to play back on Windows NT.  I've
also tested playback with the same files on a Mac (OS 9, using MacAmp), and
similar artifacts appear.  I don't think there is any clipping in the audio
stream.  The audio input format that I used was a 16 bit, 16 kHz wav file,
recorded by Goldwave from a playing CD.

the questions:

- Is this a known issue with the beta in low bitrate encoding?

-If a known issue, is it on target to be fixed in a future beta or the 1.0
final release?

thanks very much,

Nick

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>- Is this a known issue with the beta in low bitrate encoding?
>
Yes, it's a known issue.  Read the docs - it's not reccomended to encode
anything at less than 96 kbps.  In fact, the built-in help for OggEnc 
bottoms out at 96 kbps (meaning it's the lowest mentioned)
>-If a known issue, is it on target to be fixed in a future beta or the 1.0
>final release?
>
You're forgetting a minor caveat:  This is an Open-Source project.  The 
view is that it's better to finish and release a bug-free product as 
1.0, than it is to keep any kind of calendar schedule.

So as a result, the best way to describe when it'll be fixed is"When 
it's done."  However, from reading earlier posts by the developers, 
they've got quite a lot of work to do before reaching a 1.0 status.

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>  I recently downloaded Verbs and started playing with the encoder.  The
> quality was great when I encoded a few samples at medium and high bitrates,
> but when trying to encode the same clips at 16 kbps, artifacts are audible
How do you do that anyway? If I specify even "32" to oggenc, the
average
bitrate still ends up at 80 or something.

- -- 
/ Peter Schuller, InfiDyne Technologies HB

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>- Is this a known issue with the beta in low bitrate encoding?
>
>-If a known issue, is it on target to be fixed in a future beta or the 1.0
>final release?
There are two issues here:

Firstly, low-bitrate encoding is definately NOT well tuned currently. You
shouldn't expect it to work really well right now - version 1.0 will
certainly perform better on low bitrates. However, this is almost certainly
not the problem you're encountering.

The other problem was a bug in pre-beta4 decoders. They didn't implement a
feature which is used by the beta4 encoder at low bitrates, and incorrectly
didn't note this fact (so they tried to play back files that they don't
know how to). The symptoms are pretty much exactly what you described. I'm
not sure if sonique has updated the version of vorbis they use to beta4 yet
- last time I looked they hadn't. As a result, lower bitrate files will be
decoded incorrectly. I suspect that the same is true of the mac player you
said you tried. 

Could you use either freeamp (2.1, which was released a couple of days ago
with built-in vorbis support), or winamp with the beta4 plugin from
www.vorbis.com to test this, to check that this is indeed the problem it
appears to be?

Michael

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I tried the winamp plugin, and there were no artifacts in playback.
Thanks for the info!
nds

-----Original Message-----
From: Michael Smith [mailto:msmith@labyrinth.net.au]

Could you use either freeamp (2.1, which was released a couple of days ago
with built-in vorbis support), or winamp with the beta4 plugin from
www.vorbis.com to test this, to check that this is indeed the problem it
appears to be?

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