[vorbis] I hate myself for asking this, but...

Gian-Carlo Pascutto gcp at sjeng.org
Mon Sep 10 02:52:32 PDT 2001

----- Original Message -----
From: <k_myers at irito.com>
To: <vorbis at xiph.org>
Sent: Monday, September 10, 2001 2:15 AM
Subject: Re: [vorbis] I hate myself for asking this, but...

> http://www.djlithium.com:8064/djlithium.ogg (vorbis stream at 96kbps using
> 350kbps oggdrop encoded files run through Oddcast Beta 25)

If the source files are 350kbps how do you get the 96kbps stream?

There are no peelers yet, so you must be reencoding. Vorbis currently
does terrible with reencoded stuff, and problems due to reencoding
aren't real quality problems anyway far as I am concerned. One should
never ever reencode, period. Thats why offering peeling is such a big
'plus' for Vorbis. (Well, once we actually have it at least ;)

> I was listening to the native Ogg 350kbps version of State of
> the Union on-demand streaming from KasterBlaster yesterday with another
> in mp3 running on a seperate box coming from my other server at 256kps
> on-demand

Ah, so I gather those aren't reencoded streams. Are they rc2? Anything
before rc2 _did_ have bass problems.

I notice the first part of that stream has a bass sample in the
background that I know causes a lot of trouble with Vorbis, but that
wouldn't explain why you percieve an overall lack of bass. (It would
certainly explain the preecho though)

> (check my site for the on-demand links in mp3 format at
> www.djlithium.com under the streaming section), and I can definately hear
> the difference.

It could also be of course that MP3 is terribly messing up on the
bass causing it to come out louder.

(Okay okay, I know it's farfetched, but without the originals, there's
really no way I can tell anything here)

> I have tried both sets of head phones (Sony MDR-7506 and
> Sony MDJ-700's)

Sony's tend to overemphasize the bass (I guess that is why
they are popular with DJ's ?) so that would explain why you
percieve the problems so good exactly in the bass section.

That doesn't explain why you percieve the MP3's to be better
though...even if the artifacts are exagerrated Vorbis shouldn't
have more than MP3 in the first place ;)

> Does bit rate affect this in anyway? I am listening to the 96kbps ogg
> now, an its actually got more bass in it then the 350kbps files, and it
> seem there is more "pre-echo" in the 350kbps versions.

That is certainly very weird. Perhaps the 'more bass' _is_
actually an artifact after all?

> I use some spacial expansion effects on the mastering of the waves before
> I encode them, but these wave files were used to generate both the MP3 and
> Ogg versions with effects on for each, so I am guessing the outcome would
> be completely independent of that,

That's correct. If you did this _before_ encoding it should be ok.

I could imagine it's possible that some very weird stereo effects
play foul with the advanced stereo modes, but the 350kbps mode
doesn't use those.

> but I am wondering if Ogg (or Vorbis really)
> has problems with dealing with signals that are very wide in stereo image.
> this make sense??

No. Certainly not for the 350kbps stream, which would be losslessy coupled,
and very likely not for the 96kbps stream with the advanced stereo modes

If you could snap a part where you percieve the problems to be
most obvious out and put up the original of that somewhere, that
would be very helpfull. (I'm also interested in the MP3 encoder
and settings you used)


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