[vorbis] Ogg article on zdnet

[Mark Kanof]

Don't know if anyone else has read this article on zdnet yet.

http://www.zdnet.com/zdnn/stories/news/0,4586,2690855,00.html?chkpt=zdhpnews
01

Maybe someone can explain this to me.  I don't see how the ogg creators
could get sued for anything.  As I understood it, ogg encoding is not in any
way related to mp3 encoding, besides the fact that it is also a lossy audio
compression format.  But other than that I was assuming it was something
new.

Just Curious,
Mark Kanof
----- Original Message -----
From: "Aleksandar Dovnikovic" <aldov at EUnet.yu>
To: <vorbis at xiph.org>
Sent: Wednesday, February 28, 2001 11:13 AM
Subject: Re: [vorbis] Question, problems re: Ogg Vorbis ..

> "Merijn Vogel" <merijnv at sci.kun.nl> wrote:f
>
> > Good luck to the vorbis team, my ears seem to be bad to me, I still
cannot
> > hear the differences between beta1 and beta3 ;-). Therefore this
request,
> > does somebody know about a website that discusses things like pre-echo,
> > ringing and stereo errors so I can learn what to listen to ?
>
> First, one small warning/suggestion: don't do things like this. It will
ruin
> your music experience because you'll train yourself and your ears and
> you'll hear artifacts much easier. I know, I've done that... :-))
>
> Anyway, if you're still interested, you can visit a page on LAME's
> (open-source mp3 encoder) site and there you'll find many test tracks
> (with explanations) that most encoders have trouble encoding properly:
> http://www.mp3dev.org/mp3/gpsycho/quality.html
> (Hint: most troublesome tracks are castanets.wav, fatboy.wav, spahm.wav,
> velvet.wav and applaud.wav)
>
> Also, you may check this forum - it is primarily used for mp3 discussion
but
> lots of people there are also very experienced listeners:
> http://pub41.ezboard.com/br3mix
>
> Finally, check this message that David McIntyre (he works for QDesign)
> wrote on artifacts some time ago on mp3.com message board - it is a
> good starting point because it explains most common types of artifacts:
>
> Artifacts
> (by David McIntyre)
>
> A definition of artifacts is very difficult without audio examples (and I
> don't have time to make some) and again, different people hear different
> things, but here are the most common:
>
> chirps: high-frequency distortions added to the audio, will sound like
short
> chirps, whistles, sometimes can shwoosh up like a high-pitched glissando
> (slide).
>
> pre-echo: the killer artifact that everyone has trouble with and the whole
> TNS structure in AAC was designed to handle but didn't work as well as
> expected (there's sentence). To hear this find a track with very precise
> sharp hits and no background noise (the best is a castanets track we use
and
> is part of the SQAM testing disc). When you code it the attacks will be
> smeared - if you listen closely or look in Cool Edit you will see that
there
> is an attack before the real attack, thus "Pre-echo". This is a huge
problem
> for MP3. The reason no one has completely solved it is basic filter
theory -
> as you improve time resolution, you lose harmonic resolution and/or vice
> versa. Codecs that have little pre-echo tend to sound less warm and more
> brittle.
>
> Imaging: (my worst, so my description may be bad) listen to the placement,
> in the stereo field, of all the parts. Also, get a sense for how "big" the
> stereo field seems. When you listen to compressed audio you will find that
> parts get moved towards the center or pushed out to the extreme edges.
Also,
> you will find that smooth pans from side to side seem to get quantized
into
> steps instead of a smooth continuum. The other thing is a simple, general,
> loss of "width".
>
> Pumping: pumping is a general term that can apply to frequency, amplitude,
> imaging, etc.. This simply means something, lets say left channel
amplitude
> is going up and down fast enough to be bothersome and unatural, but slow
> enough to be really noticeable. Maybe 2-4 times per second. Amplitude
> pumping is the most common type and has been solved in most codecs, but
can
> be a problem.
>
> Harmonic content/depth: simply, does it sound shallow or brittle (PAC's
> biggest problem), or does it sound warm and ful.
>
> Noise: has noise (static, hum, etc.) been added or removed. Is it centered
> on one particular event or frequency range.
>
> Other time resolution problems: other than pre-echo the most noticeable is
> the watery sound many codecs get, particularly on voice. This has to do
with
> insufficient time resolution on the rich harmonic content in the vocal
> spectrum.
>
> Phasing: to kill AAC, or the QDesign Music Codec, trickling water, or rain
> on a sheet metal roof with other sounds in the background will be very
> difficult. In particular, the definition of the water will be lost and it
> will start to sound like frying oil and not water drops. This is due to
> quantization of the phase information in the audio. With all these water
> drop hits - a series of like sounds close together - you get a lot of
> signals that are similar and slightly out of phase with one another adding
> up to make a noise-like sound. Usually, a codec will screw up these
delicate
> phase differences and tend to make it sound more like white noise (I don't
> understand the details, but I know this is THE KILLER SIGNAL for AAC).
>
>
>
> --- >8 ----
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> Ogg project homepage: http://www.xiph.org/ogg/
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--- >8 ----
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