[vorbis] 16 KHz clip-off?

[Maik Merten]

Hello!

Gian-Carlo Pascutto schrieb:
> 
> On Tue, 14 Aug 2001, Maik Merten wrote:
> 
> > Hello,
> >
> > congratulations to the Ogg Vorbis team - RC2 sounds good.
> > But... RC2 in 128 kbps mode seems to clip off all frequencys
> > beyond 16 KHz. On the tracks I tested Beta 4 gave response
> > even beyond 18 KHz.
> 
> It is better to cut off at 16kHz than to try to
> go higher and only introduce artifacts anyway in these
> modes.

Of course, I agree upon this.

> Even if you can hear above 16kHz, that does _NOT_ mean
> you will be able to detect a cutoff at 16kHz. In fact,
> this is extremely hard.

I agree here, too.

> It is much better to encode what we can hear good rather
> than to encode what we can't hear and artifact what we can.
 
(I´m going to be a bit repetitive) Agreed.

> MP3 was never designed to handle more than 16kHz either.
> Trying to go beind that usually only worsens the sound
> unless real high (>=256kbps) bitrates are used.
 
MP3 is old, old, old. It is extremely inefficient (hope that´s
spelled right) in encoding high frequencies. I thought
Vorbis was better in high-frequencies. (I think it is!)

> Vorbis will encode fine above 16kHz in 160kbps and higher
> modes, but 128kbps is simply not enough (for now).
 
In Beta4 it was enough. (At least according to the material
I encoded. I could not hear artifacts - the high-freq-area
sounded very nice.)

> Judging a codec by its bandwidth (like with frequency sweeps and
> spectral plots) is like judging wine by its colour.
 
The red one is better. ;-)

I know. But I though channel coupling would save enough
bits/s to ensure high-freq-content is encoded properly.
Instead I´m seeing the opposite. Low- and Mid-freq content
now may be better in quality but *I* never felt that
those were critical. (On the other hand: I neither have
$10000 equipment nor "golden ears".)

I did the frequency-analysis because I felt something
was strange when I listened to some samples.
It was not the other way round.

> > Some testings on a randomly chosen track:
> > (other tracks gave similar results)
> >
> > Artist: Judas Priest
> > Album: Jugulator
> > Title: Bullet Train
> >
> > Beta4: 127 kbps, ~ 18 KHz (!)
> >   RC2: 132 kbps (!), ~ 16 KHz
> >
> > This seems even more strange to me as RC2 benefits from channel
> > coupling...
> 
> Have you done a listening test on both files to see which _sounds_
> better?
> 
> (Granted, RC2 isn't tuned that well yet so it may be worse.)
 
Beta4 is my favorite on this track. I don´t hear any annoying
artifacts but it sounds brighter and "cleaner". (opinions may
vary - no... they *will* vary) But differences are small.
And, as said above, I don´t have golden ears and I am not an
experienced "test-listener" (I can hear MP3 artifacts, no
problem, but this is a completely different story...)

> >
> > BTW: As 128 kbps mode produces average bitrates higher than 130 kbps
> > (please keep in mind that I am testing with Heavy Metal music, so
> > results for Britney Spears and Back Street Boys may vary ;-) )I would
> > be happy if 112 kbps mode is back in RC 3...
> 
> I think this is normal. Metal tends to bloat the bitrates of VBR
> perceptual codecs.
 
In Beta4 it did not. Why was the 112 kbps mode removed? No time
to tune it?

> --
> GCP

bye,

Maik Merten


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