Vorbis dev - Jul 2002 - Why Point-Stereo at 160 kbps ?

Hi there !

I checked Vorbis' performace for mono files at
approx. 64-80 kbps (it does a good job) and I'm 
wondering why the current OggEnc still uses
Point-Stereo (>10kHz) for -q4 and -q5

I know, we're usually unable to percieve those
phase correlations above 10 kHz, But a
Dolby Prologic Decoder isn't.

I think a future version of OggEnc which is able
to use a user-selectable stereo mode would be graet.

I think back to the time, where everyone just
realized that the old L3ENC destroyed
phase correlations using intensity stereo and thus
being unable to handle dolby surround effects
correctly.
Most people switched to "Pure"-stereo hoping to get
a better sounding file...

And as a Ogg/Vorbis fan...
i don't want its reputation to be harmed.
;-)

thanks and bye,
Sebastian

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On Tue, Jul 30, 2002 at 04:02:15PM +0200, Sebastian Gesemann
wrote:
> 
> Hi there !
> 
> I checked Vorbis' performace for mono files at
> approx. 64-80 kbps (it does a good job) and I'm 
> wondering why the current OggEnc still uses
> Point-Stereo (>10kHz) for -q4 and -q5
-q4 is currently ~128kbps.  Without point stereo it would be about 180kbps.
> I know, we're usually unable to percieve those
> phase correlations above 10 kHz, But a
> Dolby Prologic Decoder isn't.
Hiding surround encoding in the inadible parts of an audio signal is
so far outside the Vorbis design spec it's hard to know where to
begin.  I'll say this: the whole point of a lossy perceptual encoder
is to lose what you can't hear.
> I think a future version of OggEnc which is able
> to use a user-selectable stereo mode would be graet.
Such a switch will be implemented, promise.

Monty

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