Vorbis dev - Feb 2004 - Stereo mode settings

Hi everyone,

I'd like a bit of information about the stereo mode settings in 
psych_44.h of libvorbis.  Specifically, about the adj_stereo structure:

typedef struct {
  int   pre[PACKETBLOBS];
  int   post[PACKETBLOBS];
  float kHz[PACKETBLOBS];
  float lowpasskHz[PACKETBLOBS];
} adj_stereo;

What I am attempting to do is bring lossless stereo coupling down to the 
lower quality levels in order to test out whether the high frequency 
boost is present (and caused by point stereo).  So I'd like some advice 
on how to set up this adj_stereo for uncoupled stereo, lossless coupled, 
and lossy coupled, etc.

Best regards,

Steve.

<p>
-- 
--------------------------------------------------
Stephen So, BEng(Hons)

PhD Student, 
Signal Processing Laboratory,
School of Microelectronic Engineering,
Faculty of Engineering and Information Technology,
Griffith University, Nathan Campus,
Brisbane, QLD, Australia, 4111.

Phone: +61-7-3875 3754
E-mail: s.so@griffith.edu.au
--------------------------------------------------

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On Tue, 3 Feb 2004, Stephen So wrote:
> What I am attempting to do is bring lossless stereo coupling down to the
> lower quality levels in order to test out whether the high frequency
> boost is present (and caused by point stereo).
my 2 cents:

You could test this effect on monoaural files.
The "HF boost" will still be present.
It's because of heavy quantization. The SNR is *so*
low at high frequencies in low bitrate modes, that the
quantization error increases energy noticably.

Test it yourself:
- generate some random numbers p_i (around -1..1)
- round them to the nearest int q_i:=round(p_i);
- compare the "energy":
  \sum{i} p_i^2
  \sum{i} q_i^2

The bad news:
I don't know how to avoid this in general.

Ghis!
Sebastian
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