[Vorbis] stereo couple

[Balatoni Denes]

Hi!

AIFAIK for a pair of frequency/mdct coefficients the magnitude is the total 
energy, and angle is the "balance" (i.e. distance from center position).
These are somehow quantized and converted to square polar mapping (see 
psychoacustics). 

Compression gain when encoding the coefficients comes from @) the quantization 
A) full stereo is rarely used, rather mono (point sterto) or stereo with a 
limited difference between the two channels (i.e. abs(l-r)<x but abs(l)<2x 
and abs(r)<2x) B) the codebooks used are such that residue coefficients for 
the two channels are always coded as (at most) one codeword, thereby 
exploiting any corellation between the two channel's residue (residue type 2 
is used with vectors of even length).

csütörtök 29 szeptember 2005 14.01-kor fangchao ezeket a bolcs gondolatokat 
fogalmazta meg:
> Dear All:
>     I studied the stereo couple documents and now confused, I wonder
> why it can be done like that, and what is the principle behind that.
> I think i am confused perhaps because i have no background knowledge,
> can you help me out?
> Also, when doing the T/F transform,we used MDCT, so it means no imaginary
> part. And i am much puzzled about the angle in the stereo couple,what does
> it mean? and where does it come from ?
>
> Thank you and looking forward to your letter!
> BEST REGARDS.
>
>
> 　　　　　　　　LISA(^_^)
> 　　　　　　　　fangchao_dlut at sina.com
> 　　　　　　　　　　2005-09-29

bye
Denes

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