Howdy Robert,
Thanks for the quick response.
> > 2) In layer-II coding, the first band to code using
> intensity is specified
> > by the mode extension - in layer-III it can by dynamically
> varied and is
> > understood implicitly from the bitstream by the decoder.
> But the spec gives
> > no suggestions for algorithms on where to begin using
> intensity. (I used a
> > fixed #define.) Does anyone have a reference on this?
> (Exhaustive search
> > is not really an option?)
>
> If I understand the DOCs right, then in IS mode, starting at
> lower frequency bands, the last right channel scalefactor band
> not completely zero marks the last MS or LR coded band.
> All bands
> above are intensity stereo coded, magnitudes in left channel,
> position in right channel. Bands with illegal intensity position
> have to be MS or LR decoded.
Yes, this is how the decoder figures out the break between M/S or L/R and
intensity. But how does the encoder decide where to put the break? Clearly
it is a tradeoff between quality and bit usage. A naive algorithm would
exhaustively try all 13 or 21 possibilities for intensity start bands and
choose the one which had the highest quality/lowest bit usage (reconciling
the two is clearly a problem), but this seems prohibitively computationally
intensive...
I'm wondering if anyone knows of a less naive approach.
Thanks,
Alex
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