::
:: Also, does anyone know the basis for the ISO switching criterion? Do they
:: really mean square energy (quadrupled magnitude)? They give no hints as to
:: how to reconcile the mid/side samples with the right/left psychoacoustics in
:: the loop section of the encoder. Computing psychoacoustics for the sum and
:: difference signals makes no sense to me, as one is never going to listen to
:: them and thus the psychoacoustic threshold figures are irrelevant, but the
:: alternative of trying to simultaneously allocate bit/noise for both channels
:: seems overly complicated/possibly impossible (oxymoron strikes!). I'm
:: compromising right now by just calculating the distortion thresholds using
:: the L/R SMR and the M/S signal and bandwidths (and the loop distortions with
:: the M/S signal), but this seems like a pretty silly way to do things, and it
:: doesn't sound very good. I'm trying not to plagiarize LAME (I still use the
:: ISO/ATT psych model, for one), but I gather that LAME does some sort of
:: mid/side psychoacoustic processing?
::
1st step:
- Calculate diffuse field corrected ear-drum SPL°):
L' = a(w) L + b(w) R, R' = a(w) R + b(w) L w is a small omega, a(w),b(w)
complex
Note: different for loudspeakers and head phones
(where a \approx 1 and b \approx 0)
Note: search for HRTF to get usable approaches for a and b.
Note: for very good results you must take into consideration that a and
b changes depending on the temporal direct/indirect sound ratio
- ignore in-brain talk over (ca. -60 dB @1 kHz, much lower than accoustic talk over)
- calculate threshold for the left and the right ear
2nd step:
if frame can be coded in LR mode
- code L using L and threshold(L)
- code R using R and threshold(R)
if frame can be coded in MS mode
- code M using M and 0.6...0.8 * min(threshold(L),threshold(R))
- code S using S, decoded coded M, threshold(L) and threshold(R)
3rd step:
select MS/LR depending on:
- br(MS)/br(LR) ratio
- the past of the audio file
- bit pool fuel
- (the future of the audio file using one mechanism I mailed before)
- user options?
--
Mit freundlichen Grüßen
Frank Klemm
°) SPL = Sound preasure level
eMail | [EMAIL PROTECTED] home: [EMAIL PROTECTED]
phone | +49 (3641) 64-2721 home: +49 (3641) 390545
sMail | R.-Breitscheid-Str. 43, 07747 Jena, Germany
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