Now I am studying FAAC 1.24 source code.But I am puzzled by
the algorithms of CalcAllowedDist(), FixNoise() and
BalanceEnergy() in aacquant.c.
They are totally different from their conterparts in ISO standard.

Then could anyone please show me the rationale underlying these
functions ? Or you can just give me reference papers' name or related
links.

Thanks in advance.

AFAIK they are from knik (FAAC developer), and indeed they dont correspond to anything in the AAC spec.

I'd also be interested if someone figures them out completely. It's not at all obvious.