MPEG 2 AAC codec

Hi,
I want to know the working of bit alocation block in the AAC codec.
Currently its allocate the bits depending upon the SMR it got from the
phychoaucostic block. But we can also use the perceptual error as one
of the criteria to allocate the bits optimally. In this case we can
improve the quality of audio at the same bitrate.I am working on it
and changing the C code for that. SO can anybody guide me any papers
or document releted to it. C code is also help full.

Regards.

--
RONAK BHALODIA
M. E. COMMUNICATION SYSTEMS,
BITS-PILANI.