www.mp3tech.org In the programmers' corner you can find links to several papers.
NDTC Speech and Audio Coding Page This page contains a detailed and very well written review article on psycho-acoustics.
Davis Pan has a couple of usefull overviews of MPEG audio encoding:
http://ftp.digital.com/pub/Digital/DECinfo/DTJ/v5n2/Digital_Audio_Compression_01oct1993DTJA03SC.txt
http://www.bok.net/~pan
Here are some papers by Frank Baumgarte:
http://www.tnt.uni-hannover.de/project/coding/audio/perception/publications.html
The paper by Baumgarte, Ferekidis and Fuchs describes an alternative
psycho-acoustic model for MPEG encoding.
Here is a complete (non MPEG) MDCT based audio encoder (MUS420 class
project). The assocated paper gives some good information on audio
encoding.
http://www-ccrma.stanford.edu/~bosse/
Here is some very detailed documentation on a parallel layer II
encoder:
http://www.ece.miami.edu/~fernando/html/thesis/thesis.html
A good paper on mid/side stereo encoding:
Johnston and Ferreira, Sum-Difference Stereo Transform Coding, Proc.
IEEE ICASSP (1992) p 569-571.
A lot in the MPEG2-AAC can also be used in MP3:
Bosi et al. "ISO/IEC MPEG-2 AAC", J. Audio Eng. Soc. 45 (1997) p 789-814.
And the original MPEG1 reference:
Brandenburg & Stoll, "ISO-MPEG-1 Audio: A Generic Standard for
Coding of High-Quality Digital Audio", J. Audio Eng. Soc 42 (1994) p 780-792.
Some original papers on the psycho-acoustics used by MPEG:
Johnston, "Transform Coding of Audio Signals Using Perceptual Noise
Criteria", IEEE J. Selected Areas Communications, (1988).
Brandenburg and Johnston, "Second Generation Perceptual Audio coding:
They Hybrid Coder", AES 89th Convention, 1990.