What additional encoding strategies does AAC use that make it technically (not necessarily implementation/compatibility) superior to mp3? I always here this as a reason for why AAC is marginally better, but what exactly are these additional encoding techniques?

Can someone point me to a technical document/site that explains this?

There are several limitations inherent to the MP3 format that cannot be overcome by using a better encoder.

Newer audio compression formats such as Vorbis and AAC no longer have these limitations.

In technical terms, MP3 is limited in the following ways:
Bitrate is limited to a maximum of 320 kibit/s
Time resolution can be too low for highly transient signals
No scale factor band for frequencies above 15.5/15.8 kHz
Joint stereo is done on a frame-to-frame basis
Encoder/decoder overall delay is not defined, which means lack of official provision for gapless playback; gaps may be introduced between tracks, although this can be avoided to a degree by using LAME to encode.

Nevertheless, a well-tuned MP3 encoder can perform competitively even with these restrictions. [wikipedia]

These are some of the more interesting ones from a technical perspective.

PNS - Perceptual Noise Substitution
TNS - Temporary Noise Shaping
SBR - Spectral Band Replication
LTP - long Term Prediction

http://www.audiocoding.com/modules/wiki/?p...+Technical+Info here you go. Have a field day . The scale factor band 21 issue has always pissed me off with MP3 though. If something was encoded with LAME, however I wouldn't be as bitter about it.

http://www.mp3-tech.org/content/?Mp3%20Limitations

SBR can be applied to MP3 too (MP3Pro) and LTP is never used. So these don't count.