The site says: FAAC is a MPEG4 GA (General Audio) encoder, that supports only the LOW and MAIN profile. Which are derived from MPEG2-AAC, adding some functionalities to further improve the bitrate efficiency (LTP and PNS).

http://sourceforge.net/projects/faac/

Here Fraunhofer IIS institute provides description of it`s AAC related technologies.

http://www.iis.fraunhofer.de/EN/bf/amm/projects/mpeg/index.jsp