dont get fooled by the low bitrate, its not MP3, its HE-AAC. you cant compare it to any mp3 bitrate.
as you can see, in in listening tests the quality is very close to the uncrompressed original.
source:
http://tech.ebu.ch/docs/techreview/trev_305-moser.pdf
see also:
http://en.wikipedia.org/wiki/High-Ef...d_Audio_Coding