MPEG Advanced Audio Coding (AAC), also known as MPEG-2 NBC (Non-Backward Compatible) represents the actual state of the art in natural audio coding.
It is able to handle a lot more channels than MP2 or MP3 (48 full audio channels and 16 low frequency enhancement ones compared to 5 full audio channels and 1 low frequency enhancement one for MP2 or MP3), and it can handle higher sampling frequencies than MP3 (up to 96kHz compared to 48kHz). MPEG formal listening tests have demonstrate that for 2 channels it is able to provide slightly better audio quality at 96 kb/s than layer-3 at 128 kb/s or layer-2 at 192 kb/s.
AAC uses the coding tools already present in MP3, but uses them in a better way:
This first part is mainly a removal of MP3 limitations, as AAC standard doesn't have to preserve compatibility. AAC also introduces some new tools over previous coding schemes:
The MPEG-4 standard adds some new tools in AAC, in order to improve coding quality at low bitrates:
AAC has been selected for use within the Digital Radio Mondial (DRM)
system. Due to its superior performance, AAC should also play a major role for
the delivery of high-quality music via the Internet.
High quality AAC implementations is available for licensing from Fraunhofer-Gesellschaft. An AAC encoder plug-in is available from Ahead.
© 1998-2003 Gabriel Bouvigne for MP3'Tech - www.mp3-tech.org