The MPEG-4 Standard defines maybe one of best audio formats available at the moment: AAC (Advanced Audio Coding)
AAC is able to include 48 full-bandwidth (up to 96 kHz) audio channels in one stream plus 15 low frequency enhancement (LFE, limited to 120 Hz) channels, up to 15 data streams and much more
AAC Profiles
Like with MPEG-4 Video, AAC comes in different Profiles, from which the Low Complexity (LC AAC) Profile is the one most widely used in the consumer market (for example in Apple's very popular iTunes music store)
other profiles are for example the MAIN Profile, Long Term Prediction (LTP), Scalable Sampling Rate (SSR) or Low Delay (LD)
quality comparison of LC AAC with other good formats @ 128kbps (thanks to rjamorim):
note that lame (the best mp3 codec available) provides far less quality than the others at the same bitrate
also note that the wma codec used in this test is wma9 pro, which is a totally different and better quality providing codec than the standard wma9 codec (which is the one used in music stores and cd players) and to which its not backwards compatible
when it comes to low bitrates and multichannel encoding AAC offers the High Efficiency extension (HE AAC), making it one of the best formats in the low bitrate range too:
quality comparison of HE AAC with other popular formats @ 64kbps (thanks to rjamorim):
note that QT is the LC AAC codec offered in Quicktime, He is the HE AAC codec offered in Nero
available AAC Codecs
AAC codecs are available atm from Quicktime/iTunes, Nero, FAAC (binary), Psytel, Compaact!, Winamp5, Real and Sorenson
rjamorim's quality comparisons: 1 2
further documentation
If you want to read more about the AAC Audio Format have a look at the AAC FAQ in the Audio Encoding forum or at the audiocoding.com wiki
A FAQ especially about MPEG-4 Audio is available from the Motion Picture Experts Group (MPEG)
Drafts of the MPEG-4 AAC Specs can be downloaded here, here and here
__________________
Between the weak and the strong one it is the freedom which oppresses and the law that liberates (Jean Jacques Rousseau)
I know, that I know nothing (Socrates)
Last edited by bond on 31st May 2004 at 20:05
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