Apple has posted an AppleCare Knowledgebase Document that compares the differences in the AAC and MP3 codecs that can be used in iTunes 4.
Yesterday, various discussion boards around the Net featured posts by Windows users who assumed the 128 kbps AAC equalled a 128 kbps MP3 and then denigrated Apple’s new iTunes Music Store accordingly.
Apple says, “AAC-encoded files sound as good as or better than MP3 files encoded at the same or even a higher bit rate. For example, a 128-kilobit-per-second (kbit/s) AAC file should sound as good as or better than a 160 kbit/s MP3 file. Because the bit rate is lower, the AAC file will also be smaller than the MP3 file. AAC files allow you to store the most music on your hard disk or iPod. The High Quality AAC setting creates files that are usually less than 1 MB for each minute of music.”
Link to the document here.