Apple's latest deal with U.K.-based major record label EMI
means that starting in May, much of EMI's famous catalog of music will be available not only in iTunes' standard, DRM-protected
AAC format of compression that's set at 128Kbps, but additionally, the catalog will be available as unprotected files compressed using AAC set at a higher-quality 256Kbps. People are excited about this because unprotected--or DRM-free--
songs can be played in a wide range of devices and because the higher-
quality compression, if properly done, should deliver nearly CD-quality sound.
Understanding how this will affect sound quality means understanding a little about how data compression works. As it relates to audio, the term Kbps
(kilobits per second) is used to show how many pieces of digital information (bits) are used every second to describe what you're hearing. A song encoded at 1Kbps uses 1,000 bits per second to digitally approximate the original recording. The more bits used to describe a piece of music, the better job it can do at accurately interpreting the original sound. Encoding music at EMI's proposed 256Kbps instead of 128Kbps effectively doubles the resolution of the final product. How well you'll be able to hear the difference depends on many things: the quality of your playback device and your headphones or speakers, as well as the level of background noise and the quality of the original recording.
For more information on digital audio quality and file formats, check out CNET's MP3 player buying guide
as well as News.com's article on the EMI-Apple partnership