What is AA?

AA is an audio format which is commonly used for downloadable audio books. The thing was created to protect audio files sold by Audible.com. All books in Audible.com are of four protected formats. The first three formats use speech compression at varying levels, and the fourth format is a version of MP3 encoded at a low bit rate. That allows it work better for spoken word than music and all in all is more efficient for downloading in the Web.

Each format is designed to deal with particular sourse audio and listening device that will be use to play back the AA file. Audible makes its own desktop player (called AudibleManager). So AA files can be played on a desktop or transferred to a select group of portable players. Unfortunately, not many portable digital audio players support AA.