.AAC File Extension

Compressed audio file similar to an .MP3 file, but offers several performance improvements; examples include a higher coding efficiency for both stationary and transient signals, a simpler filterbank, and better handling of frequencies above 16 kHz; maintains quality nearly indistinguishable from the original audio source.

Advanced Audio Coding (AAC) is the default encoding used by Apple iTunes and the iTunes Music Store.

NOTE: While the ".aac" extension is sometimes used for AAC-encoded files, they are typically saved with an .M4A file extension.