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Definition: AIFF

(Audio Interchange File Format) A digital audio file format from Apple. When a music CD is inserted into a Mac, its contents appear as AIFF files using the same specifications as CD music tracks (uncompressed, stereo, PCM, 16-bit, 44.1 kHz). However, AIFF is capable of supporting mono and stereo, 8- and 16-bit samples and rates both higher and lower than the standard CD (see CD-DA).

Modeled after the Interchange File Format (IFF) developed by Electronic Arts, Apple's AIFF breaks apart the file into chunks. The Common chunk holds file parameters such as sampling rate, and the Sound Data chunk contains the digital sound.

Theoretically, the "C" in AIFC and AIFF-C stands for compressed versions of AIFF. However, starting with Mac OS X, music CDs that are ripped to AIFF in iTunes or copied to the Mac desktop are stored in the AIFF-C/sowt format, which is not compressed. The "sowt," which stands for "twos" in reverse, refers to the little endian byte order of the Intel architecture (see byte order). Older Mac applications may not recognize this AIFF format and require conversion.

AIFF and AAC Files
These iTunes examples from the Mac show the contents of the CD in uncompressed AIFF format (top), very close in size to the disc's CD-DA music tracks. The bottom shows the file sizes after the music was ripped to AAC, Apple's featured, compressed format, at a recording rate of 128 Kbps.