MP3

• MP3, which is short for Moving Picture Experts Group (MPEG), audio layer 3, is one of the most popular digital music file formats as of 2011. "Layer 3" refers to a specific type of compression technology, which uses psychoacoustic compression and perceptual audio coding to remove the irrelevant and redundant parts of sound signals that human ears are unable to recognize. Layer 3 compression also incorporates Modified Discrete Cosine Transform (MDCT) technology for shrinking sound data without reducing sound quality. Specifically, the iPod shuffle can support MP3 files with bit rates of up to 320 thousand bits per second (Kbps). Higher bit rates correlate to superior sound quality, and 320 Kbps is one of the highest MP3 bit rates available. The iPod shuffle also supports variable bit rate (VBR) MP3 files. These files automatically encode sound signals based on their complexity, assigning lower bit rates to less-complex sounds and higher bit rates to more-complex sounds.
  
  

AAC

• Advanced Audio Coding (AAC) files can rely on the MPEG, audio layer 2 or audio layer 4 standards for digital audio compression. According to Webopedia, AAC files allow for higher audio quality in comparison to MP3 files, while also requiring 30-percent less data. Specifically, the iPod shuffle is compatible with three file extensions of the AAC file format: M4A, M4B and M4P. M4A is the most basic type of AAC file that utilizes MPEG audio layer 4 compression. M4B is different from M4A in that it supports bookmarking, which means the iPod shuffle can return to the point it leaves off at when playing an M4B file. For this reason, M4B files are popular for podcasts and audiobooks. M4P is the same is as M4A, only that it has digital rights management (DRM) protection; Apple used DRM protection on songs sold through the iTunes Store until early 2009. As of the date of publication, the iPod shuffle can support all three AAC file extensions with bit rates of up to 320 Kbps.
  
  

WAV

• Also known as WAVE, the Waveform Audio File Format (WAV) stores audio data in bit-streams or chunks of data. WAV files store these chunks of data using the Resource Interchange File Format (RIFF) architecture. IBM and Microsoft jointly developed the WAV file format for storing audio data on PCs; however, the iPod shuffle is also compatible with it. Unlike MP3 and AAF files, WAV files do not compress audio data, which means that WAV files generally take up more storage space.
  
  

AA

• AA is a proprietary, spoken word audio file that Audible.com established for allowing users to download audio files from its website. The iPod shuffle is compatible with three formats of AA files: Format 2, which has a bit rate of 8 Kbps and is the sound quality-equivalent of an AM radio, Format 3, which has a bit rate of 16 Kbps and is the sound quality-equivalent of an FM radio and Format 4, which has a bit rate of 32 Kbps and is the sound quality equivalent of an MP3 file.