A CD player is an electronic device that plays audio compact discs. CD players are often a part of home stereo systems, car audio systems, and personal computers. They are also manufactured as portable devices. Modern units can play other formats in addition to PCM audio coding used in CDs, such as MP3, AAC and WMA. DJs often use players with an adjustable playback speed to alter the pitch and tempo of the music. CD playback functionality is also available on CD-ROM/DVD-ROM drive equipped computers as well as on DVD players and CD-ROM/DVD-ROM based game consoles. Multi-channel surround sound recordings have been available for years but their acceptance in the indusry seems to be diminishing.