Source : Free On-Line Dictionary of Computing

Adaptive TRansform Acoustic Coding
     
         (ATRAC) An audio compression {algorithm},
        introduced by {Sony} for its {Mini Disk}, which relies on the
        masking of low-amplitude frequency components by temporaly
        adjacent high-amplitude components.  ATRAC consists of a
        three-band {subband encoder} (0...5.5, 5.5...11, 11...22 kHz)
        and a {MDCT} based transformation encoder.
     
        [Does Sony Minidisk use {ADPCM}?]
     
        (2001-12-13)