V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

ATRAC
       Adaptive TRansform Acoustic Coding (Sony, Digital audio, CODEC)


The Free On-line Dictionary of Computing (30 December 2018):

Adaptive TRansform Acoustic Coding
ATRAC

    (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)