Source : Free On-Line Dictionary of Computing

A3D
     
         (Aureal 3-Dimensional?) A technology developed by
        {Aureal} that delivers sound with a three-dimensional effect
        through two speakers.  Many modern {sound cards} and PC games
        now support this feature.
     
        A3D differs from the various forms of {surround sound} in that
        it only requires two speakers, while surround sound typically
        requires four or five.  It is sometimes less convincing than
        surround sound but is supposedly better in {interactive}
        environments.  For example, PC games in which sounds often
        move from one speaker to another favour A3D, while
        pre-recorded video favours surround sound.
     
        {Home (http://www.a3d.com/)}.
     
        (1999-01-26)