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

digital audio

    A sequence of discrete samples taken
   from a continuous sound (audio) waveform.  Tens of thousands
   of samples are taken each second.  Each sample represents the
   intensity of the sound pressure wave at that instant.  Apart
   from the sampling frequency, the other parameter is the
   digital encoding of each sample including the number of bits
   used.  The encoding may be linear, logarithmic or mu-law.

   Digital audio is typically created by taking 16-bit samples
   over a spectrum of 44.1 thousand cycles per second (kHz), this
   means that CD quality sound requires 1.4 million bits of data
   per second.  Digital telephone systems use lower sample rates.

   Filename extension: .au (Unix), .snd (MS-DOS, MS
   Windows).

   See also Audio IFF, MP3, wav.

   Usenet newsgroups: alt.binaries.sounds.*.

   A FAQ on audio file formats is available.  Part 1
   (ftp://ftp.cwi.nl/pub/audio/AudioFormats.part1), Part 2
   (ftp://ftp.cwi.nl/pub/audio/AudioFormats.part2).

   (1999-07-30)