资料来源 : Free On-Line Dictionary of Computing

A-law
     
         The {ITU-T} {standard} for {nonuniform quantising
        logarithmic compression}.
     
        The equation for A-law is
     
              |    A
              | ------- (m/mp)                   |m/mp| =< 1/A
              | 1+ln A
          y = |
              | sgn(m)
              | ------ (1 + ln A|m/mp|)   1/A =< |m/mp| =< 1
              | 1+ln A
     
        Values of u=100 and 255, A=87.6, mp is the Peak message value,
        m is the current quantised message value.  (The formulae get
        simpler if you substitute x for m/mp and sgn(x) for sgn(m);
        then -1 <= x <= 1.)
     
        Converting from {u-LAW} to A-LAW introduces {quantising
        errors}.  u-law is used in North America and Japan, and A-law
        is used in Europe and the rest of the world and international
        routes.
     
        [The Audio File Formats FAQ]
     
        (1995-02-21)