A-law

standard The ITU-T standard for nonuniform quantisinglogarithmic 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 quantisingerrors. 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)