A-law

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A-law

(standard)
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]

A-Law

An ITU standard for converting analog data into digital form using pulse code modulation (PCM). A-Law uses a companding technique that provides more quantizing steps at lower amplitude (volume) than at higher amplitude. Europe uses A-Law, while North America and Japan use mu-Law (µ-Law). See PCM and mu-Law.