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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]

(1995-02-21)


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