A-law algorithm

The A-law algorithm is a companding method used in European eight-bit pulse code modulation systems for digital telephony. Companding means compressing the dynamic range of an analog signal before it is digitized and expanding it again afterwards. Speech covers a very wide range of loudness, which does not suit efficient linear digital encoding, so A-law uses a curve that is linear for small signal values and logarithmic for larger ones, controlled by a compression parameter that is 87.6 in Europe. The result is a better signal-to-distortion ratio than linear encoding gives for the same number of bits. A-law is one of the two companding algorithms in the ITU-T G.711 standard. The other is the similar mu-law, which is used in North America and Japan and gives a slightly larger dynamic range at the cost of worse proportional distortion on small signals. By convention A-law is used on an international connection whenever at least one of the countries involved uses it.