An A-law algorithm is a standard

companding In telecommunication and signal processing, companding (occasionally called compansion) is a method of mitigating the detrimental effects of a channel with limited dynamic range. The name is a portmanteau of the words compressing and expanding, ...

algorithm, used in

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an 8-bit PCM

digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals **Digital camera, which captures and stores digital i ...

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systems to optimize, i.e. modify, the

dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of signals, like sound and light. It is measured either as a ratio or as a base- ...

of an

analog signal An analog signal or analogue signal (see spelling differences) is any continuous signal representing some other quantity, i.e., ''analogous'' to another quantity. For example, in an analog audio signal, the instantaneous signal voltage vari ...

for digitizing. It is one of two versions of the G.711 standard from

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, the other version being the similar μ-law, used in North America and Japan. For a given input

x

, the equation for A-law encoding is as follows:

\dfrac, & \dfrac \leq , x, \leq 1, \end

where

A

is the compression parameter. In Europe,

A = 87.6

. A-law expansion is given by the inverse function:

F^(y) = \sgn(y) \begin
    \dfrac, &  , y,  < \dfrac,
    \\
    \dfrac, & \dfrac \leq , y,  < 1.
\end

The reason for this encoding is that the wide

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does not lend itself well to efficient linear digital encoding. A-law encoding effectively reduces the dynamic range of the signal, thereby increasing the coding efficiency and resulting in a signal-to-

distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio s ...

ratio that is superior to that obtained by linear encoding for a given number of bits.

Comparison to μ-law

The

μ-law algorithm The μ-law algorithm (sometimes written mu-law, often approximated as u-law) is a companding algorithm, primarily used in 8-bit PCM digital telecommunication systems in North America and Japan. It is one of two versions of the G.711 stan ...

provides a slightly larger dynamic range than the A-law at the cost of worse proportional distortion for small signals. By convention, A-law is used for an international connection if at least one country uses it.

External links

Waveform Coding Techniques
- Has details of implementation (but note that the A-law equation is incorrect)
A-law implementation in C-language with example code
{{Compression Methods Audio codecs

Comparison to μ-law

See also

External links