 Alaw algorithm

An Alaw algorithm is a standard companding algorithm, used in European digital communications systems to optimize, i.e., modify, the dynamic range of an analog signal for digitizing.
It is similar to the μlaw algorithm used in North America and Japan.
For a given input x, the equation for Alaw encoding is as follows,
where A is the compression parameter. In Europe, A = 87.7; the value 87.6 is also used.
Alaw expansion is given by the inverse function,
The reason for this encoding is that the wide dynamic range of speech does not lend itself well to efficient linear digital encoding. Alaw encoding effectively reduces the dynamic range of the signal, thereby increasing the coding efficiency and resulting in a signaltodistortion ratio that is superior to that obtained by linear encoding for a given number of bits.
Comparison to μlaw
The μlaw algorithm provides a slightly larger dynamic range than the Alaw at the cost of worse proportional distortion for small signals. By convention, Alaw is used for an international connection if at least one country uses it.
See also
 μlaw algorithm
 Audio level compression
 Signal compression
 Companding
 G.711
 DS0
External links
 Waveform Coding Techniques  Has details of implementation (but note that the Alaw equation is incorrect)
 ALaw and μlaw Companding Implementations Using the TMS320C54x (PDF)
 Alaw and μlaw realisation (in C)
Data compression methods Information theory Lossless Shannon–Fano · Shannon–Fano–Elias · Huffman · Adaptive Huffman · Arithmetic · Range · Golomb · Universal (Gamma · ExpGolomb · Fibonacci · Levenshtein)RLE · Byte pair encoding · DEFLATE · Lempel–Ziv (LZ77/78 · LZSS · LZW · LZWL · LZO · LZMA · LZX · LZRW · LZJB · LZS · LZT · ROLZ) · Statistical Lempel ZivOthersAudio Audio codec partsLPC (LAR · LSP) · WLPC · CELP · ACELP · Alaw · μlaw · ADPCM · DPCM · MDCT · Fourier transform · Psychoacoustic modelOthersImage TermsMethodsOthersVideo TermsVideo characteristics · Frame · Frame rate · Interlace · Frame types · Video quality · Video resolutionOthersSee Compression formats for formats and Compression software implementations for codecs Categories: Audio codecs
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