A-law


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Related to A-law: Law society, u-Law

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.
References in periodicals archive ?
In the chapter two, A-law quantizer is described and its distortion is presented.
Based on that, we propose a closed-form solution for determination of the support region of semilogarithmic A-law quantizer for Laplacian source for a set of bit-rates 6 bits/sample-10 bits/sample (which corresponds to the set of 64-1024 quantization levels)
Then this model has been compared with standard semilogarithmic A-law companding, in order to show the benefits of its applying.
This paper is organized as follows: A general analysis of non-uniform scalar quantization and A-law companding is given in Section 2.
Also includes 8-bit a-Law and mu-Law Raw PCM files.
* Accepts A-Law, [micro]-Law, 16-bit PCM (Intel), 16-bit PCM (Motorola), MS Wave, G.726 (40 Kbps, 32 Kbps, 24 Kbps, and 16 Kbps), and G.722 (64 Kbps) input data formats
He explained, “Applications Supporting G.722 over TDM: In both A-Law and [micro]-Law PCM (64kbps), 8 bits are required to represent each sample.
Different encoding formats like [micro]-law, A-law, 16 bit, and 13 bit PCM captures are supported (requires VBA038 License) and also it can process V.34 T.38 and SIP/RTP PCAP captures (requires PKV104 License) Win PCAP captures can be processed from T.38 packets alone or as part of a capture file with multiple sip calls."
The files are recorded in mu-law format for tProbe[TM] T1 and in A-law for tProbe[TM] E1.
Kulkarni further added, “The enhancements introduced to Oscilloscope and Power Spectral Display applications include options for displaying all signaling formats - A-Law, Mu-Law, PCM 16 bit, PCM 13 bit, PCM 14 bit, PCM 8 bit and different byte order for INTEL (Little Endian) and MOTOROLA (Big Endian) 16 bit signals sampled at 16 KHz can also be displayed.
The latest version of Smart Audio Converter supports a larger variety of audio formats, now enabling users to convert between WMA, WAV, WAV - PCM, WAV - ADPCM, WAV - IMAADPCM, MP3, MP2, MPEG, OGG Vorbis, VOX, GSM, AC3, MPC, G.72, RAW (A-Law), and RAW (U-Law).