u-LAW and A-LAW definitions

最新推荐文章于 2023-12-10 18:45:57 发布

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本文介绍u-LAW和A-LAW这两种在电话网络中常用的压缩方案，它们可以将12到14位的线性采样转换为8位的对数比例采样，以便通过64kbit/s的数据通道进行传输。文章还详细解释了这些方案的具体应用以及在全球不同地区的使用情况。

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u-LAW and A-LAW definitions A-law and u-law are companding schemesused in telephone network to get more dynamics to the 8 bit samplesthat is available with linear coding. Typically 12..14 bit samples(linear scale) sampled at 8 kHz sample are companded to 8 bit(logarithmic scale) for transmission over 64 kbit/s data channel.In the receiving end the data is then converter back to linearscale (12..14 bit) and played back. converted back u-law definitionu-LAW (pronounced mu-LAW) is

u-LAW and A-LAW definitions

a-law definition A-LAW is

u-LAW and A-LAW definitions

Values of u=100 and 255, A=87.6, mp is the Peak message value, m isthe current quantised message value. (The formulae get simpler ifyou substitute x for m/mp and sgn(x) for sgn(m); then -1<= x <= 1.) Converting from u-LAW toA-LAW is in a sense "lossy" since there are quantizing errorsintroduced in the conversion. "..the u-LAW used in North Americaand Japan, and the A-LAW used in Europe and the rest of the worldand international routes.." References: Modern Digital and AnalogCommunication Systems, B.P.Lathi., 2nd ed. ISBN 0-03-027933-XTransmission Systems for Communications, Fifth Edition, by Membersof the Technical Staff at Bell Telephone Laboratories, BellTelephone Laboratories, Incorporated, Copyright 1959, 1964, 1970,1982

Read more at: http://www.epanorama.net/documents/telecom/ulaw_alaw.html