G.711

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Wed, 11/18/2009 - 18:28
Jun 17th, 2009
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Description


G.711 Voice codec standard


Complete  Definition

There are two main compression algorithms defined in the standard, the u-law algorithm  (used in North  America & Japan) and a-law algorithm (used in Europe and the rest of  the world). Both are logarithmic, but  a-law was specifically designed  to be simpler  for a computer to process. The standard also defines a sequence of  repeating  code values which defines the power level of 0 dB.


The u-law and A-law algorithms encode 14-bit and 13-bit signed linear PCM   samples (respectively) to logarithmic 8-bit samples. Thus, the G.711 encoder   will create a 64 kbps bitstream  for a signal sampled at 8 kHz.


G.711, also known as Pulse Code Modulation (PCM), is a very commonly used waveform codec.   G.711 uses a sampling rate of 8,000 samples per second, with the tolerance on   that rate 50 parts per million (ppm). Non-uniform quantization with 8 bits is   used to represent each sample, resulting in a 64 kbit/s bit rate. There are two   slightly different versions; μ-law, which is used primarily in North America,   and a-law,  which is in use in  most other countries outside North America. G.711 u-law tends to  give more resolution to higher  range signals while G.711 a-law provides  more quantization levels at lower signal levels. When using u-law G.711 in  networks where  suppression of the all 0 character signal is required, the  character signal  corresponding to negative input values between decision values  numbers 127 and  128 should be 00000010 and the value at the decoder output is  -7519. The  corresponding decoder output value number is 125.


Wikipedia G.711  Definition


ITU  G.711 Status


Also See


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