G.711 Voice codec standard
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.