# G.711

**G.711**is an ITU-T standard for audio compression. It is primarily used in telephony.

There are 2 main algorithms defined in the standard, mu-law algorithm (used in America) and a-law algorithm (used in Europe and the rest of the world). Both are logarithmic, but the later a-law was specifically designed to be simpler for a computer to process.

The equations are:

mu-law:

y = ln(1 + ux) / ln(1 + u) with u=255

A-law:

y = Ax / (1 + ln A) for x <= 1/A where A=87.6

y = (1 + ln Ax) / (1 + ln A) for 1/A <= x <= 1

a-law encoding thus takes a 12 or 16 bit audio sample as input and converts it to an 8 bit value as follows:

Linear Input Code |
Compressed Code |

s0000000wxyza... | s000wxyz |

s0000001wxyza... | s001wxyz |

s000001wxyzab... | s010wxyz |

s00001wxyzabc... | s011wxyz |

s0001wxyzabcd... | s100wxyz |

s001wxyzabcde... | s101wxyz |

s01wxyzabcdef... | s110wxyz |

s1wxyzabcdefg... | s111wxyz |

Where s is the sign bit.