Description:
Companding technique commonly used in North America and Japan. U-law is standardized as a 64-kbps CODEC in ITU-T G.711. This is a CCITT-ratified audio encoding and compression technique supported by Windows 95 and Web phones. Among other implementations, u-law was originally intended as a phone-communications standard.
Complete Definition:
The µ-law algorithm (pronounced mew-law) is a companding algorithm, primarily used in the digital telecommunication systems of North America and Japan. As with other companding algorithms, its purpose is to reduce the dynamic range of an audio signal. In the analog domain, this can increase the signal-to-noise ratio (SNR) achieved during transmission, and in the digital domain, it can reduce the quantization error (hence increasing signal to quantization noise ratio). These signal-to-noise ratio (SNR) increases can be traded instead for reduced bandwidth for equivalent SNR.
Both a-law and u-law are companders for the G.711 voice codec
U-law Compander formula (from Cisco's Waveform Coding Techniques)
Also useful is the : ITU website and search on u-law