G.711

G.711, Pulse code modulation (PCM) of voice frequencies, is a narrowband audio codec originally designed for use in telephony that provides toll-quality audio at a bit rate of 64 kbit/s. It is an ITU-T Recommendation (standard) for audio encoding first issued in December 1972. G.711 passes audio signals in the frequency band of 300–3400 Hz and samples them at the rate of 8000 Hz, within a tolerance of 50 ppm. It uses one of two different logarithmic companding algorithms: μ-law, which is used primarily in North America and Japan, and A-law, which is in use in most other countries outside North America. Each companded sample is quantized to eight bits, resulting in a 64 kbit/s bit rate. G.711 is a required standard in many technologies, such as the H.320 and H.323 standards. It can also be used for fax communication over IP networks (as defined in the T.38 specification). Two enhancements to G.711 have been published: G.711.0 utilizes lossless data compression to reduce bandwidth usage, and G.711.1 increases audio quality by increasing bandwidth usage.