ABSTRACT
The ITU-T Recommendation that’s become the standard for converting analog toll-quality voice lines into toll-quality digital ones. G.711 is also used extensively in newer forms of IP telephony. G.711 is a Pulse Code Modulation (PCM) scheme operating at a 8 kHz sample rate, with 8 bits per sam ple. Since a signal must be sampled at twice its highest fre quency (as dictated by the Nyquist theorem), G.711 can thus encode frequencies between 0 and 4 kHz. The algorithm allows for the transmission and reception of A-law and u-law voice by converting linear Pulse Code Modulation (PCM) input signals (13 bits for the international A-law standard and 14 bits for u-Law) sampled at an 8 kHz sampling rate into an 8-bit compressed floating-point PCM representation. The actual technique of converting between linear PCM and G.711 PCM is known as “com panding” (compressing/ expanding). The analog-speech waveform, once having been encoded as binary words is then transmitted serially, at dig ital bit rates of 48, 56, or 64 Kbps. ISDN channels and digital phone sets on digital PBXs use G.711. Support for this algorithm is required for ITUT compliant videoconferencing (the H.320 / H.323 standard).
