G.726 Vocoder

GAO’s G.726 vocoder converts a 64 Kbps A-law or μ-law PCM channel to or from a 40, 32, 24 or 16 Kbps channel. The conversion is applied to the PCM bit stream using an ADPCM transcoding technique. Thus, the scheme has switchable transmission rates providing 4 kHz of audio bandwidth in conformance with the ITU-T standard. It is used in numerous applications such as speech transmission over digital networks, video conferencing, multimedia, and ISDN communications.

ITU-T G.726 is a superset of the ITU-T G.721 and G.723 standards and was originally designed as a half-rate alternative to G.711 audio companding. G.726 can encode 13 or 14-bit PCM samples or 8-bit, A-law or μlaw encoded data into 2, 3, 4, or 5-bit code words. Since the algorithm encodes one sample at a time, the coding or decoding delay is effectively zero, providing for robust, quality audio.