Overview of CCITT embedded ADPCM algorithms

G.EMB is a draft CCITT recommendation for embedded ADPCM (adaptive differential pulse code modulation) encoding with five, four, three, and two core bits. The main properties of the algorithms of G.EMB are reviewed, and their performance for speech traffic is discussed. The embedded ADPCM algorithms allow the dropping of up to three least-significant bits to relieve congestion at any point between the transmitter and the receiver without the need to inform the receiving end. This bit dropping does not cause decoder divergence. Test results indicate that a mid-rise quantizer provides better voice transmission performance than its mid-tread counterpart when two bits are used in the feedback path. Subjective data show that the 40 kb/s mid-rise ADPCM algorithm with two feedback bits performs just as well as 64 kb/s PCM for up to four tandem encodings. G.EMB embedded algorithms are thus suitable for congestion control in multipoint and multinode network configurations