A.D.P.C.M Algorithms applied to wideband speech encoding (64 kbit/s, 0-7 kHz)

The application of ADPCM coding technique with adaptive predictors (A.D.P.C.M (V)) and its performances, to transmit 7 kHz bandwith speech signals at 64 kbit/s is presented in this paper. Subjective performances of one ADPCM(V) with two different sets of parameters are evaluated by means of direct comparison tests, with respect to the classic 64 kbit/s P.C.M coder, a 128 kbit/s P.C.M coder and a 64 kbit/s subband coder. The results of the tests show that the ADPCM coding technique can be an efficient mean to transmit wideband speech signals. The quality of the A.D.P.C.M(V) coded speech compares well with that obtained with subbands coding technique. The quality of the transmitted speech, though slightly worse than "high fidelity speech", could be sufficient for communications systems such as audio or video conferencing systems, commentary links for broadcasting.