Digital Signal Processor: Adaptive Differential Pulse-Code-Modulation Coding

Adaptive differential pulse-code-modulation (ADPCM) encoding has been shown to be a simple and effective method for digitally encoding speech at bit rates in the range of approximately 24 to 48 kb/s. 1 " 6 At a rate of 24 kb/s, A D P C M can provide a good quality reproduction of speech that is acceptable for applications such as computer-controlled digital voice response systems. 4 At a rate of 32 kb/s, it can provide essentially a telephone bandwidth "transparent quality" (a quality that is indistinguishable from the original uncoded source) for a single tandem encoding. Adaptive differential pulse-code modulation has been studied for use in some types of transmission systems, 6 and for message storage and retrieval systems in which a reduction by a factor of two in bit rate over that of conventional 64 kb/s i-law companded PCM is desired. 4 Various forms of hardware have been suggested for the implementation of A D P C M coders. Some designs are based primarily on analog hardware 1 3 where parameters Eire pair-wise tuned between transmit1547