ABSTRACT -- This paper presents speech coding by Adaptive Differential Pulse Code Modulation (ADPCM) by using the dual autocorrelation to predict the signal. Generally, the autocorrelation of adjacent speech sample is greater than the autocorrelation of several order time delayed samples. So, the prediction of present sample by using the one past and next sample is more effective than only using the several order time delayed past samples. This prediction method is used in ADPCM encoding and the result compares with the standard ADPCM encoding.

KEYWORDS -- ADPCM , Dual autocorrelation