Codebook Based Digital Speech Compression

Abstract

Speech compression has been an area of interest for many researchers, and their objectives remained to reduce the bit rates, also to maintain the speech quality. Adaptive Differential Pulse Code Modulation (ADPCM) was first such scheme that evolved out of PCM and in low bit rate source coding techniques; Code Excited Linear Prediction (CELP) was adopted as standard in the Department of Defense (DoD), USA. In this research a novel approach is developed and compression up to 50% is achieved with negligible loss of quality. This coding technique is developed to use a PCM coded speech, initially, and then substituting 3 to 5 Least Significant Bits (LSB) of every byte at the decoding end from a fixed codebook, randomly.