A 9 kb/s CAPDM speech coder based on pitch synchronous substitution for wireless PCN applications

Abstract

This paper describes a low data rate speech coder, which is based on CAPDM (Controlled Adaptive Prediction Delta Modulation) algorithm [2] and operates at about 9 kb/s. It combines the features of one-step looking forward decision, syllabic companding, instantaneous companding, pitch detection, and adaptive prediction. A packet-based CAPDM speech coder for PCN applications, which operates at 16 kb/s, was presented previously and showed near toll quality performance [3]. In this paper, the data rate of CAPDM is further reduced by exploiting the quasi-periodic property of speech vowel waveform and by dropping speech samples every other pitch period. The dropped speech samples are recovered at receiver by duplicating the decoded speech samples according to the pitch periods. The MOS listening test results of the 9 kb/s CAPDM coder are compared with those of the 16 kb/s continuous variable slope delta modulation (CVSD), 16 kb/s CAPDM, and 32 kb/s ADPCM.