J. Turner, D. C. Stevenson, P. Kabal, and P. Mermelstein
"A Comparative Study of Digital Coding Techniques at 16 kb/s and Below", IEEE Canadian Commun., Power Conf. (Montreal, QC), 4 pp., Oct. 1980.
Four recently-developed coding techniques are surveyed: Adaptive Predictive Coding (APC), Adaptive Transform Coding (ATC), Residual-Excited Linear Predictive Coding (RELP) and Sub-band Coding (SBC). These techniques have the common property of trying to minimize the perceived distortion by exploiting characteristics of both the speech signal and the listener. APC and ATC use adaptive techniques to track the short-time statistics of the input speech. At 16 kb/s, the reconstructed speech quality from these coders approaches that of telephone toll standards (56 kb/s companded PCM). Sub-band coding allows the quantization noise in each of several frequency bands to follow the short-time speech energy. Residual-excited Linear Predictive Coding transmits only a low frequency base-band and uses that component to regenerate the higher speech frequencies. Both RELP and SBC produce speech whose quality is acceptable for many communications applications at 9.6 kb/s. The results of subjective preference testing of these coders are presented and their relative complexities are discussed.