This paper presents a systematic study of CELP coders at 4. 8 Kbps, where some alternatives and trade-offs between perceptual quality, overall delay, complexity and memory requirements are considered. This study has used the version adopted as a standard by the U. S. D. o. D. (United States Department of Defense) as a reference coder, and compares the results obtained with this version with the ones obtained by using different approaches, namely in terms of overall delay and codebook search procedures. Two post-processing techniques are also studied: envelope post-processing and harmonic post-processing. An adaptive pitch pre-filter is also implemented, with the same rule of the harmonic post-processing, that is to improve the harmonic structure of voiced regions. The large number of options considered in this work reflects the existence of more than one "optimum" solution. The choice of one of them must be dictated by the delay and quality requirements and hardware resources. Keywords: CELP Coding, Post-processing
Bibliographic reference. Ribeiro, C. M. / Trancoso, Isabel M. (1991): "A 4. 8 kbps celp coder with post-processing", In EUROSPEECH-1991, 817-820.