An Efficient Search Strategy for ACELP Algebraic Codebook by Means of Reduced Candidate Mechanism and Iteration-Free Pulse Replacement

  • C. -P. Chu National Chin-Yi University of Technology
  • C. -Y. Yeh National Chin-Yi University of Technology
  • S. -H Hwang National Chin-Yi University of Technology
Keywords: speech codec, algebraic codebook search, reduced candidate mechanism (RCM), iteration-free pulse replacement


This work aims to present a combined version of reduced candidate mechanism (RCM) and iteration-free pulse replacement (IFPR) as a novel and efficient way to enhance the performance of algebraic codebook search in an algebraic code-excited linear-prediction (ACELP) speech coder. As the first step, individual pulse contribution in each track is given by RCM, and the number N of candidate pulses is then specified. Subsequently, the replacement of a pulse is performed through the search over the sorted top N pulses by IFPR, and those of 2 to 4 pulses are carried out by a standard IFPR. Implemented on a G.729A speech codec, this proposal requires as few as 24 searches, a search load tantamount to 7.5% of G.729A, 37.5% of the global pulse replacement method (iteration=2), 50% of IFPR, but still provides a comparable speech quality in any case. The aim of significant search performance improvement is hence achieved in this work.