Efficient codebook search method for ACELP speech codecs

Speech codecs with ACELP structure are widely used due to their high performance for the bit rates between 4 kbps and 16 kbps. In ACELP codecs, the search for the best code vector from a huge codebook is the crucial part in both performance and complexity. In most cases, a non-optimal search method is used in order to reduce the search load with minimal performance degradation. However, its complexity is still the major part of the overall codec complexity. Furthermore, there is no unified method for ACELP codebook search; a rather different method is developed for each ACELP codec. In this paper, a unified framework for the efficient ACELP codebook search method based on the pulse replacement procedure is proposed, and is applied to standard ACELP codecs. It is confirmed that the proposed method provides the same performance as the standard method with much less search load.