| 摘要 |
A speech signal coding system for coding a speech signal at a bit rate of 8 to 4 kb/s wherein the mount of calculation in fractional search of delays of an adaptive codebook is reduced significantly. Before a fractional delay of the adaptive codebook is found, candidates of integer delay are found by an open-loop using correlation values. A search of a fractional delay by a closed loop is performed for a search range for fractional delays which is provided by samples of each integer delay candidate thus found using the correlation values. The fractional delay search is realized by polyphase filtering of excitation signal in the past. In the search, a plurality of candidates of fractional delay may be found for each integer delay candidate from the adaptive codebook. In this instance, a fractional delay is determined decisively from the decimal delay candidates after a search of a excitation codebook. |
