Excitation codebook search method in a speech coding system

Abstract

A method for searching an excitation (or fixed) codebook in a speech coding system. In a speech coding system including a synthesis filter for synthesizing a speech signal, a fixed codebook searcher according to the present invention segments a speech signal frame into a plurality of subframes to generate an excitation signal to be used in a synthesis filter, segments again each of the subframes into a plurality of subgroups, and searches the respective subframes each comprised of a plurality of pulse position/amplitude combinations for pulses. The fixed codebook searcher searches the respective subgroups for a predetermine number of pulses having non-zero amplitude, and generates the searched pulses as an initial vector. Next, the fixed codebook searcher selects a pulse combination including at least one pulse among the pulses of the initial vector, and then substitutes pulses of the selected pulse combination for pulses in other positions in the subgroups. The selection and the substitution are repeatedly performed on all the pulses of the initial vector.

1 . A method for segmenting a speech signal frame into a plurality of subframes to generate an excitation signal to be used in a synthesis filter, segmenting each of the plurality of subframes into a plurality of subgroups, and searching the respective subframes, each comprised of a plurality of pulse position/amplitude combinations for pulses in a speech coding system including the synthesis filter for synthesizing a speech signal, comprising the steps of: 
 searching the respective subgroups for a predetermined number of pulses having non-zero amplitudes, and generating the searched pulses as an initial vector;    selecting a pulse combination including at least one pulse from among the searched pulses of the initial vector; and    substituting pulses of the selected pulse combination for pulses in other positions in the subgroups;    wherein the selecting step and the substituting step are-repeatedly performed on all the pulses of the initial vector, and the pulses in the other positions are adapted to minimize an error between original speech and synthetic speech synthesized by the synthesis filter when the pulses of the selected pulse combination are substituted for the pulses in the other positions.    
   
   
       2 . The method as claimed in  claim 1 , further comprising the step of substituting amplitudes of the pulses of the selected pulse combination of amplitudes of the pulses in other positions in the subgroups.