Method and apparatus to search fixed codebook using tracks of a trellis structure with each track being a union of tracks of an algebraic codebook

A method and apparatus to search a codebook including pulses that model a predetermined component of a speech signal. The method includes the operations of selecting a predetermined number of paths corresponding to a predetermined number of pulse locations that are most consistent with the predetermined component, from among paths corresponding to pulse locations of a predetermined pulse location set allocated to at least one branch that connects one state of a predetermined Trellis structure to another state, performing the path selecting operation on each of states other than the one state, and selecting a path corresponding to pulse locations that are most consistent with the predetermined component, from among paths including the selected paths, wherein each path corresponds to a union of plural tracks of an Algebraic codebook. Accordingly, the number of calculations required during a codebook search is reduced.