1. An excitation vector generator for generating an excitation vector comprising: a pulse vector generator having at least one channel for generating pulse vectors; a storage that stores at least one type of dispersion pattern for each of the at least one channels; a selector that selectively extracts a dispersion pattern from said storage for each of the at least one channels; and a disperser that generates a dispersed vector for every channel by convolution calculation using the extracted dispersion pattern and the generated pulse vectors; and an excitation vector generator that generates an excitation vector from the dispersed vectors generated by the disperser.