PURPOSE: To curtail the arithmetic quantity without deteriorating the estimation accuracy of a pitch period by executing a thinning-out retrieval at intervals within a pitch period retrieval range in a first time, and subsequently, executing the retrieval within an adjacent prescribed sample range centering around a value of the pitch period in which error electric power is minimized in that which is retrieved in a first time.
CONSTITUTION: First of all, in a first retrieval, in a pitch period portion delay of a prescribed sample piece number N being a retrieval range of a memory 1, with regard to each pitch period at prescribed M (M<N) sample intervals, error electric power between a signal obtained by reproducing the respective past prediction residual signals by a reproducing filter 2 and an input sound signal is calculated by an arithmetic part 3, and a pitch period for minimizing this error electric power is searched by a search part 4. At the time of a retrieving secondly, centering around the pitch period for minimizing the error electric power derived in a first retrieval, with regard to adjacent prescribed sample portions before and after it, a retrieval of each pitch period is executed, and in the end, an optimum pitch period is determined. In such a way, the arithmetic quantity required for the retrieval can be curtailed without deteriorating the estimation accuracy of the pitch period.
TANIGUCHI TOMOHIKO
SASAMA AKIRA
OTA TAKASHI
AMANO FUMIO
UMIGAMI SHIGEYUKI
