OPERATION METHOD OF VOCODER

摘要

PROBLEM TO BE SOLVED: To realize a vocoder and a method of operating such the vocoder, capable of more accurately expressing a fixed code book response of a signal frame (or sub-frame) in the state in which the number of bit positions is limited in a bit frame. SOLUTION: A vocoder 50 has a fixed code book 52 having plural entries of a pulse train to compare a residual signal of a signal frame. The entry of the fixed code book 52 is set according to the signal frame to be encoded. A noise signal is stored in the transmission vocoder 50. During encoding, the noise signal is reshaped by filtering dependent on a decided parameter characterizing the signal frame or the sub-frame. The reshaped noise signal is passed through a threshold filter to obtain the pulse train. A fixed code book response is selected as a part (entry) which is matched best with the residual signal of the signal frame or the sub-frame among the pulse trains.