摘要:
For use in deciding optimum pole and zero parameters for an input signal with reference to an input cepstrum of the signal, candidate pole and zero parameters are stored in advance in a table. Supplied with an impulse and controlled by a candidate set pair of a pole parameter set and a zero parameter set selected from the candidate pole and zero parameters of the table, first and second filters produce first and second outputs defined by terms of up to a certain order. Responsive to the first and second outputs and to factors of multiplication which are given by inverse numbers of time intervals related to the respective terms, an analysis filter produces a converted signal which is equivalent to a model output cepstrum of a model output signal produced by a pole-zero model defined by the candidate set pair. A cepstrum subtracter calculates a cepstrum difference between the input cepstrum and the converted signal. In connection with a few candidate set pairs, cepstrum differences and then squares of the respective cepstrum differences are calculated to decide the optimum pole and zero parameters by a focussing technique. Alternatively, a square of the cepstrum difference is used together with partial derivatives of the square to decide the optimum pole and zero parameters.