METHOD OF TRANSFORMING PERIODIC SIGNAL USING SMOOTHED SPECTROGRAM, METHOD OF TRANSFORMING SOUND USING PHASING COMPONENT AND METHOD OF ANALYZING SIGNAL USING OPTIMUM INTERPOLATION FUNCTION

At a smoothing spectrogram calculation portion, a triangular interpolation function having a frequency width twice that of the fundamental frequency of a signal is obtained based on information on the fundamental frequency of the signal. The interpolation function and a spectrum obtained at an adaptive frequency analysis portion are convoluted in the direction of frequency. Then, using a triangular interpolation function having a time length twice that of a fundamental period, the spectrum interpolated in the frequency direction described above is further interpolated in the temporal direction, in order to produce a smoothed spectrogram having the space between grid points on the time-frequency plane filled with the surface of a bilinear function. Using the smoothed spectrogram, a speech sound is transformed. Therefore, the influence of periodicity in the frequency direction and the temporal direction can be reduced.