Patent ID: 7957958

Claim:
A pitch period equalizing apparatus that equalizes a pitch period of voiced sound of an input speech signal, comprising: pitch detecting means that detects a pitch frequency of the speech signal; residual calculating means that calculates a residual frequency, as the difference obtained by subtracting a predetermined reference frequency from the pitch frequency; and a frequency shifter that equalizes the pitch period of the speech signal by shifting the pitch frequency of the speech signal in a direction for being close to the reference frequency on the basis of the residual frequency, wherein the frequency shifter comprises: modulating means that modulates an amplitude of the input signal by a predetermined modulating wave and generates the modulated wave; a band-pass filter that allows only a signal having a single side band component of the modulated wave to selectively pass through; demodulating means that demodulates the modulated wave subjected to the filtering of the band-pass filter by a predetermined demodulating wave and outputs the demodulated wave as an output speech signal; and frequency adjusting means that sets, as a predetermined basic carrier frequency, one of a frequency of the modulating wave used for modulation of the modulating means and a frequency of the demodulating wave used for demodulation of the demodulating means, and sets the other frequency to a frequency obtained by subtracting the residual frequency from the basic carrier frequency.