Pitch extraction apparatus for an acoustic signal waveform

DETAILED DESCRIPTION In order to achieve the first object, a pitch extraction apparatus according to a first aspect of the present invention comprises pitch extraction means for extracting a pitch of an acoustic signal waveform, means for calculating, on the basis of the acoustic signal waveform, stability which exhibits a larger value as an amplitude of the waveform which is larger and a frequency of the waveform which is lower, and multiplying means for calculating a product of the stability and the acoustic signal.
The pitch extraction means performs pitch extraction on the basis of a product signal output from the multiplying means.
In order to achieve the second object, a pitch extraction apparatus according to a second aspect of the present invention comprises pitch extraction means for extracting a pitch of an acoustic signal waveform, means for calculating, on the basis of the acoustic signal waveform, stability which exhibits a larger value as an amplitude of the waveform is larger and a frequency of the waveform is lower, and control means for, when the pitch extracted by the pitch extraction means abruptly changes and the stability is low, controlling to stop pitch output.
In order to achieve the third object, a pitch extraction apparatus according to a third aspect of the present invention comprises pitch extraction means for extracting a pitch of an acoustic signal waveform, noise level discrimination means for comparing the input acoustic signal waveform with a predetermined noise level to discriminate whether or not the input waveform is a voiceless sound, and gate means, arranged at an input or output side of the pitch extraction means, for, when the noise level discrimination means determines that a input waveform is the voiceless sound, inhibiting an input to or an output from the pitch extraction means.