Patent ID: 7490035

Claim:
A pitch shifting method, comprising: a step of transforming input time domain representation sound data into frequency domain representation sound data; a step of generating pitch-shifted sound data by compressing or expanding amplitude spectra of the transformed frequency domain representation sound data on a frequency axis; a step of transforming the pitch-shifted sound data from the frequency domain representation sound data into time domain representation sound data; and a step of outputting the transformed time domain representation sound data; wherein the step of generating pitch-shifted sound data, including, a step of selecting, among the amplitude spectra of the transformed frequency domain representation sound data, at least two peak spectra that are a first peak spectrum and a second peak spectrum having a second frequency higher than a first frequency which is a frequency for the first peak spectrum; a step of shifting the first peak spectrum on the frequency axis so that the first peak spectrum becomes an amplitude spectrum for a pitch-shifted first frequency which is a frequency obtained by multiplying the first frequency by a given pitch shift ratio k; a step of compressing or expanding, on the frequency axis, each of amplitude spectra in a first frequency region which is a given frequency region including the first frequency so that each of the amplitude spectra in the first frequency region becomes an amplitude spectrum for a frequency obtained by adding a value which is obtained by multiplying a result of subtraction of the first frequency from a frequency for the each amplitude spectrum by a local shift ratio m closer to 1 than the pitch shift ratio k, to the pitch-shifted first frequency; a step of shifting the second peak spectrum on the frequency axis so that the second peak spectrum becomes an amplitude spectrum for a pitch-shifted second frequency which is a frequency obtained by multiplying the second frequency by the given pitch shift ratio k; a step of compressing or expanding, on the frequency axis, each of amplitude spectra in a second frequency region which is a given frequency region including the second frequency so that each of the amplitude spectra in the second frequency region becomes an amplitude spectrum for a frequency obtained by adding a value which is obtained by multiplying a result of subtraction of the second frequency from a frequency for the each amplitude spectrum by the local shift ratio m, to the pitch-shifted second frequency; and a step of compressing or expanding, on the frequency axis, each of amplitude spectra in an intermediate frequency region between the first frequency region and the second frequency region so that each of the amplitude spectra in the intermediate frequency region becomes an amplitude spectrum for a frequency obtained by multiplying a frequency for the each amplitude spectrum by each pitch shift ratio depending on the each amplitude spectrum.