Sound pitch converting apparatus

A sound pitch converting apparatus for shifting a pitch of sound signal by a predetermined rate comprising:

• first windowing means for dividing said sound signal inputted to said apparatus, into a series of multiple frames including a first frame and a second frame subsequent to the first frame, and for shaping an envelope of head and tail parts of each of the first and second frames into a sine-wave of first 1/2 .pi. period and a cosine-wave of first 1/2 .pi. period respectively and forming a constant level part between said head and tail parts;
• pitch frequency detecting means for detecting a pitch frequency within each of said series of multiple frames outputted from said first windowing means;
• Fourier transform means for transforming said series of multiple frames of the sound signal outputted from said first windowing means, into a frequency domain signal;
• frequency shift means for shifting all frequency components in an output of said Fourier transform means by a desired degree;
• harmonics level control means for controlling levels of harmonics contained in an output of said frequency shift means in response to a detected pitch frequency by said pitch frequency detecting means;
• inverse Fourier transform means for transforming an output of said harmonics level control means into a time domain signal;
• wherein said harmonics level control means operates such that when an output or the pitch frequency detecting means is zero, the levels of harmonics in the output of said frequency shift means are not controlled whereby the output of the frequency shift means is passed to said inverse Fourier transform means, and when the output of the pitch frequency detecting means is present, the levels of harmonics in the output of said frequency shift means are controlled;
• second windowing means for shaping an envelope of head and tail parts of each of the first and second frames included in an output of said inverse Fourier transform means, so that said head part is a sine-wave of first 1/2 .pi. period and said tail part is a cosine-wave of first 1/2 .pi. period and forming a constant level part between said head and tail parts;
• and
• coupling means for coupling said tail part of said first frame with said head part of said second frame so that said tail-and head parts overlap each other.