| 摘要 |
PROBLEM TO BE SOLVED: To reduce noise without distorting a voice signal by independently controlling the parts different in a frequency spectrum. SOLUTION: An impulse response of an LPC filter 10 is converted into a frequency area by a high speed Fourier transform (FFT) function 11 to obtain single approximation of a spectrum envelope of a voice signal. A formant discriminating function 12 discriminates maximum and minimum positions of a vector envelope respectively corresponding to a trough of a formant and a spectrum by finding out a first differential coefficient on a spectrum bin to respective output points of the FFT function 11. The formant discriminating function delivers a position of the discriminated formant to a spectrum envelope correcting function 13. The correcting function 13 calculates a frequency response of a back-end filter by normalizing respective points of the spectrum envelope on amplitude of the closest formant.
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