Patent ID: 8694311

Claim:
A sound quality improvement method for a noisy speech signal, comprising the steps of: estimating a noise signal of an input noisy speech signal by performing a predetermined noise estimation procedure for the noisy speech signal; measuring a relative magnitude difference to represent a relative difference between the noisy speech signal and the estimated noise signal; calculating a modified overweighting gain function with a non-linear structure in which a higher gain is allocated to a low-frequency band than a high-frequency band by using the relative magnitude difference; and obtaining an enhanced speech signal by multiplying the noisy speech signal and a time-varying gain function obtained by using the overweighting gain function; wherein the step of estimating the noise signal comprises the steps of: approximating a transformation spectrum by transforming an input noisy speech signal to a frequency domain; calculating a smoothed magnitude spectrum having a decreased difference in a magnitude of the transformation spectrum between neighboring frames; calculating a search spectrum to represent an estimated noise component of the smoothed magnitude spectrum; calculating an identification ratio to represent a ratio of a noise component included in the input noisy speech signal by using the smoothed magnitude spectrum and the search spectrum; and estimating the noise signal by using a recursive average method using an adaptive forgetting factor defined by using the search spectrum and the identification ratio, the adaptive forgetting factor becomes 0 when the identification ratio is smaller than a predetermined identification ratio threshold value, and the adaptive forgetting factor is proportional to the identification ratio when the identification ratio is greater than the identification ratio threshold value.