PROBLEM TO BE SOLVED: To solve the problem that it is difficult to calculate a linear reverberation removal filter for removing a non-variable reverberation component with high accuracy when there is a variable reverberation component in a conventional reverberation removal system.SOLUTION: In an integrated algorithm between a reverberation removal system using a linear filter and a reverberation removal system using a non-linear filter, the non-linear filter at the rear stage has a function for measuring the amount of fluctuation of a transmission function for every time, and intensity of the non-linear filter for every time is controlled based on the function. Thus, since the integrated algorithm is constituted so as to apply intense non-linear processing only when the fluctuation of the transmission function is large, distortion of a voice component is maintained to the minimum. In addition, an influence that estimation accuracy of the transmission function drops is reduced by reducing weight of such a time zone that the transmission function fluctuates to a linear filter estimation value by feeding the amount of the fluctuation of the transmission function for every time by the same function back to estimation of the linear filter at the front stage.
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