Patent ID: 8223829

Claim:
An adaptive digital filter, realized by hardware or a non-transitory computer readable medium storing a program executed by a computer, comprising: a filter unit for generating an output signal by a convolution operation of an input signal and a filter coefficient and supplying the result as output; and a coefficient control unit for controlling said filter coefficients based on error between a target signal and an index value derived from said output signal and controlling the update amount of said filter coefficients based on the estimated value of the amplitude of at least one of said input signal and said output signal; wherein, when said coefficient control unit controls said target signal based on the amplitude of said output signal, said coefficient control unit makes said target signal smaller when the amplitude of said output signal is increasing, makes said target signal larger when the amplitude of said output signal is decreasing, and moreover, makes the speed of making said target signal smaller faster than the speed of making said target signal larger.