Frequency-domain block-adaptive digital filter

Claim 1

A frequency-domain block-adaptive digial filter having a finite impulse response of length N for filtering a time-domain input signal in accordance with the overlap-save method, comprising: first sectioning means for segmenting the time-domain input signal into blocks of length 2N, each block overlapping its preceding block over a length N; first transformation means for obtaining 2N frequency-domain components of the Discrete Fourier Transform of length 2N of each input signal block; first multiplier means for multiplying each of the 2N frequency-domain components with an associated frequency-domain weighting factor for obtaining 2N weighted frequency-domain components; second transformation means for obtaining 2N time-domain components of the inverse Discrete Fourier Transform of length 2N of the weighted frequency-domain components; second sectioning means for discarding the first N time-domain components and conveying the last N time-domain components as the time-domain output signal of the filter; means for generating a time-domain error signal as a difference between the filter output signal and a reference signal; third sectioning means for segmenting the time-domain error signal into blocks of length 2N, each block overlapping its preceding block over a length N, and for assigning the zero value to the first portion of a length N of each block; third transformation means for obtaining 2N frequency-domain components of the Discrete Fourier Transform of length 2N of each error signal block; conjugation means for forming the complex conjugate value of the 2N frequency-domain components produced by the first transformation means; second multiplier means for multiplying each of the 2N frequency-domain components produced by the third transformation means with the associated frequency-domain component produced by the conjugation means and with a gain factor for obtaining 2N frequency-domain products; window means for performing an operation on the 2N frequency-domain products, whose time-domain equivalent is a multiplication by a window function, to obtain 2N frequency-domain weighting factor modifications; accumulator means for accumulating on a block-by-block basis each of the 2N weighting factor modifications for obtaining the 2N frequency-domain weighting factors; characterized in that the window means are arranged for convolving the 2N frequency-domain products by a function having one real and two mutually conjugate complex coefficients and corresponding to a time-domain window function g(k) of length 2N defined by g(k)=(1/2)[1+cos ((k-k.sub.o)π/N] for k=0, 1, . . . , 2N-1, where k o is a constant with 0≦k o <N.