Frequency-domain block-adaptive digital filter

Claim 1

A frequency-domain block-adaptive digital 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 - k₀) π/N] for k = 0, 1, ..., 2N-1, where k₀ is a constant with 0 ≦ k₀ < N.