Abstract: A method for filtering digital input signals (e) makes use of all-pass filters of a first-class having the transfer function S1 and all-pass filters of a second-class having the transfer function S2, as well as all-pass filters of higher order, derived therefrom, having the transfer functions S1' and S1" or S2' and S2". The all-pass filters (10 to 36) are arranged in several stages in such a manner that the number of all-pass filters of higher order for a predetermined filter function is reduced. The output signals (A1 to A8) of the all-pass filters of the lowest order (22 to 36) are combined in a logical operation stage to filter output signals (d1,d8), the respective filter characteristic of which is determined by the logical operation. By the method of this invention, the steps necessary for the filtering can be carried out faster than in the prior art.

Abstract: A wave digital filter has one input set to zero and a signal to be distortion-compensated or simply to be subdivided into signals occupying different frequency ranges is supplied at the other input. The attenuation/frequency characteristics of the respective paths from the signal input of the filter to the respective outputs have transmission functions that are complementary to each other. Further subdivision into frequency sub-bands is provided by cascading another such wave digital filter at one or both outputs of the first wave digital filter. The coefficients (g) of the wave digital filters can be used for control purposes. The several outputs of cascaded filters are multiplied by weighting factors and thereafter added together to provide an output compensated against variation of attenuation with respect to frequency to which the input signal has been subjected.