Patent US 4,623,980

In order to upgrade input signals for further processing, one or more of the input signals is split up by a decimating technique into spectral component signals which are processed according to the desired purpose and recombined by means of an interpolation technique into an output signal. In this manner a digital filtering device can be selectively employed for achieving an arbitrary combination of simultaneous filtering, signal improvement, echo or feedback compensation, or signal masking of the input signals.