Digital filter (104), comprising: a first frequency shifting mechanism (106) configured to shift an input spectrum (H(f)) of an input signal (100) by a first frequency distance (F1) to obtain a shifted frequency signal (122) with a shifted spectrum; a filter (108), configured to filter said shifted frequency signal with a predetermined transfer function to obtain a filtered signal (130); and a signal processor (110), said signal processor including: an adder (202), and at least a second frequency shifting mechanism (222), said signal processor (110) being configured to generate an output signal (140), which is a sum of said filtered signal (130) and said shifted frequency signal (122) and said output signal (140) has an output spectrum, which is shifted by a second frequency distance (DF) with respect to said shifted spectrum, wherein said second frequency distance (DF) is independent of said first frequency distance (F1).