An active bandpass filter has been developed with the desirable feature of wideQcontrol over the range of frequencies extending to ∼4 kc. TheQhas been made as high as 250 with good stability characteristics over this range. The flexibility of the filter has been illustrated by the construction of a filter bank tuned to select Fourier components of a 50‐cps periodic wave in a typical noise environment and recombine them with no added relative phase shift and with equal gain to improve the signal‐to‐noise ratio.