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Circuit symbol of a bandstop filter

A bandstop filter , also known as a bandstop filter or bathtub filter in audio engineering , is a filter in electrical engineering that attenuates a certain, mostly wide frequency band and, in borderline cases, does not allow it to pass. In analog circuit structures, series and parallel resonant circuits are interchanged with respect to the bandpass filter , which results in the opposite behavior.

In contrast to a notch filter ( English notch filter ) which in the transfer function of a single zero which which is placed ideally exactly to a single to be suppressed frequency may comprise the transfer function of the band-stop filter also different zero points and thus a wider bandwidth include in the stopband .

The cut-off frequencies of a bandstop filter are those frequencies at which the ratio of output to input voltage

or −3  dB .

The center frequency is the geometric mean of the upper and lower limit frequency:

With the static frequency response change, the emphasis and the deemphasis, the time constant is usually given instead of the cutoff frequency .


  • T. Deliyannis, Yichuang Sun, JK Fidler: Continuous-Time Active Filter Design . CRC Press, Boca Raton FL et al. 1998, ISBN 0-8493-2573-0 .

Individual evidence

  1. Horst Wupper, Ulf Niemeyer: Electronic circuits 2: operational amplifiers, digital circuits, connecting lines . Springer, 1996, ISBN 978-3-540-60745-8 .

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