A band pass filter allows the energy concentrated between two given frequencies (X and Y) to pass while it attenuates the signal's energy at other frequencies. It is equivalent to applying a high-pass filter at X and a low pass filter at Y.
A band stop filter attenuates the energy in the frequencies between two given frequencies (X and Y). It is equivalent to applying a low pass
filter at X and a high pass filter at Y.
Note that filters do not remove all of the energy outside of their pass band (the pass band is the frequencies between X and Y for a band pass filter, and below X and above Y for a band stop filter). Generally, the further away from the cut off frequencies (X and Y), the greater the attenuation of the energy. How fast the attenuation increases as a function of frequency is established by parameters (primarily “Q”) of the filter. Real filters will also attenuate within the pass band, and there are some tradeoffs in the selection of parameters.
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