A bandpass
filter is an
analog device which receives an
audio or
radio signal and
amplifies the
frequencies within a certain range, while
attenuating the frequencies on the edges of that range.
A bandpass filter can be devised by combining a
high pass filter with a
low pass filter, thus passing only the frequencies in between.
This type of filter is used in
radio,
sound, and
tone detection, among other things.
A bandpass filter is the inverse of a
notch filter.