A bandpass (BP) is a frequency-dependent quadripole that only allows frequencies in a certain frequency range to pass. Since the wavelength of the frequency occurs in optical transmission systems
, the statement applies equally to frequencies and wavelengths. A bandpass filter is a series connection of a highpass and a lowpass. Such a filter allows only those signals
to pass that are in the frequency range or wavelength range for which the filter is designed. The rest of the frequency spectrum cannot pass the quadripole.
. In audio technology, there is a bandpass filter standardized by the AudioEngineering Society (AES) under the designation AES17-1998 that is used to limit the measurement bandwidth. This filter has a frequency response between 10 Hz and 20 kHz, +/- 0.1 dB and an attenuation of at least 60 dB at 24 kHz.