Band-pass filter

Band-pass filter

A band-pass filter is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. An example of an analogue electronic band-pass filter is an RLC circuit (a resistorinductorcapacitor circuit). These filters can also be created by combining a low-pass filter with a high-pass filter. [cite book | title = Time Sequence Analysis in Geophysics | author = E. R. Kanasewich | publisher = University of Alberta | year = 1981 | isbn = 0888640749 | pages = p.260 | url =,M1 ]

"Bandpass" is an adjective that describes a type of filter or filtering process; it is frequently confused with passband, which refers to the actual portion of affected spectrum. The two words are both compound words that follow the English rules of formation: the primary meaning is the latter part of the compound, while the modifier is the first part. Hence, one may correctly say 'A dual bandpass filter has two passbands'.

An ideal bandpass filter would have a completely flat passband (e.g. with no gain/attenuation throughout) and would completely attenuate all frequencies outside the passband. Additionally, the transition out of the passband would be instantaneous in frequency. In practice, no bandpass filter is ideal. The filter does not attenuate all frequencies outside the desired frequency range completely; in particular, there is a region just outside the intended passband where frequencies are attenuated, but not rejected. This is known as the filter roll-off, and it is usually expressed in dB of attenuation per octave or decade of frequency. Generally, the design of a filter seeks to make the roll-off as narrow as possible, thus allowing the filter to perform as close as possible to its intended design. Often, this is achieved at the expense of pass-band or stop-band "ripple".

The bandwidth of the filter is simply the difference between the upper and lower cutoff frequencies. The shape factor is the ratio of bandwidths measured using two different attenuation values to determine the cutoff frequency, e.g., a shape factor of 2:1 at 30/3 dB means the bandwidth measured between frequencies at 30 dB attenuation is twice that measured between frequencies at 3 dB attenuation.

Outside of electronics and signal processing, one example of the use of band-pass filters is in the atmospheric sciences. It is common to band-pass filter recent meteorological data with a period range of, for example, 3 to 10 days, so that only cyclones remain as fluctuations in the data fields.

In neuroscience, visual cortical simple cells were first shown by David Hubel and Torsten Wiesel to have response properties that resemble Gabor filters, which are band-pass. [cite book | title = Tutorial Essays in Psychology | author = Norman Stuart Sutherland | publisher = Lawrence Erlbaum Associates | year = 1979 | isbn = 047026652X | pages = 68 | url =,M1 ]

References in popular culture

In his novel, "V.", Thomas Pynchon writes that a schematic for the band pass filter was the origin for the popular graffiti character, Kilroy. [cite book | title = V. | author = Thomas Pynchon | publisher = HarperCollins | year = 1999 | isbn = 0060930217 | pages = p.470 | url = ] [cite book | title = Sites of Exchange: European Crossroads and Faultlines | author = Maurizio Ascari and Adriana Corrado | publisher = Rodopi | year = 2006 | isbn = 9042020156 | pages = p.211| url =,M1 ]

ee also

* Atomic line filter
* Audio crossover
* Band-stop filter
* Bias tee


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  • band-pass filter — /band pas , pahs /, Elect., Electronics. a filter that attenuates all frequencies except those of a specific band, which it amplifies. [1920 25] * * * ▪ electronics       arrangement of electronic components that allows only those electric waves… …   Universalium

  • band-pass filter — [band′pas΄] n. Electronics a filter which will pass frequencies within a desired range but will virtually cut out all other frequencies …   English World dictionary

  • band-pass filter — ˈ ̷ ̷ˌ ̷ ̷ noun : filter 3a * * * /band pas , pahs /, Elect., Electronics. a filter that attenuates all frequencies except those of a specific band, which it amplifies. [1920 25] * * * band pass filter noun (telecommunications) A filter which… …   Useful english dictionary

  • band-pass filter — juostinis filtras statusas T sritis fizika atitikmenys: angl. band filter; band pass filter vok. Bandfilter, n rus. полосный фильтр, m; полосовой фильтр, m pranc. filtre de bande, m; filtre passe bande, m …   Fizikos terminų žodynas

  • band-pass filter — praleidžiamasis juostinis filtras statusas T sritis fizika atitikmenys: angl. band pass filter vok. Bandpaß, n; Bandpaßfilter, n rus. полосно пропускающий фильтр, m; пропускающий полосовой фильтр, m pranc. filtre passe bande, m …   Fizikos terminų žodynas

  • band-pass filter — /ˈbænd pas fɪltə/ (say band pahs filtuh) noun (in electronics) an electrical network which allows only signals with frequencies between certain values, which may be fixed or variable, to pass. See high pass filter, low pass filter …  

  • band-pass filter — noun Date: 1926 a filter that transmits only frequencies within a selected band …   New Collegiate Dictionary

  • Band-stop filter — A generic ideal band stop filter, showing both positive and negative angular frequencies In signal processing, a band stop filter or band rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a specific… …   Wikipedia

  • Low-pass filter — A low pass filter is a filter that passes low frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter …   Wikipedia

  • All-pass filter — An all pass filter is an electronic filter that passes all frequencies equally, but changes the phase relationship between various frequencies. It does this by varying its propagation delay with frequency. Generally, the filter is described by… …   Wikipedia

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