- 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 resistor– inductor– capacitorcircuit). These filters can also be created by combining a low-pass filterwith 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 = http://books.google.com/books?id=k8SSLy-FYagC&pg=PA260&dq=band-pass-filter&lr=&as_brr=3&ei=7Y2uR4nCEoOssgPO7bD8BQ&sig=a3fmpt4zGisnq4vIt6Bi2urgb-U#PPA260,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.
neuroscience, visual cortical simple cells were first shown by David Hubeland Torsten Wieselto 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 = http://books.google.com/books?id=yFbf_mulFuUC&pg=PA68&dq=bandpass-filter+Wiesel+Hubel&lr=&as_brr=3&ei=EJCuR8b1Ipm-swP7uKnyBQ&sig=0nmhJ6afsDuet2Eis-HA6wrPwdU#PPA68,M1 ]
References in popular culture
In his novel, "
V.", Thomas Pynchonwrites that a schematic for the band pass filter was the origin for the popular graffiticharacter, Kilroy. [cite book | title = V. | author = Thomas Pynchon | publisher = HarperCollins | year = 1999 | isbn = 0060930217 | pages = p.470 | url = http://books.google.com/books?id=jqS2pmUIfOAC&pg=PA470&dq=band-pass-filter+kilroy&lr=&as_brr=3&ei=_IuuR_3ODaautgO77vj6BQ&sig=q2eTF8Sc0jNw4do4h6zaMyPuf0E ] [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 = http://books.google.com/books?id=nFUjWY7-nYwC&pg=PA211&dq=band-pass-filter+kilroy&lr=&as_brr=3&ei=_IuuR_3ODaautgO77vj6BQ&sig=CJYum4nUa5FuJrz3hiqPGbviK3Y#PPA211,M1 ]
Atomic line filter
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