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[[File:Filter Example.png|thumb|upright=1.75|Frequency response of an example bandpass filter. The frequencies between a stopband and a passband define the transition band.]]

A '''stopband''' is a [[Band (radio)|band]] of frequencies, between specified limits, through which a [[electrical circuit|circuit]], such as a [[Filter (signal processing)|filter]] or [[telephone]] circuit, does not allow signals to pass, or the [[attenuation]] is above the required stopband attenuation level.<ref>{{cite web|url=https://www.its.bldrdoc.gov/fs-1037/dir-035/_5133.htm |title=Stopband, version of FS-1037C was last generated on Fri Aug 23 00:22:38 MDT 1996}}</ref> Depending on application, the required attenuation within the stopband may typically be a value between 20 and 120 [[decibel|dB]] higher than the nominal passband attenuation, which often is 0&nbsp;dB.

The lower and upper ''limiting frequencies'', also denoted lower and upper stopband [[corner frequency|corner frequencies]], are the frequencies where the stopband and the [[transition band]]s meet in a filter specification. The stopband of a low-pass filter is the frequencies from the stopband corner frequency (which is slightly higher than the passband 3&nbsp;dB cut-off frequency) up to the infinite frequency. The stopband of a high-pass filter consists of the frequencies from 0 hertz to a stopband corner frequency (slightly lower than the passband cut-off frequency).

A band-stop filter has one stopband, specified by two non-zero and non-infinite corner frequencies. The difference between the limits in the band-stop filter is the stopband [[Bandwidth (signal processing)|bandwidth]], which usually is expressed in [[hertz]].

A bandpass filter typically has two stopbands. The shape factor of a bandpass filter is the relationship between the 3&nbsp;dB bandwidth, and the difference between the stopband limits.

== See also ==
* [[Passband]]
* [[Band-stop filter]]
* [[Band gap]] in solid state physics
* [[Band rejection]]

==References==
{{Reflist}}

2.{{FS1037C MS188}}

[[Category:Filter theory]]


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[[sv:Stoppband]]