Editing Audio filter

{{Short description|Frequency dependent circuit}}
{{More citations needed|date=December 2023}}

[[File:EQ parametrique.jpg|thumb|250px|Digital domain parametric equalisation]]

An '''audio filter''' is a frequency-dependent circuit, working in the [[audio frequency]] range, 0&nbsp;Hz to 20&nbsp;kHz. Audio filters can amplify (boost), pass or attenuate (cut) some frequency ranges. Many types of filters exist for different audio applications including [[hi-fi]] stereo systems, musical [[synthesizer]]s, [[effects unit]]s, [[sound reinforcement system]]s, [[instrument amplifier]]s and [[virtual reality]] systems.

==Types==
;Low-pass
:[[Low-pass filter]]s pass through frequencies below their cutoff frequencies, and progressively attenuate frequencies above the cutoff frequency.<ref>{{cite book
	| last1 = Smith
	| first1 = Julius Orion
	| date = 2008 | orig-date=1st pub. 2007
	| title = Introduction to Digital Filters: With Audio Applications
	| url = https://books.google.com/books?id=pC1iCQUAsHEC
	| location = United States of America
	| publisher = W3K
	| page = 3
	| isbn = 9780974560717
}}</ref> Low-pass filters are used in [[audio crossover]]s to remove high-frequency content from signals being sent to a low-frequency [[subwoofer]] system.

;High-pass
:A [[high-pass filter]] does the opposite, passing high frequencies above the cutoff frequency, and progressively attenuating frequencies below the cutoff frequency.<ref name="audio-effects-2015">{{cite book
	| last1 = Reiss | first1 = Joshua D.
   	| last2 = McPherson | first2 = Andrew
	| date = 2015
	| title = Audio Effects: Theory, Implementation and Application
	| url = https://books.google.com/books?id=pC1iCQUAsHEC
	| publisher = Taylor & Francis
	| page = 59
	| isbn = 9781466560284
}}</ref> A high-pass filter can be used in an [[audio crossover]] to remove low-frequency content from a signal being sent to a [[tweeter]].

;Band-pass
:A [[band-pass filter]] passes frequencies between its two cutoff frequencies while attenuating those outside the range.<ref name="audio-effects-2015"/> A band-reject filter attenuates frequencies between its two cutoff frequencies while passing those outside the 'reject' range.

;All-pass
:An [[all-pass filter]] passes all frequencies but affects the [[phase (waves)|phase]] of any given sinusoidal component according to its frequency.

==Applications==
In some applications, such as in the design of [[graphic equalizer]]s or CD players, the filters are designed according to a set of objective criteria such as [[passband]], passband attenuation, stopband, and stopband attenuation, where the passbands are the [[frequency]] ranges for which audio is attenuated less than a specified maximum, and the stopbands are the frequency ranges for which the audio must be attenuated by a specified minimum. In more complex cases, an audio filter can provide a [[audio feedback|feedback]] loop, which introduces [[resonance]] (ringing) alongside attenuation.  Audio filters can also be designed to provide gain (boost) as well as attenuation.
In other applications, such as with synthesizers or sound effects, the aesthetic of the filter must be evaluated subjectively.

Audio filters can be implemented in analog circuitry as [[analog filter]]s or in [[digital signal processing|DSP]] code or computer [[software]] as [[digital filter]]s.

==Self-oscillation==
[[Self-oscillation]] occurs when the [[resonance]] or [[Q factor]] of the cutoff frequency of the filter is set high enough that the internal feedback causes the filter circuitry to become a sine tone [[sine wave]] oscillator.

==See also==
*[[Electrical resonance]]
*[[Electronic filter]]
*[[Equalization (audio)]]
*[[Feedback]]
*[[Linear filter]]
*[[Oscillation]]
*[[Self-resonant frequency]]

==References==
{{Reflist}}

{{Music production}}

{{DEFAULTSORT:Audio Filter}}
[[Category:Tone, EQ and filter]]
[[Category:Synthesizer electronics]]
[[Category:Electronic circuits]]