Difference between revisions 256307675 and 256307685 on enwiki

{{about|correction for frequency-dependent processing of audio signals}}
<br>{{Unreferenced|date=July 2007}}
[[Image:Equaliser-section.jpg|thumb|150px|right|The equaliser section from the Audient ASP8024 Mixing console. The upper section has high and low shelving EQ, the lower section has fully parametric EQ.]]
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[[Image:Behringer 3102 equalizer.jpg|thumb|600px|31-band [[Behringer]] equalizer with feedback detection]]
[[Image:Graphic equalizer.jpg|thumb|260px|Stereo graphic equalizer, 15 bands per channel]]


== Uses ==

In [[Multitrack recording]] and [[sound reinforcement system]]s, individual channels have equalization for [[aesthetic]] reasons, while the combined mix of sound is processed through equalization for practical reasons. Any acoustic space will cause some sound frequencies to be louder than others. This is due to [[standing waves]] produced by the size of the room and the materials in it. Equalization is used to compensate for the discrepancies of a room's [[acoustics]]. Ideally, a sound system would produce a flat frequency response. The frequency response of a room is examined with a [[Spectrum analyzer]] and usually a graphic equalizer, with matching frequency bands, is used to compensate for the room acoustics. This is standard practice for sound [[recording studios]], live [[sound reinforcement system]]s and some [[High fidelity]] sound systems.

One of the most direct uses of equalization is at a live event, where microphones and [[Loudspeaker|speaker]]s operate simultaneously.  An equalizer is used to ensure that there are no frequency bands where there is a round trip gain of greater than 1, as these are heard as audible [[Audio feedback|feedback]]. Those frequencies are cut at the equalizer to prevent this.

All [[Gramophone record|audio records]], or vinyls, have had equalization applied to the sound waveform before the consumers' record was made because of the limitations of equipment for recording and manufacturing the record.  One scheme was used prior to 1940.  Some 100 formulae were used until 1955, when the [[RIAA equalization|RIAA standard]] formula was implemented. As an example of the use of equalization in record production, low frequencies are reduced before the sound is imprinted onto the vinyl, making the groove take up less physical space so that more music can fit on the record. For this reason, record players boost the low frequencies back up to their original level before playback, to compensate for the reduction during printing.

Early [[telephone]] systems used equalization to correct for the reduced level of high frequencies in long cables, typically using [[Zobel network]]s. These kinds of equalizers can also be used to produce a circuit with a wider bandwidth than the standard telephone band of 300&nbsp;Hz to 3.4&nbsp;kHz.  This was particulary useful for broadcasters who needed "music" quality, not "telephone" quality on landlines carrying program material.  It is necessary to remove or cancel any [[loading coil]]s in the line before equalization can be successful.  Equalization was also applied to correct the response of the transducers, for example, a particular [[microphone]] might be more sensitive to low [[frequency]] sounds than to high frequency sounds, so an equalizer would be used to increase the volume of the higher frequencies (''boost''), and reduce the volume of the low frequency sounds (''cut'').  

Modern digital telephone systems have less trouble in the voice frequency range as only the local line to the subscriber now remains in analog format, but [[Digital Subscriber Line|DSL]] circuits operating in the [[MegaHertz|MHz]] range on those same wires may suffer severe [[attenuation distortion]] which is dealt with by automatic equalization or by abandoning the worst frequencies.  [[Videophone|Picturephone]] circuits also had equalizers.

The individual channels of a mixing board and the sound of electric instruments are equalized for [[aesthetic]] reasons. Some guitar [[effects unit]]s, in particular, the [[wah-wah pedal]] is based on equalization. Equalization is used to manipulate the [[timbre]] of musical instruments and sounds.

==See also==
{{Wiktionarypar2|equalisation|equalization}}
*[[Equalization filter]]
*[[Parametric equalization]]
*[[Blind equalization]]
*[[Electronic filter]]
*[[Bandpass filter]]
*[[High-pass filter]] 
*[[Low-pass filter]]
*[[Adaptive equalizer]]
*[[Loudness compensation]]
*[[Zobel network]]
*[[Smiley face curve]]

==External links==
*[http://www.songstuff.com/articles.php?selected=53 Effect of EQ frequencies]
*[http://www.sengpielaudio.com/calculator-bandwidth.htm Calculator: bandwidth per octave ''<math>N</math>'' to quality factor ''<math>Q</math>'' and back]
*[http://www.idc.ul.ie/idcwiki/index.php/Equalisation EQ Condensed Overview]
*[http://www.wikirecording.org/EQ WikiRecording's Guide to Equalization]

[[Category:Audio effects]]
[[Category:Audio engineering]]
[[Category:Linear filters]]

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[[pl:Korektor graficzny]]
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