Difference between revisions 255412789 and 256307632 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.]]
'''Equalization''' (or '''equalisation''', '''EQ''') is the process of changing the frequency envelope of a sound in [[audio processing]]. In passing through any channel, an audio signal will "spread" from its original qualities. The goal of equalization is to correct, or make equal, the [[frequency response]] of a signal.

The term "equalizer" is often incorrectly applied to [[audio filter]]s, such as those included on [[Disc Jockey|DJ]] mixing equipment and [[high fidelity|hi-fi]] [[Sound recording and reproduction|audio components]]. However, these "equalizers" are typically general all-purpose audio filters, which can be arranged to produce the effect of [[low-pass filter|low pass]], [[High-pass filter|high pass]], [[Band-pass filter|band pass]] and [[Band-stop filter|band stop]] filters. Such filters are true equalizers only when arranged to ''reverse'' the effects of internal circuitry on sound output.

== Overview ==
[[Image:Peaking-eq.svg|thumb|right|200px|Two examples of the frequency response of a peaking EQ]][[Image:Shelving-eq.svg|thumb|right|200px|Two examples of the frequency response of a shelving EQ]]There are many kinds of EQ. Each has a different pattern of attenuation or boost. A peaking equalizer raises or lowers a range of frequencies around a central point in a bell shape. A peaking equalizer with controls to adjust the level ([[Gain]]), [[Bandwidth (signal processing)|bandwidth]] ([[Q factor|Q]]) and center frequency ([[Hertz|Hz]]) is called a ''parametric'' equalizer. If there is no control for the bandwidth (it is fixed by the designer) then it is called a ''quasi-parametric'' or ''semi-parametric'' equalizer.

A pass filter attenuates either high or low frequencies while allowing other frequencies to pass unfiltered.  A [[high-pass filter]] modifies a signal only by taking out low frequencies; a [[low-pass filter]] only modifies the audio signal by taking out high frequencies.  A pass filter is described by its ''cut-off point'' and ''slope''.  The cut-off point is the frequency where high or low-frequencies will be removed.  The slope, given in decibels per octave, describes a ratio of how the filter attenuates frequencies past the cut-off point (eg. 12 dB per octave).  A [[band-pass filter]] is simply a combination of one high-pass filter and one low-pass filter which together allow only a band of frequencies to pass, attenuating both high and low frequencies past certain cut-off points.

Shelving-type equalizers increase or attenuate the level of a wide range of frequencies by a fixed amount. A ''low shelf'' will affect low frequencies up to a certain point and then above that point will have little effect. A ''high shelf'' affects the level of high frequencies, while below a certain point, the low frequencies are unaffected.

One common type of equalizer is the ''graphic'' equalizer, which consists of a bank of sliders for boosting and cutting different bands (or frequencies ranges) of sound.  Normally, these bands are tight enough to give at least 3 dB or 6 dB maximum effect for neighboring bands, and cover the range from around 20 Hz to 20 kHz (which is approximately the range of [[Hearing (sense)|human hearing]]). A simple equalizer might have bands at 20 Hz, 200 Hz, 2 kHz and 20 kHz, and might be referred to as a ''4-band equalizer''. A typical equalizer for [[Live sound reproduction|live sound reinforcement]] might have as many as 24 or 31 bands.  A typical 31-band equalizer is also called a 1/3-octave equalizer because the center frequencies of sliders are spaced one third of an octave apart.

[[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 sy(contracted; show full)[[pl:Korektor graficzny]]
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