Equalization 480939 225493276 2008-07-14T00:02:02Z 189.71.115.9 /* Overview */ {{For|information about Canada's fiscal transfer system|Equalization payments}} {{For|information about computer bandwidth management|Equalization (computing)}} {{For|information about the process of relieving pressure in the ear|Ear clearing}} {{Unreferenced|date=July 2007}} {{technical}} [[Image:Equaliser-section.jpg|thumb|150px|left|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 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. 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 systems have less trouble in the voice frequency range, 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. Telephone companies use equalization to reduce bleed-through or [[crosstalk]] between adjacent telephone wires. This occurs due to [[inductance]], [[capacitance]] or [[electrical conductance]] coupling. The higher frequencies are more likely to transfer to adjacent wires. The [[bandpass]] that the phone company allows through is 400 through 3,400 Hz. Any frequencies above or below this are filtered out. These frequencies are acceptable for voice speech to be transmitted clearly. 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]] ==External links== *[http://www.songstuff.com/articles.php?selected=53 EQ frequencies] *[http://www.ukslc.org/ Uk Sound And Lighting Community] *[http://www.blue-room.org.uk/ Blue Room Technical Forums] *[http://tons-of-tone.tripod.com/index.html Equalisation for Guitar Multi-Effects] *[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.youtube.com/watch?v=lyV4c0vCyik Parametric Equalizer Example] *[http://www.wikirecording.org/EQ WikiRecording's Guide to Equalization] *[http://dj-music.org.uk/dj-eq-music-controls DJ Music looks at EQ controls for DJs] [[Category:Audio effects]] [[Category:Audio engineering]] [[Category:Linear filters]] [[bg:Еквалайзер (аудиотехника)]] [[cs:Ekvalizér]] [[da:Equalizer]] [[de:Equalizer]] [[es:Ecualizador]] [[fr:Égaliseur]] [[nl:Equalizer]] [[ja:イコライザー (音響機器)]] [[pl:Korektor graficzny]] [[pt:Equalizador]] [[fi:Ekvalisaattori]] [[sv:Equalizer]] [[tr:Eşitleme (ses)]] [[uk:Еквалайзер]]