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.

In audio processing, equalization (or equalisation, EQ) is the process of changing the frequency envelope of a sound. Audio signal processing, sometimes referred to as audio processing, is the processing of a representation of auditory signals, or Sound. Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies In passing through any channel, temporal/frequency spreading of a signal occurs. Channel, in communications (sometimes called communications channel) refers to the medium used to convey Information from a Etymologically, it means to correct, or make equal, the frequency response of a signal. Etymology is the study of the History of Words &mdash when they entered a language from what source and how their form and meaning have changed over time Frequency response is the measure of any system's spectrum response at the output to a signal of varying Frequency (but constant amplitude at its input The term "equalizer" is often incorrectly applied as a general term for audio filters. An audio filter is a type of filter used for processing Sound signals. DJ mixing equipment and hi-fi audio components often include so called graphic equalizers or simply equalizer. A disc jockey (also known as DJ or deejay) is a person who selects and plays recorded music for an audience High fidelity or hi-fi reproduction is a term used by home stereo listeners and home audio enthusiasts ( Audiophiles to refer to high-quality reproduction These are in fact general all-purpose filters, which can be arranged to produce the effect of low pass, high pass, band pass and band stop filters. A low-pass filter is a filter that passes low- Frequency signals but Attenuates (reduces the Amplitude of signals with frequencies A high-pass filter is a filter that passes high frequencies well but attenuates (reduces the amplitude of frequencies lower than the Cutoff frequency A band-pass filter is a device that passes frequencies within a certain range and rejects ( Attenuates frequencies outside that range In Signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered but Attenuates Only when these filters are arranged so as to reverse the effects of the internal circuitry on sound output, are they operating as equalizers.

Overview

Two examples of the frequency response of a peaking EQ

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 (Q) and center frequency (Hz) is called a parametric equalizer. In Electronics, gain is a measure of the ability of a circuit (often an Amplifier) to increase the power or Amplitude of a For other uses of the terms Q and Q factor see Q value. In Physics and Engineering the quality The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. 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 high-pass filter is a filter that passes high frequencies well but attenuates (reduces the amplitude of frequencies lower than the Cutoff frequency A low-pass filter is a filter that passes low- Frequency signals but Attenuates (reduces the Amplitude of signals with 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. A band-pass filter is a device that passes frequencies within a certain range and rejects ( Attenuates frequencies outside that range

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 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 reinforcement might have as many as 24 or 31 bands. A live sound reproduction system has two main forms A "sound reinforcement" system enhances the Volume of the initial Sound and will be designed so 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.

31-band Behringer equalizer with feedback detection. BEHRINGER International GmbH ( Behringer) is a Global Audio equipment manufacturer founded in its present form in 1989.

Uses

In Multitrack recording and sound reinforcement systems, individual channels have equalization for aesthetic reasons, while the combined mix of sound is processed through equalization for practical reasons. Multitrack recording ('multitracking' or just 'tracking' for short is a method of Sound recording that allows for the separate recording of multiple sound sources to create A sound reinforcement system is an arrangement of Microphones electronic Signal processors Amplifiers and Loudspeakers that makes live or pre-recorded Aesthetics or esthetics ( also spelled æsthetics) is commonly known as the study of sensory or sensori-emotional values sometimes called Pragmatism generally considered to have originated in the late nineteenth century with Charles Peirce, who first stated the Pragmatic maxim. 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. A standing wave, also known as a stationary wave, is a Wave that remains in a constant position Equalization is used to compensate for the discrepancies of a room's acoustics. Acoustics is the interdisciplinary science that deals with the study of Sound, Ultrasound and Infrasound (all mechanical waves in gases liquids and solids 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. A spectrum analyzer or spectral analyzer is a device used to examine the spectral composition of some electrical, acoustic, or optical This is standard practice for sound recording studios, live sound reinforcement systems and some High fidelity sound systems. A recording studio is a facility for sound recording. Ideally the space is specially designed by an acoustician to achieve the desired acoustic properties (sound A sound reinforcement system is an arrangement of Microphones electronic Signal processors Amplifiers and Loudspeakers that makes live or pre-recorded High fidelity or hi-fi reproduction is a term used by home stereo listeners and home audio enthusiasts ( Audiophiles to refer to high-quality reproduction

One of the most direct uses of equalization is at a live event, where microphones and speakers operate simultaneously. For the Marty Friedman album see Loudspeaker (album A loudspeaker, speaker, or speaker system is an electroacoustical 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 feedback. Audio Feedback (also known as the Larsen effect after the Danish scientist Søren Larsen who first discovered its principles is a special kind of Feedback Those frequencies are cut at the equalizer to prevent this.

All 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. A gramophone One scheme was used prior to 1940. Some 100 formulae were used until 1955, when the RIAA standard formula was implemented. RIAA equalization is a specification for the correct playback of Gramophone records established by the Recording Industry Association of America (RIAA 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. Basic principle A traditional landline telephone system also known as "plain old telephone service" (POTS, commonly handles both signaling and audio information 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). Frequency is a measure of the number of occurrences of a repeating event per unit Time. Modern systems have less trouble in the voice frequency range, but DSL circuits operating in the MHz range on those same wires may suffer severe attenuation distortion which is dealt with by automatic equalization or by abandoning the worst frequencies. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. Attenuation distortion is the Distortion of an Analog signal that occurs during transmission when the Transmission medium does not have a flat Picturephone circuits also had equalizers. A videophone, also known by the trademarked name Picturephone, is a Telephone which is capable of both audio and Video Duplex transmission

Telephone companies use equalization to reduce bleed-through or crosstalk between adjacent telephone wires. In Electronics, the term crosstalk ( XT) refers to any phenomenon by which a signal transmitted on one circuit or channel of a Transmission system This occurs due to inductance, capacitance or electrical conductance coupling. In Electrical circuits, any Electric current i produces a Magnetic field and hence generates a total Magnetic flux \Phi acting Capacitance is a measure of the amount of Electric charge stored (or separated for a given Electric potential. Electrical conductance is a measure of how easily Electricity flows along a certain path through an Electrical element. 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. A band-pass filter is a device that passes frequencies within a certain range and rejects ( Attenuates frequencies outside that range 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. Aesthetics or esthetics ( also spelled æsthetics) is commonly known as the study of sensory or sensori-emotional values sometimes called Some guitar effects units, in particular, the wah-wah pedal is based on equalization. Effects units are devices that affect the sound of an electric instrument or other audio source (such as recorded material when plugged in to the electrical signal path the instrument A wah-wah pedal (or just wah pedal) is a type of Guitar Effects pedal that alters the tone of the signal to create a distinctive effect intended to mimic Equalization is used to manipulate the timbre of musical instruments and sounds. In Music, timbre (ˈtæm-bər' like timber, or, from Fr timbre tɛ̃bʁ is the quality of a Musical note or sound that distinguishes different

See also

• Equalization filter
• Parametric equalization
• Blind equalization
• Electronic filter
• Shelving filter
• Bandpass filter
• High-pass filter
• Low-pass filter
• Adaptive equalizer
• Loudness compensation

External links

• EQ frequencies
• Uk Sound And Lighting Community
• Blue Room Technical Forums
• Equalisation for Guitar Multi-Effects
• Calculator: bandwidth per octave N to quality factor Q and back
• Wavebyte GFX Equalizer
• EQ Condensed Overview
• Parametric Equalizer Example
• WikiRecording's Guide to Equalization
• DJ Music looks at EQ controls for DJs