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Encyclopedia > Parametric equalization

Parametric equalizer (or parametric "EQ") is an electronic multi-band variable equalizer device used in sound recording and live sound reproduction with Public Address systems ("PA systems"). Parametric equalization devices allow audio engineers to control the parameters of the internal band-pass filter sections (amplitude, center frequency and bandwidth). The amplitude of each band can be controlled, and the center frequency can be shifted, and widened or narrowed. It has been suggested that this article or section be merged with Equalization filter. ... A public address system, abbreviated PA system, is an electronic amplification system used as a communication system in public areas. ... The frequency axis of this symbolic diagram would be logarithmically scaled. ... Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation, that is, magnitude of the maximum disturbance in the medium during one wave cycle. ... The frequency axis of this symbolic diagram would be logarithmically scaled. ... This article or section does not cite its references or sources. ...


Parametric equalizers are typically housed in a rack-mounted, rectangular metal chassis with a patch bay at the rear of the unit with inputs and output connectors and knobs and switches on the front of the unit that can be turned to the desired levels.


History

Prior to the development of the parametric equalizer in the late 1960s, sound recordings or live sound reproduction equalizers typically had pre-set band-pass filters that allowed sound engineers to make broad, overall changes to a signal, such as increasing the bass response or decreasing the treble. While graphic equalizers gave sound technicians the ability to control a greater number of center frequencies, they were still limited to the center frequencies on a particular graphic equalizer.


With the development of the parametric equalizer by George Massenburg in 1969, sound technicians were able to make much more precise modifications to a sound signal. The parametric equalizer allows to control the amplitude (e.g., the volume) of each band, and shift the center frequency and widen or narrow the width of the center frequency that is affected. George Massenburg, who works at McGill University in Montreal, Quebec, Canada as the Adjunct Professor of Recording Arts and Sciences and as a visiting lecturer at UCLA and USC in Los Angeles, and at MTSU in Murfreesboro, Tennessee. ...


A variant of the parametric equalizer is the semi-parametric equalizer. It allows users to control the amplitude and frequency, but uses a pre-set width of the center frequency. In some cases, semi-parametric equalizers allow the user to select between a wide and a narrow pre-set width for the center frequency.


Applications

Parametric equalizers can be used to precisely remove unwanted, excessive resonance, which can create a "boomy" sound. For instruments such as acoustic guitars which may have excessive "boominess," a parametric equalizer can be used to select the frequency band that is overly resonant and reduce its volume. Parametric equalization can also be used to remove extraneous noises such as the sound of the pick or the left-hand fingers for string instruments, or the creaking of a damper pedal of a piano.


An extreme case of execessive resonance is feedback, an undesirable "shrieking" sound which occurs in live music or sound reproduction situations when the amplified sound from a speaker is picked up by a microphone. To use parametric equalization for "feedback cancellation", a notch filter is created by cutting the frequency where feedback is occurring. A notch filter, also called a band-stop filter, sometimes a narrow band-pass filter, or T-notch filter, is an electronic filter typically used when the high frequency and the low frequency are less than 1 to 2 decades apart (that is, the high frequency is less than 10...


Parametric equalization is not only used to cut unwanted frequencies; it can also be used to enhance frequencies which are not "speaking" well on a specific instrument. For example, string instruments such as the double bass may have certain notes which cannot be produced at same volume as the other notes on the instrument. A subtle, precise boost of the frequency which does not respond well may help to resolve this problem.


 
 

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