Editing Sound reinforcement system (section)

====Equalizers====
[[Image:Graphic equalizer.jpg|thumb|200px|Graphic equalizer]]
[[Equalization (audio)|Equalizers]] are electronic devices that allow audio engineers to control the tone and frequencies of the sound in a channel, group (e.g., all the mics on a drumkit) or an entire stage's mix. The bass and treble controls on a [[home stereo]] are a simple type of equalizer. Equalizers exist in professional sound reinforcement systems in three forms: shelving equalizers (typically for a whole range of bass and treble frequencies), graphic equalizers and [[parametric equalizer]]s. Graphic equalizers have [[fade (audio engineering)|faders]] (vertical slide controls) which together resemble a frequency response curve plotted on a graph. The faders can be used to boost or cut specific frequency bands.

Using equalizers, frequencies that are too weak, such as a singer with modest projection in their lower register, can be boosted. Frequencies that are too loud, such as a "boomy" sounding [[bass drum]], or an overly resonant [[dreadnought guitar]] can be cut. Sound reinforcement systems typically use graphic equalizers with one-third [[octave]] frequency centers. These are typically used to equalize output signals going to the main loudspeaker system or the monitor speakers on stage. [[Parametric equalization|Parametric equalizers]] are often built into each channel in mixing consoles, typically for the mid-range frequencies. They are also available as separate rack-mount units that can be connected to a mixing board. Parametric equalizers typically use knobs and sometimes buttons. The audio engineer can select which frequency band to cut or boost, and then use additional knobs to adjust how much to cut or boost this frequency range. Parametric equalizers first became popular in the 1970s and have remained the program equalizer of choice for many engineers since then.

A [[high-pass]] (low-cut) and/or [[low-pass]] (high-cut) filter may also be included on equalizers or audio consoles. High-pass and low-pass filters restrict a given channel's [[Bandwidth (signal processing)|bandwidth]] extremes. Cutting very low-frequency sound signals (termed ''[[infrasonic]]'', or ''subsonic'') reduces the waste of amplifier power which does not produce audible sound and which moreover can be hard on the subwoofer drivers. A low-pass filter to cut [[ultrasonic]] energy is useful to prevent interference from radio frequencies, lighting control, or digital circuitry creeping into the power amplifiers. Such filters are often paired with graphic and parametric equalizers to give the audio engineer full control of the frequency range. High-pass filters and low-pass filters used together function as a [[band-pass]] filter, eliminating undesirable frequencies both above and below the auditory spectrum. A [[band-stop filter]], does the opposite. It allows all frequencies to pass except for one band in the middle. A feedback suppressor, using an [[embedded system|microprocessor]], automatically detects the onset of feedback and applies a narrow band-stop filter (a [[notch filter]]) at specific frequency or frequencies pertaining to the feedback.