Equalizer is part of sound equipment that allows the tone qualities of the sound signal to be changed, usually in two or more bands, such as treble and bass. The name "equalizer" comes from the original application of correcting distorted audio signals to sound closer to the original source. The two basic types are "graphic" equalizers (which allow fixed bands of audio frequencies to be boosted or attenuated), and "parametric" equalizers (which let the operator also vary the center frequency and width of any band that is boosted or attenuated. Audio systems typically use a graphic equalizer which can freely change the frequency characteristic of a reproduced signal to create the desired reproduction sound field characteristic. The graphic equalizer is a popular equalizer apparatus which divides the frequency band of audio
signals into a large number of
frequency subbands or channels and which can vary the frequency characteristics at the respective channels, and thereby change the frequency characteristics over the entire band as desired. In general, the graphic equalizer includes a combination of a simulated inductor and a bridging amplifier which are constructed of operational
amplifiers.
