Tone control circuits

Tone control circuits are electronic circuits used to modify an audio signal before it is fed to speakers, headphones or recording devices by way of an amplifier. They are akin to and sometimes called filters. In their most basic form, they elevate or attenuate the high and low frequencies of the signal. This is called treble or bass boost or cut, respectively, in the vernacular of audio engineering. More elaborate tone control circuits can elevate or attenuate the middle range of frequencies too. Really elaborate tone controls provide elevation or attenuation in 1/3 octave bands spanning from approximately 30 Hz to 18 kHz. These units are called graphic equalizers because their controls are in the form of sliders that are arranged so as to graphically display the amount of boost or cut being applied at any frequency of interest. The most elaborate units can control not only the boost and cut but also the frequency at which the boost and cut takes place and the bandwidth of the control's action. These are called parametric equalizers because they control all of the equalization parameters.

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