An audio equalizer is used to boost or cut specific frequency ranges to improve sound, add clarity and depth and balance elements in a mix. A basic equalizer allows the user to adjust fixed high and low frequencies and sometimes midrange frequencies.
The most common types of equalizers are parametric, graphic and shelving equalizers. Shelving equalizers are the most common type. They allow for boosting and cutting at fixed frequency ranges with low and high knobs, with the low shelf rolling off at around 150 hertz, and the high beginning to roll off around 10,000 hertz. Graphic equalizers may have two to 30 bands. According to Rory PQ from Sub-Divizion Music, the graphic equalizer is not a very effective tool in mixing modern music, as there is no control over the filter shape and bandwidth of each individual band.
The parametric equalizer is the most flexible form of equalization. Common parameters found on a parametric equalizer include the frequency knob, which adjusts the frequency range of each selected band; the gain knob, which controls how much boost of cut to the selected frequency; the resonance knob, which allows the user to widen or narrow the frequency range; the slope button, which sets the steepness of the filter; and the filter type, a set of buttons that allows the user to set the shape for the selected frequency band.