A parametric EQ (or equalizer) is a multi-band variable EQ that offers control of amplitude, center frequency, and bandwidth. Because of this control, you can raise or lower the amplitude of each band, adjust the center frequency or “Q” and widen or narrow the width of the affected area. This type of EQ has many uses. One of the most common is for feedback cancellation in a live performance. A parametric EQ can be used to create a notch filter by very steeply lowering the amplitude and narrowing the “Q”-width. The center frequency can then be swept throughout the band to determine and effectively eliminate the offending frequency.