An electronic device used to change the frequency response of a given audio signal; a device which provides signal equalization. here are two primary types of equalizers – parametric and graphic. Parametric equalizers allow you to choose the specific frequency you would like to adjust, usually within a range of frequencies. For instance, you may be able to choose a frequency between 1 kHz and 10 kHz. A graphic equalizer uses a range of pre-set frequencies. You adjust the frequencies closest to where the signal needs adjustment; however, you may not actually adjust the specific frequency unless it happens to fall at one of the graphic equalizer's pre-sets. A parametric equalizer provides a greater degree of precision although if you have multiple frequency anomalies needing correction, a graphic equalizer may best suit your needs. ost equalizers have two channels for use with a stereo system and its two channels of audio. However, there are equalizers available for multi-channel home theater systems that can adjust frequencies for all channels including subwoofers.