EQ, or equalisation, is used to shape the tonal balance of a sound by boosting or cutting specific frequency ranges. Common controls include bass, mid, and treble, or more detailed bands that allow precise adjustment of problem areas or tonal character.

EQ is an essential tool in guitar rigs, recording, and live sound, helping instruments sit properly in a mix and sound clear without unwanted harshness or muddiness. It can be used subtly to refine tone or more aggressively to dramatically reshape a sound.