Equalizers are like expanded tone controls that permit more accurate adjustment of the sound. Equalizers come in two types, graphic and parametric. A good rule to follow when adjusting an equalizer is to cut a frequency whenever possible instead of raising a frequency. For example, if you want more high frequencies, try reducing the midrange instead. Or if you want more midrange, try reducing the bass or the higher frequencies instead of raising the midrange. Raising a frequency can add small amounts of distortion, while reducing a frequency does not. Read my full article about how to adjust an audio equalizer.