Distortion

Distortion units distort the tone of an instrument by adding "overtones", creating a "warm" sound. To create a "dirty" or "gritty" sound, a unit further alters the tone by re-shaping or "clipping" its sound-waves so that they have flat, mesa-like peaks instead of curved ones. Distortion effects differ from overdrive effects in that that the former produces roughly the same amount of distortion at any volume.