The single knob EMG-EXG Guitar Expander® simultanteously boosts the highs (around 4000Hz) and the lows (centered at 40Hz) while dipping the midrange (1000Hz). The net effect is is a solid, clean low end, sharp attack and improved clarity from the reduced mids. Picking and rhythm chording come through with an acoustic-like quality which is fully adjustable from flat to full effect