The Electro-Harmonix Riddle is a powerful and precise envelope filter fine-tuned for guitar frequency response. The Riddle guitar effect will deliver tight and smooth control over the complete 80 Hz to 5 k Hz range, with a consistent and even sweetness. Need some edge? Engage Riddle's analog distortion and dial in anything from subtle bite to dominating crush. You can even plug in an optional expression pedal to control the filter sweep with your foot. With the ability to adjust Q, sweep range, and filter type, you'll also wind up with of the most versatile wahs available. Envelope controlled filters are a unique type of sound modifier where the intensity of the effect is controlled by the user's playing dynamics. The volume and dynamic of the incoming audio signal is used to control a swept filter. As the volume increases or decreases so does the frequency of the filter. With 3 selectable filter modes, along with Start, Stop, Attack, Decay, Q and Sensitivity controls, The Electro-Harmonix Riddle guitar pedal makes all of the classic Q sounds available to you.