The Electro Harmonix MQTRON Micro Q-Tron Envelope Filter is a smooth envelope filter with a funky wah-wah tone. The filter is controlled by its internal envelope follower, analyzing the volume of your notes and the dynamics of your playing to directly sweep the filter's center or cutoff frequency. A stronger attack or louder note will produce a wider frequency sweep while softer playing produces more subtle effects. Use the Q control to make the effect more dramatic.