“The Electro Harmonix Q-Tron Plus electric guitar envelope filter pedal. Based on and designed in conjunction with the maker of the infamous Mu-tron III, the Q-Tron provides a faithful reproduction of the original with loads of authentic 70’s mojo.”
“Features include controls for Peak, Gain, Range (Hi/Lo), Mode (Mix, HP, BP, LP), Response (Fast/Slow), as well as selector switches for Drive On/Off and Normal/Boost modes. As well, this pedal features 4 1/4 jacks: Input, FX
Send, FX Return and Output.”
More information on the newest version here.