The Electro-Harmonix Effect Pedals - Nano Q-Tron Envelope Controlled Filter is a classic envelope filter tones in a small package. The Volume knob controls the pedal’s output volume, which is helpful to make this effect stand out. The drive control adjusts its filter sweep sensitivity and how the pedal responds to the user’s playing dynamics. Q Control sets the peak bandwidth of the filter determining how subtle or dramatic the effect will be. LP BP HP Mode Switch controls what frequency range the filter will pass. .