It works like a Wah pedal, respnse sensitivly and feedback sound precisely, it has four knobs: Sensitivity, Bias, Resonance, Decay. "Sensitivity" adjusts the trigger level of the envelope filter, so that the sensitivity can be set. "Bias"adjusts the resonance frequency of the envelope filter. "Resonance" adjusts the Q value of the filter. "Decay" adjusts the decay rate of wow to match with different performances.