The Micro Q-Tron is identical to the Mini Q-Tron but in a compact pedal. The envelope controlled filter is a unique type of sound modifier in which the user s playing style controls the effect. The volume of the input signal (also called the envelope) controls the cutoff frequency or center frequency of a swept filter. As your instrument s volume increases or decreases, so does the pitch of the filter. Runs on 9V battery or optional AC adapter.