Electro Harmonix Bi Filter Analog Dual Envelope FollowerMulti mode filters and an all analog signal path pumps up your sound with the world's fattest, sweetest filter power. Two separate filter sections can be used in serial or parallel with different tonal sweeps, which react individually or interactively. Phase control allows for further contouring. Individual outputs for each filter plus a mixed output. In addition an external CV in or Expression Pedal in for controlling the filters with external