Electro-Harmonix Bassballs Twin Dynamic Envelope Filter PedalThe Electro Harmonix Bassballs Twin Dynamic Envelope Filter Pedal has twin tuned filters that sweep your signal creating a unique vocal tone. Two narrow filters sweep your tones under control of the envelope, generating very unique vocal like sounds. It comes with an analog circuit, true bypass, mono audio, and a tough and compact die cast chassis. The Dist. Switch introduces an additional harmonic that accentuates the filters action. The Response