Electro harmonix - Bassballs Twin Dynamic Envelope Filter

Not one, but two narrow filters sweep your tones under control of the envelope, generating very unique vocal-like sounds. A distortion switch enriches the harmonics. The response control varies the sweep range determined by your attack. Not only designed for and great on bass guitar, but also very funky on guitar.

Quick Specs

True bypass

Tough and compact die-cast chassis

9-volt battery included

Optional 96DC-200BI power supply available (not included)

Source: youtube/EHX