You've heard the Phase 90 shaping the sound of Van Halen records since the 70's. It helps to add some velocity to lead lines or a more dramatic swoosh to palm-muted playing. Not just for guitar, this effect sounds great with bass, keyboard, and even vocals. Vary the speed from a slow, long cycle to quick swishy warble and everywhere in between. Powered by a standard 9V battery or power supply.