Electro-Harmonix BassBalls Twin Dynamic Envelope Filter Pedal 2 sweeping filtersSmall die-cast case The human vocal-like sound of its two sweeping filters gives bass a strong presence under leads, or a commanding quality when out front The resonant frequencies are engineered solidly into the full range of the bass guitar's strongest harmonics Bassballs will respond to every bass note The sweep is widely variable, and harmonic enrichment is available with the distortion switch