Electro‑Harmonix Nano Bassballs is a twin dynamic envelope‑filter designed for bass (though it works on guitar too). It features two narrow filters that “sweep” in response to how you play, creating a vocal‑like, funky tone. There’s also a Distortion (Fuzz) switch to add harmonic richness. Use the Response knob to control how much the filters sweep based on your playing volume and dynamics.