The System-500 Series - 521 from Roland is a dual, voltage-controlled filter (VCF) in a single Eurorack module. Each independent VCF offers a three inputs with level slider controls, dedicated cutoff and resonance knobs, and three modulation inputs with inputs two and three offering attenuation sliders. Additionally, each filter has a 3-way switchable high-pass filter with off/1/2 settings. The 521 ships with four rack screws and a ribbon cable to connect to an optional Eurorack modular power supply.