A state variable filter (SVF) is a design that produces several filter responses at once, typically low pass, band pass, and high pass, from the same input. Many include a notch output too, which is made by mixing low pass and high pass.
Because all outputs run in parallel, you can use them separately or mix them for custom responses. Resonance and cutoff are often voltage controlled, and the design is popular in modular filters for its flexibility.
