Anyone know the difference between sallen-key and a state variable VCFs? Perhaps an example of a synth that uses each?
Sallen-Key is a 12dB/oct fixed filter. Resonance and cutoff frequency is dependent on the combination of the components and you cannot assign a simple variable control or control voltage for either parameter. You cannot get high resonance out of them. About the only places I’ve seen them is the Polymoog and the ARP ProSoloist. Maybe the preset-only Satellite/Minitmoog. Only one filter response is available at a time.
State variable filters can be voltage controlled and can simultaneously provide lowpass, highpass, and bandpass outputs albiet 12dB/oct only. With some clever summing you can also get a notch filter output.