Welcome To KenSeibert.Com Audio
State variable filters are so named because each of the parameters on the filter can be set independently of the others. It is also capable of very high Q, unlike other topologies, such as the Sallen Key. It also features the high-pass, band-pass, and low-pass outputs simultaneously. The drawback of this circuit over others is that it requires three op-amp stages vs one stage.
The diagram below shows the circuit diagram for the state variable filter.
The transfer functions of this circuit are:
All three transfer functions share the same solution for :