State variable filter

It is essentially used when precise Q factor is required, as other multi-order filters are unable to provide.

The example given below can produce simultaneous lowpass, highpass, and bandpass outputs from a single input.

In more general state-variable-filter examples, additional filter orders are possible with more integrators (i.e., more states).

[3][4] For simplicity, we set: Then: The pass-band gain for the LP and HP outputs is given by: It can be seen that the frequency of operation and the Q factor can be varied independently.

State variable filters are frequently used for modifying frequency response in audio signal processing.