Introduction
There was a requirement for a filter which would minimize wind noise below 500 Hz, have low noise, and be suitable for protected field use. The final circuit was a 4-pole state variable filter with differential input and either 0 or 10 db gain. Additionally, a 1-pole lowpass filter was added to reduce high frequency noise.
The Circuit
The following circuit uses two Burr-Brown UAF42 state-variable filters to implement the required filter.
The UAF42 module itself is defined in the EWB file, which you can download and use if you are running Electronics workbench.