This is a fully parametric mastering EQ. It's based on the KHN State Variable Filter used in many consoles and rack EQs, most notably the Barry Porter NetEQ.
My version has 5 bands with individual band bypass and shelving, along with low and high pass filters. I have redesigned the circuit to attain a lower Q of 0.3 (standard design minimum is 0.7) making it extremely flexible. The EQ summing section is driven by two SQ10 discrete opamps. Noise is around -90dBu and distortion is less than 0.1%.
This EQ is built to order and can be completely customized to suit your particular needs. It can be configured as stereo ganged or with separate left/right controls using high quality Grayhill and Elma rotary switches. Price for a full 5 band stereo ganged build with HP and LP filters is $5,500. Below are examples of some previous 4 band builds.