The SeM20² is a classic 2 pole state variable Eurorack filter based on the Oberheim SEM's filter with the resonance section of the MS20 grafted on for extra bite and the input section modified to overdrive the single, much like the OSCar. The Dual SeM20² manages to put 2 in a 16HP module without sacrificing any of the features or the sound of the original.
The Dual version has a 4 input mixer section. Each channel can be assigned to either filter, to both for either stereo filtering or to get the Korg MS-20 or OSCar dual filter effect. The 4 input mixer and 8 outputs make feedback loops and self oscillation patches extremely easy and almost required. When the input is at 5(noon) it's full volume. Beyond 5 the filter will begin to overdrive and distort, just like the original SeM20².
In Single Mode both filters act independently with their own Freq pots and 2 attenuated CV inputs each. They are 2 full featured SeM20² filters in one module. In Dual mode the upper Freq pot and CV 1.1/1.2 control both filters. This is great for stereo filtering and would work especially well with the new stereo effects from Audio Damage. There is an offset pot for the second filet when it's in Dual mode and this works like the spread feature on the OSCar. You can feed the same input to both filters, offset the second one and then use the 1 CV inout or the Freq pot to sweep both.
This filter can go from a very smooth Oberheimy sound to aggressive, overdriven acid dipped screeching.
It doubles as a pretty good kick drum, too.