This is an analogue switch on steroids. The concept came from a 60s chopper modulator circuit. It can be used as a VCO, a VCF, a waveshaper, ring modulator, analogue switch, LFO and VC gate generator....probably more. It can switch between two input signals with the actual input signals deciding when to switch, or the change can be VC or manually controlled. There is also a bi-directional switch as a separate circuit on the same PCB. this is functionally the same as the early Serge bi-di Router but uses a DG411 analogue switch rather than a 4007 to do the work.