Korg Sigma

YouTube via ikworgek. via this auction
"Korg Sigma with a Kenton pro-solo.
Weird old Korg synth with nice filter (same as MS20) and ringmodulation"
via this auction
"Its classified as bi-timbral synthesizer with sound sources coming from two sections the "synthe" section and the "instrument" section. You have control over the mix of these sections, you can also ring modulation the synth section with the instrument section for some really wild sounds.

The really unique portions about this synth are the two joysticks for multi dimensional control over filters, pitch, noise, and vibrato. Sample and Hold. The keyboard is pressure sensitive like aftertouch, portamento. There is also a quartertone rocker for switching to micro tuning! :) What's also interesting is it seems as though you can play up to 18 voices at a time with all synths and instruments enabled, create a mega wall of sound, then filter it, ring mod, and twist it."