opsix 37-Key FM Synthesizer (Certified Refurbished)opsix 37 Key FM Synthesizer features 32 voices of polyphony, 6 Operator FM synthesis, and 5 Operator modes, you can create hundreds of fresh, cutting edge sounds. Rearrange the building blocks of FM sound, and customize the sound with the front panel controls. Enjoy 30 Effects types and 16 Step sequencer with logue style motion sequencing for maximum expression. Take your music to bold new places with the ease and precision of this versatile synth.