The Voltage Controlled Oscillator is a soundsource, capable of creating sine- triangle-, square- satooth- or spaced sawtooth waves. All waves have their own timbre and can even be combined to create unknown waves shapes. A pitch Control Voltage from a keyboard should be connected to the EXT input to let the Oscillator follow your keyboard. The LED switch needs to be ON to make that work. To set the basic frequency of the oscillator you use the FINE and COARSE knobs. When a signal is copnnected to the left FM input, the FM knob sets Frequency Modulation for the VCO. When a signal is connected to the right PWM input, the PWM knob sets the level of Pulse Width Modulation. A square wave needs to switched on to hear that effect. The Pulse Width of a square wave can be set to a basic percentage using the PW knob. The Out knob finally defines the overall level of the Oscillators’ output signal.
Manufacturers presets can be downloaded from: https://www.dropbox.com/home/RFM/F-syn/RFM_presets
Make your own presets available here: https://www.dropbox.com/home/RFM/F-syn/user%20presets