VCO is short for "voltage-controlled oscillator." There's just one oscillator per voice, but the Pro Soloist's unique architecture gets a heck of a lot of mileage out of it. Here's the rundown of its controls:
VCO Modulation Sliders
ADSR PWM- Sets the amount of modulation of pulse wave width via the ADSR envelope generator.
AR PWM- Sets the amount of modulation of pulse wave width via the AR envelope generator.
LFO PWM- Sets the amount of modulation of pulse wave width via the low-frequency oscillator.
LFO FM- Sets the amount of oscillator frequency modulation via the low-frequency oscillator.
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Range- Coarsely sets the VCO pitch range in octaves. These are at standard organ footage settings of 32', 16', 8', and 4'.
Fine- Detunes the oscillator by slightly over a fifth, up or down. This can be used to fatten up multiple oscillator patches by detuning a small amount, or for "building-in" a set interval.
Super Wave- Toggling this engages what's sometimes known as a "super saw" mode, i.e., a big fat, chorusey version... and best of all Super Wave works for the saw and pulse waves. Super Wave is a quick way to make really large poly sounds if you don't want to delve into dual-layer patches.
Pulse Width- Sets the width or "duty-cycle" of the pulse width. A setting of 50% creates a perfect square wave. Pulse Width has no affect on the ramp wave.
Ramp (icon) Level- Sets the volume of the ramp wave that gets routed to through the highpass filter and then to the VCF section.
Pulse (icon) Level- Sets the volume of the pulse wave that gets routed to through the highpass filter and then to the VCF section.
Highpass Frequency- Sets the highpass filter cutoff frequency from 20 Hz (essentially bypassed) up to 1300 Hz. This is used to remove low frequencies from the ramp and pulse waves.
Resonator Bank Input Mix- In addition the ramp+pulse>highpass filter>VCF routing explained above, the oscillator also feeds the Resonator bank in parallel fashion (i.e., simultaneously). Unlike the ramp+pulse>highpass filter>VCF chain, Resonator Bank Input Mix acts as a balance knob between the ramp and pulse wave. The Resonator Bank signal path can be effectively turned off by making sure the Enable Resonator button is toggled off for all five tabs (tabs have white backgrounds if they're not visible but active - see the following Resonator Bank section for more information).