Overdrive the ES1 filter in MainStage
If you increase the filter Resonance parameter to higher values, the filter begins to internally feed back and, as a consequence, begins to self-oscillate. This results in a sine oscillation—a sine wave—that is actually audible.
You can make the ES1 filter output a sine wave by following the steps below. This lets you play the filter-generated sine wave with the keyboard.
Output a sine wave from the filter
In MainStage, switch the Sub knob to Off.
Drag the Mix slider to the very bottom (Sub).
Drag the Resonance slider to the maximum position (full).
If you want, click the disclosure arrow at the lower left to open the extended parameters, then click the Filter Boost button.
Filter Boost increases the output of the filter by approximately 10 decibels, making the self-oscillation signal much louder.