The Vacuum Mixer is where the signals from the two oscillators are mixed together, their levels balanced relative to one another. Also, an effect called Ring Modulation can be added, and Drive can be applied to the sum of both signals.
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Sets the relative volume of the two oscillators. One (or even both) oscillators can be reduced to silence, if needed.
Adds a variable amount of the VTO 1 and VTO 2 signals, multiplied together. This is called Ring Modulation, and can create interesting metallic or abrasive effects.