First knob ("out balance"): crossfade from left shape to right shape for signal going to Output (selected by sliding switches). Second knob ("mod balance"): crossfade from left shape to right shape for signal going to Modulation section. Small knob on bottom ("modulation"): amount of output signal modulating base frequency, center is zero. Big knob ("Hz"): base frequency of LFO before modulation applied. Lamps monitor output (+-).