There is no such thing as both LEDS lit at once in reality. When you have one frequency, with no offsets, each LED is lit independently. However, if the frequency is fast enough, the blinking so rapid, that it appears both are on fully at the same time.
When you use the Scoon Effect, you are no longer doubling amplitude with the use of inverse+sync. Instead you are now combining both frequencies into one output.
The effect of the frequencies being so close to each other (preset uses a value of 1 Hz) is that there will be an effect where one frequency is just slightly faster than the other. Over time, the actual points where they overlap and where they do not, results in the effect you see.
Think of it like the spinning wheel with a strobe light. Under the right conditions you can make the wheel look like it is not spinning (strobe rate matches spin rate). Set the strobe rate slightly slower than the spin rate, and you can make the wheel look like it is spinning backwards, even though in reality it still is spinning forward.
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