Looks like around 12Hz, counting the forward rock and back rock as distinct chops. I'm not sure a rocking motion is what people mean here, though. This only works for mincing something you've already cut up, not slicing an onion.
Maybe the solution is an ultrasonic slap chop? (https://www.amazon.com/Slap-Chop-Stainless-Vegetable-Accesso...) Many slices at once, preserve whatever the ingredient is without crushing it, doesn't stick to the blade. It may sound ridiculous, but if it makes kitchen prep easier and faster, I might cook more.