Saturation where you decide how much of the low end goes into the drive. What you leave out comes through the output the way it went in.
The low end is usually the first thing to suffer when you drive a signal. So it tends to end one of two ways: a workaround that costs you time and brings its own artefacts or latency, or less drive than you actually wanted. Neither is necessary here.
Nothing is removed
Sub Protect filters what goes into the saturation, not what comes out of it. Below the point you set, nothing reaches the nonlinearity, so those harmonics are never generated in the first place. The signal itself passes through at full bandwidth, with the drive added on top.
Four ways to drive
Gentle stays subtle, Round pushes harder, Bite starts to cut and Crush is as far as it goes. Sub Protect stays where you set it in all four, so changing character does not change what happens at the bottom.
Room to push
16× oversampling keeps the harmonics where they belong instead of folding back down the spectrum.
