Harmonic randomization settings in ZynAddSubFX. The slighter adjusts which harmonics to randomize, the function by which to randomize, and by how much.
A harmonic randomizer is a setting or a group of settings meant to partially and randomly nudge the harmonics of a synth to randomize its timbre, usually only slightly.
Harmonic Selection[]
Straightforward; some dials allow for negative values for grouping everything above the setting and randomizing all of those.
Harmonic Amplitude Randomness[]
This selects the function by which the harmonic randomizes itself. You may additionally get to set how much variety is in that randomization.
The same effect can be achieved with a low-volume LFO following a noise wave attached to the harmonics.