Collectiony wrote:But what happens when I set it to negative values?
The same.
The parameter is intended to find the minimum distortions between (+) and (-) values.
Past this minimum, distortions increase in either direction.
There is a difference: the even order harmonics (k2, k4,...) change their phase one way or the other.
This way they could even remove / cancel out (!) a tiny amount of harmonics from the music, but that depends on the very music you listen to.
As constructor of tube amps I can assure you:
• There‘s more about tube amp’s special sound than just distortions.
If it was that simple real tubes would have already died out.
• To make the distortions effect audible you need at least 1-5%, and the “fitting” music.
• People tend to not know that nonlinear distortions (k2, k3, k4, ...), with music signals, do not just generate harmonic content (like when measured with a single frequency), but inextricably non-harmonic “dirt” of the same amount, called “Intermodulation Distortions”.
You don’t get one without the other.
The more complex the music is, the more “dirt” is generated.
The nice thing is, you don’t need to take my word for it, just try and listen by your own.