Variable DRIVE_CHARACTER_RANGEConst

The EVEN/ODD harmonic balance. −1 is pure odd (the curve itself), +1 is pure even, 0 an equal blend — the kernel splits its own distortion residue into an odd and an even half and fades between them, so the two ends are exact rather than approximate (mix_drive.h, measured: H2 at −317 dBc at −1, H3 at −118 dBc at +1).

Unitless, and signed by construction. NOT NORMALIZED_RANGE: this is a BALANCE with a meaningful centre, and a 0..1 travel would put its centre at 0.5 and its neutral nowhere.