Every shape is ODD, monotone through the origin, and normalised to F'(0) = 1 — a small
signal passes at unity, so the SHAPE adds no level of its own. (The stage's own driveDb
still does: u = 10^(driveDb/20)·x, and §4d's measured auto-gain is what takes that back
out. The normalisation is the shape's, not the stage's.)
The roll-off order is the opposite of the obvious guess and was MEASURED, not assumed:
tanh is analytic and its series dies away fastest, while tube's |u| has discontinuous
higher derivatives and spreads energy furthest up the series — the gentlest knee sounds the
richest. See mix_drive.h's own table.
ONE knee, evaluated at
u(already drive-scaled).Every shape is ODD, monotone through the origin, and normalised to
F'(0) = 1— a small signal passes at unity, so the SHAPE adds no level of its own. (The stage's owndriveDbstill does:u = 10^(driveDb/20)·x, and §4d's measured auto-gain is what takes that back out. The normalisation is the shape's, not the stage's.)The roll-off order is the opposite of the obvious guess and was MEASURED, not assumed:
tanhis analytic and its series dies away fastest, whiletube's|u|has discontinuous higher derivatives and spreads energy furthest up the series — the gentlest knee sounds the richest. Seemix_drive.h's own table.