(Experimental) If OCTTargetOperator = oct_tg_plateau, then the function to optimize is the integral of the
harmonic spectrum $H(\omega)$, weighted with a function $f(\omega)$
that is defined as a string here. For example, if
you set OCTHarmonicWeight = "step(w-1)", the function to optimize is
the integral of $step(\omega-1)*H(\omega)$, i.e.
$\int_1^{\infty} H \left( \omega \right) d\omega$.
In practice, it is better if you also set an upper limit, e.g.
$f(\omega) = step(\omega-1) step(2-\omega)$.