Non-linear techniques with filters

[Grant Richter]

Now that Terry and Juergen have brilliantly dissected the mechanism at work
in the transistor ladder, it suggests another class of filter which
deliberately exploits this perceptual effect.

That is introduction of a non-linear network before a linear filter with a
complimentary (or otherwise) transformation on the output. As I understand
it, the non-linearities are then incompletely cancelled at the crossover
point.

The easiest to achieve would be log-filter-expo or the inverse
expo-filter-log. I believe Terry told me the transistor ladder is of the
expo-filter-log type.

Certain of the Electronotes articles suggest the log-filter-expo could
produce interesting results since if H(t) = X(t) * Y(t) then expo H(t) = log
X(t) + log Y(t) so the excitation and formant are combined additively.

Please excuse my crude and possibly erroneous mathematics.