Here's an interesting waveshaping distortion that is not linear and
gives an interesting effect. I once ported it to pd but I did not
quite finish it (I didn't get the coefficient calculations right and
it would blow up in some unpredictible ways).
http://csounds.com/ezine/winter1999/processing/
A gentler (than abs(),[abs~] or similar) way of rectifying a signal is
multiplying it by itself.
./MiS