Cool - you should check Badass out and see what else can be brought to the table.
CD
I couldn't find a very good technical description of what it does, but it looks like an EQ / distortion type effect with a ring modulator thrown in. When you distort (clip) something, you automatically create a lot of harmonics (but not sub-harmonics, which are defined as harmonics below the fundamental). A ring modulator is basically the multiplication of two signals, your instrument and a carrier, from which you get sum and difference frequencies of the source and carrier. The problem with Ring Modulation is that it suffers from a lot of artifacts and something called inter-modulation distortion, which are harmonics not related to the fundamental, aliasing is also a sometimes a problem. A better way (without using a carrier) to generate sub-harmonics is to half wave rectify the signal (which in itself creates harmonics) and then to start muting out say every other peak, which then effectively halves the frequency and creates harmonically related sub-harmonics to the fundamental. With a bit of filtering to eliminate the unwanted harmonics, it's possible to get a better quality enhanced bass if you mix this with the original signal. The trick will be to get as good a quality sub-harmonic generated, substantiated by mathematical models. There are as good as no papers on this.
Another thing I was also working on was to develop a pinch harmnic generator, which involves calculating the fundamental in a windowed sample and applying it to a bank of high Q bandpass filters, where only the desired harmonic(s) are let through.. worked quite well but only offline... developed it in MATLAB and used guitar samples to test it.
