low pass filter with overtones

I’m wondering if it’s possible to use a Nyquist plug-in to Audacity to accomplish the following:

Create a low pass filter w/ steep attenuation except for dynamic narrow-band pass filters to pick up the overtones of frequencies below the cut-off. The narrow-band filters would constantly shift in time based on the content of the source sound.

I guess there’d have to be a cutoff or attenuation of the overtone-pass effect for very low source frequenies. And perhaps it would involve many, many passes at differing time scale resolutions.

Has anyone ever built such a thing or have any ideas how to do it?

I expect that it could be done with Nyquist, but it would be a rather complex project, and not one that I have come across by anyone else.

Have you done any programming, in particular any Lisp (XLisp) programming? If not, then I would suggest starting with something a lot simpler. Nyquist is not a difficult language, but the documentation, though improving, is still a bit limited, and Lisp syntax takes a bit of getting used to.

My guess, for your effect, would be to look at “Linear Prediction Analysis and Synthesis”, then combine that with the necessary low pass filter functions.
http://www.audacity-forum.de/download/edgar/nyquist/nyquist-doc/manual/part10.html#92