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.