I’d love to see what you have for those PLL’s, @stschoen. “Wrong” PLL’s can be fun. I found Mr. Syrett’s efforts on the forum here, that was interesting. In fact it inspired me at the time to try a woggle bug thing in some other software.
Anyway, to the author here, I’m guessing from your post that instead of MIDI clock you might just mean clock, as in a steady gate signal derived from an audio source, if what you want to do is adjust delay time for effects and what not and not try to track someone singing, etc.
A PLL by design tracks frequency, but you also might be able to get somewhere using amplitude and filtering, esp. with drums – when a loud thing in this frequency range happens, use the envelope follower to get a threshold for a gate, then you can reset a timer or use the zero crossing node to get a hz value. It won’t be consistent but maybe something “close enough” might be satisfactory?