Interesting, I am also just getting back to FFT stuff in vvvv. The frequency bins being distributed somewhat unfortunately (not many on the low end) is a general problem.
I am looking into implementing Mel scaling to get a more linear distribution of values (linear in the human hearing sense).
There is a LinToLog node, but it is not built very well since it converts the FFT Spreadbuilder into a Spread, which gets recreated every frame.
There is also the conversion from actual FFT values (representing power) to how we perceive them (loudness), but I have found a good formula for that using Log10.
I’ll post some of the progress once it’s ready and maybe it can make its way into the library.