It seems that [sigmund~] is really great for frequencies from 200hz - 15000hz, but when it gets below 200hz it starts having problems (especially below 100hz).

[helmholtz~] on the other hand works great all way down to 20hz, but it cuts off at 2000hz.

Is there a good way to combine them so that sigmund~ could handle the upper range and helmholtz~ handle the lower range? For example, should I route the audio to sigmund and helmholtz at the same time and then let helmholtz have preference if they both find a value? Or should I do some kind of cutoff filter and send the highs to sigmund and the lows to helmholtz?

Or maybe I have the wrong parameters for lower notes in sigmund?

i don't know how high would [fiddle~] go. Did you try it ?

Yeah, [fiddle~] becomes unstable around 3000hz and can only go as low as 108hz.

[helmholtz~] is the most stable overall, but it has a hard cutoff at 2000hz.

So my only thought was to combine two and sigmund is faster and more stable than fiddle.

If you increase the FFT size in [sigmund~] or [fiddle~], you can get lower pitches. I've tracked the lowest string on my guitar before, which goes down to MIDI note 40, which is about 82.4 Hz.