A tracking resonator bank should self-tune to any frequencies... so as long as the density of resonators is adequate, after convergence, it should paint a representative picture of the tone profile. Then you can try funny chords, or see how harmonics interfere, or see what happens when you hit 2 adjacent keys, etc.

Fun analysis experiments like this are why I made the free demo app (it runs on iPhone/iPad/Mac):

https://alexandrefrancois.org/Oscillators/

Check out the big brain on Brad....

Impressive. Thanks for the pointer.

Why does it only go down to 32.70 Hz? I just learned that watermelon ripeness can be determined by the FFT of 17Hz. Tried thumping my phone on th watermelon with your app. No luck. Can you make it go lower? Or is this some fundamental limit of iPhone hardware?

32.7 Hz is C1, lowest C on a standard piano (A440 tuning).

No inherent limitation of the technique, the resonators can be tuned to much lower frequencies. But indeed you‘ll need a better mic than the iphone’s to get frequencies below 50Hz iirc… too bad - the watermelon ripeness checker could be a really cool app :-)

There apparently are a bunch of watermelon ripeness checker apps. None get great reviews. Maybe you can get it to work. I only learned about this phenomenon while walking through Costco trying to pick out a good watermelon and asked Claude to explain what characteristics are most strongly correlated with Brix (sugar) levels. This sound check had the highest correlation.

Let me know if you update your app or make a watermelon version.

I just tried a watermelon app called MelonAid. It predicted my melon was ripe to overripe. Cutting it up, my son seems to agree with the assessment.

Side note, I was playing with your app on my piano, checking each key. I noticed that the lowest keys didn't actually have the lowest values in your app. Maybe I'm misunderstanding how the app works?

Most likely microphone lower range limitation. The fundamental frequency is out of the microphone’s range, so you only see the harmonics.

Dang. I wanted to try tuning my piano.

Can you reduce the lower limit? I think my piano is tuned to just under that lower frequency and thus those fundamentals aren't showing up.