[hgomersall]

If you know you have a single frequency close to an actual frequency of interest, you can use the fact you know you're in an aliased band to get a precise frequency estimate.

[superxpro12]

I guess thats sort of like a weird PLL thing? But I'd imagine you'd have to have prior knowledge of which string you're tuning otherwise the analysis is going to alias against every harmonic.

[regularfry]

Every non-linear mixing of signals gives you sum and difference frequencies. It's less a weird PLL thing and more a weird trig function thing.

[kayson]

Its not even a non linear thing. Its a sampling thing. Even ideal sampling exhibits aliasing.

https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampli...

[regularfry]

Yes, and. You can look at aliasing as a special case of heterodyning. Sampling is a nonlinear mixing.

[jonathrg]

Presumably there is an antialiasing low pass filter somewhere before JS gets to the data. I have a similar sample rate and it certainly didn't work at all for me.

[ErroneousBosh]

If the accelerometer samples at 50Hz, how could there be an antialiasing filter?

What would that filter look like?

[colanderman]

Anything physical which dampens higher frequency oscillations would act as an antialiasing filter.

[ErroneousBosh]

What sort of size do you think something that would damp 25Hz vibrations in something that weighs a gram or two would need to be?

[regularfry]

They have analogue AA filters just before the sampler.

[ckocagil]

aka a stroboscopic measurement,

but I don't think it will work well for this case.

[KeplerBoy]

It's just higher nyquist zones.