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Is it possible to record very faint sounds like, say, the bending of a strand of hair? Part of the problem, I imagine, would be the need to find a way to isolate the target sound from other sounds. But assuming that's achievable, what other problems would one run into along the way?

(Any resources/further reading would be appreciated)

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  • $\begingroup$ Appropriate transducer for the expected frequency band. Low noise amplifier. Noise rejection techniques (e.g. lock in amplifier, frequency filtering, ...). Low noise environment. Probably more. Mostly engineering issues, not physics per se. Years ago I was able to detect light absorption by surface plasmons by using a piezo transducer. Currently available electronics would make it much easier today. $\endgroup$ – Jon Custer Dec 16 '15 at 19:56
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I would say that's the problem of the recording system inertia. Microphone membrane (electrodynamic case) or piezo devices etc. are not infinitely sensitive. This would lead to the low signal to noise ratio.

That means you would need special statistic signal processing or sound engineering procedures. For such questions I would recommend other SE sites.

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    $\begingroup$ Yes, exactly. I recall a paper that suggested human hearing was more sensitive than QM noise limit, and thus impossible. The answer was discovered recently: hair-cells essentially cancel their own inertia using active drive, and ears are like "superregen" receivers tuned to the edge of self-oscillation. (Tinnitus oscillation-malfunctions can be picked up by microphones inside ears!) A similar trick works on radio antennas: active antennas which behave as infinite-Q superconductors when driven with a power supply and carefully adjusted feedback loop. $\endgroup$ – wbeaty Dec 16 '15 at 21:29
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The signal level must exceed any notable low-signal-level non-linearities in the system (digital quantization, static friction/crinkle of the sensor, etc.) and other noise like systemic, thermal, environmental, etc.. If you can overcome all these, then you'll hear the bending hair just fine. You ~could~ repeatedly bend the hair and integrate the sound to increase the SNR.

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