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Title pretty much says it all. I imagine it would take specialized gear through the entire signal chain - more like lab equipment than studio recording equipment. Probably a combination of inputs to capture different portions of the audio spectrum. It wouldn't need to be capable of recording for long periods of time - a few seconds would be sufficient. The recorded data should be able to be either visualized or translated into the audible spectrum.

This is all hypothetical - I'm not seeking to actually build this - just wondering if it's feasible/possible.

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It's totally feasible. But...

Microphones generally have a bias towards the audible range (20Hz-20kHz) simply because that's what we generally want them for, but the mechanism is capable of recording pressure waves outside of that range at either end of the scale.

In the most simple terms, microphones convert pressure waves in the air into electrical fluctuations which we can amplify and output through speakers to hear, record as audio to playback or manipulate, or record as information that can then be used to create visual representations of the original pressure waves in the air.

As an example: bat detectors often use mics to "hear" the ultrasonic signals of the bat and then drop the frequency of that sound into the audible range for humans while seismic events around the world are often recorded electronically using subsonic microphones buried in the ground so that the waves can be analysed visually.

Subsonic sounds (<20Hz) are longer pressure waves (peak to peak) while ultrasonic sounds (>20kHz) are shorter waves.

A regular mic is technically capable of picking up both subsonic and ultrasonic sound but, due to things like diaphragm size and electronic biases, sounds outside of the normal hearing range will be of lower quality and at a lower volume - again, this is simply because these sounds are not normally what we want from a microphone.

Technically speaking, the upper limit for sound in air is around 5GHz (5 million vibrations per second) due to the atomic structure of air molecules but there isn't a limit to how low a 'sound' can get although you may have to add your own definition for a lower limit. For instance, one cycle per minute would be 0.0166Hz and one cycle per hour would be 0.000277Hz but are they really sound at that point?

If you wanted to try recording a wide band of frequencies in the manner you described, then you'd probably need an array of mics and sensors each geared towards capturing a specific part of the range you wanted to record.

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  • Yes! Yes, I do! Thanks! Apr 25, 2022 at 13:31
  • Thank you. I wonder if there is existing lab equipment that is actually designed for this. WRT the upper limit for sound in the air, good info - thank you. That gave me the search terms to find more good info[0]. It seems like for very high frequency sound, it would only propagate very short distances (makes sense - you hear the bass first going to an outdoor concert). For my purposes though, I think audio in the tens of MHz range would be sufficient. [0] physics.stackexchange.com/questions/23418/…
    – Alex G
    Apr 27, 2022 at 2:05

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