Feasibility: ultrasonic or infrasonic real-time pitch shifting

Projects General Guidance
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I have been thinking about building a device that would allow one to hear frequencies outside of human hearing range, potentially in stereo headphones. This is not for bat detection or any specific purpose, but just as a curiosity project, to see what one can hear in different environments. The recorded sounds would be put through a filter to cut off the sounds that one can already hear, and then the pitch would be shifted to make them audible. I was thinking of using a pair of microphones to make stereo sound in real time. I was hoping that Teensy 4 could provide the necessary computing power. My idea was for this device to be portable (powered by a battery and not hooked up to a computer), so the user could explore the inaudible sounds of different places.

I have very little experience with electronics, and from what I could understand for ultrasonic sounds I could use the Teensy 4.x with its Audio Adapter Board, and I was looking at a pair of Primo EM258 mics. I know they need 48V but the forums above suggest that I could use a Rode VXLR+ adapter.

Do you think either infrasonic or ultrasonic range real-time processing could be feasible? If so, what would be the budget (I was hoping for under $200)? Which one is easier to build? I read that one would need something with 192 ksps at 24 bits to achieve clean ultrasonic recording, would this be a problem for the Teensy audio board?

I would appreciate any and all help with this!

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P.S. I have already looked at

Feasibility ultrasonic recorder - #6 by MarkT, Bat detector | Teensy Forum,
XLR Input on Audio Shield | Teensy Forum,
but I still have questions about the feasibility of my project.

Thank you!

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This was done decades before any micro controllers were available! Mix a frequency near to the desired frequency and filter the result so the difference frequency is amplified so you can hear the difference frequency. It is an exact copy of the original sound, but at an audible frequency.

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But it's not a straightforward linear mix, which is superposition (done by summation) and doesn't add any new frequencies. It's done with modulation. (Amplitude modulation?)

You might want to experiment with Audacity first. It doesn't work in real time but it's easy to pitch-shift a recording.

I assume you are familiar with The Nyquist Limit, and of course microphones are designed to audio and they lose sensitivity at subsonic or ultrasonic frequencies (and at some point they don't work at all).

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Thanks for the recommendations, I haven't purchased the components I listed yet since I was not sure if they would work together. I believe the microphones I linked are specifically designed for ultrasonic frequencies, but it is the Nyquist limit I am worried about. I was wondering if anyone has tried sampling at such high rates using the Teensy 4 or any other audio board, or if you have other ideas on how to do this.

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