Neat, but I wish this wasn't a phone app (and Apple exclusive at that). My computer already has a high quality microphone that I assume would be more suitable for this purpose.

Piezo mics are pretty cheap, and if wired up to the microphone input of a computer or phone you could probably get better accuracy as well if you used the same signal processing techniques.

Seems some people have done this already with a PC app: https://timeandtidewatches.com/how-to-make-your-own-timegrap...

I used flutter so maybe some day!

It's in open beta testing on the Play Store for Android. You can also find low cost external mics for your devices that work well.