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