This app was mentioned in 1 comment, with an average of 9.00 upvotes
https://play.google.com/store/apps/details?id=com.synaptik.soundwave&hl=en
https://play.google.com/store/apps/details?id=radonsoft.net.spectralview
https://play.google.com/store/apps/details?id=com.needom.recorder&hl=en
Well, that is, if you're not in communist iOSSR-land.