Edit: https://play.google.com/store/apps/details?id=org.intoorbit.... this is the app I use most. Phyphox (https://f-droid.org/en/packages/de.rwth_aachen.phyphox/) seems to only go until 6 kHz but has a lot of other tools. For those wanting to avoid GPlay, this F-Droid app seems to go slightly above 20 kHz but I don't like the interface as much as spectroid: https://f-droid.org/en/packages/org.woheller69.audio_analyze...
Edit: https://play.google.com/store/apps/details?id=org.intoorbit.... this is the app I use most. Phyphox (https://f-droid.org/en/packages/de.rwth_aachen.phyphox/) seems to only go until 6 kHz but has a lot of other tools. For those wanting to avoid GPlay, this F-Droid app seems to go slightly above 20 kHz but I don't like the interface as much as spectroid: https://f-droid.org/en/packages/org.woheller69.audio_analyze...