Spectrum Analyser

Let Chrome use the microphone here

You've opened the radio's own copy of this page, which works with no internet (on the radio's own Wi-Fi, for example). Chrome only lets pages on secure addresses use the microphone, so tell it this one is fine. Once per phone:

1. Open a new tab and go to chrome://flags.
2. Search for Insecure origins treated as secure and set it to Enabled.
3. In its box, type http://sleepradiopi.local (add the radio's other addresses too, separated by commas, e.g. http://192.168.4.1 for its hotspot).
4. Tap Relaunch, then come back to this page.

With internet, the same page also works from GitHub without this.