A spectrograph, fractional-octave RTA (1/3 … 1/48), and A/C/Z weighted SPL meter that runs entirely in the browser.
Tap start and allow the microphone. Mic processing (AGC, noise suppression) is disabled so the
measurement isn't colored — but the absolute dB number is only as good as the calibration offset
and the mic itself, so treat it as relative until you set the offset against a known reference.
Note: the mic only prompts when this runs as its own page on an HTTPS URL. Inside an embedded/sandboxed frame the browser blocks it with no prompt.