Live FFT spectrogram of what the phone's microphone hears, log-scaled from 20 Hz to Nyquist. Pair with the Hearing Range demo on a second phone to see what the speakers actually emit at each frequency.
Browser audio filters off. This page disables echo cancellation, noise suppression, and AGC on the mic stream. Without that, the browser would silently kill the very signals we want to see (low rumble, ultrasonics, narrow tones) before they reach the FFT.
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max-hold (best response per bin)noise floor baseline