One note: it shows large. Several strings strummed together: one gauge per string.
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Press “Start the microphone”, then play a note.
Your browser is waiting for a gesture before it listens: tap anywhere on the page.
Reference
The frequency of the reference A: usually 440 Hz.
The microphone turns on as soon as the page opens; the sound stays on your device, nothing is recorded or sent.
Space: start or stop the microphone