How your mic becomes a pitch detector
12 Jul 2026
Every note has a fundamental frequency — middle C sits at roughly 261.6 Hz — and Piano's listening feature works by identifying that frequency from the raw audio your phone's microphone captures, many times per second, while you play.
The tricky part isn't detecting a single clean note in a quiet room; it's detecting the right note when a piano's overtones, sustain pedal resonance, and any background noise are all present in the same signal. Piano uses a frequency-domain analysis that looks for the strongest fundamental against that noisy backdrop, rather than just the loudest frequency present.
Once a fundamental frequency is identified, it's mapped to the nearest note name and compared against what the reference performance expects at that point in the piece — if you're a few cents sharp or flat, that shows up as partial accuracy on that note rather than a flat pass or fail.
Polyphony — multiple notes played together, like a chord — is harder than a single melodic line, since several fundamentals overlap in the same audio window. Piano handles common chord voicings well, though very dense chords with many closely spaced notes are the current edge of what listening-based detection can reliably separate.