🎹 Overtone

Piano tuning device · measures inharmonicity & builds a stretched tuning

Concert A4 (Hz) Style Temperament FFT size Pitch raise Overpull %

Tuning — smart

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target —

f₀ —

stretch —

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cents vs stretched target

Play and sustain a single note with the sustain pedal held. The strobe drifts right when sharp, left when flat — tune until it freezes.

Inharmonicity B

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Target offset

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Partials

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Measured / 88

Keyboard — measured & tuned

untouched B measured tuned ±0.5¢ current · click a key to target it

Inharmonicity B across the keyboard

Tuning curve (cents stretch vs equal temperament)

Violet dots = notes you've measured. The curve is recomputed live from your measurements by matching coincident partials — bass tunes flat, treble sharp.

Spectrum & partials

hold partials

n	Measured Hz	Pure n·f₀	Model Hz	Δ pure (¢)
no signal

How this tuner works

A stiff piano string's partials run sharp of pure harmonics: Pₙ = F·n·√((1+B·n²)/(1+B)). Overtone measures the inharmonicity B of each note you play (by fitting its overtone series), then builds a keyboard-wide model of B and computes a stretched target for every key so the best coincident partials between octaves beat as little as possible. A4 is anchored to your concert pitch; the bass is tuned slightly flat and the treble slightly sharp — the Railsback curve shown top-right. The needle/strobe shows your deviation from the stretched target, not naïve equal temperament — that's what makes a piano sound in tune. All audio stays on your device.

Serve over https:// or localhost for mic access. Use a quiet room, hold the sustain pedal, and play one note at a time for the cleanest inharmonicity reading. Your measured tuning is saved in this browser.