Instrument tuner

Press Start tuner, allow the microphone, and play a string. The big letter is the string (or note) it heard, the needle and the number show how far off it is in cents (a hundredth of a semitone), and the strobe’s bands stand still when it’s right. It works on a phone: the screen stays on while it listens, and the string buttons are big enough to hit with a thumb.

For looking at a signal — scope, spectrum, a plain tuner beside them — use the audio oscilloscope. To learn songs on piano or guitar, try the music trainer; for chords, scales and fretboard patterns, the chords and scales explorer.

How to use it

Choose the instrument and tuning. Guitar has standard, drop D, half and whole step down, drop C, DADGAD, open G, D, E, C and A, Nashville and 7-string; bass has 4, 5 and 6 strings; ukulele re-entrant, low G, D and baritone; violin, viola, cello, double bass; mandolin, mandola, octave mandolin; 5-string banjo (open G, double C, open D), tenor and Irish tenor. Custom strings… takes any list of notes, low to high, such as C2 G2 D3 A3 E4 A4. Chromatic shows the nearest note to whatever you play.
Play one string at a time and let it ring. Auto string picks the string nearest the pitch and sticks with it while you turn the peg, so it doesn’t jump to the next string half-way. Tap a string’s button to lock the tuner to that string (useful when it’s a long way out — a semitone or more) and hear its reference tone; tap again to unlock.
Turn until the needle is in the green band, the readout turns green and In tune appears. The stability bar shows how steady the pitch is over the last second: a plucked string goes sharp for a moment as you pluck it, then settles; wait for Steady before you trust the reading.

Demo signal plays a synthetic string, a little out of tune and then tuned up, through the same detector — a way to try the tuner without a microphone.

Reference pitch and temperaments

A4 can be set anywhere from 415 to 466 Hz, with buttons for 415 (Baroque), 430 (Classical), 432, 440, 442 and 443 (orchestras) and 466 (Chorton). The string targets move with it.

Temperaments are for keyboard players and anyone matching one: equal, Pythagorean, ¼- and ⅙-comma meantone, Werckmeister III, Kirnberger III, Vallotti, Young (1799), and 5-limit just intonation. Each is built from its chain of fifths (the tests check the results against the published tables), can be laid on any key, and keeps A at the reference pitch; the grid under the menu lists every note’s offset from equal temperament in cents. Tuning a harpsichord in Vallotti at A = 415: set both, choose Chromatic, and tune each note until the needle centres.

Reference tone

Reference tone plays the chosen note (or the string you tap) at the current reference pitch and temperament — as a sine, a warmer tone with harmonics, or a plucked note that dies away. Use it to tune by ear, or to check a speaker.

How it works

The detector looks for the period of the sound with the McLeod pitch method (MPM): the normalised square difference between the signal and itself delayed, whose first high peak is the period. YIN, the other common method, is there too. Both are worked out with an FFT so the window can be long enough (up to about a sixth of a second) for a 5-string bass’s low B at 31 Hz. The low strings of a guitar or bass often have a weaker fundamental than their second harmonic, which tricks simple detectors into reading an octave high; the detector checks the lag twice as long, and the string picker knows that half the frequency is the string you’re tuning. Readings go through a median filter, so one bad frame doesn’t make the needle jump, and then a short average. Echo cancellation, noise suppression and automatic gain are switched off: they’re meant for voices and change the very pitch you want to measure.

Browser support

Any current browser with a microphone: Chrome, Edge, Firefox and Safari, on desktop, Android and iPhone. The microphone needs the page to be served over HTTPS (it is) and your permission. Keeping the screen on uses the Screen Wake Lock API, where the browser has it. If there’s no microphone the reference tones and the demo still work.

Privacy

The sound from the microphone is analysed in the page and thrown away; nothing is recorded or sent anywhere. Your choices (instrument, tuning, A4, temperament) are kept in this browser’s local storage. The Share link button puts them, and nothing else, in the link.