Online tuner

How to tune with it

Press Start tuning and allow the microphone. Pick your instrument if it is listed, which makes the tuner name the nearest string rather than the nearest note. That matters when a string is badly out: a low E that has dropped to D# shows up as "E, 100 cents flat, tune up" instead of as a perfectly good D#. Play one string at a time and let it ring. The needle sits in the middle and the dial turns green when you are within 3 cents, which is closer than most people can hear on a single note.

Tune up to the note, not down to it. If a string is sharp, go below the note and come back up. The gears on most tuning pegs have a little play in them, and a string tuned from above tends to slip flat within a song. Tune the whole guitar, then check the first string again: raising one string's tension pulls the neck forward a fraction and flattens the others slightly, most noticeably on a guitar with a floating bridge.

How accurate is it?

The pitch is found with YIN, a detector designed to avoid the classic tuner mistake of reading a note an octave too high or low. It is the same code behind this site's audio to MIDI and autotune. On every release it is checked against test tones with six harmonics, from the low B of a five-string bass (31 Hz) up to E6 (1.3 kHz). That runs at both common sample rates, with each note exactly in tune and 23 cents either side. It has to read every one within a cent, and the worst case measured was a quarter of a cent.

A real instrument reads less steadily than a test tone, because a plucked string starts a little sharp and settles as it rings. The needle shows the median of the last five readings, a quarter of a second of sound, so it settles instead of twitching. The first instant of a hard pluck is best ignored anyway. Tune against the ringing note.

Reference pitch

Almost all modern music tunes to A = 440 Hz. Some orchestras tune a little higher, to 442 or 443, for a brighter sound, and some players prefer 432. Change the A4 box and every note moves with it. It is also how to match a recording that was not made at 440. Run the recording through the key finder, which reports how far it sits from 440 in cents. At 440 Hz, every 4 cents of difference moves A by about 1 Hz.

Getting a clean reading

Pitch detection needs one clear note. Chords, two strings ringing together or a noisy room make the reading jump, and the tuner ignores any reading it is not sure of rather than guessing, so the needle holds still until it hears a clean note. Mute the strings you are not tuning. A phone microphone works fine at arm's length, and a laptop's microphone is better with its fan quiet. For an electric guitar without an amp, hold the body close to the microphone: the strings are loud enough acoustically.

Browser voice processing is turned off for the microphone here. Echo cancellation and noise suppression are built for calls, and they can remove or bend a steady tone, which is exactly the sound a tuner needs to hear.

Tuning to a recording

To play along with a song, you need to be in its key as well as its tuning. The key finder tells you both. If the song is in an awkward key for your voice or instrument, the key changer moves it by semitones without changing its speed. Keeping time is the other half of practising; there is a metronome too.

Privacy

The microphone signal goes into the page, is analysed, and is dropped. Nothing is recorded and nothing is uploaded. The browser shows its microphone indicator while the tuner is listening, and pressing Stop turns the microphone off completely.