The microphone is not used until you press that. When you do, the audio is analysed frame by frame in this page to find the pitch, and then discarded. It is never recorded, never stored, and never sent anywhere — there is no upload in this tool and nothing to upload to. Stopping releases the microphone immediately, and your browser lets you revoke the permission at any time.
| String | Note | Frequency | Play |
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A tuner does not measure frequency directly. It measures how long the waveform takes to repeat, and divides. This one uses the McLeod pitch method: it computes a normalised correlation of the signal against a delayed copy of itself, finds the delays where the two line up, and takes the shortest one that is nearly as good as the best. The peak is then interpolated between samples, which is what gets the answer below a cent — at 48 kHz a single sample is already 5 cents wide at the top E.
Because the loudest partial of a plucked low E is usually not the fundamental. Small microphones roll off below 100 Hz, so the second and third harmonics often dominate, and anything that picks the biggest peak in a spectrum reports the octave. Correlation asks a different question — when does the whole waveform repeat — and the answer is the same whether or not the fundamental is present.
The signal is high-pass filtered at 62 Hz first, forwards and backwards so no phase shift is added. Mains hum at 50 or 60 Hz, air conditioning and handling noise all sit below the lowest note a guitar plays, and leaving them in cost up to 25 cents of error on a low E.
Measured against synthesised tones of known frequency, on the reading the tool actually displays rather than on a single frame: 0.19 cents median error on a clean signal and 0.64 cents with mains hum, air-conditioning rumble or handling noise added, worst case 2.0 cents across 75 cases. For comparison, most people cannot hear a 5-cent error, and a fretted guitar is further out than that by design.
It refuses to read rather than guess. When consecutive frames disagree by more than 10 cents it shows the reason instead of a number, which is why a very noisy signal sometimes says nothing at all — 9 of those 30 contaminated cases decline.
Almost always because a second string is still ringing. Two notes together have their own repeating period, and it distorts the answer even when the search is narrowed to one string: on tests with an adjacent open string sounding, the tool declines to read in 23 of 25 cases and the two it does read land about a third of a semitone out. That is a real limit, not a bug to work around — damp the other strings and it resolves immediately.
No. The microphone is only opened when you press start, the audio is analysed in this page and discarded frame by frame, and nothing is recorded, stored or transmitted. There is no upload in this tool. Stopping releases the microphone, and the permission is your browser's to revoke whenever you like.
It does not have to — leave it on auto and it will name whatever it hears. But if another string is still ringing, the two notes together have their own repeating period, and a pitch detector that reports it is not making a mistake: the sum really does repeat at that rate. Naming a string narrows the search to a minor third either side, which is the only way to answer "how far is this string out" while another one sounds.
Intonation. Pressing a string down stretches it slightly sharp, and the amount depends on the action, the gauge and where the saddle sits. That is why saddles are set individually, and why a guitar tuned perfectly open is never perfectly in tune everywhere at once.
440 Hz unless something else in the room says otherwise. Orchestras often sit at 442 or 443, some recordings are at 432, and baroque ensembles commonly use 415 — a semitone flat, which is why the tool goes down that far.
This page has changed in 1 archived release, but each of those was a site-wide pass, so none is attributable to this tool on its own and none is listed here. That is not a claim that the tool never changed — a release that reworked many pages at once may well have altered this one too. The changelog has them.