Guitar Tuner
Press start, play one string, and let it ring.
Standard tuning, and the reference notes
The six buttons above play each open string of standard tuning, low to high: E A D G B E. Tap one to hear the pitch you are aiming for; the tuner highlights whichever string you are nearest as you play.
Notice that the gaps are not even. Most adjacent strings are a fourth apart, but G to B is a third. That irregularity is what makes standard chord shapes possible and is also why the B string is the one that most often sounds slightly wrong in a chord.
How the tuner works out the note
Your microphone gives the page a stream of amplitude samples — a wave. Working out which note that wave represents is the interesting part.
The method here is autocorrelation: slide a copy of the signal along itself and see at which offset it matches best. A periodic sound matches itself after exactly one period, so the offset that produces the strongest match is the period. One divided by that is the frequency.
The result is then refined by fitting a parabola through the peak, which gives sub-sample accuracy, and smoothed across several readings so the display does not flicker on every tiny variation.
Why not just use the frequency spectrum
Because a plucked string is not a pure tone. It produces a fundamental plus a stack of harmonics, and on many instruments a harmonic is louder than the fundamental. A tool that simply picks the strongest frequency regularly reports a note an octave too high. Autocorrelation locks onto the repeating period of the whole waveform, which is the fundamental, so it is much harder to fool.
Cents, not hertz
The tuning error is shown in cents because hertz are useless for comparing pitches. A cent is one hundredth of a semitone, and there are 1,200 to an octave, so the same number of cents means the same perceived error whether you are tuning a low E or a high one.
In hertz that low E is a 4 Hz error and the high one a 16 Hz error for exactly the same amount of out-of-tune. Cents describe what you hear; hertz describe the arithmetic.
- Within 5 cents — in tune. The display turns green and most people cannot hear the difference.
- 5 to 15 cents — close. Audible against another instrument but fine alone.
- Over 15 cents — noticeably out.
The reference pitch slider
A4 = 440 Hz is the modern standard, and the default here. It has not always been: pitch drifted between about 415 and 450 across Europe for centuries, and 440 was only fixed by international agreement in the twentieth century.
The slider exists because some ensembles still differ. Many European orchestras tune to 442 or 443 for a slightly brighter sound. Baroque ensembles playing period instruments commonly use 415, which is almost exactly a semitone below 440.
Getting a good reading
- Play one note at a time and let it ring. Chords cannot be read, because there is no single period to find.
- Get reasonably close to the microphone in a quiet room.
- Read it just after the attack has settled. The first fraction of a second of a plucked note is chaotic, and many strings sharpen briefly before settling.
- Tune upwards to the note rather than down onto it. This leaves the string under tension against the tuning peg and holds far better. If you overshoot, go below and come back up.
Common uses and tips
- Tuning before you play, which matters more than any other single habit.
- Checking an instrument holds its tuning over an hour.
- Matching another instrument that is not at concert pitch, using the reference slider.
- Checking intonation — a fretted note twelve frets up should read the same as the open string. If it is sharp, the string length needs adjusting at the bridge.
New strings will not hold pitch for a day or two. Stretch them gently and retune several times rather than fighting it.
Questions people ask
Why does the reading jump around?
Usually background noise, or a chord rather than a single note. Play one string, let it ring, and read it just after the attack settles.
What is a cent?
One hundredth of a semitone, and 1,200 to an octave. It is used instead of hertz because the same number of cents means the same audible error at any pitch.
How accurate is it?
Within a few cents in a quiet room with a clear note — better than most people can hear. Background noise and very low notes are the limiting factors.
Why can I change the reference from 440 Hz?
Because not everyone uses it. Many European orchestras tune to 442 or 443, and baroque ensembles often use 415, almost exactly a semitone lower.
Should I tune up to the note or down to it?
Up. It leaves the string under tension against the peg and holds much better. If you overshoot, drop below and come back up.
Is my microphone recorded?
No. The audio is analysed as it arrives and discarded. Nothing is written down or sent anywhere.
What are the standard guitar tunings?
Standard is E2 82.41, A2 110.00, D3 146.83, G3 196.00, B3 246.94 and E4 329.63 Hz.
Why does my guitar sound out of tune even when the tuner says it is right?
Probably intonation. Check a fretted note twelve frets up against the open string — if it reads sharp, the string length needs adjusting at the bridge.
Nothing is recorded or sent
Where a tool needs your microphone, your browser asks first and then passes the audio straight to the page. It is analysed as it arrives and discarded. Nothing is written to disk, nothing is uploaded, and there is no server here that could receive it.
Pressing stop releases the microphone, and the in-use indicator your operating system shows will go out. The about page lists every network request this site makes, live, so you can check.