Playground · Tuner
Guitar tuner: pluck a string and see how many cents it's off.
Press start, allow the microphone and pluck a string. The meter finds the note, names the nearest string and shows how many cents sharp or flat it is. Tap a string to hear its reference tone and keep the meter on that string. If your guitar isn't tuned to A4 = 440 Hz, change the tuning or the reference pitch.
Meter
not listeningpluck a string
Strings
E A D G B E
Reference
A4 = 440 Hz
How it hears
The microphone is read in windows of 4,096 samples. Each window is compared with itself at every lag (McLeod’s normalised square difference), and the first strong peak gives the string’s period, refined between samples with a parabola. On a phone’s microphone, plain autocorrelation tends to take a low E for its octave; this method doesn’t. The frequency becomes a note and a cent offset with 1200 · log₂(f / f₀). The needle shows the median of the last five readings so it doesn’t shake, and it rests when the note dies away. Within five cents counts as in tune, which is finer than most ears can hear.
What this page sends
Nothing leaves your browser. The microphone opens when you press start and closes when you press stop or leave the page. Each window of sound is measured and thrown away; the tuner keeps only its last five pitch readings, and it makes no request to a server while you tune.