About FretPitch
FretPitch is a free guitar tuner that runs entirely in your web browser — no app to install and no account to create.
It began as a small project with a simple goal: a tuner that opens instantly, is accurate enough for serious players, and is pleasant to use on a phone propped on a music stand.
How it works
When you press Start tuning, the browser gives the page access to your microphone through the Web Audio API. Around thirty times a second, the tuner takes a short snapshot of the sound and looks for the length of the repeating wave in it — its period — using the McLeod pitch method, a refined form of autocorrelation. That approach copes well with the strong overtones of guitar strings, which often fool simpler tuners into jumping an octave.
The frequency is then compared with the nearest note (in Chromatic mode) or with the nearest string of your chosen tuning, and the difference is shown in cents — hundredths of a semitone.