Updated October 5, 2026
1. Listening to the microphone
When you press Start, the browser asks to use your microphone. Then it turns the sound into a stream of numbers, tens of thousands of air pressure measurements every second. Everything below happens inside your browser, and the audio is never recorded or uploaded.
2. Finding the pitch
A plucked string makes a repeating wave. Its pitch is how many times per second the pattern repeats, measured in hertz (Hz). The hard part is that an instrument plays many frequencies at once. There is the main one, called the fundamental, plus overtones at two, three and four times that frequency. On a low guitar string, the overtones can be louder than the fundamental itself.
That is why urTuner doesn’t just pick the loudest frequency. It uses the McLeod pitch method. This compares the wave with delayed copies of itself (autocorrelation) to find how long the whole pattern takes to repeat. It does this about 30 times per second.
3. From hertz to a note
Western music divides each octave into 12 equal steps called semitones. They are all calculated from one reference note, A4 = 440 Hz. Each semitone multiplies the frequency by the twelfth root of two. The tuner finds the note closest to the measured frequency, or the closest string in your chosen tuning.
4. Cents and the needle
Each semitone is divided into 100 cents. The needle shows how many cents the note is above (sharp) or below (flat) the note it should be. Within about ±5 cents, most people hear the note as in tune, so that is where the display turns green.
What affects accuracy
- Background noise blurs the repeating pattern. Lower the sensitivity in noisy rooms.
- Very low notes, such as a bass guitar’s low E, are hard for small microphones to pick up. Use harmonics instead.
- The attack, the first moment of a note, is unstable. Read the needle once the note settles.
- Chords contain several pitches, but tuners measure one note at a time.
Try it on the guitar tuner or see raw frequencies with the pitch detector.