How to use it
- Press Start tuner and choose Allow when the browser asks.
- Play one note and let it ring. The big letter is the nearest note with its octave (A4 is the A above middle C).
- If the needle is left of centre the note is flat, so tighten the string or raise the pitch; if it is right of centre the note is sharp.
- When the cents value is within ±5, the needle turns green. That ±5 cents window is a rule of thumb, not a standard.
- Press Stop when you are done.
How it works
The page connects the microphone to the browser’s audio analyser and, every 100 ms, compares the last 4096 samples with delayed copies of themselves (autocorrelation). The first strong repeat gives the period of the wave, so the frequency is the sample rate divided by that period. The last five readings are combined by taking the median to steady the needle.
The note comes from the frequency: the number of semitones from A4 is 12 × log2(f / A4), and the cents are the remaining fraction of a semitone × 100.
Worked example
With A4 = 440 Hz, a string sounding at 110 Hz is 12 × log2(110 / 440) = −24 semitones from A4, which is exactly A2: 0 cents. A string at 112 Hz gives 12 × log2(112 / 440) = −23.69 semitones, so it is A2 about 31 cents sharp.
Tips
- Tune in a quiet room and hold the microphone near the instrument.
- Play one string at a time and let the attack die down; the first moment of a pluck is the least stable.
- Phones and laptops may change the sound with their own filters; this page asks the browser to switch those off, but not every device obeys.