Pitch detector

Find a note in three steps

1. Press Start listening and allow the microphone. A quiet room and a phone or laptop held about an arm’s length away work best.
2. Sing or play a single steady note. The big letter shows the note and its octave (A4 is the A above middle C), the needle shows how far you are from that note in cents, and the trace draws your pitch over the last ten seconds.
3. To check a recording instead, choose an audio or video file, or try the sample. You get a chart of the pitch over time and a list of the notes with their start times and how far each one was from the nearest note.

How the note finder works

A pitch detector has to answer one question many times a second: after how many samples does this sound repeat? We use the McLeod Pitch Method, published by Philip McLeod and Geoff Wyvill in 2005. It compares each 40–90 ms slice of sound with shifted copies of itself, picks the first shift where the slice lines up with itself almost perfectly, and refines it between samples. That repeat time is the period; one second divided by the period is the frequency in hertz. How well the slice lines up also gives a “clarity” score, and the page only shows a note when the clarity is high and the sound is loud enough, so breaths, hiss and room noise do not make the needle jump.

Octave mistakes, and how we avoid them

The classic failure of a pitch detector is naming the right letter in the wrong octave. A voice or an instrument whose lowest harmonic is weak can look like it repeats twice as often as it really does, and a long window can see a pattern that repeats every two periods. The detector takes the first strong repeat rather than the strongest one, checks whether twice that period lines up clearly better (the sign of a missing fundamental), and the live display ignores a one-off jump of exactly an octave unless it persists. In our tests with synthetic tones, including ones whose fundamental is 20 dB quieter than the second harmonic and ones with no fundamental at all, it named the correct octave every time.

Notes, hertz and cents

Notes are named in scientific pitch notation: C4 is middle C, A4 is the A above it, and the octave number goes up at each C. The page uses equal temperament with A4 = 440 Hz, the international standard, and you can change the reference for an orchestra tuned to 442 Hz or a baroque group at 415 Hz. A cent is a hundredth of a semitone. Most listeners notice a difference of about 5–10 cents between two steady tones, so the needle turns green within ±5 cents. Singers naturally drift and use vibrato, so a moving needle on a held note is normal; the trace shows whether you are centred over time.

Accuracy and honest limits

On clean synthetic tones from 41 Hz (the low E of a bass guitar) to 1.5 kHz, the detector's error was under 0.5 cent, and it stayed silent on white noise. Real conditions are harder: a cheap laptop microphone removes most of the sound below about 100 Hz, room echo smears note changes, and background music confuses any single-note detector. Phone browsers may apply their own noise suppression; we ask the browser to turn it off, but not every browser obeys. If you need a tuner for a guitar, any of these readings works, but a clip-on tuner that feels the vibration directly will be steadier in a loud room. Microphone use has been tested in Chrome; Firefox, Safari and phones have not been tested yet.