Pitch Detector

How a microphone becomes a tuner

When you sing a note or pluck a string, the air pressure rises and falls in a repeating pattern. The number of times that pattern repeats each second is the fundamental frequency, measured in hertz (Hz), and it is what your ear hears as "pitch." This tool captures that pressure wave through your microphone using the browser's Web Audio API, then measures its period directly with an autocorrelation algorithm. There is no machine-learning model and no server involved — the maths runs in a tight loop on the raw audio samples on your own device.

Autocorrelation works by sliding a copy of the waveform against itself and asking, "after how many samples does the signal line up with itself again?" That offset, called the lag, is the length of one cycle. If the strongest match happens at a lag of 100 samples and your microphone records 48,000 samples per second, then one cycle takes 100/48000 of a second, so the frequency is 48000 ÷ 100 = 480 Hz. The tool ignores quiet input (anything below a small loudness threshold reads as silence) and trims the buffer to whole cycles before correlating, which keeps the reading stable.

From frequency to note name

Western music divides each octave into twelve equal semitones, and frequency doubles every octave. The tool converts a frequency to a note using A4 = 440 Hz as the anchor and the formula semitones = 12 × log2(freq ÷ 440). Rounding that result to the nearest whole number gives the closest note; the leftover fraction, multiplied by 100, gives the cents deviation — how sharp or flat you are within that semitone.

A worked example

Suppose you play the open A string on a guitar and the detector reads 448 Hz. Plugging in: 12 × log2(448 ÷ 440) = 12 × log2(1.0182) ≈ 0.31 semitones. The nearest whole semitone is 0, so the note is A4. The remaining 0.31 of a semitone is 0.31 × 100 ≈ +31 cents. The display shows A4, +31 ¢, the needle swings to the right, and its colour shifts toward yellow because you are noticeably sharp. Loosen the string slightly until the needle centres and turns green — the tool treats anything within ±10 cents as in tune, ±10 to 25 cents as close, and beyond that as off.

Reading the cents needle

The horizontal bar maps the range of −50 to +50 cents onto its full width, with the centre line marking perfect pitch. A semitone is 100 cents, so ±50 cents is exactly halfway to the next note. The needle colour gives you a glance-able verdict:

Practical tips for a stable reading

• Play one note at a time. Autocorrelation finds a single dominant period. A chord or two strings ringing together produces competing periods, so the readout jumps. Mute everything except the note you are tuning.
• Sustain the note. The pluck or attack is full of noise and overtones. Let the sound settle into a steady tone and read the value after the first half-second.
• Get close and reduce background noise. Fans, traffic, and voices add energy that can fool the period search. A quiet room with the source near the mic gives the cleanest result.
• Mind octave errors. If a reading sits exactly an octave too high or low, the algorithm has locked onto a harmonic instead of the fundamental. Re-attack the note more firmly to strengthen the fundamental.
• Tune low strings carefully. Very low notes (a bass low E is about 41 Hz) have long cycles, so give the tool a clear, loud sample to measure.

Common use cases

The detector works with anything that produces a clear, sustained pitch: tuning a guitar, violin, or ukulele; checking the intonation of a piano note; warming up your singing voice against a target pitch; verifying that a wind instrument is not running sharp as it warms up; or simply identifying what note a hum, whistle, or appliance is producing. Because it reports the exact frequency in Hz alongside the note name, it doubles as a quick way to measure the pitch of any tone, not just instruments built around standard tuning.

A note on accuracy and privacy

This is a chromatic tuner pinned to A4 = 440 Hz, the modern concert-pitch standard. If your ensemble tunes to a different reference (some orchestras use 442 or 443 Hz), every reading here will appear a few cents off by design. For most practice and quick checks, 440 is the right benchmark. Crucially, your audio never leaves the page: the microphone stream is processed locally and discarded, and releasing the mic with the Stop button ends all capture. Nothing is recorded, uploaded, or stored.