Instrument Tuner | Natalie Perret

How this tuner works

After you grant microphone access, the tuner reads short snapshots of the audio waveform through the Web Audio API. It compares each 4,096-sample snapshot with delayed copies of itself. The strongest repeating interval gives the fundamental frequency of the note you are playing.

R (k) = \sum_{i = 0}^{N - k - 1} x_{i} \cdot x_{i + k}

Here, x is an audio sample, N is the snapshot length, and k is a trial delay. Once the strongest repeating delay is found, a small interpolation term improves the estimate:

f = \frac{f_{s}}{k_{peak} + δ}

The detector takes the median of the five latest readings to calm down small jumps, then holds the last reliable pitch for up to 1.5 seconds. It converts that frequency to the nearest chromatic note using A4 = 440 Hz.

m = round (69 + 12 \cdot \log_{2} (\frac{f}{440}))

Reading the display

The large note is the pitch the microphone hears. In Chromatic mode, the needle compares it with the closest equal-tempered note. With an instrument preset, it compares the pitch with the closest open string and highlights that string's card. One semitone is 100 cents.

c = 1200 \cdot \log_{2} (\frac{f}{f_{ref}})

A centred green needle means the target is within 5 cents.
A needle to the left means the pitch is flat, so tune it up.
A needle to the right means the pitch is sharp, so tune it down.

Instrument presets

Presets cover ukulele, guitar, four- and five-string bass, violin, viola, cello, and mandolin. Common alternatives include Low-G and baritone ukulele, Drop D guitar, and DADGAD. A preset only changes the reference strings; the detected note remains chromatic.

Limitations

Play one clear, sustained note at a time. Chords, speech, background noise, and nearby instruments can confuse the detector.
Strong overtones can make autocorrelation choose the wrong octave, especially with a very bright attack. Let the note settle briefly.
Detection is limited to roughly 30-1,200 Hz and depends on the quality and placement of your microphone.
The reference pitch is fixed at A4 = 440 Hz. This is useful for everyday tuning, but it is not a calibrated replacement for a strobe tuner or workshop equipment.
Microphone access requires browser permission and a secure page. Some browsers may pause audio processing when the tab is in the background.

Privacy

Audio is analysed locally in your browser. The tuner does not record or upload it, and the microphone stream stops when you stop the tuner or leave the page.