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. The needle compares it with the closest string in the selected tuning and shows the difference in cents. One semitone is 100 cents.

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

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

High-G and Low-G

The mode changes the four reference strings used by the comparison. High-G uses G4, C4, E4, A4. Low-G replaces G4 with G3. The pitch detector itself remains chromatic, so it can still identify notes outside those four strings.

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 180-1,200 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.