You need to tune your guitar and don't have a clip-on tuner handy. Any laptop or phone microphone, combined with a pitch-detection algorithm, does exactly the same job as a physical tuner — it detects the frequency of the string that's ringing and tells you how close or far it is from the correct note.
How it detects the exact note from sound
The technical method this tool uses is called autocorrelation: it compares the captured audio signal against a time-shifted copy of itself at various intervals, looking for the shift where they match best. That shift corresponds to the wave's period, from which the fundamental frequency is calculated directly.
This beats simply looking for the strongest peak in a frequency analysis (FFT), because a plucked string doesn't just produce its fundamental frequency — it also produces harmonics (multiples of that frequency) that are sometimes stronger than the fundamental itself. A naive peak detector can "lock onto" a harmonic and detect the wrong note; autocorrelation is much more robust against that problem because it analyzes the wave's full repetition pattern, not just its energy peak.
Standard EADGBE tuning
A guitar's six strings in standard tuning, from lowest to highest:
- E2 (82.41 Hz) — the sixth string, the thickest
- A2 (110.0 Hz)
- D3 (146.83 Hz)
- G3 (196.0 Hz)
- B3 (246.94 Hz)
- E4 (329.63 Hz) — the first string, the thinnest
The tuner automatically identifies which string you're closest to based on the detected frequency, no need to select it manually.
What "cents" are and why they matter
A cent is one hundredth of a semitone — the standard unit for measuring fine tuning error. The tuner shows how many cents above or below the target note you are: values within ±5 cents are considered "in tune" for most purposes, while ±20-30 cents is already clearly audible mistuning.
Frequently asked questions
Do I need an electric guitar with a direct connection? No, it works with the microphone picking up the acoustic sound of any guitar, electric or acoustic.
Why does it sometimes detect the wrong string? If there's significant background noise or you pluck two strings at once, the algorithm can get confused. Pluck a single string in a relatively quiet environment for best results.
Does it only work for standard tuning? The tuner compares against the six notes of standard EADGBE tuning; for alternate tunings you'd need to go by the detected frequency in Hz instead of the highlighted string.
Is the microphone audio uploaded to a server? No, the analysis happens entirely in your browser with the Web Audio API.
Tune your guitar with your microphone, with real-time note and cents detection, using the guitar tuner, free and nothing to install.