How the tuner listens.

Three test signals per note, the same ones the tuner's own test suite uses: a clean tone with the partials of a bright string, a plucked string made by physical modeling (its attack starts sharp, like a real pluck) and the same tone sent through a phone microphone model, a high-pass filter that turns the deepest notes down, with the slight stiffness of a real string on top. The last column shows how much quieter that filter makes each fundamental.

Phone and laptop microphones are built for voices and fade out below about 100 Hz. In the phone model the fundamental of B0 (30.87 Hz, the low string of a 5-string bass) arrives 20.5 dB quieter, and A0, the lowest key of a piano, 22.5 dB quieter. The period is still there in the overtones, so the tuner still finds it: within 1.76 ¢ for B0 and 1.92 ¢ for A0 in the table above.

Deep notes also need time. Four periods of B0 take a window of about 341 ms, against 85 ms for the low E of a guitar, so give a bass string a second to settle. If the reading still wanders, play the 12th-fret harmonic and switch on the ×2 harmonic mode, or plug in through an audio interface.

On a single note, most people cannot hear a difference of about 5 cents; in chords, a few cents already make a slow wobble. So the tuner gives you three windows: Relaxed ±5 ¢, Normal ±3 ¢ and Precise ±1 ¢. Once a string is in, it stays in until it drifts 2 ¢ past the window, so the ✓ does not flicker.

The reading itself is far finer than any of those windows: within 0.2 ¢ on clean tones, 0.2 ¢ on plucked strings and about 1 ¢ through a simulated phone mic for everything from E2 up (2 ¢ for the deepest bass notes).

Pick All strings in the bar at the bottom of the tuner (or in Settings), strum every open string and let them ring. Each string gets its own bar, like a row of tuner needles: the middle line is in tune, the number on top is how far off it is, and the word under it says tighten or loosen. Turn one peg while the strings ring and watch its bar move.

How it hears six notes at once: the tuner knows which notes your tuning should have. It looks for each string's own row of overtones in the sound and fits all the strings together, so an overtone of the low E is not taken for the B string. It reads about ten times a second, in a background thread of the page, still on your device.

Where it stops

• Far off: a string more than about 60 ¢ off (a bit more than half a semitone) is only flagged, with an arrow and tighten a lot or loosen a lot. Tap its bar to tune it alone first.
• Octave strings: a string an octave or two above another one, and in tune with it, can hide under it. Its bar then shows only a guess (≈ and a hollow mark, or ? when there is none), and a guess never counts as in tune: a muted string would look the same. Tap it to check it alone.
• Pairs and repeated notes: the two strings of a 12-string pair are read together and shown apart only when they differ enough. Two strings on one note on separate bars, like a balalaika's two E strings, read as one: tap each to tune it alone.
• Tested on simulated strings so far. A quiet room, a firm strum and open strings that ring help most.

• One string at a time. In Guided and Auto, let the other strings stop ringing, or touch them lightly: two strings at once make a mix. To read them all together, use All strings.
• Pluck, then wait. Read the note while it rings, not in the attack. A firm pluck near the neck gives a strong, steady fundamental.
• Use the built-in mic. Bluetooth headsets squeeze the sound for calls; the phone's own microphone or a cable is cleaner.
• A quiet room helps. Fans, hum and talk compete with the string: the less noise there is, the faster the reading settles.

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