How to tune a guitar with your phone

The phone in your pocket is a better tuner than the pedal on your board. Here is how to use it well.

What the app is doing

The microphone picks up the string, the app chops the audio into short windows and, for each one, works out the period of the waveform: how often it repeats. The inverse of that period is the frequency, and the frequency is the note. Good tuners do this forty or fifty times a second and smooth the result so the needle moves like a needle rather than a nervous insect.

The display then compares that frequency with the nearest note of the tuning you have chosen and shows the difference in cents, hundredths of a semitone. Zero is in tune. Negative is flat (tighten the string), positive is sharp (loosen it).

Tuning, step by step

1. Put the phone where it can hear. On your knee or the sofa arm, screen up, within arm's length of the guitar. For an acoustic, anywhere near works. For an unplugged electric, closer: ten to twenty centimetres from the strings.
2. Play one string and watch the note. The app names the string it thinks you are playing. If it says the wrong one, you are a long way off; keep turning in the direction of the right note.
3. Turn the peg until the needle centres. Tighten for sharp, loosen for flat. Make small moves and let the note ring between them.
4. Approach from below. If you overshoot sharp, go flat and come back up. The string then holds.
5. Do all six, then do them again. The second pass is quick and catches the drift the first pass caused.

Auto or manual

Most apps have both. Auto listens for any string and names the nearest one; it is what you want nearly all the time. Manual locks the target to one string, which helps when you are a long way off (tuning up to standard from a slack string, say) or when the app keeps guessing a neighbouring string on a detuned guitar. In TuneGlass the switch is at the bottom of the screen, and tapping a string circle in manual mode selects it.

Reading the needle

Three things on a tuner display matter: the note, the needle, and some kind of confidence. A needle that twitches wildly is usually a quiet or noisy signal rather than a wildly out-of-tune string. Pluck once, firmly, and let it ring. TuneGlass fades the display as the note dies away so you are not reading the tail of a string that has stopped vibrating, and in Precision mode it shows signal level and confidence as bars so you can see why a reading is unstable.

What makes a tuner app good

• It opens into the tuner. No splash, no sign-in, no "rate us", no lesson funnel. You pick the guitar up to play, not to tap through screens.
• It hears the low E. The sixth string is where tuner apps fail, especially on electrics. Octave errors on the low E are the most common complaint in reviews of the popular tuners.
• It does not nag. Ads between strings and a subscription for Drop D are why people hate tuner apps. One purchase for the extras, or none at all, is the honest model.
• It respects the room. Audio stays on the phone. There is no reason for a tuner to send sound anywhere.
• It knows your instrument. Bass, 7- and 8-string, 12-string and ukulele all have different ranges and string counts; a tuner that only knows six strings and 80 to 330 Hz is guessing on the rest.

Alternate tunings

A phone tuner's real advantage over a pedal is that any tuning is one tap away. Drop D, half step down, DADGAD, Open G: each is a set of six target notes, and the app simply compares your strings against a different set. Every tuning TuneGlass supports is documented with notes and frequencies in the tunings reference, and the standard tuning for every instrument is free.

Questions