How to tune an electric guitar without an amp

You can. An unplugged electric is quiet, not silent, and a tuner built for it reads every string, including the low E that most apps lose.

Why it is harder than an acoustic

An acoustic guitar has a soundbox that turns string vibration into air pressure; that is its whole purpose. A solid-body electric has a plank. The strings still move the air a little, and that is what your ears hear when you practise unplugged, but it is roughly twenty to thirty decibels quieter than an acoustic at the same distance.

For a tuner app that means two problems. The signal is close to the room's noise floor, so the app has to decide whether a faint periodic wobble is a note or the fridge. And the low strings are the faintest of all: a solid body radiates high frequencies better than low ones, so the low E arrives mostly as its overtones, with the fundamental almost missing. Tuners that do not expect this read the second harmonic and show E one octave up, or lock onto B, the third harmonic.

What to do

1. Get close. Hold the phone ten to twenty centimetres from the strings, above the body, roughly over the neck pickup. Every doubling of distance costs six decibels.
2. Find a quiet moment. Not silence, just no TV or conversation right next to the phone. A tuner that filters the audio band already ignores most room rumble and hiss.
3. Pluck once, moderately, over the neck. Plucking near the neck pickup produces more fundamental and fewer overtones than plucking at the bridge. Then leave the string alone: repeated plucks give the detector overlapping notes and a jumpy reading.
4. Mute the other strings. On an unplugged electric the sympathetic ringing of the other five strings is comparable in level to the string you want. Rest the edge of your picking hand across them.
5. Read the low E last and patiently. It takes the longest to settle. If the needle still jumps between octaves, see below.

How TuneGlass handles it

We built the detector on an unplugged electric because that was the case every other tuner we tried got wrong. A few things it does that a generic tuner does not:

• A low input gate. It listens about thirty decibels below the level most tuners treat as silence, and uses the shape of the signal, not its loudness, to decide whether a note is present.
• Band-limiting. Everything below 40 Hz and above 1.5 kHz is filtered out before detection, which removes hum, hiss and most of the overtones that cause octave errors.
• Octave reasoning. The detector keeps several candidate pitches, not one. When the strongest candidate is an octave above the string you have selected or were just tuning, and the lower candidate is plausible, it picks the lower one.
• Boost low E. A setting for the hardest case: a longer analysis window, a narrower filter and heavier smoothing on the sixth string. It adds a tenth of a second of lag and makes the low E read steadily on guitars where nothing else does.
• Hints. In Precision mode the app tells you when the signal is too quiet, when other strings are ringing, or when it suspects an octave slip, so you know what to change instead of guessing.

When you should plug in anyway

If you are on a stage, in a rehearsal room with a drummer, or anywhere with constant noise, a microphone tuner will struggle, unplugged or not. A clip-on tuner (which senses vibration through the headstock) or a pedal tuner in the signal chain is the right tool there. At home, on the sofa, with the amp off, the phone is enough.

A note on intonation

If the open strings tune perfectly but chords up the neck sound sour, that is intonation, not tuning, and no tuner fixes it: the saddles on the bridge need adjusting so that the 12th-fret note is exactly an octave above the open string. A tuner is how you check it, though: compare the open string and the 12th fret, and if the fretted note reads sharp, the string needs to be longer (saddle back).

Questions