What common mistakes do people make when tuning their guitars? Not changing their strings.
You might say, “What? I thought this was a tuning tip?” Simply put, it affects your ability to get your guitar in tune.
According to Jim Ferguson, the harmonics on old strings start to go bad (become inharmonic) when dirt and oils from your hand coat the strings. Plus, the frets dent the strings, making them asymmetrical, also leading to inharmonicity.
Check your intonation at the 12th fret by first playing the fretted note then playing the 12th fret harmonic for each string. (See the harmonics video below.)
“The fretted tone should be exactly the same pitch as the harmonic tone. Usually, in the case of old strings, the fretted tone will be flat – just how flat is one method for determining how bad the strings are.
“A noticeable difference should prompt a change in strings. A quarter-step is intolerable to most musicians, and anything beyond that could affect your ear for true tones” (The Guitar Player Book 381).
When the string’s harmonics become “inharmonic,” it makes it impossible to get all the different chord voicings on your guitar in tune. You may get one or two chords in tune, but the rest will be out of tune. This’ll also be bad for your ear.