Guitar Intonation

Intonation

Guitar intonation refers for the fact that each string on a guitar needs to be a slightly different length for the notes to sound at the proper pitch when the strings are depressed/deflected at each fret. If your guitar sounds in tune when the open strings are plucked but drifts out of tune as you travel up the fret board, then poor intonation is the problem. Please Note that most acoustic guitars do not have a movable bridge/saddle, so intonation issues will probably require the assistance of a qualified technician. Intonation issues on a well constructed acoustic with a fixed bridge usually means you may have other serious problems with the instrument that need to be addressed.

Every time a string is fretted it is stretched or deflected. As you stretch the string the pitch rises. This rise in pitch is not the same at every fret, as you go further up the fret board the amount of the rise in pitch increases. Simply put, pressing the string to the fret board results in deflection (stretching of the string) thereby changing the pitch which requires some measure of compensation at the bridge.

The rise in pitch is also different for each string, as the diameter or mass of each string differs so does the amount of stretch. Due to this shift in pitch the treble string nut to saddle length is slightly shorter than the bass string.

1) Tune your instrument. To adjust intonation you must tune your guitar properly, the more accurately tuned, the more accurate your adjustments will be, let me say that again, the more accurately tuned, the more accurate your adjustments will be, so take your time. The main reason for tuning the whole guitar is to apply proper tension to the neck, since the instrument was designed to be played in tune, and at this tension.

2) Play the harmonic on the 12th fret of the string you are adjusting and tune this string again, if necessary, until the harmonic is in perfect pitch.

3) Play the octave by pressing down at the 12th fret with just enough force to clearly sound the note. This fretted note is the pitch you are using to determine sharp or flat, NOT the harmonic

4) Adjust the saddle. If the pitch is the same no adjusting is necessary, if it is SHARP the string is too short and the saddle needs to be moved away from the nut thereby lengthening the string, if it is FLAT the string is too long and the saddle needs to move closer to the nut. Small movements are usually all that are required to correct intonation, so easy does it.

Intonatio Fretboard

Note - Since the adjustment of the saddle changes the pitch you will need to re-tune the string each time you go through these steps until there is no further need of adjustment, at which point the open string, the octave and the 12th fret harmonic should be in tune.

WHY?

The 12th fret on a guitar is usually positioned at half the distance between the nut and the bridge. All 12 notes of the chromatic scale from the open string to its octave fit in this space.

The 24th fret marks the octave of the distance between the 12th fret and the saddle which is half of the remaining string length. All of the notes between the first octave (12th fret) and second octave (24th fret) have to fit in half the length of the string, or all 12 notes of the chromatic scale have to fit in the space between the 12th fret to its octave at the 24th fret. This is basically why the frets/notes of the second octave are closer together than the frets/notes of the first octave, and the reason why the deflection increases as we go up scale. The shorter the string gets, as we progress up the fret board, the change of length required to generated a higher pitched note becomes less. So the frets get closer and closer together as we produce higher pitched notes on any given string.

Other aspects of intonation not often mentioned is what to do if the guitar intonation seems to be correct except at the first 2-3 frets (usually sharp when fretted) , this is a result of the nut piece being too high and can be easily remedied by cutting the string notches deeper or removing the nut and shaving the bottom. *CAUTION* a little goes a long way when making these adjustments. If the guitar intonation is fine at the high end and low end of the scale but runs off in the middle the truss rod needs to be adjusted accordingly. Basically any excess deflection of the string before it makes contact with the fret can throw the intonation off, too much deflection and the note tends to go sharp. Achieving the proper balance throughout the guitar's scale length is the main objective and can make the difference between a mediocre or a well polished performance.

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