Setting Guitar Intonation

You know something doesn’t sound right with your guitar. It’s been tuned up, but fretted notes are still sharp. These are intonation problems, A sign it’s time to ask these 18 questions.

1. Is it all in your head?

Humans can detect about a three cent error in a note. Intonation errors are around three cents as well. It’s right on the edge of what you can hear. In precision all tone wood guitars this effect matters more. For poorly made ones the source of error might be from the build of the guitar itself.

Take Away: These errors are real, and detectable as shown by data from multiple guitars playing the B string at the 12th fret. A whopping 6.7%.

2. Are your nut and saddle Compensated?

Alterations to the nut and saddle can fix the sharpness. They do this by changing the scale length and fret position.

Take Away: It is possible to set true intonation this way but often requires a new saddle or bridge.

3. Is your action high?

When a string is pressed down, fretted, its total length rises and so does its tension. This increased tension will cause the note to play sharp. Higher action means more tension which causes the note to play sharp. Low action means less tension. As well, where you play the note on the fretboard effects the amount of stretching and thus error. Action is upstream from intonation so any change in action will affect it.

Take Away: Try to lower your action for less errors.

4. Is your guitar responsive?

Sometimes the tones of the guitar body can interact with the string and cause a note to play sharp or flat. These errors are real and difficult to track down. They are largely a result of how responsive your guitar is.

Take Away: This error is baked into your guitar. Can’t do much.

5. Is your playing style aggressive?

When a musician frets a note, it is possible to push on the string parallel to the frets causing the note to play sharp. This “bending” must be taken into account if one does this often. It is also possible to press on the string perpendicular to the fret either toward or away from the bridge causing the note to play sharp or flat (vibrato). When a string is pressed down between two frets the tension will increase as it is pushed and stretched further into place. This will cause the note to play sharp. The effect is small, but real, and the harder you push the sharper the note. Someone with a very strong grip may play the note sharper than someone with a light touch. Also, as you play you may change your finger pressure depending on the passage being played. How a person plays influences the intonation and is a factor when setting up the guitar.
Take Away: Consider while Tuning. If aggressive compensate more. 6. Is the string height high at the nut? The height of the string at the nut controls the amount of extra stretching to the string when it is fretted near the nut. A higher string has more stretching. This suggests that getting the nut height as low as possible may be helpful 

Take Away: lower your string height or replace your nut.

7. Is the top very flexible?

As the top vibrates the bridge is carried along with it. Our “fixed” saddle is no longer in a fixed position. Imagine the string as it vibrates. It takes on a curved shape that comes to a point right at the saddle. On a real guitar though the saddle is still moving, so the imaginary fixed point is behind the saddle a bit. This effect has the result that the string thinks it’s longer. It’s sort of like looking into a mirror that is slightly convex; objects are closer than they appear. This effect depends on how much the top vibrates. If this didn’t happen our guitars wouldn’t make much sound at all.

Take Away: This is another one that’s baked in.

8. Are the strings worn out?

As strings are used, they wear away in spots at the frets, and collect gunk from the oils, acids, and dirt on our fingers. Wear can occur anywhere along the string and is likely to be spotty. All these things cause the string to have an uneven thickness along its length. This can cause the string to play sharp or flat in different amounts depending on its use and where it’s been fretted.

Take Away: Consider buying new strings

9. How is the tuner measuring the notes, attack or decay?

If you listen to or measure the frequency of a plucked note on a guitar you might notice the tone is not constant. When the note is first plucked it will play a bit sharp and then as it decays away the tone drifts back with a long tail. The right tone is up to you. For example, if you play lots of short notes, you might choose to intonate the guitar to the first part. If you play lots of really longs notes you might want to intonate to the end. This is truly your decision.

Take Away: Depending on how you play, use the tuner during that phase.

10. Are you using heavy gauge strings?

When changing strings, the type, make, and gauge of the strings may affect the intonation. When changing to a new type of string you might expect the quality to change. New strings will be different than old used strings of the same make.
Take Away: Heavier Strings means more error. Try something lighter.

11. Is it humid?

As the environment or seasons change, a wooden guitar will expand and contract along with the moisture in the air and temperature. The length and shape of the guitar will alter. These changes will cause the intonation to drift either sharp or flat with the seasons. The guitar needs to be retuned and the quality of the intonation may be affected.

Take Away: Adjust your compensation every season.

12. Has the neck or body crept?

Our poor guitars are expected to withstand 160 pounds of tension for fifty years or more without changing more than a millimeter. You try that! All the while the guitar is expected to be as lightly constructed as possible to enhance the acoustics of the instrument. This might be considered a set of unreasonable expectations if one were reasonable, a trait sometimes lacking. In the real world our guitars are in the slow-motion process of collapsing under tension. For a high-performance guitar that is built on the cusp of breaking the effect might be expected to be larger than on an overbuilt off the shelf guitar. Over time the neck angle will change, the top of the guitar deforms, and the woods age and mature. These things can make the intonation change and might require the guitar to be adjusted, or worse a neck reset, or worse yet a new top!

Take Away: If it is out of your ability take it to a luthier or guitar shop.

13. Was the action changed?

Sometimes you may want to change your playing style and choose to modify the setup, or the guitar gets old or sold or passed on. A little lower action might be nice, or it might be good to just tighten things up. This may change the intonation depending on what is done. For example, when the action is lowered the strings will stretch less when they are fretted, and the errors will be different.

Take Away: A Change in action leads to a change in intonation.

14. Are there fret position and saddle placement Errors?

We know with detail where the frets and the saddle belong on the instrument, but it can be difficult to get them just right. With our modern tools we can cut the fret slots to a few mil (1/1000”) accuracy. When cut by hand the slot positions are less accurate. When the frets are recrowned it is important that the peak of the crown is directly over the slot If any of these things are off even a little bit, the only solution may be to rework the instrument.

Take Away: Do a visual inspection and measure the scale length.

15. Did the guitar get heat shocked?

Metal strings are particularly susceptible to heat changes. The metal will expand as the heat increases causing the string to lose tension and go flat. Believe it or not, the strings warm up as they are played, but this effect is very small. However, if you bring your guitar in from a cold car into a warm room, it will likely be out of tune. Wood also expands and contracts as it heats up, but much less than metal.

Take Away: Re tune your guitar when entering a radically different environment

16. Are the strings just bad?

it has been reported that a string has been unevenly wound or has other manufacturing problems. The best solution if this is the case is to replace the string.

Take Away: Always start with new strings.

17. Is there saddle slop?

For a straight-line slanted saddle, if the saddle doesn’t fit snuggly into the saddle slot it can tilt forward leading to errors.

Take Away: Loosen the strings and see if the saddle moves in the saddle slot if so replace the saddle.

18. Was the guitar set high?

Among other things, the playability of a guitar is greatly influenced by the height of the strings above the fretboard (the action). Generally, the higher the strings are set above the fretboard the harder it is to play, the lower the strings the easier it is to play. The height of the strings also influences the quality of the sound that the guitar makes. Set the strings too low and the sound gets thin and ultimately starts to buzz as they hit the frets. Make the strings too high above the fretboard and it sounds great but is too hard to play. Once the action is ultimately set, a fine-tuning is achieved by controlling the longitudinal shape of the neck with the truss rod. Ideally there is a slight concave bow at the 12th fret that helps to prevent buzzing. So, for every guitar and musician there should be a setup that makes the player most happy. The player’s objective is to find that happy medium and then make the guitar intonation as perfect as we can with what we are given.

 

Take Away: Intonation is hard to adjust.

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