Guitar Intonation
Intonation- Having an instrument "in tune" throughout the scale is the goal of every player and luthier. Different string gauges, scale lengths, set ups, fret sizes, playing techniques and other variables can effect your instruments intonation. While it is true that there is a certain amount of compromise on equal tempered instruments, my goal is to have the best possible intonation.
The problem is best described by saying that the notes of some chords sound in tune while others seem far from it. And re-tuning to bring one chord in to tune only throws the others out...and so it goes. This condition is present even though the instruments individual strings are said to be in "perfect tune" (E,A,D,G,B,E). Welcome to the world of the equal tempered scale!
To help explain this occurrence it's important to realize that the differences in the strings mass, tension, length and fretting stretch all effect the notes pitch. There are also other factors that can affect the instruments ability to play in tune which I'll mention later.
The strings scale length* begins at the nut and ends at the saddle. If you look at the saddle(s) of guitar or bass you will quickly realize that they do not sit parallel with the last fret (with the exception of some classical guitars), they are compensated. String length is actually added to the actual scale length in order to off set the sharpening of the note which occurs when the string is stretched while being fretted.
The dramatic string size differences on acoustic steel string guitars make this compensation more pronounced than one would see on a classical for example where the individual string diameters are more similar.
*Literal scale length can be determined by measuring the distance from the nut end of the fingerboard to the center of the 12th fret and doubling it. Compensation is added to the scale length so measuring from the nut to the saddle would actually give you a figure slightly longer than your instruments "scale length".
If notes played at the 12th fret are dramatically sharp or flat, changes to the strings length and position of the saddle (or shape of it's crown) are necessary.
When inspecting the crown of a compensated saddle you will notice that's it's crown (highest peak) does not run right down the center of the saddle but instead wavers a bit fore and aft. This variance in the crown changes the strings length ever so slightly allowing for a greater fine tuning of the strings length.
Some things that can cause poor intonation are:
Incorrect positioning of the saddle or bridge This error renders the strings either too long causing intonation to be flat or too short causing the instrument to play sharp. This can be a problem with the saddles crown or the actual position of the saddles slot on an acoustic guitar.
High action An instrument with high action will of course cause the string to be stretched further before contacting the fret, this stretching sharpens the note slightly. High action at the nut is particularly troublesome as chords played in the 1st to 3rd position can sound terribly out of tune.
Excessive Relief The strings distance to the fret can be dramatically increased on necks that have far too much relief or other problem with the necks shape.
A sloppy or loose saddle The saddle can lean forward when not held firmly in the slot and cause the strings scale length to shorten thus shortening the strings.
A grooved/worn saddle Wear and tear can change the shape of the saddles crown, changing the strings length.
Frets - Frets that are badly grooved or have flat crowns will also throw off intonation as the strings length is changed. Frets must be leveled and dressed to remove the grooves or replaced if necessary.
Fret height will also effect intonation...instruments with truly tall fret wire will play incredibly sharp if the string is fretted hard and your fingertip is bottoming out on the board. To see for yourself what effect your fretting technique has on the instruments tune watch the pitch of the note on our tuner when fretting with different pressure. Yes, you can be the culprit!
A mathematical error If the bridge itself has not been positioned on the top correctly it must be corrected. In some cases the slot can be filled and recut. More here.
In other instances the bridge must be physically moved. More here.
Poor Quality / Defective / Worn Strings Ever been tempted by those super cheap strings you find on auction sites? All strings are not created equal and I have personally encountered the problem first hand with a client using some no name strings which would not play in tune down the neck. You may also find tuning problematic on worn strings. If your intonation issue is a brand new problem, the instrument played in tune before and NO changes have been made to the instrument you may wish to change strings first, just to rule out the easy stuff.
Fret Layout/Spacing I hate to mention this as I fear far too many people will jump to this conclusion in error, but I still encounter this on occasion, usually on inexpensive imported instruments. This is more likely to be an issue on a fretboard that was slotted by hand. Factories are using sophisticated machines that carefully, correctly and consistently cut fingerboard slots.
Technique Well this isn't actually a defect, it's a "style". Some players have a rather powerful fretting technique in which they place excessive pressure on the strings when fretting and if the instrument in hand happens to have fairly tall frets this is more than enough to mess with your intonation. Some players may actually have a tendency to bend a string sharp when fretting.
Improving Your Intonation
The first step to improving your instruments intonation is to eliminate any issues that I've mentioned above which could be causing problems. When clients come to me with intonation concerns I can usually determine whether I can improve the intonation by inspecting the instrument and checking it on a strobe tuner. It is a fact that some players have more sensitivity to the compromises in the equal tempered scale. When that is the case I normally must do my best to explain the compromises of a fretted instrument and offer my condolences. :) Having every single note in perfect tune is beyond the abilities of many equal tempered instruments.
On a happier note, most do not hear the subtle differences in pitch in such a pronounced way that we listen in agony.
The most common "upgrades" to improve intonation are compensated saddles and nuts. These give us the ability to tweak the individual strings length and minimize some of the most offensive spots.
Nut Compensation - As I have already explained, fretting the string stretches it...so length is added to the instruments string to prevent sharpening of the note, once that has been done however we have also lengthened the open strings, the only one that isn't fretted and therefore did not require the compensation. In order to improve the tuning further some will compensate the nut. Compensation of the nut can be achieved in different ways and you are likely to find many opinions on the subject, I am by no means an authority and have not intended to cover this vast subject in this article.
But to keep it simple, either the fingerboards length is shortened at the nut end or the nut will be made to over hang the fingerboard to decrease it's length without modifying it.
Earvana® is one example of a pre-fab compensated nut, but there many others being offered today.
The Buzz Feiten Tuning system® is another popular intonation compensation method though not for do-it-yourselfers. Modifications are made to the saddles position and fingerboard length according to several factors such as string gauge, scale length and action.
Tuning
For me personally, intonation became an issue once my playing began to improve. I think this may be the case for many budding musicians...until one's ability and ear develops they are "blessed" not to hear the inconsistencies on their fretboard.
And to the opposite extreme I know people that hear things I can not.
Just as there are several theories about ideal saddle and nut compensation, there are also different ways in which we can tune our instrument. What? Some may be asking...I thought you just took a tuner and when the green light lit up you were in tune?
While this may be one of the most common methods of tuning guitars it isn't the only method.
You will find that some use harmonics to tune, some will tune 2 particular chords until they are in tune with one another and still others have devised off-set tuning charts that detail how many cents sharp or flat each individual note should be tuned.
Whatever method you find best suits your ear, simply know that there is far more than one way to skin a cat, I mean tune a guitar!
Related Articles:
Electric Guitar Intonation
Intonation Correction (Bridge Replacement)
