Intonation Subtopics
Check out your fretboard
Comparing two notes cents-off
Advantages of Low Nut Action
Zero Fret
Sweetened Tuning
Skinny Bridge Saddles
Closed Position Players
First Position Players - skip Readjusting The Saddle?
String Slippage
Using a Capo With Nut Compensation
Fanned Frets
Stretch Tuning
Check Out Your Fretboard
The fretboard must be laid out accurately - most are. Are you skeptical of the accuracy of your fretboard?
Steven Delft at http://www.mimf.com/nutcomp/ gives you a method of checking the accuracy of your entire fretboard.
You can determine the scale length of your guitar by measuring the length from fret 1 to fret 13 and multiplying that by 1.0595 x 2. You can then print a chart of your calculated scale positions at http://www.stewmac.com/FretCalculator/ (Specific charts for popular guitar scale lengths are also provided.)
Note on the chart, the calculated length from the nut to first fret. (The standard Martin measurement is 1.422; the short scale Martin is 1.394”.) Compare that length to the actual length from the nut to the middle of fret 1 on your guitar. If it is shorter than the calculated length, then you will need less nut compensation than if it is equal.
Measuring suggestion: It’s difficult to measure to the middle of a fret wire, so in order to get a good measurement from the nut to the middle of the first fret wire, use your caliper to make an “inside” measurement from the nut to the near edge of the first fret wire. Then measure the width of the fret wire, and add half of that to the first measurement. Return to top
Comparing Two Notes - Cents-Off
If someone wants to get serious about intonation work, or even, to be able to really check out an existing guitar, he must become familiar with measuring the cents-off error between two notes. A Peterson 490 strobe tuner would be great for doing this, but not everyone can afford that piece of equipment. For more information and techniques, please go see Tuners and Tuning.
Advantages of Low Nut Action
I know that there are people who like higher action, and don’t want to even consider changing. These people are usually professionals or the more proficient amateurs. They are not bothered by the high action, and they like to feel the resistance wherever they play on the fretboard. I wouldn't try to change their minds (but they should be aware of the need for added compensation with the extra height).
However, I think there are way too many people who have just accepted what was handed to them, not really realizing what they could gain with a little nut slot filing. There are several advantages to having low nut action:
Most of us can play better with low action.
While higher action at the saddle, increases the sound volume on an acoustic guitar, higher action at the nut does not.
While higher action at the saddle reduces buzz from heavy play; higher than necessary action at the nut does not. (See the nut action check below.)
Higher action at the nut greatly increases intonation error.
Higher action hurts your fingers.
Higher action at the nut also increases the action height needed at the bridge saddle. This is how it works: As soon as you play at the first fret, you have eliminated the extra nut height, and the action at the 13th fret will have been reduced by an amount equal to about half of the extra height at nut. This extra height is not useful, either at the nut or at the octave, and just causes more distance to have to move the string.
Most string height recommendations, specify nut action that I would consider to be excessive, especially for the bass strings.
Nut action check: While fretting at the first fret, check the fret-to-string height at the second fret. If the open-string height at the first fret excedes the second fret string height by more than 2 thousandths, it is extra, wasted height. You can safely take the action down to as little as .0005" above the fret plane (as measured above).
As the years have gone by, and I play harder, I have had to raise the saddle to prevent buzz, but never the nut. Return to top
Zero Fret
Using a zero fret on a guitar could minimize the need for nut compensation, because it eliminates the usual extra string height at the nut. (This assumes that the zero fret is the not oversized.) This would eliminate the possibility of compensation on each individual string, but the zero fret could be moved forward of the calculated nut position, producing partial compensation. This may be a practical alternative to full nut compensation on, say, an electric guitar with light strings, and where intonation is pretty good to start with.
The same effect could be achieved by lowering the slots on the existing nut until the gap above the first fret is just a hair greater than the gap above the second fret while fretting at the first fret. For professionals who play hard, there may be a concern that wear on the slots over time might cause a buzz, necessitating replacement or shimming the nut.
Sweetened Tuning
Almost every guitar player does some sweetening, whether they know it or not. If the nut has not been compensated, then no chord will sound good without some adjusting.
Ideally, we think of sweetening as tweaking the tuning away from equal temperament, in order to produce more pleasing chords and natural intervals, at least in our favorite positions. We can do this by ear, or tune with a special tuner, according to various available tuning offset charts. But, in practice, I think that most of the tweaking is done because the intonation is bad to start with, the guitar never having been properly intonated to equal temperament!
Guitars with the Feiten System should be tuned to the Feiten patented offsets. Other charts are available with some of the Peterson tuners, including the Stroboflip, the Stroboclip, and Strobosoft. (The Peterson offsets are kept trade secret, but take effect when selected on the tuners.) Monte Allum offers his tuning offsets at a very low price, and I expect that other offset charts are available, as well. These "custom" offsets can be coded into the peterson tuners, or into the AP Tuner.
Ask yourself this question: "What will these offsets do if the guitar has not first been fully intonated, including nut compensation?". I suppose the best answer would be to use the computer saying: "garbage in, garbage out"! No, seriously, If you don't know How far "out" your guitar is, then how do know how much to adjust it, and what the effect will be?
In actuality, since most guitars lack nut compensation, most sweetening is done by ear, and is needed to make the guitar sound acceptable, and that usually means closer to equal temperament. Return to top
Skinny Bridge Saddles
Acoustic guitars have skinny saddles – why? They are often insufficient for proper intonating of each string. Even when it is possible to intonate the 2nd and 6th string, there often is not enough material to properly round the string down to the bridge pin. I would like to see all saddles at least 1/8" thick - 3/16 would be better yet (but where can you find a 3/16" blank?).
I saw some oversized blanks at: Guitar Parts and More.
So, would it add too much weight? If so, you could shape it to only extend where needed for intonation (or shave a little off the bridge?).
Here is an example of a wide compensated saddle by Mike Doolin at doolinguitars.com. Wide is beautiful! Return to top
Closed Position Players
If you don’t play open strings at all, and you set bridge saddle intonation comparing fret 12 or 14 to fret 2, then you could tune only to fretted notes and eliminate the need for nut compensation. This could be a good temporary measure, but you would probably want to do the nut compensation later – it’s easier to tune open strings than fretted ones. Return to top
First Position Players - Skip Readjusting The Saddle?
For acoustic players who only play low on the neck, nut compensation is much more important than improving bridge saddle compensation, and there are situations where readjustment of the saddle would be very difficult. Adjustments you can't make without replacing the saddle could be skipped or postponed. First, check the amount of error when comparing fret 12 or 14 to fret 2, and decide whether you can live with it. Go ahead and compensate the nut, maybe leaving just a tiny bit of extra material if a string is flat at the 12th fret, and you plan to adjust the saddle later.
If you decide later to adjust the saddle, be consoled that it won’t effect your nut compensation very much. Nut compensation adjusts the first fret width, which is about 1.4“. The scale length is about 25.5”. A change at the saddle, would change the nut compensation in the proportion of 1.4” / 25.5” = .055. For example, if you later extended the saddle by .020”, that would only change the nut comp by -.0011”. Return to top
String Slippage
We all know that nut slots so tight that they bind the strings, will cause tuning problems, and can possibly even damage string windings. The tight slots cause the strings to hang on the nut slots. Therefore, when making adjustments, it is always good to be aware of keeping the nut slots smooth and even, just a little wider than the string width, and at a gentle downward angle at the leading edge of the nut (about 8 degrees).
But, I want to persue that concept farther - there are situations where it is important and desireable to facilitate string slippage during actual play. This is the case, especially with electric guitars, where string bending is common, and also tremelo bars are often in use. After a string is "bent", or pulled, it's important that it returns back to it's normal pitch. (The alternative is to use a locking nut, so the srings won't slip at all, or a headless guitar, where the distance from nut to anchor point is extremely short.)
A shallow head angle, such as those on fender guitars, will actually facilitate string slippage at the nut. Also, nut materials such as Delrin or graphite can be used to increase slippage. Slippage can also be facilitated at the bridge saddle on archtops.
There are two more great benefits of planned string slippage! With slippage, when fretting, the added tension will be distributed over a greater length than the playing length. Rather than just over the scale, the tension is, at least partially, distributed from the tuning capstan to the the saddles (or perhaps the tailpiece). That produces a lower dynamic tension, which means that the finger pressure to fret a note is reduced - the action feels lighter!
This magazine article reveals a great example of pioneering excellence in this area by Ken Parker.
The other result of the added length is that less compensation is needed for the guitar to play in tune. Luthiers have verified this by measuring the open to first fret intonation on Telecasters, with string tees on vs off.
Ok, just one more thing about slippage. Your capo should not be too tight! Slippage at the capo will insure that fretted note tension will be distributed over the whole scale, not just from the capo upward. See: Using a Capo with Nut Compensation.
Using a Capo With Nut Compensation
 In order to minimize sharping, with or without nut compensation, the front edge of
the capo should be placed right over the nut, or just behind. Also, the capo needs to fit the arch of the strings, and should not be over-tight.
I use a Kyser capo for jams, because they are so quick to apply. The problem is that they have a very strong non-adjustable
spring so they can work, even with really high action. To tone it down, I installed a 1 1/4” wide rubber band, made from a
skinny bike tube.) The G7th Nashville is quick, and does not squeeze so hard.
There are better capos available that are adjustable and interfere less with playing. If done properly, the capo will not noticeable sharp the notes.
Besides the right pressure, its important that the arch of the capo fit the arch of your fretboard (actually the arch of the tops of the strings will be a little more shallow than that of the fretboard).
I got a Paige capo (pictured here) and was surprised that it was arched too much for my acoustic guitars. All was well, however, when I discovered that I could easily adjust it to fit perfectly! With the rubber removed, I compressed it with a vice, and then finished it off with a small hammer. The capo now works perfectly with a very slight pressure.
There, of course, several other capos, similar to the Paige, that many people like. These capos slide back over the nut when out of use, but some guitar necks do not allow that, so try it on before you buy.
Though I rarely bend a note, I'm aware that capos can be a problem with bends or tremelo bars, so I tested it. With the very light pressure of the Paige, the strings will slide easily, and return to in-tune.
Barred, and other closed chords, will play in tune (that includes being in tune with
other instruments.) This is because the
Guitar has been intonated to play in tune wherever a note is fretted on a
string. That is the case for all of the
strings in closed chords. (It should be
noted that proper saddle adjustment is also necessary for this to be true.)
  However, when an open chord is played with a capo, then the “open” strings could play
a tiny bit flat. That is because they
will not have the increased tension from being fretted all the way. (Only the larger cored strings will be noticeably affected by this.) However, if you didn't get the capo on just right, maybe the fretted notes will be a hair sharp, and the open will be perfect!
Overall, playing with a capo is greatly improved with nut and saddle compensation. Exact? Maybe not, but much improved! Return to top
Fanned Frets
Fanned fret guitars have increasingly longer scale lengths from the first string through the sixth. The scales can be laid out by drawing the first string scale, and then drawing the sixth string scale. The other four scales are on a line between the first string scale and the sixth string scale at each fret. So, the frets are straight, but are placed at a slant which progressively shifts more counterclockwise, as you move up the scale. Each string scale is fretted in the same mathematical relationships as on a standard fretboard – just different lengths.
The lower the pitch of a string, the more it
needs length, in order to produce a rich tone; that’s why bases have longer
strings than a guitar, and guitars have longer strings than mandolins.
The main advantage of the fanned fret designs is that they
provide that extra length for the base strings, producing improvements in both tonality and harmonicity (better refinement of overtones on the bases) while
maintaining the desired scale length of the trebles. Although these results are significant, the length differences
are small compared to those of a piano.
I have read forum posts saying, to the effect, that you
cannot fully intone a guitar unless it has fanned frets. This is very misleading! The principles of intonation are the same
for fanned fretted guitars as they are for other guitars. However, the bass strings being longer, do
require less compensation.
Fanned fret guitars are said to be more ergonomic, but there
is disagreement about that. Maybe it is
different depending on playing style. I
can’t say, because I’ve never tried one.
More information, and pictures can be seen at Tom Bills
Custom Guitars.
Stretch Tuning
Stretch tuning means progressively making higher notes more sharp. Pianos are usually stretch-tuned. That is because, at the highest octaves, there are problems with the overtones matching the notes on the octaves below, and at the lower octaves, there is a problem matching the overtones with the lowest octaves. Correction for these problems results in an S-shaped curve of intonation, with the higher notes being raised even higher, and the lowest being lowered even more. On a piano, each note is intoned separately. Because of longer string length, concert grand pianos need the least correction from equal temperament.
On a guitar, however, notes cannot be intoned separately, so, in order for a particular note to be the same on multiple strings, for stretch tuning, it would be necessary to stick with a constant rate of pitch increase, the same on all strings. The guitar does not have nearly the range of the piano, so there is really no need for stretch tuning. The piano plays 8 octaves, while the guitar plays only 4.
Stretch Tuning should not be tied to nut compensation, but it could be used in conjunction with nut compensation. As I understand the Buzz Feiton System, it does not seem to use overall stretch tuning, but uses stretch on some strings in order to effect particular harmony tweaks.
Still want to try it? To effect stretch tuning, the strings are shortened at the bridge saddle so that the notes from low to high are progressively sharpened - by how much? Pianos stretch about 2 1/2 cents per octave, on the lowest and highest octaves. It would depend on preference – try it and see if it sounds nice to you (usually not difficult on an electric guitar, unless you reach the saddle adjustment limits). Remember to consider what other instruments you will be playing with, and how they will be tuned. Oh, and you’ll need a special tuning procedure!
As an acoustic guitarist, stretch tuning holds no appeal for me, but if I were playing high, soaring solos on an electric guitar, I might possibly think differently.
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