There seems to be this general perception among a lot of guitar and bass players that the process of intonation is some sort of mystical and highly technical 'thing' better left to guitar techs. That statement may have a tiny grain of truth to it but the fact is, it's really just a simple mechanical adjustment. Armed with only an electronic tuner and a suitable screwdriver, you too can join the ranks of those who know the intricacies of intonation.

So exactly what is "intonation"?

Proper intonation of a string results in each note having a more true pitch, fret to fret, relative to scale length. Scale length is the distance from the nut to the bridge with frets positioned to work within that measurement. The interesting thing is that skinny strings will have a physically shorter span when compared to larger ones and whether a string is wound or not also has an affect on intonation length. This is due to some funky physics involving mass, frequency and tension. To keep it practical, we'll look at how it works on common instruments and find that when all the strings are intonated properly, those nasty slightly sharp or flat sounds around the neck can be eliminated.

Let's see if I can give you an idea of how this works on an instrument. Put your guitar, or bass, in your lap and look at the strings.

Now imagine the bridge positioned much closer to the fretboard;

If you were to play some notes way up the neck, closer to the bridge, what would they sound like? ..... High - too high or sharp.

Conversely, imagine the bridge positioned well away from the fretboard;

You don't have to be a brainiac to guess this one. Any notes played high on the fretboard would sound low - too low or flat.

That's pretty much it in a nutshell. If your notes sound sharp in the upper frets, the string is too short and has to be lengthened. Likewise if they sound flat, the string is too long and has to be shortened. If you can remember either one of of these situations you'll have a good grip on string intonation orientation.

Which leads us to the next step; exactly how do we make these adjustments?.

On an electric guitar, or bass, the bridge usually has some mechanical means of moving the saddles a short distance to intonate each string;

And now to the business of actually making an adjustment. Plug the instrument into a tuner and, using the fifth string as a starting point, play a note at the 5th fret. Remember exactly what the tuner tells you. Now go to the 17th fret on the same string, an octave up, and see what the tuner says. If it reads identical, yipee!, you don't do anything. But if it reads sharp or flat, the string has to be adjusted accordingly. Move the saddle just a bit in the proper direction, and repeat the fretting, reading process until it's bang-on.

Okay, a couple of comments to make here. Personally, I never use the open string with the 12th fret octave method since I found the nut on some instruments isn't where it's supposed to be. And I don't mean a "Buzz Feiten" or other other compensated tuning system thing. It's just that some instruments are built uhm ... sloppy. Secondly, using corresponding octave notes on a string, i.e.; a B near the end of the neck and a B an octave up on the same string, results in more accurate intonation across the entire playing surface. Lastly, it's important to use a moderate and realistic finger pressure on the notes when taking readings. None of this pussyfooting around the neck stuff. Real men play with conviction under their fingers and it should be reflected in the intonation process.

On most acoustic instruments, the saddle is usually one uniformly straight piece but angled to provide some degree of intonation;

Sometimes a customer will bring an acoustic in for a setup and make a comment about wanting it intonated. Well, that's a bit of a problem because they're pretty much nonadjustable. Although better instruments will have a "compensated" saddle;

This certainly helps, but it's still in a static position and doesn't accommodate the differences found in string gauges, i.e.; super light or mondo heavy sets.

Similarly, archtops and jazz instruments employ a compensated bridge system. These nicely adjustable units are usually held in place by string pressure which allows them to be moved forward or back to achieve a better degree of intonation accuracy.

Finally, only use fresh new strings when you intonate your instrument. Old strings will give you false readings because of the finger gunk and goo that makes them deteriorate - in as little as a few hours of playing! Ultimately, the most important things to remember about intonation are: if the upper notes are sharp increase the string length, if they're flat decrease the string length.

And that's the long and short of it.