Guitar Intonation Demystified

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 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.

Proper intonation of a string results in each note having a truer pitch, fret to fret, relative to scale length.

Scale length is the distance from the nut to the bridge with frets positioned in such a way so as to work within that measurement. Due to some funky physics involving mass, frequency, vibration and tension, skinny strings will have a physically shorter span when compared to larger ones. And whether a string is wound or not also influences intonation length.

To help understand the concept of adjusting for string length, we’ll use some extreme examples.

First, we’ll use a typical scale length with the bridge in normal position. The 12th fret is positioned exactly in the middle of the string span:

Now imagine the bridge positioned much closer to the fretboard. The 12th fret, what should be the middle of the string, is now far too close to the bridge:

If you were to play some notes in the upper frets, closer to the bridge, they would sound far too high or sharp.

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

Notes played high on the same fretboard would sound low - too low or flat.

In short, if notes sound sharp in the upper frets, the string is too short and should be lengthened. Likewise, if they sound flat, the string is too long and should be shortened.

In practice, it’s much easier to focus on committing one condition to memory. By remembering one point of reference, either sharp or flat, you’ll have a clearer grip on intonation orientation.

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

Plug the instrument into a tuner and, using the fifth string as a starting point, play a note at the 5th fret which is a D. Remember exactly what the tuner tells you, what you see.

Now go to the 17th fret on the same string, an octave up, and see what the tuner says. If it reads identical, great! you don't do anything. If it reads sharp or flat, the string must be adjusted accordingly.

For example, if the 17th fret D reads sharp, the string is too short and the intonation point must be moved back to make the string longer.

Now adjust the saddle just a bit in the right direction – a quarter turn of the screw or so. Then repeat the fretting, reading process until the intonation bang-on.

A couple of comments to make here.

Personally, I never use the open string with the 12th fret octave method. Factory nuts can be imprecise or poorly cut. After working on literally thousands of instruments, I learned that eliminating the nut from the process resulted in much more reliable and accurate results.

Secondly, using corresponding octave notes on a string, i.e.; an E at the second fret on the fourth string, and an E at the 14th fret octave on the same string results in more accurate intonation across the entire playing surface.

Lastly, it's important to use moderate and realistic finger pressure on the notes when taking readings. Deflection through uneven finger pressure can give misreads. Think of how you play normally and keep it in mind as you go through the intonation process.

On most acoustic instruments, the saddle is usually one uniform piece but angled to provide some degree of intonation. They are nonadjustable as they are in a static position and don't accommodate the differences found in string gauges.

Similarly, archtops and jazz instruments employ a compensated bridge system. These more 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 freshly installed new strings that are fully stretched when you intonate your instrument. Old strings will give you false readings because of wear and tear, plus the finger gunk that builds up and changes the mass. The high-end frequencies get thrown out the window too - even in as little as a few hours of playing!

Ultimately, the most important things to remember about intonation are:

In the 90’s, he spent the decade working in a popular local music shop refining his guitar setup skills, managing sales, actively gigging, and teaching as many as 60 students per week. When their operation closed in 2000, he opened his own store which he ran successfully for 15 years.

Steve Blundon has been in the music business since his first stint with touring bands in the 80’s.

Today he still maintains a healthy list of guitar service clients and spends his time developing websites associated with the music industry, the main site being GuitarNiche.com.