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Edge guitar services

Eltham Jones, guitar repair and technical services :Bristol : Cardiff : Bridgend : Tel. 07971 240296

It often surprises people that I disapprove of the use of digital tuning meters for setting the intonation of guitars. While these devices are occasionally useful for tuning in noisy environments there is a problem associated with them when it comes to our perception of pitch.

Digital meters, you see, are very good at metering the rate of the fundamental; what they cannot do is tell us how in tune the note sounds.

This is because of the mechanism our brains employ in recognising pitch or any other stimulus, auditory, visual or olfactory...

It's called pattern recognition.

When we hear a sound we are aware of only a part of the information that our brains are processing. Rarely is a sound composed of just a single frequency; far more common is for the sound to be layered with multiples of the lowest or fundamental frequency. We call these harmonics and although we are not normally aware of them as separate frequencies it is the content of the harmonic spectrum that determines other qualities in the sound that we are aware of such as tone and timbre.

A feature of vibrating strings is that they are affected by a phenomenon called inharmonicity.

In brief, inharmonicity is acceleration of the high end harmonics under the influence of the forces contained in the body of a bending string.

When a string is plucked the main forces acting upon it are those of tension, causing the string to straighten and occupy the shortest length between its two anchor points, and momentum causes it to continue it's movement against the action of tension.

For the high frequency harmonics however, whose wavelengths occupy little more than a couple of inches, the shorter lengths of string over which they are active are behaving more like bending bars than flexible strings.

A bent elastic bar stores energy on the outside of the bend as tension, and on the inside of the bend as compression.

Between them these two reciprocating forces act to accelerate the movement of the smaller string partials and the frequency of the harmonics associated with them.

Simple harmonic theory dictates that the harmonics occupy a series of perfect whole number multiples of the fundamental. Under the accelerating action of the additional restoring forces however, the higher harmonics race up and down the string significantly faster than dictated by simple harmonic theory. The shorter and heavier the string, the further down the harmonic spectrum the harmonics are affected.

Our brains, subliminally processing the harmonic information, are accustomed to the pattern dictated by harmonic theory. Upon detecting the expanded harmonic spectrum we are forced, unconsciously, to a "best guess" assessment of pitch. As the fundamental is unaffected by inharmonicity (because it's the basal or reference pitch) on hearing the expanded harmonic spectrum we naturally assess the pitch as sounding flat.

The corollary of this is that if we tune a string to its exact theoretical pitch using a meter and that string is affected by inharmonicity it is likely that we will assess the pitch as slightly flat. Because of this, although we can legitimately use digital tuners to tune open strings using one to set the intonation on the higher frets will lead to errors in our perception of the accuracy of the intonation in that area.

Just as piano tuners use their trained ears to tune a piano, so accurate intonation is best accomplished by an experienced ear.

Why I never use a digital tuner to set intonation

partial section of vibrating string

© Eltham Jones, EDGE Guitar Services

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