(C) 2005 Hank Wallace
If you play an instrument other than a piano, it’s likely that you own a small device that helps you tune, if even only a tuning fork. For guitar players, the tuner can be anything from the micro, to the macro, such as rack mounted tuners costing hundreds of dollars.
Each of these tuners has manufacturer specifications for accuracy. What do these mean? They stipulate how accurate their internal pitch reference is, and by corollary how accurately you can tune your instrument using their product.
The units of tuning accuracy are cents. A cent is one hundredth of a semitone. Since there are 12 semitones in an octave, there are 1200 cents in an octave.
It is commonly agreed that the human ear can notice a pitch change of about five cents. How good is your ear? You can test your pitch discrimination skill by listening to the following sound clip of the note A at 440Hz, plus and minus certain errors. There are five tones, played in this order:
A-440 -10 cents A-440 -5 cents A-440 exactly A-440 +5 cents A-440 +10 cents
Can you hear the difference between successive tones? It is easier to hear the difference when just the first and last tones are played, as in the following clip. The pitch difference is 20 cents.
A geek reader with a frequency counter may write to chide me because these tones are not exactly A-440, but are a little off. Actually, the clock reference for most PC’s is not exact by any means, and my PC on which these were recorded will likely not match yours. However, I want you to notice the difference in the pitches between the sound files, not the absolute pitch.
Play the sound clips repeatedly and determine how good your pitch detection wetware is.
What does this little test tell us about tuner accuracy? It tells us that the tuner should be considerably more accurate than the just noticeable pitch difference of five cents. If your tuner differed from your bandmate’s tuner by more than five cents, you might be accused of being out of tune! Ten cents difference is certainly noticeable between two guitars.
Other issues come into play in the tuning of your instrument. The intonation adjustments must be correct. These settings ensure that the fretted notes are as in-tune as the open ones, and that chords sound in-tune when played anywhere on the neck. Special tuning and construction techniques have been invented to minimize these errors, but they affect your instrument’s tuning in ways beyond the raw accuracy of your guitar tuner.
When you fret a string, finger pressure bends the string toward the fretboard, between the two frets. Every chord you play results in a differing string pressure for every note on every string. Guitar players will even grip the neck more tightly in louder passages. This pressure changes the tension on the string, which changes the pitch.
You can hear this effect yourself by fretting a string and pressing between the two adjacent frets. It’s just a small difference, but it’s there.
If you use a capo, its pressure on the strings between two frets can drag your whole instrument out of tune. When I use a capo, I place it almost over one of the frets, to minimize added string tension and detuning. Most capos exert way too much force on the strings.
An acoustic guitar player who ties the guitar strap to the head stock will also cause some pitch change because the neck warps a slight amount when the instrument is suspended in that way. She should tune the guitar in that position.
Another issue is the fact that the simple act of plucking a string causes it to initially ring sharp. Most sweep tuners will show this phenomenon, indicating a pitch that is sharp by five or ten cents just as the string is plucked. Why does this happen? When the string is just plucked, it is moving back and forth a large distance and the average tension on the string is higher, causing a slight pitch increase. As the note decays, the motion is not so large and the average tension and the pitch decrease to their expected values.
The temperature of the instrument and environment will also cause pitch changes. This effect is easily noticed by players who bring their instruments indoors from cold or hot autos. It takes a half-hour or more for the instrument to settle down, depending on the materials it is made of, and every instrument responds differently.
Just as with amplifiers and cables and automobiles and computers, there is a marketing war going on regarding tuner accuracy. More accurate is better, of course, but there is a region of diminishing returns. Tuner manufacturers know this and only design their tuners to be as accurate as is commonly needed.
I recently tested ten inexpensive (less than $100) tuners and found that they all were accurate to within +/-5 cents. They work better or worse depending on their display format, but they all tune a guitar well enough.
How is it possible that even a $10 tuner can tune your instrument decently? The secret is the frequency reference, a quartz crystal. Such crystals can be made to vibrate at many different frequencies depending on the thickness of the quartz slab. These parts cost about 50 cents and have an accuracy of better than 0.01% (even the cheapest ones). That accuracy equates to only 0.173 cents pitch error. A 0.005% tolerance crystal breaks the 0.1 cent error barrier. The rest of the error in a guitar tuner is related to the software techniques used to detect and display the pitch.
Given the ear’s limitations in discerning pitch differences (about five cents), and all the other contributors to pitch changes in a guitar as it is being played, it does not make a lot of sense to spend hundreds of dollars on an expensive tuner with accuracy of 0.1 cents. One cent accuracy is all a guitar player needs. But since one cent accuracy is so cheap (remember the quartz crystal), you can easily buy a very accurate tuner without breaking the bank.