Measuring the Intonation Difference Between Two Notes
For intonation work, or even for determining the need for intonation work, it is important to be able to carefully measure the cents-off accurately when comparing any two notes.
we measure pitch differences in cents. A cent is 1/100 of the pitch difference between any two adjacent frets, (a musical half-step).
We need to be aware that the advertised accuracy of electronic tuners refers to the devices internal sensing accuracy, and not to the pitch accuracy that is available to the user. While an electronic tuner may claim accuracy of within 1/10 cent, we can not realize such accuracy meaningfully presented. Many tuners have a green light showing when a string is in tune, but over how much pitch change is permitted, still getting a green light?
Precise reading of guitar string pitch is even more of a challenge. The string pitch fluxuates quite a bit, and the pitch drop from picking attack to it’s decay may be several cents, depending on the string and on how hard you pick.
Actual strobe tuners used to be the only convenient way to accurately measure pitch. They are expensive, and are used by professionals. A real strobe tuner has an actual rotating disk freeze-framed by flashing lights synced to the input signal pitch, whereas a virtual strobe tuner uses electronics and/or software to emulate the real strobe.
Although the internal accuracy of strobe and virtual strobe tuners is declared to be 1/10 cent, it is difficult for the user to actually see the difference of a few cents by the tuner needle or the minimal rotation on the strobe screen.
Thankfully, we now we have very accurate tuners available for free or for very cheap on our cell phones! Some are very ‘tite’, requiring very small and careful use of the tuning keys. These are excellent for finely tuning your guitar. There are also some very accurate non-strobe apps having a wide meter type display of cents off. Some of the tuners use very interesting display graphics. Most have free versions, but then they encourage in-process upgrade charges for valuable features, like chromatic notes. Many display a cents-off field, but, it may change too rapidly to be of readable. It is very interesting to try several of these!
A few examples of strobe tuner apps – with a wide variety of features:
A few examples of precise non-strobe tuner apps – with precise display of cents off, or a ‘tite’ precision of ‘in-tune’:
Experimenting with these tuners will show you how tiny tuning key movement can are necessary for the desired pitch precision.
For accurate intonation work, I use a tuner which has control ability to adjust the tuner pitch by cents. My Peterson Stroboplus HD , and also a few cellphone tuners, allow me to tune the 2nd fret pitch, and then to adjust the tuner to match the 14th fret pitch, thereby showing me the pitch error cents.
Intonation work should be done much more accurately than daily tuning. When the guitar intonation is more perfect, it allows slight pitch changes while playing for a reasonable length of time, to still be within pleasant limits. Nut slots should be smooth and wide enough so that the strings don’t bind. Lubricate the slots with a tiny drop of fret board oil (olive oil is fine – I use mineral oil) right over the string and slot.
Be aware that, when plucked, the pitch will momentarily go high (attack) and then die down to a lower pitch (decay). Normally, it’s best to read the tuner after the attack has settled, but not too long into decay. Someone who normally plays very fast may want to tune to the attack I find it best to pick the string near the 12th fret. Depending on the tuner, you can often get faster, clearer readings by changing the tuner from chromatic mode to an instrument mode and to particular notes.
It’s best to assume a natural playing position when testing pitch, and to try to use the same finger pressure as you (or your customer) would normally use. To minimize the attack/decay disturbance, don’t pick too hard, and pick with a regular cadence of about 1 or 2 plucks per second. (A reader suggested using an e-bow instead of a pick. Anyone done that?)
To get the most accurate readings for Intonation work, my strategy is to tune the guitar string to within a few cents at the first fret position, Then I measure the cents-off of the second fretted note, using the tuner cents control. The cents difference between the two fretted notes is the intonation error. In other words, do the final precision pitch adjustments on the tuner cents adjustment, not with the guitar string tuning key. Keep in mind that, for intonation measurement, it is the pitch difference that matters, not absolute pitch.
Tune the first note on the guitar as well as is practical (within a few cents). Always end tuning by turning upwardly. Lastly, press the string firmly, close to the nut (to insure that the tuning will not slip during the measurements.) Then advance the cents control of the tuner, up or down, until you see the very least rotation of the strobe.
When you are satisfied with the reading, record the cents off, set the tuner cents back to zero, and then perform the same cents control process on the other test fret pitch, recording the second pitch cents off.
Optionally, you can go back and confirm the first measurement.
Virtual Strobe Tuners
There are some new options for strobe tuning devices that are less expensive than were previously available, yet they pack a big array of features. Players and hobbyists should also take a look! They are inexpensive compared to what you may have paid for your guitar. If you are thinking of doing some serious intonation work, you will also want to make the most of that by being able to tune quickly and accurately on an ongoing basis.
There are a few electronic tuners that have a strobe type of display capability;  They are not strobe tuners, but the display can enhance the pitch readability. The
Electronic Tuners
In the past, I have produced excellent results using chromatic electronic tuners for intonation work, but it takes a lot of patience and re-testing. Software strobe tuners are much more accurate. While electronic tuners are fine for practice tuning, if you don’t have a strobe tuner with either cents-off display or cents adjustment, use a software strobe tuner for intonation work (see below).
Beware: tuner manufacturers claim very good internal” or “detection”acuracy, but that means very little. The important feature would be “display” accuracy, but nobody ever specifies that! For older popular types, If you turn on the tuner and carefully hold it sideways to the light, you can see that the LCD tracks for displaying the readings are only at every 2 or 2 1/ 2 cents apart. This can still work well, though, because the reading actually wavers over a range of about 2 cents. If you can keep it on the mark for a few seconds, the reading will be pretty accurate for tuning.
Most clip-on tuners have 2 1/2 cents between the indicators. I haven’t tried many, but I know that the Snark Tuners and the Sabine clip-on tuners are 2 1/2 cents, I am also disappointed with their Super Tite.
For inexpensive bench tuning, find a larger one with 2 cents between the display marks, such as the Boss TU-80
Another type of electronic tuners has LCD indicators typically 10 cents apart. They are able to give more precise readings, by simultaneously illuminating adjacent LCD’s when the pitch is off. The pitch is correct only when the green LED is the only one on.
I had a Korg SHPRO
Hardware Strobe Tuners
Older strobe tuners used a rotating metal disk back-lit by lights to measure pitches – primary and several overtones. Most modern hardware strobe tuners use virtual strobe software, (and not a rotating disk). Peterson, in business since 1948, offers a substantial line of virtual strobe tuners and also a few actual mechanical tuners. Peterson Strobe Tuners
Software Tuners
It is important to note that the accuracy of any software tuner pitch is dependent upon the reference frequency of your sound card. Notebook sound cards are especially prone to be a bit off pitch, so check the pitch of the tuner with a tuning fork or your best tuner, and adjust accordingly. My desktop computer is just .02 cents off, but my notebook is 11 cents sharp. Adjust the cents as needed.
There are many tuners available on cell phones and tablets, including some virtual strobe tuners that are good for intonation work.
Peterson offers Strobosoft, a software tuner in standard and deluxe versions. Lots of features for sweetened tunings, temperaments, intonation mode, spectrum analysis, etc. Also, there is a mobile App called Strobe from Peterson priced at under $10.
For PC, the TB Strobe Tuner software features a circular strobe display, and is very accurate. It enables tuning calibration adjustments in cents, so you can accurately measure the difference between two notes (see below). In addition to equal temperament, it provides a list of scale selections for a variety of instruments, DADGAD, Drop D, etc (but does not provide for temperaments nor tuning offsets). You can set a specific note to test, or use the automatic chromatic mode, or others. It works best in an instrument mode, or by selecting each particular notes (with a little practice, this goes quickly). This program is great, very accurate and very inexpensive at $4.90! This was, for a time, my choice for both convenience and accuracy! for Windows 10 and 11, the AP Tuner, by Joseph Broms, provides a high degree of accuracy. It displays the note and cents-off, making it really easy to determine the intonation difference of two notes. It also has nice extra features, including tuning offsets and tone graphing. AP Tuner is shareware, $35, but you can evaluate it as long as you want. The tuner registers cents-off in real time, but freezes when the note amplitude drops below the sensing threshold, so adjust the slider at the left at a little below your normal note volume, so it stops recording before too much decay. This results in a fairly consistent measurement.