You can use harmonics to tune your guitar. You can generate a harmonic wave by lightly touching plucking and releasing a string directly over the fret wire at any of the 5th, 7th, 12th, or 19th fret positions. I personally do this by gently touching (not pressing) the selected string with my index finger and plucking with the thumbnail of the same hand. At the same time I perform the plucking motion, I release the touch. This will require a little effort to perfect if you've not done it before, but it's well worth the time to add to your skills.
To offer a bit of description, a harmonic is a multiple of the predominant frequency and also the lowest frequency of the tonal waveform generated (fundamental).
To further simplify, as you play the selected note the most dominant sound you'll hear is known as the fundamental frequency. When executed correctly, as the string responds it vibrates differently. In order to achieve the harmonic frequency successfully this must be executed at the fret positions I mentioned earlier (5th, 7th, 12th, 19th). This will then result in the generation of frequencies commonly referred to as harmonic overtones.
This technique by which overtones are accentuated is what enables the instrument's timbre (or voice) to be heard. Reiterating my earlier statement in a slightly different manner, harmonics are simply overtones that are multiples of the fundamental tone generated. For example, a 3rd harmonic will vibrate at 3 times the frequency of the fundamental of the note played.
The primary advantage of tuning by way of the harmonic method is that it's not necessary to keep your hand on the fretboard as is required by the standard tuning method. This is due to the fact that the harmonics will continue to sing out after the given note has been stricken. Another advantage to the harmonic tuning method is that when fretting a note (as per the standard tuning method) you risk stretching the reference string and therefore a possibility of the note that's sounded being slightly up (or sharp) in pitch which can affect tuning accuracy.
Basic Instructions for the Harmonic Tuning Process
As with any tuning method, there is a required pattern to use when tuning with harmonics.
1st make sure the 6th string (typically low E) is in tune using a known reference (pitch pipe, piano, tuning fork, etc.).
Now play the harmonic at the 5th fret on the 6th (typically low E) string and then take your hand away (reference the technique I described earlier in this article)
While the harmonic of the previously stricken string is still ringing, play the 7th fret harmonic on the 5th (typically A) string and compare. If the A string harmonic is exactly the same as the 6th (E) it is in tune. If it is clearly a different tone, perform this method adjusting the 5th string until it matches the harmonic of the 6th. As you adjust the A string the tonal waves will become shorter until eventually, they are indistinguishable from one another, signifying the strings are now in tune.
Repeat this process for all remaining strings on the guitar until you reach the 2nd string (typically the B string).
To precisely tune the 2nd string to pitch, play the 7th fret harmonic on the 6th string and match this to the open B string (playing the harmonic of the B string is not necessary for this step).
As with the other strings above adjust the 2nd (open) string until it matches the pitch of the 7th fret harmonic on the 6th string.
Repeat the process as used on 5th - 3rd strings and tune the 1st string (the high E) referencing the 5th fret harmonic on the 2nd (B) string to the 7th fret harmonic of the 1st string (high E). At the successful completion of this process your guitar should now be tuned to what is known as "Concert Pitch".
What exactly is concert pitch? Concert pitch is a standardized pitch reference based on the frequency of the A (above middle C) at 440Hz. This is the most commonly practiced reference point so that all instruments tuned to concert pitch can be in tune with one another. It has been a standard since the early 1900's. During the classical era, the typical tuning frequency that was used ranged from 430Hz to 435Hz. The preferred frequency of Mozart and others was said to be at 432Hz.
My wife and play together, her on keyboard and I on guitar, using the 432Hz pitch. We find it to be much more pleasing (less harsh) to our hearing tonally. The instruments have a much more rich or sweet sound to them tonally. When this is an option, it is our chosen preference. We've also found it's much easier on our voices. Below is an image for instance that shows the affect of a frequency played at 432Hz vs. 440Hz. Our ears can definitely tell the difference and the image speaks for itself.
Tips for Keeping Your Guitar in Tune
Too much or too little humidity can have adverse affects your guitars. Since many guitars are made of wood laminates, and virtually every high end guitar such as Rhema Guitars crafted primarily out of solid wood, by nature the wood will absorb or lose moisture in order to match the relative humidity of the environment it is in.
If the humidity is high, the wood of your guitar will in turn absorb moisture causing it to expand. When this occurs it can put greater tension on the strings which also may lower the string action thus causing the guitar to play out of tune due to a slight shift in the intonation. Re-balancing the guitar's humidity level to between 45 & 60% humidity will generally correct this issue naturally. On the other hand, if the humidity is extremely low your guitar will contract or shrink, thereby causing your strings slacken and lower in pitch and often will cause the action to raise. Addressing the need to return to the humidity levels mentioned above will often remedy this as well. This is a good reason (especially for hand made solid wood guitars) to keep your guitar in a hard case with a guitar humidor.
Don't Forget to Change your strings
If you're a regular player and take your talent seriously, you should make it a practice to frequently change out your old strings. I highly recommend Elixir Nanoweb strings for all my acoustic guitars. I've found that they do indeed last 3 - 5 X longer just as they claim and I play often. Typically I find myself changing the strings at least once every 3 months max and if I play more, 2 months max. Gigging musicians may want to do so even more often. Old and frequently played strings won’t stay in tune as well and won’t sound anywhere near as good as a set of fresh strings.
Summary
When I first started playing guitar @ 1971, I found tuning to be somewhat laborious because I had a cheap hand me down classical and my dad's budget was a bit too tight to be "wasting money" on guitar strings. That's OK, being many more years along in life since then I totally understand. Having said that, as a player today all these many years later, I just can't make myself skimp on strings.
Keep in mind while standard and harmonic tuning can be beneficial to learn, if you're a new player just learning, I wouldn’t recommend relying solely on either technique when starting out. Double checking with an electronic tuner (Snark is a good affordable and reliable brand) is always a good practice. As you grow accustomed to your guitar you will begin to learn to distinguish tone readily by ear whether the individual strings need to be raised or lowered in pitch.
Always tune your new set of strings and stretch each string a bit at the 12th fret. This will help preset your new strings and lessen the frequency of them going out of tune when new. Well, that's it for now. I hope you've this article to be helpful or at the least, interesting.
Until next time......Stay Tuned!!!!!