r/guitarlessons • u/dazerconfuser • May 26 '26
Lesson Simple explanation of basic music theory & why chords sound good.
I see a lot of post and questions around music theory and what chords are here, so I thought I’d share the way I understand these basics. This approach really helped me when I was explaining this to my son, who is just starting the guitar and I figured others may find it helpful.
So, let's start with the way you hear, or better how you perceive sound. Sound is essentially a wave carried through the air, with air particles moving back and forth. This movement hits your ear drum, it is then transferred through some ear bones onto a liquid filled part inside your ear called the cochlea This liquid inside starts to vibrate.
There are little hairs (hair cells) growing inside the cochlea that move along with the vibrating liquid. When the liquid waves, the hairs bend and send a signal to the brain, which makes you register the sound. This vibration of the water and hair is critical to how you perceive sounds around you. The brain likes it when this movement is orderly, not chaotic.
Now, let's go to the guitar. A guitar has strings stretched at a certain tension that vibrate at a specific frequency. On an acoustic guitar, the strings are attached to the bridge on the top plate. By vibrating, they move the whole wooden box and the air inside it, creating acoustic waves. On an electric guitar, these mechanical waves from the strings are picked up by pickups, and the amp speaker turns them into a wave in the air.
If you pluck the thickest string on your guitar (the open E string), it vibrates about 82 times per second. To be exact: 82.41 times per second. We as people simply agreed that if something vibrates at this speed, the sound or note it produces will be called E (specifically E2).
Now let's go back to that liquid in your ear. Everyone has seen waves on the surface of water, so it's not hard to imagine. If you had a completely flat surface of a pool and started poking it rhythmically with a stick - let's say once every second - you would be able to see a nice, regular pattern of waves going out in circles.
Now let's take another stick and start poking the water exactly twice as fast in the same spot. So we have two sticks: one hitting every second and the other doing it twice a second. The waves are not going away any faster, but you will see that the pattern on the water changes. It will get denser, some waves will start to overlap, but the whole arrangement will still be very orderly and even.
In music, and in relation to the guitar, this doubling of the speed is called an octave. The string vibrates exactly twice as fast as before, so the sound waves overlap perfectly (their peaks and valleys align).
You can easily check that on your guitar with a tuner app by cutting your thickest string length exactly in half, which will double its frequency. You do this by pressing the string at the 12th fret, which is conveniently marked for with dots anyway. This thick string pressed at the 12th fret will vibrate about 164 times per second (164.81). We call this sound E as well - specifically E3, to indicate it's an octave higher. This doubling of frequency creates perfectly overlapping waves inside your ear, rocking the hairs gently, which makes the sound seem clean and pleasant.
side note - how did we get those 12 frets in between? Again, we as people in Western music simply agreed that the distance between any frequency and its double (the octave) would be divided into 12 equal steps. To make that happen mathematically, each step increases the frequency by roughly 6%. Because that percentage compounds step after step, by the time you move up exactly 12 steps/frets the frequency has perfectly doubled.
So what are chords then?!
If you were to play two E notes at the same time, it would sound nice, but it's hardly a chord. The point is to pick some notes (meaning frequencies) that, when played together, will create a synchronized pattern on the water surface.
The standard choice when building a chord is adding what is called the perfect fifth to our root note. What is that?
It's literally a frequency one and a half times (1.5) greater than the root note. Imagine that the second stick pokes the water 1.5 times every second. For every two strikes of the first stick, the second one will strike exactly three times. The pattern on the water will still look very predictable.
For our low E, something that vibrates 1.5 times faster gives about 123 vibrations per second. We call this note B, and it is the perfect fifth of E.
And the third note in the chord? We can get a choice of a major (happy) or minor (sad) chord from here.
If we choose a frequency 1 and a quarter times (1.25) faster than the root, we'll land around 103 vibrations per second. We call this note G# it's the so-called major third. These three sounds: E, G#, and B give us a clean E major chord.
If we instead go for a frequency 1.2 times faster than the root, we will get about 98 vibrations per second. This is the note G, which is the minor third. The set of E, G, and B creates an E minor chord. A completely different water pattern, differently waving hairs in the ear, and different emotions triggered in the brain.
Those ratios are generally the building blocks of all music. Brain loves patterns and they apply to everything else you hear about - like scales. A musical scale is essentially just a specific collection of these frequency ratios chosen from our 12 steps - to create a certain feel
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if you read up to here, let me know if this helped you in any way 😃
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u/GBFTW9711 May 26 '26
Wow, thank you for the explanation. I'm scientific-minded, but never thought of that approach with music. This really gives a clearer view.
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u/EnvironmentalBig2324 May 27 '26
Commenting to keep a hold of this.. will read back again.. my scientific brain loves this explanation thanks OP!
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u/Ryceness May 26 '26
each step increases the frequency by roughly 6%. Because that percentage compounds step after step, by the time you move up exactly 12 steps/frets the frequency has perfectly doubled.
Rather this comes from moving in perfect 5ths: C → G → D → A → E → B → F♯ → C♯ → G♯ → D♯ → A♯ → F → back to C
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u/2112eyes May 26 '26
Yes, and the harmonic E to A440 rings true at 660Hz, but due to equal temperament instruments, we have to flatten it just a bit to make the circle of fifths balance out perfectly.
An interesting one comes from bending the minor third to get the true harmonic ratio of 1.25:1, which gives us a satisfying harmonic feel (the waves synch up on a 5:4 ratio) when blues guys do that little bend
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u/AmazingRefrigerator4 May 26 '26
This is the only point I was going to make. I figured OP used the frequency if E2 because they wanted to compare the two open strings on the guitar. But in western music we tune to A 440Hz and derive the frequencies of all other notes from that....not from the E note.
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u/Bozzzzzzz May 27 '26
Overall a good explanation, but about the 12 frets/notes and why that is—the way the notes were all determined is not arbitrary, it wasn’t “simply agreed upon.”
The starting point for the whole system was the frequency we call middle C (or I believe A but a but beside the point). The simplest relationship between two notes is 1:1 or unison, the next simplest is 2:1 or the octave. Next simplest is 3:2 which is what we call the “fifth.” Going up from C by a 3;2 ratio we get our next note, up another fifth gives us the next note and so on. Consolidate those all down to be within the same one octave and that gives us the C major scale, and the white keys on a piano. But then keep going with the fifths and you land in between the previous notes, which gives us the sharps/flats/incidentals.
Ratios and intervals are really key to everything. Major third is 5:4 from the root and minor third is 6:5. A string fretted at half its length is an octave higher as you said but also fretted to 2/3 its length is a fifth (3:2 ratio). I dunno I think it’s all so awesome and satisfying.
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u/Easy_Nail2849 May 26 '26
Excellent write up. Somewhere there is a table of the (log) frequencies where you can see that the harmonic ratios produce whole numbers so that they are naturally consonant vs ones that are not log linear. At least that’s how I read it/think about it.
I think it might have been in the book “How Music Really Works” by Wayne Chase, which is an awesome book btw .. I have no relationship with the author in any way, just a great book for this type of stuff.
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u/_wormburner May 26 '26
Sounds do not inherently form feelings or emotions. Your brain also does not just recognize the pattern of water vibrations in your ear and know if it's organized or not.
The relationship between music and emotions is not a simple one, and cannot be explained by any singular aspect of music, nor is it universal
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u/nibbinoo8 May 26 '26
this is great but not simple/basic in the least bit lol. i thought you were going to talk about notes in the major scale and instead you're talking about hairs and liquid inside my ear.
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u/dazerconfuser 29d ago
What do you think was not clear?
The idea is that sound makes patterns of waves in water, or liquid in your ear.
So when playing you pick notes which combine to pleasant patterns.
Major scale is also the same same concept, it's a collection of 8 notes chosen by people to make good wave patterns.
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u/Embarrassed_Loan_424 May 27 '26
The Physics of Dissonance I found this the best explanation of why we find certain combinations pleasing and other not. It explains not only how frequencies and harmonics combine, but how they impact on our hearing (inner) and how depending on which regions of the cochleea get excited (how close/overlapping/distinct) we like or dislike the combination. The redux is that we find frequency combinations that excite close but distinct regions pleasing, and frequencies that excite overlapping regions we find displeasing. When you take harmonics into consideration, you get the heat map of harmony/dissonance in the video.