Why are there only 7 musical notes? Was it decided to divide sounds like that or are there no more in nature?
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It was decided by people…and it’s not the only choice. The familiar (to most Western ears) ABCDEFG scale is called the heptatonic (“seven note”). The intervals between notes vary, and the different combinations of whole tones and half tones is what gives you the different “modes”. There’s nothing magic about these choices, they’re just convention. There’s also multiple pentatonic scales…pentatonic is, among other things, why most people so can rapidly identify “Japanese” classical music.
There’s technically an infinite number of possible notes in an octave, but human hearing doesn’t have enough resolution to distinguish them all so the number of practical notes is a lot smaller (but much larger than the number of notes in typical music).
Octaves are physical & biological…when you double the frequency (half the string length), it “sounds” like the same note to us. Technically, it has the same harmonics. But how you divide the notes between octaves is arbitrary.
There are actually 12 notes. It’s called 12 tone equal temperament. The piano has 7 white notes, and 5 black notes. 12 in total (before repeating of course).
All 12 notes are equal distance apart from the next one, therefore ‘equal temperament’.
It’s a convention that developed in western music, and I believe a large part of why is that large orchestra needed to be able to play together and sound in-tune with each other.
Other parts of the world have used different types of tuning.
There are 7 notes in most musical scales in western music. But there are 12 notes in western music, we just don’t use all 12 notes for every scale.
The reason we have these notes is mostly because of a thing called *[harmonics](https://en.wikipedia.org/wiki/Harmonic_series_(music))*. Harmonics are a natural phenomenon of how waves propagate in various ways.
One way is plucking a taught string, like on a guitar. When you pluck a string, you get a note. We call this the first harmonic, or the fundamental. If you hold your finger down at the point in the exact middle of the string (this means that you’re dividing the length of the string in half), then you get a note that is an octave of the open note. This note is the second harmonic of that string. If you divide the string into a third of the length, you get the 3rd harmonic, which is called a perfect 5th from the open note. Divide it into a 4th of the length, another harmonic. [And so on](https://upload.wikimedia.org/wikipedia/commons/c/c5/Harmonic_partials_on_strings.svg).
The first 27 harmonics of any note essentially lay out the other 11 notes (this isn’t exact, since pitches are not of equal distance to each other and we can only approximate them in western music). But why 7 notes instead of 12?
The first two harmonics are essentially the same note. But the third harmonic is what is called a perfect 5th. We call it that because of a long history of it being the most *consonant* note, other than the octave. Consonance basically means that two notes sound good together. There’s a physiological reason for this, but there is also a mathematical reason for this. Both are a bit complicated.
Since octaves and 5ths sound good to us, it is natural that our ancestors started to build their idea of music from both. Our notes repeat at the octave, but they do something weirder with the 5th. If you start at a note, then move up a 5th, then move up a 5th from that, and keep going until you have 7 notes, then you have just found the 7 notes of a major scale. And this is likely why we have 7 tones in the major scale, which is the basis for most of western music.
##edit: beyond ELI5
there’s a lot more to this that I think is really cool. The harmonics of a note (any note) are based on integer multiples of its frequency. Which means that if the note A has a frequency of 220 Hz, then all of its harmonics will be multiples of 220:
Harmonic | Frequency | Note
—|—|—-
1 | 220 | A3
2 | 440 | A4
3 | 660 | E5
4 | 880 | A5
5 | 1100 | Db6
6 | 1320 | E6
And they continue infinitely, getting harder and harder to hear with each multiple. Other than the fundamental (A), E is the strongest harmonic, and the most pleasing to our ears (since it has a simple ratio from the fundamental). E is the fifth of A.
These harmonics aren’t just created by “dividing the string length”, *they exist in the fundamental itself*. If you were to decompose the sound of a single string pluck the same way you decompose light through a prism into its rainbow components, then you would find some combination of these harmonics (and more, but the harmonics would be strongest).
So in a lot of ways our system of 12 notes with 7 notes in a scale (or key) is based upon the relationship of the 5th from the fundamental. And this relationship is encoded in the very nature of every single individual note. And not only notes, but the harmonic series shows up in other natural phenomenon.
Or course, all of this is ignoring the difference between [just intonation](https://en.wikipedia.org/wiki/Just_intonation) and equal temperament, other tuning systems, as well as the [pythagorean comma](https://en.wikipedia.org/wiki/Pythagorean_comma)).
Sound is vibrating air. The vibration can be faster or slower, and you’ll perceiving it as higher or lower pitch. For example, if you play A on a tuned piano, it will cause a string to vibrate 440 times a second, producing a sound wave at 440 Hz. If that string were not tuned correctly, it could vibrate 439 times or 441 times a second.
You might not be able to tell the difference immediately, because the human ear is not very sensitive to the absolute number of vibrations in a second — but it can readily tell the difference between two notes played together, or shortly separated in time. Some intervals will sounds good, and others will sound bad.
It turns out that notes that are related to each other by simple fractions (2/1, 3/2, 4/3, etc) tend to sound “good”. That’s because a string vibrating at 440 Hz is also producing *overtones*, which are sounds at integer multiples of 440 Hz (880 Hz, 1320 Hz, etc) — not as strongly, but in a way that your ear and brain will notice. This is why if you play the “A” at 440Hz together with the “A” one octave higher, at 880 Hz, they will sound almost perfect together — as if they are the same note, because they are producing the same overtones. In fact they are so similar that in music we call them the same note, “A”.
Another note that sounds good with A is E, at or around 660Hz. That’s because E is producing sounds at 1320 Hz and 1980Hz, which A is also producing. The ratio between E and A is that simple fraction, 3/2.
So: you can play a note at any pitch you want, but music is about playing notes that sound good together. In Western music, we’ve standardized on a scale of seven notes, which mostly have simple fraction relationships with each other, or close to it.
It’s not the only possible scale, but it’s by far the most common. Even cross-culturally, music from regions in the world have a lot of the same notes as in Western music, because of the physical principles involved.
Now, the choice to call 440Hz “A” is a perfectly arbitrary one, because again, the human ear is not sensitive to the exact number of vibrations, only the relationships between notes. Historically in some countries, “A” was something else, like 432 Hz. So long as **every** note is lowered by the same proportion, the overall music might sound lower in pitch, but the melody would still sound essentially unchanged — it would not suddenly sound discordant. Musical arrangements sometimes will raise or lower the pitch of the entire piece to accommodate the range of a vocalist, for example replacing all “A”s with “B”s. This is why pianos have 12 keys in an octave, because the notes A-G are not all equally spaced and sometimes you’ll need to have access to a note “in between” when you’re changing the key of the music.
The modern tuning system was developed around the 1500s. There is no real foundation for it in nature, and some cultures use very different tuning systems. It’s just a mathematical formula that’s founded on the idea of the octave (which, I should note, *is* in fact a natural phenomenon).
The western tuning system divides the octave into 12 steps, but there are also systems that divide the octave into 15, 16, even 21 steps. Many scientists believe that the only reason the 12 step scale is so pleasing to our ears is because we are used to it, not because it’s any more “natural” than some other scale.
If you are interested in other scales, [this](https://youtu.be/Ur6GOoSNGN0) is a great video explaining the Bohlen-Pierce scale, a 13 step scale discovered in the 70s. And [here](https://youtu.be/60SYLdMYvcE) is a video of a woman performing a song in the scale. She had a custom built keyboard to play it! To me, it literally sounds like music from another planet. Pretty cool stuff.
It should be pointed out that 12-tone equal temperament is a Western invention. Many cultures have either a greater number of possible “notes” or a fewer number available. For instance, in Indian music, there are only 7 notes available:
https://en.wikipedia.org/wiki/Svara#:~:text=The%20seven%20notes%20of%20the,Pa%2C%20Dha%2C%20and%20Ni.
These systems come about through convention over millennia of making and producing music, and different cultures will build different systems.
There are actually 12, but 7 in a key
Short, hyper simplified answer
Because we decided to stop at 12
Keys just sound good together, and 7 is the number that works
For a better answer, I think they’ve been provided
I’ll explain, but I have to correct you on something. There are twelve notes in an octave, if you only go by half step (including flats/sharps).
There was a smart guy a long time ago named pythagoras.
He had a theorum named after him. Smart guy. Also a rock star for his day.
Found out that if you take two equal strings, then cut one so that it is in a 2:3 ratio to the first, it will be a perfect fifth higher. He kept doing this.
C to G, G to D, D to A, A to E, E to B, B to f#, f# to c#, c# to g#, g# to d#, d# to a#, a# to e# (which is f natural), F back to C.
This is called the circle of fifths. This includes every note of the modern keyboard.
Nonwestern music has quarter tones or nontonal music, but western music (derived from the old dead guys you know, from bach to Wagner) uses almost entirely these twelve tones.
Source: I have a music degree from a prestigious big ten university. Coincidentally, I’m a weld inspector because fuck the fine arts and fuck me for trying to get a career in it.
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There are actually 12 notes, of which 7 are chosen to make up a major scale.
No, this is not the only way to divide pitches. It’s the standard for traditional western music.
Why 12? Because some powers of the number 2^1/12 make rational numbers (with remarkably little error) with small denominators. For instance:
2^7/12 = 3/2
2^5/12 = 4/3
2^4/12 = 5/4
Humans can hear the relationship between pitches. When two pitches are related by a rational number, they sound pleasant.
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