A key a basically just a guideline of which notes sounds good when played together or sequentially.
For example, if a piece is in the key of “C”, then you might want to stick to the notes Dm, Em, F, G, and Am. C, being the root note, is the note that the piece will most often come back to. So it is in the key of “C”, and the other notes I listed have been observed to sound the best when played with C in mind.
You don’t *have* to follow these rules, like I said it’s supposed to be more of a guideline than a rule.
A key is just a series of notes (a scale) that forms the basis of a piece in Western music – those notes give a piece structure and help it to tell a story. The Do-Re-Me pattern is what we call a *major scale*, if you sing along it, you’ll hit every note in a major key, going up an octave. So if I start on the note C (Do), I would hit the following notes:
Do- Re- Me- Fa- Sol- La- Ti- Do (again)
C – D – E – F- G – A – B – C (again)
So those are all of the notes in the C major scale, going up an octave (an octave is the distance between two notes with the same name – a C and a C or an A and another A). If I’m composing a piece in C major, I’m going to be using mostly those notes. Going outside of those notes will sound unusual – and that will help to tell part of my story. If I stick to those notes and familiar chords (notes sounded together) within this key, my music will sound familiar and harmonious, for the most part.
Using notes like Bb or F# that aren’t normally in that key will sound unusual around those other notes – maybe I can use that to make part of my music sound a little more tense. Maybe I’ll use those off-notes in order to resolve comfortably to the notes that are part of my key. Maybe I’ll use those off-notes to change keys, and switch to the key of Eb minor in order to create an interesting bridge in my music, before coming back to C major. There are a million ways to play with that structure – like all art, we have rules in place to provide a starting point, and breaking those rules allows us to mess with expectations in interesting and unique ways.
Of course, the whole topic can get a lot more complicated than that (there are minor keys, different modes of scales, complex chords and inversions, etc), but them’s the basics. A key exists to give a general, familiar structure to music. How much we choose to use those keys, move between them, find places where they match and intersect, or find ways to break them entirely, is what making music is all about.
It can help to think of it from its base level in musical theory, at least how I understand it. Sound (music) is merely different frequencies of air vibrating picked up by your ear drums. Certain frequencies create harmonics when they mesh with each other mathematically or dissonance when they don’t. From that starting point, “keys” are mostly a cultural thing that have been ingrained in us depending on the musical systems we grew up with. For instance the western musical system (Beethoven through modern day rock and roll) has 8 separate pitches defining an octave, while some native American musical systems had 12 distinct pitches that are mathematically describing the same thing but musically used in different ways
There are lots of possible answers, depending on what specifically you’re most interested in understanding.
From a “what are they, really?” perspective: All notes are just sound waves with different wavelengths. As you go higher up a scale, the wavelengths get smaller, sometimes in ways of simple fractional relationships. For a simple example: the same note an octave higher is exactly half as long a sound wave. This puts the notes in such perfect sync that they sound almost the same.
Other notes along the way, though, may be 3/4ths as long, etc. These notes played together will create a BIT of disconnect (tension) because they don’t sync up perfectly. But they’ll sync up well enough to create a pleasing mix of “not quite the same but they sound like they still fit together”. So this relationship will create notes that are in the same key as each other because it works well.
You can pick the starting note of your key to be anywhere, but the principles of those fractional wavelength relationships will stay the same as you move up the scale.
Music is generally about finding a balance between tension (imperfect relationships) and satisfaction. Songs all in the same note provide no tension. Songs all in haphazard and random wavelengths create no satisfaction. Songs in a single “key” provide a balance of both for composers to work within.
*”Do – Re – Mi – Fa – Sol – La – Ti/Si”* is just a system to assign syllables to musical notes, created so people could sing in tune more easily.
You may have heard of *”C – D – E – F – G – A – B” (which are the white keys on a piano)*. Well, that’s another system to organize notes, but singing syllables (say, *Fa*) instead of letters (*F*) is much easier. Singing “*Sol/So*” is stronger than singing “G”. This is called **solfège**.
Now, it gets a bit confusing when you learn that English speaking countries use what’s called “movable solfège” instead of “fixed solfège”.
For example, Spanish speakers use “fixed solfège”, meaning “Do” always represents the same pitch: a “C” note for an English speaker. But English speakers/movable solfège users adjust “Do” to represent the first note of any scale, rather than the specific “C” pitch.
[for more details: Most countries don’t use ABCDEFG for note names](https://www.youtube.com/watch?v=MVA8bgSBt5A)
There are twelve basic notes, but it’s common to only use seven of them at a time. Different combinations of seven out of those twelve notes are the different keys.
Now, it also turns out that even if you use seven notes, which one of the seven you start or end changes how the combination sounds. So, for instance, if I play A B C D E F G and then end on an A, it sounds sad. But if I play C D E F G A B and end on C, it sounds happy. The former sad sound is called a minor key and the happy one is called major. Every
Combination of seven notes can made major or minor (or something else) depending on which you start and end on.
So when you sing Do-Ray-Me what note (pitch or frequency) do you start on? Whatever it is, I am sure you can imagine that if someone else were to sing Do-Ray-Me they might start their Do on a different note, a different pitch, a bit higher or a bit lower perhaps and then carry on from there with every note being a bit higher or lower than yours. If they do, then they are most probably singing in a different **key.** Even though their Do-Ray-Me will go up in steps just the same as your does, each note will not be the same as yours, it will be a bit higher or lower depending on where they started.
**Lets start with notes**
Notes have names : A, B, C, D, E, F & G. There are also some other notes in-between those. For example, there is an F# squeezed in between the F and the G. In fact the whole set of notes numbers 12 in total and looks like this:
A, A#, B, C, C#, D, D#, E, F, F#, G, G#, and then A gain.
If you start on a C and make that your Do then as you sing up the Do Ray Me scale, the notes you will be singing will be C,,D,E,F,G,A,B and finally a higher version of C. This is known as the key of C Major because you started on a C.
But if you were to start on a G instead, this time your Do-Ray_Me sequence would result in you singing G, A, B, C, D, E, F# and then G again. This is the key of G major. [You may wonder why an F# and not an F? This is because the notes in your Do-Ray-Me scale are actually not evenly spaced. You dont notice the problem with a C major key because the spacings match but when you start on other notes than C you start noticing the differences].
So thats two keys, C major and G major. But in fact you could start your Do-Ray-Me scale on any note and that would result in you singing in a different key named after the starting note. So since there are 12 possible places to start then there are 12 possible major keys:
C major, C# major, D major, D# major, E major, F major, F#major etc etc.
OK, that seems to have covered it except for one remaining question: why is it a **major** key? Are there other types? Yes, there are also **minor** keys.
**What are minor keys?**
When you sing your Do-Ray-Me scale you may not realise it but that is a *major* scale. As a result when you play that scale starting on different notes you get a whole bunch of different major keys.
But there is a sequence that is similar to Do-Ray-Me but sounds a bit different. This is a *minor* scale and the gaps between the notes are in slightly different places. The effect when you sing this scale is that whereas the Do-Re-Me scale is quite cheery and optimistic, the minor version is a bit more moody and slightly sad. However, it works just the same way, you can start the sequence on any note you like and the result will be a key named after the starting note. But this time it will be called a minor key. So there is:
C minor, C# minor, D minor, D# minor, E minor, F minor, F#minor etc etc.
**So whats the point of it all?**
Well, there are practical reasons for having different keys. Since people have different types of voice, some prefer to sing in one key rather than another because it suits their voice better. There are also some instruments that sound better in one key than another. But even on instruments where you can play in *any* key (like a piano) there is a different in “mood” between one key and the next. People argue about these differences but many people reckon that C major is the sunniest key to play in and D minor is the saddest. I find A minor always sounds mysterious.
[Note: What about sharps and flats?
The # symbol I have used is known as a sharp. So C# is called C sharp. It means “half a step higher than C”. You will also see a *b* symbol known as a “flat”. This means “half a step lower”. So you can see that all the in-between notes could be named in two different ways: a C# is the same note as a Bb. To make things simpler I have kept to using only sharps in this explanation]
Just different speeds the air vibrates as sound to your ear.
And how they sound together depends on their ratios of how many times each note has made a complete “cycle”, which is just the length of its wave.
The simpler ratios sound more “harmonic” and the more complex ratios sound more “dissonant”.
3:4, 1:2, 2:3, these are all very simply ratios. Play notes with those ratios like a C with F and you get 3:4. The C cycles 3 times and the F cycles 4 times. How neat. C with G gives an even cleaner 2:3. But play a C with the key in between F and G, and the ratio is a brutal 32:45.
Each key is tuned to be its own frequency, plus does other frequencies that that give it “character” (what makes a sound sound like its own instrument). This is also called timbre (pronounced tamber). And that frequency corresponds to a “note”, Do, Re, Mi, etc. but actually C, D, E, or whatever.
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