rghvdberg wrote:CRASH COURSE MUSIC THEORY
I'll just assume you are familiar with the layout of the piano keyboard (used in the pianoroll editor) and the names of these keys.
SCALES:
In western music we have 12 notes (thats the 7 white and 5 black keys on a piano keyboard)
Usually we don't use all these notes but just a selection; That's called a scale.
Most common scale is the major scale
If started on the C than the major scale is : C D E F G A B C ... yes all the white keys
If we count the keys between C and D we find one key (D#), this is called a whole step. Let's write this down as "1"
Between E and F there are no other keys, this is called a half step, let's write this down as "1/2"
The major scale is made of these steps
1,1,1/2,1,1,1,1/2
From C to D is 1 step
from D to E is 1 step
from E to F is 1/2 step
etc ..
Start on any key and follow the steps (1,1,1/2,1,1,1,1/2) to make any major scale
CHORDS
From this scale we can make chords : Take a note , skip a note and skip another ... thats a chord
C + E + G is a chord, D + F + A , E + G + B etc ..
DIFFERENT CHORD TYPES
Now it gets tricky (I guess)
The number of keys between the chord notes is what makes the chord type
MAJOR CHORD
Between C and E there are 3 keys (C#,D and D#) this is called a major third
Between E and G there are 2 keys (F and F#) this is called a minor third
A chord starting with a major third and ending with a minor third is called a MAJOR CHORD
So C+E+G is called C major, we usually just write it down as "C"
In the scale mentioned in this post there are 3 major chords
C,F and G
MINOR CHORD
Between D and F there are 2 keys (D# and E) -> minor third
Between F and A there are 4 keys (F#,G and G#) -> major third
A chord starting with a minor third and ending with a major third is called a MINOR chord
D+F+A is D minor, usually we write this down as Dm
In the scale mentioned in this post there are 3 minor chords
Dm, Em and Am
DIMINISHED CHORD
between B and D there are 2 notes (C and C#) -> minor third
between D and F there are 2 notes (D# en E) -> minor third
A chord starting with a minor and ending with a minor third is called a DIMINIHED CHORD
B+D+F is B Diminished, we usually write this down as Bdim
In the scale used in this post there's only one diminished chord
Bdim
THE 7 (VII) CHORDS
Sometimes the chords are given a roman numeral
I - C (c+e+g)
II - Dm (d+f+a)
III - Em (e+g+b)
IV - F (f+a+c)
V - G (g+b+d)
VI - Am (a+c+e)
VII - Bdim (b+d+f)
Remember that we can make any scale by starting on a key and following the steps (1,1,1/2,1,1,1,1/2) ?
This means that all major scales are constructed in the same manor and thus all the chords are constructed in the same manor.
So the 1st chord is always a major chord, the second is always a minor, the third always a minor etc, etc
NOTE:
1) Another important scale is the minor scale. google it

2) You can rearrange the order of notes in a chord. C+E+G is a C chord, but so is E+G+C or G+C+E
3) More chords can be created by adding more major or minor thirds ...
C+E+G+B for example or +G+B+D+F or D+F+A+C+E+G ... experiment!