Key Signature, an excellent question
So much mis-understanding. The posts which include the major scales and start you with the root, 4th, and 5th construction of chords are a great place to start. You need to study music theory or you will forever be limited in your creativity. Don't believe that "ignorance is bliss". Music theory is fun to learn and will enhance your enjoyment of music and compositional efforts. Start with the C Major scale: CDEFGABC
Root Chord, known as "tonic"
Starts on the first note of the C Major scale, CEG
The "4" Chord is built on the 4th note of the scale, FAC
The "5" Chord is build on the 5th note of the scale, GBD
These three chords are the basis of most simple harmony
and melody in a major key.
What is C Major? Why is it a "Major" scale? What makes it Major?
The Major scale is constructed of equally spaced intervals. For example:
CDEFGABC
C to D, notes are a whole step (one note exists between, C# in this case)
D to E, whole step (one note exists between, D# in this case)
E to F, half step (no notes between these two notes)
F to G, whole step (one note exists between, F# in this case)
G to A, whole step (one note exists between, G# in this case)
A to B, whole step (one note exists between, A# in this case)
B to C, half step (no notes between these two notes)
So there is half step between the 3rd and 4th note of the major scale
and a half step between the 7th and Root(1rst note) of the major scale.
This is true for all 12 major scales. Using a piano keyboard can help with
visualizing this relationship. Let's build the G major scale:
GABCDEF#G
G to A, whole step
A to B, whole step
B to C, half step
C to D, whole step
D to E, whole step
E to F#, whole step
F# to G, half step
It always works. This was invented with the modern piano and is called the equal temperment system. All keys "sound the same", although those with perfect pitch can sense the exact frequency of a pitch.
Major keys tend to sound "happy" for lack of a better term. The characteristics of this scale are heavily used in all types of music. Minor keys are a different story, not in this post.
Key signature can define the key but if your not reading music this doesn't get you to far. Sometimes a song might not start on the root chord but as mentioned they usually end on the tonic or "resolve". Half steps are used as "leading" tones that "pull" towards other chords. If you changed the order of notes in a G chord:
D, GB then follow this chord with E, GC you will hear that the B resolves to the C, the G remains common but functions as different chord tone and that D moves up to E. These relationships define the "key center". There's more background information to make this clear but this gives you a start.
The "why" and "who" said so isn't a leap of faith. When you learn about the "harmonic series" some of these mysteries are solved rather easily. Increase your knowledge of theory and you will unlock your imagination. As a composer you want to control the music not vice versa. Wow, I've said quit enough. Please feel free to ask follow up questions, as you can tell I'm not afraid to answer<G>
