It would help a great deal to have some familiarity with basic music
theory, like what we have on the web site. Especially you need to
know about:
the intervals
the chromatic scale
diatonic scales like major and minor
detrees of the scale (especially tonic, subdominant and dominant)....
those are relative positions
the notes to use when playing in a certain key.... absolute locations
which of those notes are which scale degrees in that scale converting
relative to absolute
triad and seventh chords
chord inversions and chord forms
cadences
knowledge of location of notes on the keyboard
So, here is the situation. You find a fiddle player who says he's
playing a standard fiddle tune in the key of G. So, here is what
you do.
You know the tune and you know it uses full cadences. Full
cadences use chords built on the first, fourth and fifth degrees of the
scale. The old I, IV, V ploy. Those positions
relative to the first note of the scale.
You also know that the notes in a G scale are: G, A, B, C, D, E,
F# and G. Those are absolute locations.
To find the absolute position of the I, IV and V chords, you relate
them to the notes in the G scale. So, in the G scale, I = G, IV =
C and V = D. Now, you know that normally you'll need to
play G, C and D chords, and in that order.
Now you recall how to build triad chords above a root note. Major
chords use a major second and then a minor second. And you recall
your chromatic scale, so you determine these notes for the three chords:
a G chord uses G, B, and D notes
a C chord uses C, E and G notes
a D chord uses D, F# and A notes
You know you are allowed to stack these notes in just about any order,
but to be careful of their spacing: to stick with closed or open form
chords, for the most part when possible.
That pretty much ends the theory portion of this little task.
Now, you think about the rythm in the fiddle tune, which in this case
is normally 4:4 time. Each measure has four beats, and the odd
numbered beats could do with a nice strong beat, while the even
numbered beats would be okay with a weaker sound on them.