Learn to improvise. 2004-2005. Lesson 11: leading tones and chords.
What is the temporary key (C or F) if you are playing in key C and are
going from chord C to chord F via C7? The answer is in key F, as note b
clearly does not belong to the scale during C7.
A similar function has Caug. It contains a note (g#) leading from C to
F. Caug is the third degree of Am, so you could say you are in de key of
Am during Caug. Note g indeed does not sound to belong to the scale.
However... the notes b-flat and g# are so temporary in these cases that
their leading function is much more pronounced than the temporary key.
I consider them as leading notes and the chords C7 and Caug in these
cases as leading chords. Also dim chords are used as leading chords.
C7 Caug C#dim7 Cdim7 with leading notes b-flat, g#, c#, d#+f#
Actually the feeling is ambiguous because you keep on asking whether
you are modulating or using a leading note. Perhaps a blues captivates
by this feeling during C7. A melody note b-flat (in C) asks for a
solution. Think also of the enthralling seventh note in the Rumanian
music. Unmistakably a seventh note gives an expectation.
Expectation by seventh note
There are more leading notes than the above ones.
Em with leading note b.
But especially the
seventh note has always had the special attention of the researchers. The
problem is the definition of the whole step (2 key steps), e.g. the
proportion between c and b-flat.
Point of departure always is the frequency ratio 3/2 of the perfect fifth
(7 key steps, e.g. c-g). E.g. if c would have 100 vibrations per second
than g would have 150. The next higher c would have 200 vibrations per
second. The ratio between that high c and the g is 200/150 = 4/3. That is
a perfect fourth (5 key steps). A whole step (2 key steps) can be obtained
by the difference of the fifth and the fourth (g-f). Actually it is no
difference but a ratio, so we will have to divide in stead of subtract. So
if c = 100 per second, than f = 4/3x100 per second, g = 3/2x100 per
second and the result is a whole step = (100x3/2) divided by (100x4/3)
= 3/2x3/4 = 9/8 = 1,125. So the note g vibrates 1.125 times faster than the
neighboring note f. This definition is especially suited for the function
of leading note from C to F.
But other definitions are possible. If you consider the major third (4
key steps, e.g. c-e) as the 5th overtone divided by 2 octaves, so 5/4 and
you make the whole step (d-c) from fourths and thirds (c-f-b-flat-d),
then you get fourth-fourth-major triad and divided by 2 to end up in the
right octave, you will get a whole step = (4/3x4/3x5/4)/2 = 10/9 = 1.111
But a major third (c-e) also may be seen as the 5th overtone consisting
of 2 whole steps. Then a whole step is the root from 5/4 = 1,118.
If you consider b-flat as the 7th overtone of c, shifted 3 octaves
backward, then a whole step is 2x2x2/7 = 8/7 = 1,143
A piano has the equal temperament with a whole step being 2 to the power of
1/6 = 1,122 (This is fairly good to be used as a leading note as 1.125
differs less than 0.2% from 1,122).
All these seventh notes have their own atmosphere and might be used
by the improviser who is not restricted to the piano (e.g. a singer). It
also explains the charm of a detuned piano for special cases.
Use leading notes. Use the seventh note not only as a
leading note, but also as a melodic element or in a mixolydian
Seventh note as melody note.
Use it in a blues.
Seventh note in a blues.
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