SEVENTH HARMONIC OMITTED.
The seventh harmonic is not represented on account of tempered scale
interference. This harmonic is always eliminated as much as possible
in the design and building of musical instruments employing the tempered
scale.
SUPER AND SUB-OCTAVE "COUPLER" EFFECTS.
Pipe and reed organs are usually equipped with super and sub-octave
couplers. The chief function of a super-octave is to introduce a large
second harmonic (octave pitch) into the tone quality. The sub-octave
coupler introduces a large sub-fundamental into the tone quality. On
the Hammond Organ these harmonics are readily introduced with the
appropriate draw bars.
THE BLACK AND WHITE SERIES OF HARMONIC CONTROLS.
In each group of nine controls, the two left ones are coloured brown,
while those to the right are either black or white. In the black and white
series, the white one on the left is the fundamental of the corresponding
note on the manual it controls. The next draw bar to the right controls
the second harmonic. The second harmonic is an octave higher in pitch
than that of the fundamental. If the fundamental be thought of as "doh"
in the scale doh, ray, me-then the second harmonic is also "doh" one
octave up. It is coloured white, like the fundamental, and it will be
found that every white draw bar is also a " doh "either one, two or three
octaves up.
The fifth draw bar from the left controls the third harmonic and is coloured
black. The third harmonic tone is "soh." The seventh draw bar from
the left, controlling the fifth harmonic, is black and is a" me." The eighth
draw bar from the left, controlling the sixth harmonic, is black and is
a soh."
MUSICAL SIGNIFICANCE OF BLACK AND WHITE SERIES.
The black and white harmonic series has a very real musical significance.
The harmonics associated with the white draw bars are all of octave rela-
tions. When playing a chord, for instance, the introduction of these
harmonics does not in any way change the concordance of the musical
effect. The effect is one of coupling the first, second, and third octaves
to various degrees of strength. The change in tone colour brought about
by changing from one white draw bar to four white draw bars is analogous
to the difference between a single note and a double~octave of that note.
The tonal brilliance is greatly increased, but the general effect of consonance
is the same.
The introduction of the harmonic pitches associated with the black draw
bars brings about a dissonant effect. For instance, supposing we are
playing the triad C-E-G with only the white draw bars out. All pitches
involved will then be either C, E, or G.
Now let us introduce the third harmonic which is the first in the black
series. It introduces the pitches G, B and D one octave up. B and D
are obviously" dissonant." Now suppose we draw the black fifth harmonic
control. It introduces the pitches E, G# and B two octaves up. G#
and B are dissonant. The black sixth harmonic draw bar introduces
G, B and D two octaves up. B and D are dissonant. The purpose of
this illustration is to show the dissonant effect produced by the black series.
It must not be concluded, however, that the draw bars of the black series
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