CHAPTER X.
SYNTHESIS OF VIBRATIONS.
An excellent way to determine the composition of anything is to
build it up out of elements with known characters. Applied to speech
curves the method of synthesis would have to compose curves that resem¬
ble vowel curves.
The synthesis of simple sinusoids in harmonic relations (Preece and
Stroh, Michelson and Stratton) can be made to furnish curves that resem¬
ble those from some musical instruments, but it can not furnish curves
that resemble vowel curves unless an inordinately great number of elements
is used. To have amr meaning for vowel analysis, however, the number
of elements must be small. Since vowel curves can not be counterfeited
by adding any reasonable number of harmonic simple sinusoids, we must
conclude that the vowels themselves were not produced by vibrating bodies
whose periods form a harmonic series. In other words, the overtone
theory of the vowels (p. 107) is not valid because curves produced by a small
number of elements adjusted according to that theory do not resemble
vowel curves.
The entirely different assumption that a vowel is the effect of sharp
glottal puffs acting on the vocal cavities was used as the basis for the
construction of a vibration apparatus. The apparatus was made to
record the effects of sudden magnetic impulses on a steel spring; this was
to represent the sharp glottal puffs acting upon the lowest vibratory ele¬
ment of the vocal cavity. An early form of this apparatus was described
in “Elements of Experimental Phonetics” (Chapter I); the improved
form is shown in figure 116.
A steel “vibrating spring” of any desired stiffness is held with any
desired length in a “clamp”; it is free and carries a writing point
which records its vibrations on a smoked surface. An “electromagnet”
is placed so that a current sent through it will pull the spring down; the
“magnet holder” permits adjustment at any point along the length of
the spring and at any distance from it; an extra steel cap on the core
makes it possible to allow for the bend of the spring. The “felt damper”
is cemented to a strip of steel fixed in a “damper holder” that permits
adjustment of the felt to any place on the spring ; the “damper regulator”
is a screw which bends the steel strip in the middle and presses the felt
against the spring with any desired force. m