54
THE STUDY OF SPEECH CURVES.
these only the “upper pulley” appears in the figure. A belt from the
upper pulley turns the recording disc. A belt from the lower pulley
turns a “ rotating tube,” in which there is a screw that moves the recording
disc sidewise; in this way the recording point is made to trace a spiral
line from the outside to the center. To permit the side-movement of
the recording disc the belt passes through a “ belt spanner” with weight,
which allows the belt to lengthen and yet keeps it always at the same
tension. The “belt tightener” for the belt from the lower pulley is pro¬
vided with a spring that keeps the tension constant. For many purposes
it is desirable to have the recording point trace one revolution in a circle
and not make a spiral; for this the belt tightener is loosened so that the
rotating tube remains still.
With this apparatus a single wave can be selected from the curve
and can be repeated indefinitely on the zinc strip; the gramophone disc
then produces continuously the sound of that wave. Beginning with
the first wave, we thus make a disc, one line of which will produce indefi¬
nitely the sound of the first wave, another line the sound of the second
wave, etc. In this way we have an acoustic analysis—for the ear!—
of each element in the vowel. For example, we are thus able to hear
separately the 25 different vowels that are present in the record of [c]
in “get” with 25 waves. Innumerable debated problems can in this
way be settled immediately. For example, what is the vowel in “not”
in the case of a certain speaker? The word is recorded on a gramophone
disc in natural conversation, and the curve is traced off; then a single
wave or a group of waves is etched on a zinc strip and traced repeatedly
on the gramophone disc; the disc then speaks the vowel continuously
as long as desired and affords an opportunity for deciding its resem¬
blance to [o], [a], or [a]. When this has been done for a number of persons
whose speech is recognized as having the standard pronunciation, the
proper phonetic spelling of “not” can be settled. We are quite safe in
asserting that very many—or most—of the short vowels are incorrectly
indicated in the dictionaries. By the speech curves and by this appara¬
tus it will be possible to settle the correct pronunciations.
There is still another application of interest, namely, an inquiry con¬
cerning the sounds of arbitrary curves. For example, what is the sound of
a zigzag line or of a zigzag with one element shorter than the others? What
is the sound of a curve composed of alternating positive and negative semi¬
circles? Just as each musical instrument and each vowel records its own
peculiar curve, so each peculiar curve will produce a special sound; from
curves not like those of known musical instruments or vowels we may
expect sounds representing musical instruments that do not exist.