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 an}^ 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 spri.-r;;. 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. i3i 



