The Bell System Technical Journal 



July, 1926 

 The Power of Fundamental Speech Sounds 



By C. F. SACIA and C. J. BECK 



Synopsis: This jiaper describes the continuing work on speech power by 

 means of oscillograjihic studies of vowels, senii-vowels and consonants. 

 A previous paper considered the characteristics of a few individual sounds 

 from the power standiroint, but the principal emphasis was placed upon 

 speech as a whole. In this later anah'sis, sounds are considered individually 

 on the basis of instantaneous and mean power. A practical application 

 of the results is suggested. 



CONTINUING the work done on speech power by means of 

 power oscillograms/ we have made additional reductions in the 

 data relative to the vowels, semi-vowels and consonants and have also 

 prepared a smaller amount of data on the power of the semi-vowels 

 and the consonants from the amplitude oscillograms.^ This is a pre- 

 liminary study of the subject, at least in so far as the latter two classes 

 of sounds are concerned, for these records of speech sounds were made 

 to show all sounds in their true relative value hence the consonant 

 sounds, being greatly inferior to the vowels were measurable to a 

 correspondingly smaller degree of accuracy. We have gathered such 

 data as the existing records could yield before future plans are com- 

 pleted to make a more comprehensive study of consonants. 



Stop consonants are not so well characterized by the power data as 

 are other types. The unvoiced stop consonants have two properties: 

 a pufT whose main frequency component is of the order of 50 cycles 

 with a few ripples of high frequency; and a modifying effect upon 

 the beginning or end of the vowel which immediately precedes or suc- 

 ceeds it. Hence, such a consonant is more of a controlling factor and 

 lacks the essential properties of a discrete sound. In giving the data 

 on the pufT where it is measurable, we separate the low and high fre- 

 quency components. In the case of the voiced stop consonants the 

 vocal cord vibrations give the consonant more character of its own. 



Mean Power and Peak Power 



In the paper on speech power and energy, the "mean power," P,„, 

 was derived (in the case of the vowel sounds) as the mean of the power 

 taken throughout the interval of the vocal cycle. By the assumption 

 of an appropriate arbitrary inter\-al instead, say of the order of one 



^ B. S. T. J. Vol. IV No. 4. "Speech Power and Energy," by C. F. Sacia. 

 2 B. S. T. J. Vol. IV No. 4. "Sounds of Speech," by I. B. Crandall. 



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