616 BELL SYSTEM TECHNICAL JOURNAL 



higher frequency than the corresponding peaks in the curve for the 

 male voices; but the musical interval between characteristic peaks 

 for a given sound is about the same in the two cases. It is only in 

 this way that we can account for what is a matter of universal ex- 

 perience in using the phonograph, namely that moderate variations 

 from normal speed in recording and reproducing speech leave the 

 vowel sounds still intelligible. 



V. 

 Four Semi-Vowel Sounds* 



Now consider the sounds /, ng, n, m, which pronounced with the 

 \owels 00, ee, a, following them, are arranged in Groups XIV and XV'. 

 Following the plan pre\iously used, note first the general characteristics 

 of these 24 records, made by the two male speakers MA and MB. 

 An outstanding feature of the records is the diphthong quality which is 

 clear in all: the transition is quickly made from semi-vowel to the 

 affixed vowel sound and except in two records (Plates Nos. 108 {lee) 

 and 113 {ngee) a definite transition point can be fixed. Marking this 

 point for all records we find an a\'erage duration of 0.16 second for 

 the semi-vowel sound, of 0.21 .second for the vowel sound, mean 

 total duration being 0.37 second. Noting the fundamental frequency 

 in two locations, namely at the start and just before the transition 

 point, it is found that there is a progressive rise in pitch during the 

 record of the semi-vowel sound; this effect is in agreement with the 

 indi\idual characteristics of these two speakers previously noted 

 in the pure \owel records. But in addition it is noted that the average 

 fundamental for these two speakers (see Table V below) is somewhat 

 below that previously used by them in the vowel records. (Refer 

 also to Table III). This slight lowering of fundamental pitch ma>- 

 possibly be a characteristic of the semi-vowel sounds; and this effect 

 occurs, as we shall see later, to a pronounced degree in the consonant 

 sounds. 



The amplitudes of these semi-vowel sounds are on tlic whole smaller 

 than the amplitudes of the affixed pure \owel sounds, but some of 

 them are surprisingly large. The low frequency characteristic of / 

 is (for these voices) principally a third harmonic of the fundamental. 

 With 11 and tig (which are nearly indistinguishable) the second harmonic 

 becomes increasingly important, and in the m records it is very 

 large. The high freijuency characteristics of all four sounds lie between 

 2400 and 21(00, falling somewhat as we pass through a sequence from 



' A pri'liiiiinury report has beuii inatic on the properties of these souiuis, and their 

 relation to the general vowel iliagrani. (I'hys. Rev. li, 1924, p. 309.) 



