CARRIER NATURE OF SPEECH 511 



Speech Characteristics from the Carrier Point of View 



Now that the mechanism of speech has been described in carrier 

 terms it is of interest to observe carrier features as they manifest them- 

 selves in the characteristics of speech. Some of these can be seen by 

 the eye in speech oscillograms. Some can be demonstrated to the ear 

 with a speech synthesizer such as the vocoder. 



For a visual illustration there is shown in Fig. 9 a high quality 

 oscillogram taken from Crandall ^^ of the sound "sa" (Plate No. 160. 

 Spoken by M. B.) for a medium-pitched male talker. The carrier 

 shown by the oscillogram is of the unvoiced type for the earlier and of 

 the voiced type for the later part. As one looks at the oscillogram he 

 sees a great mass of the high-frequency components of the carrier. 

 Scrutiny, however, reveals modulated on the carrier the message in- 

 formation in terms of switched energy sources, controlled fundamental 

 frequency and varied transmission characteristic. Shortly after .17 

 second the switching off of the unvoiced carrier begins. Remnants of 

 the unvoiced carrier can be seen in the voice period just before .19 

 second and the one starting at about .19 second. The switching on 

 of the voiced carrier appears just after .18 second and seems to be rea- 

 sonably well completed at the end of the second voice period just 

 before .20 second. This switching was not instantaneous. However, 

 the ear probably does not observe the duration time of the switching. 

 The fundamental frequency falls rapidly at the beginning followed by 

 a leveling out and then a final slight fall in the last few periods. It 

 starts at 140 cycles per second, dropping to around 110 in the level 

 portion, and then to 101 at the end. The resonance conditions cannot 

 be followed too well by eye. However, around .20 second there is a 

 major lower-frequency resonance of about 800 cycles. At .33 second 

 this resonance appears to have increased to 1100 cycles or so. A 

 similar alteration of resonance conditions may be observed if the little 

 shoulder on the rear side of the peak just in front of the .25 second mark 

 is traced in adjacent periods. It can readily be followed back to the 

 third period just before .20 second and can still be seen in the last dis- 

 tinct voicing period starting before .39 second. The dynamic variation 

 of the speech at syllabic rates in accordance with the message content 

 is thus revealed. 



For another visual illustration of the speech message Fig. 10 shows 

 a set of oscillograms ^^ from the vocoder analyzer for the words "She 

 saw Mary." The oscillogram of the input speech is the trace next to 



10 Bell Sys. Tech. Jour., Vol. 4, p. 586, 1925. 



" This figure is a copy of Fig. 3 in the paper "The Automatic Synthesis of Speech," 

 Dudley, Proc. Nat. Acad. ScL, Vol. 25, pp. 377-383, July 1939. 



