480 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



without postulating additional cavities. This is an advantage over the 

 lumped constant treatment, where it is necessary to postulate a different 

 cavity for each resonance, and where the interaction terms in the equation 

 do not include the higher modes of vibration. Under the distributed treat- 

 ment, dimensions for each vowel may be taken from x-ray photographs of 

 the vocal tract. The calculations then yield at least three resonances which 

 lie in the frequency regions known for the vowel, from analyses of normal 

 speech. Dependence of the different resonances upon the different cavities 

 is discussed in some detail in the paper. 



An electrical circuit based on the transmission line analogy has been 

 made to produce acceptable vowel sounds. This circuit is useful in con- 

 firming the general theory and in research on the phonetic effects of articu- 

 lator movements. The possibiUty of using such a circuit as a phonetic stand- 

 ard for vowel sounds is discussed. 



Basic Theory Underlying Bell System Facilities Capacity Tables. A. L. 

 Gracey.* A.LE.E., Trans., v. 69, pt. 1, pp. 238-243, 1950. 



Abstract — Discussion of the many considerations involved in the layout 

 of a switching network adequate for present needs and flexible for future 

 change is beyond the scope of the present paper. Rather, it deals with the 

 specific problems of determining sizes of trunk groups and quantities of 

 various components of dial central office equipment by the methods cur- 

 rently used in the Bell System. Examples are given, with illustrative tables. 

 Enough of the probability theory underlying the tables is given to bring 

 out the assumptions made to fit or approximate the various service 

 conditions. 



Binaural Localization and Masking.* W. E. Kock.^ Acoustical Soc. Am., 

 JL, V. 22, pp. 801-804, Nov., 1950. 



Abstract — Binaural experiments are described which indicate that the 

 ability of the brain to localize a desired sound and to suppress undesired 

 sounds coming from other directions can be traced in part to the different 

 times of arrival of a sound at the two ears. It is suggested that the brain 

 inserts a time delay in one of the two nerve paths associated with the ears 

 so as to be able to compare, and thus concentrate on, those sounds arriving 

 at the ears with this particular time of arrival distance. 



The ability to perceive weak sounds binaurally in the presence of noise is 

 shown to be a simple function of the direction of the desired sound and noise. 

 An explanation is given for the effect reported by Koenig that front and rear 

 confusion is avoided by head movements. 



* A reprint of this article may be obtained on request to the editor of the B. S. T. J. 



1 B. T. L. 



' A. T. & T. Co. 



