ABSTRACTS OF TECHNICAL ARTICLES 361 



Room Noise Spectra at Subscribers' Telephone Locations."^ Daniel F. 

 HoTH. That room noise can be a distinct handicap to conversation by 

 masking the speech sounds in the ear of the listener and thus impairing the 

 ease and accuracy of reception is of considerable concern to the telephone 

 engineer. Room noise not only complicates the problems involved in the 

 design and engineering of telephone systems capable of affording satisfactory 

 service, but it is also one of the factors which affect the costs of the telephone 

 plant. The effects of noise on telephone conversation depend, of course, 

 upon the characteristics of the noises which occur at the places where tele- 

 phones are being used. The arrangements and practices necessary for 

 reducing the effects of noise depend upon a knowledge of these characteris- 

 tics. As a result numerous measurements of room noise have been made 

 from time to time over a period of many years by Bell System engineers. 

 For the most part such measurements have involved the determination of a 

 single figure to represent the noise measured, as in the recent survey of sound 

 levels described by Mr. D. F. Seacord in the July 1940 issue of The Journal 

 of the Acoustical Society of America. While such measurements are in- 

 valuable in providing information on the frequency of occurrence of differ- 

 ent noise levels at telephone locations, their value is enhanced by additional 

 measurements of the distribution of the noise energy throughout the fre- 

 quency band involved in the reception of speech. The present paper de- 

 scribes such measurements and shows the effects of a number of contributing 

 factors on the spectrum of the noise. It is shown that the spectrum of room 

 noise has a characteristic shape. 



Fihn Scanner for Use in Television Transmission Tests} Axel G. Jen- 

 sen. This paper describes the design and construction of a television film 

 scanner primarily intended for use as a testing tool in designing circuits 

 suitable for television program transmission. 



The equipment employs electronic scanning and the image dissector is 

 used as the electronic pickup device. The image dissector has a high 

 degree of linearity between light input and signal output and the picture 

 signal is not accompanied by any spurious shading signals. Furthermore, 

 the direct-current component of the television signal is directly available at 

 the output of the tube. The lower sensitivity of the dissector tube is not 

 important in this case since a highly efficient optical projection system makes 

 it possible to override noise to a high degree. 



In filmscanners for entertainment purposes it is desirable to use ordinary 

 24-frame motion pictures and such film scanners therefore include a me- 



'^ Jour. Acous. Soc. Arner., April 1941. 

 5 Proc. I.R.E., May 1941. 



