202 BELL SYSTEM TECHNICAL JOURNAL 



on noisy and quiet circuits, and were set up on the basis of typical 

 talker volumes, transmission equivalents, and amounts of room noise 

 at the station terminals. Additional transmission loss was added to 

 the quiet circuits so that noisy and quiet circuits gave equal articulation 

 or were judged by the observers to be equivalent in their transmission 

 performance. Thus, the N. T. I.'s are used to indicate an additional 

 transmission loss or impairment which is occasioned by the presence of 

 the noise. 



The articulation and other tests on which these N. T. I. ratings were 

 based are now being supplemented by tests conducted under the direc- 

 tion of the subcommittee. Measurements are being made of the effects 

 of various magnitudes and sorts of line noise in the presence of typical 

 amounts of room noise, as determined from a room noise survey made 

 by the subcommittee, and for representative toll connections and 

 talker volumes. The line noises being employed are those found typi- 

 cal from an extensive survey made by the subcommittee on open-wire 

 toll circuits throughout the country. These tests will afford a basis 

 for comparing various methods of measuring line noise, including ear 

 comparison methods now in general use and new visual meter methods 

 now under development. Thus, this work should lead to a mutually 

 acceptable method for measuring noise and a basis upon which agree- 

 ment may be reached as to the impairment in telephone transmission 

 caused by noise. 



Published Results. — As various phases of the technical work being 

 done are completed, they are published in the form of Engineering 

 Reports which are released by the Engineering Subcommittee of Na- 

 tional Electric Light Association and Bell Telephone System. Eight 

 reports, of which five refer to matters concerning noise-frequency in- 

 duction, have already been issued. Other reports dealing with this 

 subject have been recently approved by the Engineering Subcommittee 

 and will soon be issued. Certain other technical results which have 

 come from the Subcommittee's work have been presented by various 

 individuals connected with the work in papers before the A. I. E. E. 

 Still other results have been published in brief articles in the X. E. L. A. 

 Bulletin. 



One of the problems upon which the technical work of the committee 

 has been completed and published is that of inductive coordination of 

 primary distribution systems and exchange telephone circuits in 

 cable. The results of this work are given in detail in a report ^ entitled 

 "Minneapolis Joint Use Investigation." This report includes infor- 

 mation on influence factors applying to various types of power distri- 

 bution sj'stems, including three-phase, three-wire and three-phase, 



