SCIENTIFIC RESEARCH APPLIED TO THE TELEPHONE 265 



flaw in their transmission performance, and then introduce measured 

 imperfections or variations. 



By this general process, we were able to determine the effect of 

 noise of chosen intensities either as noise present in the telephone 

 receiver or as noise in the room. Similarly, the effect of a line or 

 other characteristic such that voice frequencies above a certain value 

 or below a certain value were not transmitted, was determined. The 



16.35 33 



FREQUENCY IN CYCLES PER SECOND 



261 522 1044 2089 4177 8356 16,712 33.424 



200 300 400 500 600 700 



PITCH IN CENTI-OCTAVES 



900 1000 1 100 



Fig. 7 — Minimum perceptible differences in pitch in centi-octaves for various posi- 

 tions of the auditory area. 



effect of introducing a highly resonant element or of a non-linear 

 element was studied. The range in loudness of speech necessary for 

 best reception was likewise measured. 



As noise became recognized as a very real factor, a standard basis 

 for noise measurements was established. Consequently we are now 

 able to measure noise on a telephone circuit or in a room, and state 

 the result in terms of a standard unit. 



