484 



BELL SYSTEM TECHNICAL JOURNAL 



tion of this ideal are not susceptible to definite evaluation, the selection 

 of a requirement such as that for the transmitted frequency range, is 

 necessarily a matter of judgment, taking into account the various 

 factors involved. 



In Figure 1 are given the results of recent tests showing the effect 

 upon articulation of varying the upper and lower cutoff frequencies 

 of a circuit similar to the Master Reference System for Telephone 

 Transmission. These results apply to the condition of no noise and 

 the received volume at the optimum value. It will be noted from the 

 curve for the variation of the upper cutoff frequency, that the rate 



100 



90- 



i, 80 

 o 



s: 70 



2 60 

 O 



< 50 



o 



40 



< 



uj 30 



m 

 < 



■^ 20 



>- 

 in 



10 



2 34568 2 34566 



100 1,000 10,000 



CUTOFF FREQUENCY OF FILTERS IN CYCLES PER SECOND 



Fig. 1 — Syllable articulation of circuit similar to master reference system at optimum 



received volume under quiet conditions. 



of growth is relatively slower above 2,500 cycles than below, and that 

 the total gain in going from this point to infinity is relatively small. 

 Figure 2 shows on a somewhat different basis the upper part of this 

 curve and also, for comparison, corresponding data for circuits having 

 commercial terminal apparatus of the types used in the Bell System. 

 The ordinates for these curves are the ratios of the increase in articu- 

 lation in going from an upper cutoff frequency of 2,000 cycles to some 

 higher point, to the total change in articulation in going from 2,000 

 cycles to infinity. For example, referring to the curve for the effect 

 of upper cutoff frequency on articulation of the Master Reference 

 System, it is seen that the articulation for the 2,000-cycle point is 70 



