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BELL SYSTEM TECHNICAL JOURNAL 



titions occur and attention can be somewhat relaxed. It also enhances 

 the naturalness of the received speech, and so makes the conversation 

 more pleasing as well as easier. It should be noted also that the pro- 

 posed broad-band systems will transmit frequencies approximately 50 

 to 100 cycles lower than earlier systems, which, while not contributing 

 appreciably to articulation, has the effect of increasing naturalness. 



When applied in the telephone plant, the resultant effect of a given 

 increase in band width will of course depend on the other parts of the 

 circuit, and the transmission characteristics of the transmitters and 

 receivers. Improved transmitters and receivers are now being applied 



O 60 



1000 2000 3000 4000 5000 



CUTOFF FREQUENCY OF FILTERS - CYCLES PER SECOND 



Fig. 3 — Effect of cutoff frequency on syllable articulation. 



rapidly in the Bell System. They have much better transmission 

 characteristics than earlier types and an effective upper frequency of 

 transmission for the new station set which is well above 3000 cycles, 

 as shown on Fig. 4. 



The toll connecting trunks are important links in a typical overall 

 connection, and here also there has been a continued trend to provide 

 wider band circuits. Figure 5 shows the transmission frequency char- 

 acteristics of representative types of toll connecting trunks which are 

 being commonly installed at present. Both non-loaded and loaded 

 trunks are shown on the figure. Of course, in the non-loaded case, 

 there is no definite cutoff frequency. The curve for the loaded trunk 



