492 BELL SYSTEM TECHNICAL JOURNAL 



cutoff of the loaded trunk shown is about 3500 cycles based on a 

 10 db cutoff point. Other types of loading, which will also be em- 

 ployed, will have still higher cutoff points. Evidently the band widths 

 of the broad-band circuits, toll connecting trunks, and new station sets 

 are well matched. 



Laboratory and field tests have been made with circuits simulating 

 the cutoff of the new broad-band systems and using various types of 

 station sets, including the new standard. These indicate that raising 

 the cutoff from 2750 cycles to 3600 cycles is equivalent to making a 

 reduction of 3 to 4 db in the net overall loss of the circuit. Raising 

 the cutoff from 2750 cycles to 3300 cycles is equivalent to a lesser 

 reduction. With older types of instruments which reproduce speech 

 less faithfully, this difference is also less, and of course, with instru- 

 ments providing transmission up to considerably higher frequencies, 

 the difference is greater. 



It will be appreciated, of course, that the wider speech band which 

 will be made available in the new broad-band systems will not be fully 

 effective in all telephone connections unless other toll circuits and toll 

 connecting trunks and station sets are provided with improved trans- 

 mission frequency characteristics. From a practical standpoint it is 

 obvious that in a large telephone plant improvements cannot be made 

 in all parts at one time. They must be introduced gradually as new 

 systems and apparatus are applied, and with a far-sighted concern for 

 future trends. 



