68G 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 



5 



UJ 



> 



O 

 cc 



Q. 



Z 

 Q 

 Z 

 < 

 CL 



O 

 U 



30 

 28 

 26 

 24 

 22 

 20 

 18 

 16 



SIGNAL POWER IN DECIBELS BELOW FULL LOAD SINUSOID 

 5 10 15 20 25 30 35 40 45 50 



I 2 



10 



8 



6 



4 



1 



4 6 



10 20 40 60 



C 



100 



200 



400 600 1000 



Fig. 13 — The effect of a "dc component" on companding improvement for 



/i = 1,000. For further details, see the caption of Fig. 10. 

 / 



VI. APPLICATION OF RESULTS TO A HYPOTHETICAL PCM SYSTEM 



Consider the application of these results to the planning of a typical, 

 albeit hypothetical, communication system. 



A. Speech Volumes 



Suppose it is desired to transmit signals covering a 40 db power range, 

 with the strongest and weakest speech volumes each separated by 20 db 

 from the average anticipated signal power at the compressor input.* 



The strongest signal power is then used to determine the value of the 

 compandor overload voltage, V. In this case a value of V corresponding 

 to a full load sine wave 10 db above the loudest signal, [see (34)], 

 appears adequate.* Although this choice may at first appear arbitrary. 



* These values are sufficiently (iluse to those cited as representative by Feld- 

 man and Bennett, in connection with Fig. 2 of Reference 11, to be considered quite 

 realistic. 



