INSTANTANEOUS COMPANDORS 



719 



curve of Fig. 8, it is apparent that the noise at the output of the transmission 

 medium, iv, can be 35.8 db below one volt, and the corresponding value of 

 K is 20.2 db. The noise advantage of the compandor equals K, and is about 

 20 db. Figure 6 shows that, in a 20 db expandor, Vt is 13.8 db below one volt. 

 The noise voltages at the expandor input are well within the linear range of 

 its characteristic. Otherwise (15) would not be valid. 



37 36 35 



Vr IN DECIBELS BELOW ONE VOLT 



34 



33 



Fig. 8 — System parameters used to evaluate noise advantage. 



To illustrate that in the preceding example the noise advantage depends 

 upon the noise standard, suppose the noise standard, zv, had been 64 instead 

 of 56 db below one volt. Proceeding as before, the noise advantage is about 

 26.7 instead of 20 db. 



The general principles used in determining the noise advantage of in- 

 stantaneous companding as applied to telephone channels presumaby may 

 be applied with equal convenience to other systems also using instantaneous 

 companding and operating under different conditions. 



