RADIO TELEPHONE NOISE REDUCTION 



481 



Characteristics 

 Figure 4 gives the 1000-cycle input-loss characteristic for three 

 settings of the reduction control. For any setting, there is an input 

 volume above which the loss remains constant, while for volumes below 

 this the loss increases with decreasing input until the maximum loss is 

 reached. The volume regulated speech range encountered on radio 

 circuits at some point in the circuit which is 5 db above reference 

 volume as measured on a volume indicator is indicated as extending 

 from + 13 db to — 17 db referred to 1 milliwatt for the purpose of 

 showing approximate corresponding speech amplitudes. 



-40 -36 -32 -28 -24 -20 -16 -12 -8-4 4 8 12 16 20 



1000-CYCLE INPUT IN DECIBELS (RELATIVE TO I MILLIWATT) 



Fig. 4 — Loss versus input for several settings of the reduction control. 



Figure 5 shows oscillograms giving the input and output charac- 

 teristics of noise for maximum reduction and of speech for maximum, 

 medium and minimum reduction. The upper trace is the input and 

 the lower trace the output. The middle trace is not used. It will be 

 noted by inspecting the In and Out traces at the beginning and ending 

 of the word "bark" that there is some distortion in speech for the 

 maximum reduction condition, but very little distortion for minimum 

 reduction. Maximum reduction would be used only in case of high 

 noise where this distortion is less objectionable than the noise. 



