COMPANDORS ON NARROW BAND SPEECH CHANNELS 



1215 



mental. These results are indicative of the significance of such components 

 in the compressor output spectrum to distortion in the recovered signal. 



Frequency Analysis of Transmission under Reduced Bandwidth 



Conditions 



It might be concluded from the results quoted above that a wideband 



channel is required for the d 

 compressed speech. However, 



stortionless transmission of instantaneously 

 f the compressed speech is properly sampled 



(a) ASSUMED SPECTRUM 

 OF ORIGINAL SIGNAL 



(b) SIGNAL AFTER 



INSTANTANEOUS 



COMPRESSION 



(C) 



INSTANTANEOUS 

 SAMPLER SPECTRUM 



(d) 



SIGNAL AFTER 



COMPRESSING AND 



SAMPLING 



20 



4 8 12 16 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 1 — Frequency analysis of instantaneous compressing and sampling of origina 

 signal. 



before transmission, and the received signals are again sampled at the re- 

 ceiver, the bandwidth of the intervening medium can be restricted to that 

 of the original speech, and still the transmission can be distortionless. 

 Hence, the sampling must transform the broadband spectrum of the com- 

 pressed speech in such a way that it can be successfully transmitted over a 

 relatively narrow band. 



A steady state frequency analysis will serve to illustrate this phenomenon. 

 Figure 1(a) shows the 4 kc frequency spectrum assumed for the original 



