502 



BELL SYSTEM TECHNICAL JOURNAL 



shown. Fig. 10 shows oscillographs for waves of the above type for 

 /o = 260, 300, 480 and 680 cycles per second. Notice that the distor- 

 tion is much greater where /o falls near the edges of the transmitting 

 band, although in every case the wave starts noticeably building up at 

 about .0109 seconds after / = for the sent wave. This is the value of 

 {dBld(xi)m\-n. in the transmitting range of the filters. In both Figs. 8 



48 



44 



40 



36 



32 

 Si 



Z 28 



Z 



o 



P 24 

 < 



D 



^ 20 

 < 

 16 



12 



200 



300 



400 500 600 



FREaUENCY IN CYCLES PER SECOND 



700 



0.060 



0.055 



0.050 



0.045 



0.040 



<0 

 Q 



0.035 Z 

 O 

 U 

 UJ 

 « 



0.030 



z 



0.025 



< 



UJ 



o 



0.020 



0.015 



0.010 



0.005 



800 



Fig. 9 — Insertion delay and attenuation characteristics of 4 band-pass filters in 



tandem. 



and 10 some of the distortion may be ascribed to attenuation although 

 the elongation effect is primarily due to phase distortion. It is this 

 elongation effect that is noticeable to the ear in speech and music. 



Phase Distortion and Its Correction 



This section of the paper will contain a more specific discussion of 

 the phase characteristics of apparatus and the means employed for 

 keeping phase distortion within desirable limits. 



