EFFECTS OF PHASE DISTORTION 



565 



25 db. The effective band is the frequency range that will give the same 

 articulation as that given by the filter. The delay distortion is so small 

 for one filter of this type that its effects can be neglected and the ef- 

 fective band may be determined from the attenuation curve alone. 

 The effective band is given approximately when the area bounded by 

 the attenuation curve and a line parallel to the frequency axis through 

 the 25 db point equals the area under the 25 db line between the fre- 

 quency limits zero and/, where/ is the upper limit of the effective band. 



0.05 



0.04 



o 



z 

 o 

 o 



in 



Ji|3 



■0|TJ 



5 





0.03 



0.02 



0.01 



ATTENUATION 

 ATTENUATION 

 ATTENUATION 

 ATTENUATION 

 DELAY 



50 



40 



J) 

 ■0 



30 



20 



10 



Z 



o 

 I- 

 < 



D 

 Z 



500 1000 



■EFFECTIVE BAND 

 -EFFECTIVE BAND 



1500 

 20 FILTERS 

 20 FILTERS 



2000 

 Q = 80 — 

 Q-200- 



2500 



3000 3500 4000 



FREQUENCY IN 

 CYCLES PER SECOND 



■EFFECTIVE BAND 20 FILTERS Q = 20o(E;QuALrZED)~* 



)- 



■EFFECTIVE BAND I FILTER Q"oRebl 

 ALLOTTED BAND 



200 /'NEGLIGIBLE 

 DELAY 



Fig. 10 — Transmission for a filter having a rapid rate of attenuation increase. 



This is true because the effect of attenuation near the cutoff frequency 

 is to reduce the contributions of the various frequency ranges by a 

 factor that is proportional to their attenuation, for the attenuation 

 limits considered. In the above case this factor varies from zero at 3000 

 cycles to unity at 2400 cycles. The effective band width is 2825 cycles. 

 The dotted curves on Fig. 9 show the delay and attenuation values 

 for 20 filters in tandem. The effective band width that is shown for 

 "delay equalized" is that due to the attenuation distortion alone. It 

 was obtained as described in the preceding paragraph except that the 

 attenuation for zero articulation was taken as 40 rather than 25 db 

 since there is no interference from the signals in the adjacent band. In 

 this case the effective band due to attenuation distortion alone is 2550 

 cycles. The effect of delay distortion when taken into account in the 



