628 



BEI.L SYSTEM TECHNICAL JOURNAL 



tremolo. Tremolos usually occur in singing voices and \ary widely 

 in their character. They constitute modulations which in actual 

 singing sometimes occur as slowly as two per second. The slower 

 mo(liilation.s affect the ear as beats or pulses, while the most rapid 

 ones affect the (|ualit\- by the resulting sidebands of overtones. Those 



i-.li'.Lll 



li 



Hi 



k 



1 , , n -- 



n J...1 1 I •—11 



1500 

 I4O0 



<0- 



<+ eoc 

 o.- 



P„T 50 

 -1- O 



Time 3cale 



O O.OS 0.10 0/5 0.20 SEG 



l''ij,'. 1 — InslantaiK-iiiis ami mean pcnvcr. Enlarged copy of original oscillogram 

 of the word "QUITE" 



shown in the figure are of the latter l\pcs, their modulating frequency 

 being about 50 per second. 



Frt)m the instantaneous power we derive the mean power, Pm, whose 

 chief significance lies in'.'the fact that it is the kind of power that 

 would be read by a quickly acting wattmeter; it is likewise propor- 

 tional to the deflection shown by the ordinar\- a.c. \olt meter or 



