SPEECH POWER AND ITS MEASUREMENT 



649 



In connection with (a) we can use data obtained under "laboratory" 

 conditions, i.e. with the speakers, their voice levels, the talking speed, 

 etc., suitably selected. Perhaps the simplest statistical characteristic 



10 20 30 40 



PERCENTAGE OF TIME 



50 60 70 80 



INSTANTANEOUS POWER ^ 



1 xlO 



6 



4 



2 



t 



K 

 6 



4 



2 



1 X 10"' 



6 

 4 



1 X10"3 



6 

 4 



AVERAGE POWER 

 Fig. 1 — Time distribution of speech power. 



of Speech is the average power, i.e. the ratio of the total energy in a 

 large number of speech sounds divided by the total speech time. 

 The quantity immediately measured is the pressure on the transmitter 

 diaphragm. The corresponding power flow through unit area is 

 computed. In doing so it is roughly assumed that the pressure on 

 the diaphragm is twice as great as it would be in free air, which is 



