NATURE OF SPEECH AND ITS INTERPRETATION 



139 



interpretation of the received speech. These results were obtained 

 in a room which was especially constructed to exclude outside noise. 

 When noise is present at the receiving station the optimum loudness 

 increases as the noise increases. 



The articulation data were analyzed so as to show the errors of 

 each of the fundamental sounds. The curves given in big. 5 show 

 the results of this analysis. It will be noticed that the \olume at 

 which errors begin to be appreciable is different for the different 

 sounds and is usualK' higher for the consonants than for the vowels. 



10 10 10 10 ^ 10 , 10 

 g p e V f th 



Fig. 5. 



Relative Difficulty of Fundamental Sounds 



on the 



High Quality Circuit 



Articulation vs. Volume 



Abscissa measured in nopiers 



Within the precision of the test the intersection point on the X axis 

 was the same for all the sounds, namely at 11.5 napiers. 



It will be noticed that the consonants are usually harder to hear 

 than the vowels. However, the speech sounds e and I, r, ng form 

 notable exceptions to this general rule, since the former is among 

 the most difficult, while the latter are among the very easiest speech 

 sounds. The order in which the speech sounds are given here rep- 

 resents their relative difficulty of interpretation when received at 

 average intensities. At all intensities, the sounds th, f and v are 

 the most difficult. Z, h and s become very difficult at weak volumes. 

 The sounds i, ou, er and 6 are missed less than 10 per cent of the 

 time, even with "very weak" intensity. At "average" volumes 

 there are only three sounds more difficult than e while at "very 

 weak" volumes there are 23 sounds more difficult. At very weak 

 volumes 1, which is the easiest sound at "average" volumes is missed 

 three times as often as e. 



