PHYSICAL CHARACTERISTICS OF SPEECH AND MUSIC 367 



average speech power used by a person in conversation is 5 micro- 

 watts. The most probable sensation level of such speech at 1 meter's 

 distance is 61 db, at 10 meters' distance it would be only 41 db and 

 could be brought back to level of conversational speech at one meter's 

 distance only by the speaker shouting as loudly as possible. 



If we use the peak voltmeter as shown in Fig. 13 and make measure- 

 ments upon the peaks in l/8th second intervals in each of the half 

 octave bands the results will be as represented by the curves of Fig. 16. 



Fig. 16 — -Peak levels for conversational speech (3 male voices), using 32 octave 



average pitch intervals. 



The top curves give the maximum level of the peak compared to the 

 average intensity. The other two give levels such that the peak 

 levels are below them 98 per cent, 90 per cent or 75 per cent of the time. 

 It will be seen that the most intense peaks occur in the pitch range of 

 — 1 to -f 1 octaves. In this pitch range the intensity levels of the 

 maximum peaks for the different components are approximately 

 the same, being 13 or 14 db above the average speech level. 



It is interesting to note that in the higher pitch range the curves 

 in this figure are more widely separated than in the lower pitch range. 

 This illustrates an important characteristic of speech, namely, that 

 although components in the pitch range from zero to 2 octaves occur 

 which are just as intense as those in the lower range, they occur less 

 frequently. In other words, the spread in the intensities of the com- 



