PHYSICAL CHARACTERISTICS OF SPEECH AND MUSIC 363 



being required for resetting the apparatus. In F'ig. 14 an observer is 

 shown reading the message registers after a test has been taken. 

 The breakdown tubes are seen at the left and the filters at the right 

 mounted on relay racks. 



It is thus seen that with this apparatus 1000 observations may be 

 recorded on a four minute conversation, the final results being read 

 directly from the series of counters. 



By the use of this and similar apparatus the following results have 

 been obtained. The average conversational speech power is 10 micro- 

 watts or 100 ergs per second. About 1/3 of the time no sound is 

 flowing due to the pauses and the stops to form consonants so that 

 the average conversational speech power is about 50 per cent higher 

 than this value if the silent intervals are excluded. Some of the 

 speakers will use a greater and some a lesser speech power than this 

 average. In Table I are shown the results with a large number of 



TABLE I 

 Relative Speech Powers Used by Individuals in Conversation 



Region of Average Speech 

 Power 



Per Cent of Speakers . 



above 



8 







Speakers. It will be seen that about 7 per cent of the speakers will 

 use in conversation average powers less than 1/16 the average while 

 about 4 per cent will use powers which are from 4 to 8 times as much 

 as the average. This value of 10 microwatts per second is of course 

 for average conversational intensity. When one shouts as loudly as 

 possible, this average speech power is raised about 100 fold and when 

 one whispers about as softly as possible and still produces intelligible 

 speech, it is reduced to about 1/10,000. 



For describing in greater detail the powers involved in speech, we 

 will define the terms Mean Speech Power, Phonetic Speech Power and 

 Peak Speech Power. They are defined as follows: 



The Mean Speech Power is the average speech power within any 

 one one-hundredth of a second period. 



The Phonetic Speech Power is the maximum value of the mean 

 speech power of a fundamental vowel or consonant. 



The Peak Speech Power is the maximum value of instantaneous 

 power over the interval considered. 



