SPEECH POWER AND ITS MEASUREMENT 



657 



instantaneous amplitude of the speech waves on a certain laboratory 

 telephone circuit of the commercial type. 



Fig. 11 illustrates the type of data which can be expeditiously 

 secured by means of the volume indicator. Here the levels for a 



-20 -18 -16 -14 -12 -10 -8-6-4-2 2 4 6 8 10 



AVERAGE VOL. IND. READING OF SPEAKER -OB 



Fig. 10 — Instantaneous voltage V.S. Volume indicator reading 85% of observed 

 points included between outer dashed curves — ordinates of middle dashed curve 

 are inversely proportional to gain of volume indicator. 



large number of speakers and conversations (over a laboratory tele- 

 phone circuit of the commercial type) are determined. To cover the 

 same ground by means of oscillographic measurements would have 

 been a decidedly formidable task. 



Another device for the rapid measurement of speech levels is the 

 "impulse meter," i° shown in Fig. 12. This is essentially a peak 



10 D. Thierbach, Zs. F. Techn. Physik, No. 11, 1928. 



