116 BELL SYSTEM TECHNICAL JOURNAL 



TABLE IV 



Volume Indicator Readings for Same 

 Loudness as Male Speech 

 New Volume Peak Volume 



Type of Program Indicator Indicator 



Male Speech 



Female Speech -0.1 -2.2 



Dance Orchestra +2.8 -2.2 



Symphony Orchestra +2.7 —2.3 



Male Singing +2.0 -2.5 



difference was shown to exist between the average overload point of 

 the 94B ampHfier on speech and music, when measured with the r-m-s 

 volume indicator. This would seem to indicate that if allowance is 

 made for this difference between speech and music in controlling the 

 volume levels to avoid overloading, they will also then sound equally 

 loud to the listeners. 



Choice of Type 

 The tests of aural distortion due to overload showed so slight a dis- 

 advantage for the r-m-s instrument and the experiments on peak 

 checking showed such a marked advantage for this type as compared 

 with the peak instrument, that it was decided to develop the r-m-s 

 type of instrument. Another consideration was that, with the ad- 

 vances in copper-oxide types of instruments, it has become possible to 

 make r-m-s instruments of sufficient sensitivity for most purposes 

 without the use of vacuum tubes and their attendant need of power 

 supply, an advantage not shared by peak-reading instruments, at least 

 at present. Thus, the r-m-s instrument has advantages of com- 

 parative low cost, ruggedness, and freedom from the need of power 

 supply, and can, moreover, be readily made in portable forms when 

 desired. 



Dynamic and Electrical Characteristics 



It will be appreciated from the earlier discussion that, for a volume 

 indicator to be truly standard, its dynamic and electrical characteristics 

 must be controlled and specified so that different instruments will read 

 alike on the rapidly varying speech and program waves. Therefore, 

 the next step in the development was to determine suitable values for 

 these characteristics. 



In deciding upon the dynamic characteristics, an important factor 

 included in the consideration was the ease of reading the instrument 

 and the lack of eye strain in observing it for long periods. 



First, a number of existing instruments were studied, including some 

 experimental models constructed independently for the two broad- 

 casting companies prior to the start of this joint development. In 



