A New Standard Volume Indicator and 

 Reference Level * 



By H. A. CHINN,t D. K. GANNETT, and R. M. MORRIS J 



In recent years it has become increasingly difficult to correlate 

 readings of volume level made by various groups because of 

 differences in the characteristics and calibrations of the volume 

 indicators used. This paper describes a joint development by the 

 Columbia Broadcasting System, National Broadcasting Company, 

 and Bell Telephone Laboratories which resulted in agreement 

 upon, and standardization in the respective broadcast and Bell 

 System plants, of: a new copper-oxide rectifier type of volume 

 indicator having prescribed dynamic and electrical characteristics; 

 a new reference level based on the calibration of the new instrument 

 with a single frequency power of one milliwatt; and a new ter- 

 minology, the readings being described in "vu." It is hoped that 

 other users of volume indicators will join in the adoption of these 

 new standards. 



The paper gives in considerable detail the technical data and 

 considerations on which was based the choice of the characteristics 

 of the new volume indicator and the other features of the new 

 standards. Particular attention is paid to the technical data 

 supporting the decision to make the new volume indicator 

 approximately an r-m-s rather than a peak-reading type of 

 instrument. 



Introduction 

 ^ I ^HE student of electrical engineering, when Introduced to alter- 

 ■^ nating current theory, learns that there are three related values 

 of a sine wave by which its magnitude may be expressed. These are 

 the average value, the r-m-s (or effective) value, and the peak (or crest) 

 value. Certain fundamental electrical measuring devices provide 

 means for determining these values. As the student's experience 

 broadens, he becomes familiar with complex, non-sinusoidal periodic 

 waves and finds that these waves have the same three readily measured 

 values. He learns how to determine from the problem under con- 

 sideration whether the average, the r-m-s or the peak value of the wave 

 is of primary importance. 



* Presented at joint meeting of A. I. E. E. and I. R. E., San Francisco, California, 

 June 1939, and at Fourteenth Annual Convention of I. R. E., New York, September 

 1939. 



t Mr. Howard A. Chinn is Engineer-in-Charge, Audio Engineermg, Columbia 

 Broadcasting System, Inc. 



X Mr. Robert M. Morris is Development Engineer, National Broadcasting 

 Company, Inc. 



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