ABSTRACTS OF TECHNICAL ARTICLES 365 



level in db as a continuous function of either time, frequency, or any 

 other variable. The adaptability of such level recorders to acoustic 

 measurements depends, among other factors, upon the range and 

 accuracy of the logarithmic scale, and upon the effective speed of the 

 recording mechanism. This recording speed is most conveniently 

 expressed in terms of the rate, in db per second, at which the recorder 

 is capable of following changes in the input power. 



The level recorder described here consists essentially of an amplifier 

 and rectifier, the output current of which is held at a substantially 

 constant value automatically by a change in the gain of the amplifier, 

 following changes in input power. The gain is varied by means of 

 motor driven slide wire potentiometers graduated in logarithmic 

 steps, the gain settings of which are recorded. 



Some Applications of Modern Acoustic Apparatus}^ S. K. Wolf 

 and W. J. Sette. Within the past two years there have been de- 

 veloped at the Bell Telephone Laboratories several electro-acoustic 

 instruments designed to facilitate accurate measurement of a wide 

 variety of acoustic phenomena. Three of these instruments are: an 

 automatic level recorder, a crystal analyzer, and an acoustic spec- 

 trometer. Some of the types of acoustic studies for which these 

 modern devices are well adapted may be of general interest and hence 

 specific applications made at Electrical Research Products are de- 

 scribed here. These include reverberation measurements, loud speaker 

 response measurements, noise analyses, piano tone analyses, and 

 studies on the singing voice. A brief description of the operating 

 characteristics of the instruments is first given. 



" Jour. Acous. Soc. Amer., January, 1935. 



