A New Measuring Set for Message Circuit Noise

Various forms of electrical disturbances in a telephone circuit result in acoustic noise at the output of the receiver of the telephone instrument. As noise, capable of detection by the human ear, it may be merely slightly annoying or it may be obtrusive enough to seriously impair the reception of a telephone message. If good service to the telephone user is to be maintained, it is evident that the plant forces must be provided with means for measuring electrical noise on a scale which may be correlated with transmission degradation. An ideal instrument for this purpose would measure and combine, to a high degree of precision, those physical attributes of a noise voltage that contribute to the over-all subjective effect on the listener at the circuit terminal. Such a device would be complex indeed--so complex, in fact, that it would not be practical from an operational standpoint. However, it has been found feasible to provide a noise meter, based upon only the most important qualities of the human hearing mechanism, which has proved most useful to the plant maintenance forces. For the past 20 years the 2B Noise Measuring Set has served this purpose. In recent years it became evident that there was a need for an im911