On the Measurement of Rumble in Phonograph Reproduction
The nature of turntable rumble is analyzed, with the object of evolving a method for rating the performance quality of turntables with respect to rumble. Spectral distribution of rumble of a typical turntable is shown, identifying the effect of resonances of the pickup arm, and the audibility characteristics of rumble are reviewed, in the light of the equal loudness contour characteristics of the ear and the typical noie in the room. A weighting network of 6 dB per octave below 500 Hz with 12 dB attenuation above 500 Hz is suggested, and several possible methods of converting the spectral response of rumble into a number corresponding to a relative loudness level are considered. It is concluded that probably the best method, from the practical standpoint, is the measurement of the rms voltage level of rumble through the weighting network, relative to the level of a 1000 Hz 5 cm/sec rms standard tone (without the network). The resulting number, in dB, is defined as the Relative Rumble Loudness Level (RRLL).
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