A Theory of Scanning Loss in Phonographs
Scanning loss is defined as that component of the total mechanical playback loss which is independent of the driving-point impedance of the stylus. A phenomenological theory of this loss is developed to account for the main features in scanning-loss data obtained by J. G. Woodward. The theory in its simplest form states that the magnitude of the scanning loss as a function of recorded wavelength depends on three parameters: (1) width w of the stylus-groove contact region, which determines the frequencies of the dips in scanning-loss data; (2) an asymmetry parameter a that measures a component of asymmetry in the stylus-groove interaction, which determines the depths of thses dips; and (3) an envelope frequency f that measures the extent to which the groove deformation permits approaching parts of the groove modulation to influence the stylus motion before this modulation actually touches the stylus, which determines the envelope of scanning-loss data. Direct verification of the theory will be possible when measurements of the phase responses of phonographs become available.
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