Factors Affecting the Needle/Groove Relationship in Phonograph Playback Systems
It is shown that a phonograph pickup stylus riding in the groove of a record partly penetrates the groove walls because of elastic and plastic deformation of the record material. At high bearing loads complete plastic flow sets in and the needle leaves a permanent indentation track, while at lower loads the elastic deformation is predominant. This leads to amplitude distortion in the reproduced signal which may be of two types: one which is a function of the recorded wavelength (G function or translation loss), the other a function of the dynamic moving mass of the stylus/armature (H function or stylus/groove resonance). A third phenomenon (S function or scanning loss) is caused by the finite size of the stylus/groove-wall contact surface. Experiments with specially built pickups show the evolved theory to be valid even for very high frequencies. Special test records with recorded frequencies up to 100,000 Hz were used for these experiments.
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