Distortion in Sound Reproduction from Phonograph Records

When the spherical tip of an ideal reproducer stylus slides over a warped groove surface having a sinusoidal profile, the traced curve is not exactly sinusoidal. An analysis of the harmonic content of the traced curve, similar to that given by DiToro (J. Soc. Mot. Pict. Eng., Nov., 1937) but avoiding his approximations, is directly applicable to reproduction from vertical-cut records. These results may be applied to reproduction from lateral-cut records by taking the original groove surface as inclined approximately 45 degrees from the horizontal, projecting the traced curve upon the horizontal and vertical planes, and adding in proper phase the guidance of the stylus tip by both sidewalls. It is shown that there is a residual vertical component of stylus motion (“pinch” effect) and complete cancellation of all even harmonics in the tracing distortion. Computation of the remaining odd harmonics indicates that, when the ideal lateral-cut reproducer characteristics include ideal “following” for vertical motion at signal frequency, a lateral-cut record may be reproduced with one-fourth to one-tenth the rms. distortion of a similarly recorded vertical-cut record. These results are displayed for convenient reference by contours of constant distortion upon a universal chart, the dimensionless coordinates of which characterize any recording condition and allow immediate specification of the maximum permissible recorded amplitude, maximum predistortion of the frequency characteristic, and the required clearance angle of the recording stylus.

Print ISSN

0097-5834

Published

1938-08

Content type

Original Research

DOI

10.5594/J12946