On the Playback Loss in the Reproduction of Phonograph Records

A theory is set forth to explain the well known level losses, in particular of the upper frequency range, occurring in the reproduction of lateral-cut records. — The performance of a pick-up stylus with a spherical point, riding in a laterally modulated record groove, is discussed from the point of view of the elastic properties of the record material. After introducing certain permissible simplifications, the elastic deformations of the two supporting groove walls are calculated, under the influence of the steady vertical pick-up force, the stylus inertia, and the stylus stiffness. Due to the fact that both forces and geometry are different on the two walls the respective elastic deformations are also found to be different for both walls. This fact results in a displacement of the pick-up stylus from the position which it would assume in an ideally rigid record groove and is responsible for the difference between the reproduced amplitude and the recorded one. Playback loss and translation loss are thus explained and quantitatively predicted. — The discussion of the loss equation leads to a number of conclusions. It is found that in contradistinction to a theoretical pick-up with infinitely small vertical force and stylus impedance, it appears advisable to provide a practical pick-up with a definite stylus mass, in order to counteract effectively the playback loss due to the steady vertical force. The translation loss can thus be reduced to zero in systems with constant groove velocity if the pick-up constants—in particular, the stylus mass—are properly chosen. In systems with variable groove velocity (standard disk recording) the translation loss can not be made to vanish but an increase in the absolute playback level of the upper frequency range can be achieved, thus improving the signal-to-noise ratio.

Print ISSN

0097-5834

Published

1941-12

Content type

Original Research

DOI

10.5594/J09946