A Theory of Tracing Distortion in Sound Reproduction from Phonograph Records

General formulas are derived, as an expansion in powers of the amplitude and its derivatives, for the motion of a stylus of any shape sliding on the warped groove surfaces representing any arbitrary recorded signal. These formulas provide simple expressions for the second‐ and third‐order harmonic distortion of pure tones, and are also applicable for the computation of cross‐modulation products for two‐ or many‐tone signals, including a continuous recorded spectrum. Typical computations for these cases are presented and a general criterion is established for the maximum r.m.s. distortion for an arbitrary steady‐state signal. The computations provide a basis for discussing the advantages of lateral‐cut over vertical‐cut, the effect on distortion of “pre‐emphasizing” the recorded spectrum, and the efficacy of rerecording techniques.