Standardized Audio Response from Magnetically Striped Motion-Picture Films

Abstract

Test films are essential to permit simplified measurement of signal level and frequency response in magnetic recording so that the industry can conveniently achieve interchangeability of program material. For all film and tape formats, calibration of a test film requires that first a reference reproducer be established and calibrated over the audio spectrum of interest, and second that the test film be examined with this standardized reproducer. There is no other known procedure for calibrating multi-frequency magnetic test films of sufficient relevance, reliability, and reproducibility. The extensive literature on magnetic recording/-reproducing theory is reviewed to justify the details of reference reproducer calibration, and to emphasize that the magnetic film systems incorporate some parameters which have not previously been recognized in the calibration of magnetic tape systems. The theoretical basis for a recommended super-8 characteristic is presented. By reference to this broader review of the magnetic theory, intercomparisons of the U.S. and international standards for both film and tape are presented. We have used the most probable interpretations of these documents (in the absence of a precise exposition of the intent of most committees), from whence it is apparent there is a frequent need for either clarification or revision.