Journal of the Society of Motion Picture and Television Engineers (1950-1954)

which is defined as that value of bias current which gives a maximum output level for a constant input level at 300 cycles/sec. The tape speed was 7.5 in./sec. Other terms used in the table are defined as follows : 1. Saturation output is the maximum output level obtainable from the tape, irrespective of distortion, at nominal bias and at the audio frequency which gives maximum undistorted output. 2. Two per cent distortion output is the equalized output level which gives 2% distortion at a 480-cycle signal recorded at nominal bias. 3. Zero signal-to-noise ratio is the ratio of saturation output to zero signalnoise level. Zero signal-noise level is the tape noise measured after the tape has been subjected to a record head field of nominal bias but zero audio signal. 4. Two per cent distortion signal-tonoise ratio is the ratio of an audio signal of output level which results in a 2% distortion to the 2% noise level. The frequency of the signal is that which gives maximum output level at nominal bias. Two per cent noise level is the noise level when the magnetization of the tape is equivalent to that induced by a signal of such amplitude as to result in a distortion level of 2%. 5. Amplitude modulation is an undesired fluctuation in the reproduced level of a signal which was originally applied to the recorder as a signal of constant level. The amount of the fluctuation is expressed as a percentage of the average signal level. In general, the 0.100-in. tracks compare favorably with -J-in. tracks. The Eastman coating is about 0.100-in. wide compared with the 0.125-in. widths measured on the commercial tapes. This width difference accounts for about 2 db in output levels. For projector use, outputs and signal-tonoise ratios for 0.100-in. tracks are adequate. The amplitude modulation is considerably higher than for i-in. tapes. Amplitude .modulation for original photographic tracks is usually under 1%. 16mm prints often have amplitude modulation near 5%. At present, future improvements in amplitude modulation are more necessary than increased outputs or signal-to-noise ratios. However, if 0.032-in. tracks are ever used, increased outputs may be very desirable. The publication of this paper does not constitute any recommendation on the part of the author or the Eastman Kodak Co. for the manufacture, use or sale of any substance, chemical, film, apparatus or method covered by any patents now hi force or which may issue in the future. While investigation indicates that there are no patents dominating the apparatus and method hereby described, publication of this information is not any assurance, warranty or indemnification on the part of the Eastman Kodak Co. or the author with respect to the infringement of any patents now in force or which may issue in the future. Acknowledgment All sound tests of magnetic tracks were made in the Kodak Research Laboratories by W. K. Grimwood and J. R. Horak under the direction of Dr. Otto Sandvik. The author also acknowledges the assistance of D. I. Mayne, Jr. and H. J. Krall in developing the coating formula and coating technique; and H. F. Betz, R. L. White, H. L. Fitch and R. L. Wells who aided in the development of this program for commercial use. References 1. Marvin Camras, "Magnetic sound for motion pictures," Jour. SMPE, 48: 14-28, Jan. 1947. 2. R. H. Talbot, "A new treatment for the prevention of film abrasion and oil mottle," Jour. SMPE, 36: 191-198, Feb. 1941. 498 April 1953 Journal of the SMPTE Vol. 60