Modulated High-Frequency Recording as a Means of Determining Conditions for Optimal Processing
The quality of variable-width sound records depends to a great extent upon image definition. The requirements for a perfect sound-track are complete transparency in the clear portion, complete opacity in the dark portions, an extremely sharp boundary between the clear and dark portions, and exact duplication of the wave traced upon the track by the galvanometer. — Distortion is introduced by any change in average transmission in recording high-frequency waves. At high densities the average transmission is reduced, and at very low densities is increased by the presence of the high-frequency waves. The average transmission is compared to the transmission through the film for a 50 percent exposed track without signal. — It is possible to find a density at which there is little, if any, change in average transmission, and this density corresponds to most nearly perfect image definition and least distortion. On an original or negative recording, with present commercial recording stocks, this density is extremely low, of the order of 0.6 to 0.8. For least ground-noise, the negative must be recorded at much higher density. A change in average transmission of the negative can be tolerated, since by proper choice of print density, minimum distortion in the positive track can be attained. — A modulated high-frequency recording affords an extremely accurate means of determining correct negative and print densities for given conditions of laboratory processing. An oscillator, designed for several carrier frequencies, is provided with a 400-cycle modulator for recording. The modulated carrier is recorded for several values of lamp current and processed to several negative densities. Prints are then processed to various values of density, and the 400-cycle output measured on suitable reproducing equipment. The combination of negative and print densities that gives least 400-cycle output indicates the condition for best image definition and least distortion. — Care must be exercised in the design and construction of the oscillator to maintain the 400-cycle output at a minimum.
- Print ISSN
- 0097-5834
- Published
- 1938-01
- Content type
- Original Research
- DOI
- 10.5594/J14711