Direct-Positive Variable-Density Recording with the Light Valve
C. R. Keith, V. Pagliarulo · Journal of the Society of Motion Picture Engineers · 1949
A method is described for making “direct-positive” variable-density sound records. Improvements over previous records are high output level, high signal-to-noise ratio, low distortion, and elimination of printer loss and distortion. Standard light valves with a superposed high-frequency bias are used in making the record.