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A Method of DirectPositive Variable-Density Recording With the Light Valve
By O. L. DUPY
In this system the light valve is placed in the cathode circuit of a nonlinear amplifier, the nonlinearity being of such a nature that the relation between the input to the amplifier and the transmission of the developed film is linear over a large percentage of the film-transmission range. The method of determining the shape of the necessary nonlinearity and how it is produced is described.
M
.AGNETIC FILM has proved to be an excellent medium for sound recording in the motion picture industry. However, considering the well-established editing techniques and the existing editing and viewing equipment, it will be some time before the magnetic record will replace the photographic sound record for use throughout the studio. The economical method of obtaining this record is to transfer the sound electrically from the magnetic record to a film that has the characteristics of a print when developed. The making of direct-positive prints by electrical printing has several advantages. The most important is the saving of the negative film and the cost of the development and printing of this film. Also, the reduction of the time that elapses between the recording and
Presented on April 25, 1952, at the Society's Convention at Chicago, 111., by John G. Frayne for the author, O. L. Dupy, MetroGoldwyn-Mayer Sound Dept., Culver City, Calif.
the delivery of a print is sometimes of great importance. Another advantage is the reduction of the film background noise by the elimination of the film noise, inherent in the negative, which is added to the print. Another advantage is the elimination of the flutter introduced by the printer, which is generally the contributor of a good percentage of the total flutter in film recording.
The main disadvantage in obtaining a linear recording from a variable-density type of photographic characteristic is the rather elaborate amplifier system required to offset this distortion, but one or possibly two such units will handle all the daily printing for a large studio. The push-pull variable-area method of recording has been successfully adapted to produce these direct-positive prints.* With the push-pull system a higher track
*L. I. Carey and Frank Moran, "Push-pull direct-positive recording — an auxiliary to magnetic recording," Jour. SMPTE, 58: 67-70, Jan. 1952.
August 1952 Journal of the SMPTE Vol. 59
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