International projectionist (Jan-Dec 1947)

Magnetic Recording Symposium by Academy REFLECTING the ever-widening interest among motion picture technicians in magnetic recording and reproduction, the Basic Sound Committee of the Academy of Motion Picture Arts & Sciences recently held two general discussion sessions between designers and manufacturers of this recording process and studio personnel interested in its pract'cal application to film production work. The meetings considered first the replies to the following question which had been addressed to various manufacturers: "Are the manufacturers interested in developing a magnetic recorder for synchronized operation" Manufacturers' reactions follow: Equipment Manufacturers' Views (1) The Ind'ana Steel Co. believes that some types of paper or cellulose acetate could be adapted to a magnetic material coating. Either would make synchronized operation possible. (2) The Magnecord Co. now has magnetic wire which at present is "non-sync." However, the company is interested in "sync" operation and believes that it may be possible to sync wire recordings automatically. (3) Armour Research Foundation is not a manufacturing company, but concerns itself primarily with fundamental research and development. It offered to disseminate to Armour's licensees the information obtained at the Academy meetings. If these licensees are in.ter SUPER H.I. CARBON ARC LAMPS (Continued from preceding page) jection. The M-R Type 250 process projection lamphouse meets the requirements. As illustrated in Fig. 2, the unit has a water-cooled positive brush assembly. There is a flow indicator on the rear of the lamphouse which shows that the water is circulating. The water passes through a radiator similar to one used on an automobile and is re-circulated. The same cooling system may be used for re-circulating the water around the relay condenser lens in the optical train. The position of the positive carbon in relation to the condenser is maintained by means of a photocell relay control. Adjusting screws are provided to control the protrusion of the positive carbon plus vertical and horizontal negative-positive carbon alignment. The arc length is controlled by a separate negative feed motor That magnetic recording, and possibly reproducing, means have generated intense interest among motion picture technicians is attested to by the many current contributions to the literature, including ample data which appeared in I. P. Appended hereto is an abstract of proceedings at two informal discussion sessions between manufacturers and studio technicians sponsored by the Academy of Motion Picture Arts & Sciences, Research Council. Inquiries on this topic are invited by the Council at 7277 Taft Building, Hollywood 28, Calif. ested (and it is believed they are), the Foundation wil investigate the problem. (4) Brush Development Co. is interested in both phases, that is, sync and non-sync. The company is now using both the wire and the tape. Dr. S. J. Begun (of Brush) stated that before magnetic recorder manufacturers could proceed with the development of equipment suitable for studio use, it would first be necessary to know quality requirements of the studios. Do the studios want a recorder superior in quality to that of present film recorders, or one that is equivalent? I\o Release Prints Now In reply, the following studio requirements were given, in addition to those which have been incorporated into the list of suggested uses: (1) Release Sound Track. — At the moment, at least, there has been no con which is operated on a resistance balanced control and is actuated by arc voltage. The control panel includes meters for indicating arc voltage, line voltage and arc current. A ground glass screen shows the image of the arc. An indicator device shows in inches the burning of the positive carbon. Although a water cell is used in the optical train to filter out some of the heat rays and an air jet is used against the film (Fig. 3), there still is a heat problem at top current, especially with black-and-white films. A great deal of research work is being done on this problem. Higher intrinsic brilliancy and still higher current capacity carbons are available. Mole-Richardson Co. is conducting experiments with these new carbons, thus the M-R Type 250 lamp may be modified to use them when the heat-on-film problem has been overcome. si deration given to the magnetic recording medium for release purposes. (2) Production Recording. — For production recording of dialogue and music, a quality comparable to present film recording quality would be necessary. (3) Currently, the Following Frequency Ranges Are Used — For dialogue, from about 80 cycles to between 7000 and 8000 cycles; for music, from about 50 cycles to between 7000 and 8000 cycles. This means that the equipment must be of high quality from 50 to 10,000 cycles. (4) Volume Range. — With film the range is about 48 db from maximum modulation to no signal with noise-reduction applied. Through the use of push-pull, reverse bias, pre and postequalization, etc., it is possible to get a volume range up to 55 db. Through overload, for instance, in sound effects passages, a range of 60 to 65 db may be obta ned. It should be noted that even this type of overload must not destroy the character of the sound. While going into overload is not desirable, it indicates a need for a greater volume range. Our present effective range in the theatre may at times be as low as 40 db. (5) Speed. — The speed should be 90 ft. per min. for purppses of synchronizing and editing. Any other speed must have a very important advantage to be given consideration. (6) Distortion. — Film distortions are in a range from 1 to 2% total harmonic distortion between 40 and 1000 cycles. This distortion increases with frequency and is in the neighborhood of 4% at 3000 cycles. In transmission equipment, the total harmonic distortion is 1% or less through the useful frequency and volume ranges; in theater equipment this total harmonic distortion is 2% or less at (Continued on page 28) INTERNATIONAL PROJECTIONIST March 1947