Home Movies (1951)

Synchro-Sound for the amateur.. Uses of perforated celluloid tape in making perfectly synchronized movies — a new system. (IN THREE PARTS— PART ONE) By GEORGE W. CUSHMAN, S.S.C. ILLUSTRATIONS BY THE AUTHOR THE DREAM of every amateur to have synchronized sound with his home movies received a big impetus when wire and tape recorders became popular after the close of the war. For motion picture use, wire was not practicable because of the difficulty in splicing and editing. Magnetic tape has been used by many amateurs with some degree of success, although perfect synchronization is difficult with the average tape recorder because no allowance can be made for the expansion and shrinkage of the tape. Over two years ago Earl Everley and myself began experimenting with magnetic tape with an eye to synchronizing it with camera and projector. We built six recorders. None of them were satisfactory. The seventh was successful. We tried coupling recorder to projector and projector to recorder, but the expansion and contraction of the tape always beat us. It would be off as much as a half second per 400 foot reel, which, to us, was too much. It was not until perforated tape was announced about a year ago that we were able to achieve perfection in synchronization between camera and recorder. The reader may be interested in knowing that several large research organizations including Western Electric, have spent much time and money in trying for perfect synchronization with paper or plastic tape, but have concluded it cannot be done except by one highly complex method of electronic control. Their engineers told Everley and myself that it was not practical to couple camera and recorder if one of these kinds of tape were used. Approximate synchronization for musical background or running commentary is satisfactory with many coupling methods which have been successfully attained and described in past issues of Home Movies. But for accurate synchronization such as lip sync or a tap dancer, a better system has to be devised. This we discovered as we built and then destroyed one recorder after another. Our primary idea was to run camera and recorder with separate synchronous motors. If we could couple recorder with camera, we could then save the cost of one motor, so we decided to try this idea first. If it worked, all well and good. If not, we could still fall back on a second synchronous motor. Actually, our system is built around a 60 cycle synchronous motor, having 1 /75 horsepower, which, we have since found, is more than ample to drive both recorder and camera, and both recorder and projector when showing the films. The secret of the entire system is the use of the perforated tape which, we are told, is made only by the Minnesota Metal and Mining Company in St. Paul, and which is available at the present time only from their two branches in New York and Hollywood. Correctly, the substance is celluloid and not plastic or paper, and we understand standard DuPont film stock is used, being coated by MMM at its main plant in St. Paul. At the present time three widths of this magnetic film are available, 35mm, \iy2mm (which is 35mm split in half) and 16mm, which is obtainable single perforated, and perforated on both sides. The author with set-up showing recorder with camera in action enclosed in sound-proof blimp. Recorder with synchronized motor coupled to 1 6mm projector The 35mm width is now in use at many of the major motion picture studios here in Hollywood, and the 16mm width is being used by many • See "SOUND" on Page 209 195