Exhibitors Herald and Moving Picture World (Apr-Jun 1929)

June 9, 1928 EXHIBITORS HERALD and MOVING PICTURE WORLD Synchronized Pictures 11 gn Do you understand the operations involved in the JJ recording and reproducing of sound, synchronized with motion pictures? In this first article on synchronized pictures, Mr. Richardson tells in a clear but nontechnical manner the varied operations and principles involved in the two chief methods of recording and re producing sound accompaniment for moving pictures. In forthcoming articles the subject of synchronization will be treated more fully. This first article will aflFord you an intelligent and fundamental understanding of the subject. Articles on synchronization will be carried regularly in Better Theatres. Disc and Film Processes Used in Sound Films By F. H. RICHARDSON IT has been suggested that I write something concerning synchronization of sound with motion as appHes to motion pictures. I am glad to comply and to try to give you some idea as to what it is all about, but without any attempt to deal with the technical side of it, because that is altogether too wide and too deep to cover in even a half way adequate manner in any single article. In synchronizing sound with motion in motion pictures, two very different and distinct methods are used. In one, the sound record is on a disc similar to an ordinary disc phonograph record, only of greater diameter. The other is the photographic impression of the sound record upon the film itself. This latter is in the form of a band 1/10 inch wide on one side of the film. It reduces the width of the scene photographed on the film by that much, but that is not noticeable, except to those who know of the reduction. The height of the film photograph remains the same. Equipment is now supplied to theatres by means of which either or both of these methods may be utilized. The apparatus is identical, except that part of it attached to the projectors. It is quite possible to project productions using the disc method, and productions utilizing the film method in one program. Only a simple switching operation is necessary to effect a change from one to the other. * * * In both methods electricity is the medium utilized for recording the sound. Whatever the sound to be recorded may be it is picked up by a microphone, which instrument generates a very small electric current, the vibrations of which correspond exactly to the sound waves. In recording the sound upon the film the density of light falling upon the negative film is made to vary precisely in the same way as the fluctuations of the current generated by the microphone. It therefore follows that since the microphone current is an exact electrical reproduction of the sound, the light record impressed upon the negative film must also be an exact photographic record of the sound. In the disc method the microphone current controls and operates an electro-magnetic recording stylus, the movements of which cut or engrave the record upon a wax disc, exactly the same as is done in making a regular phonograph record. The recording needle moves sidewise in relation to the length of the groove, thus making the latter sinuous ; the width of these little sinuousities corresponds to the loudness of the sound being recorded, while their number corresponds to the pitch. I might mention in passing that in film recording two methods are used for controlling the amount of light reaching the negative sound band, namely (a) the "flashing lamp" method, in which the microphone current controls the brightness of the lamp suppling the light for making the record, and (b) the "light valve" method, in which the microphone current opens and closes a tiny narrow aperture through which the light must pass to reach the film. ♦ * * The equipment for all systems here described is supplied by the Western Electric Company. The equipment for projection, as now supplied, is interchangeable, as I have said, so that either the disc or the film method may be used, the change from one to the other being made to all intents and purposes instantly. A disc record runs at about half the speed usually employed on phonographs. A single record will suffice for a whole reel of film. The film used with the disc method is similar to any other film, except that a single frame at the beginning of each reel is specially marked as the starting point. In the film method the sound band or sound track consists of microscopic lines, and here is, to you, an interesting point. The spacing of these tiny horizontal lines is according to the pitch of the sound reaching the microphone at the instant they were made. The difference in the density of the lines is dependent upon the loudness of the sound they represent. That is to say, the greater the contrast between the light and dark lines, or the darker appearance, the lines as a whole have the louder sound they represent. Sound film is otherwise exactly similar to any other film, except that, as I have said, the photograph is 1/10 inch less in width. I suppose you are curious concerning amplification of the sound and desirous of knowing how it is done. Well, I'll try to tell you very briefly if you want to know all the details of its accomplishment. Watch the Better Theatres Projection Department, in which, in due time, it will be fully explained. * * * I have told you, in a very crude way, how the sound is recorded upon the film or disc. Well, in projection that process is exactly reversed, and an electrical current precisely the same as that set up by the microphone is reproduced by either the disc needle or by light projected through the sound band of the film. This tiny current is passed along by electrical reproducer (disc method) or the photo-electric cell (film method) to one or more vacuum tube amplifiers similar in their operating principles to the tubes used in radio audio-frequency stages. These tubes of course put forth a greatly amplified, or magnified exact copy of the current reaching them. This current is carried, by suitable wire circuits, to receivers and horns located at the screen, the size of the horns and their number being determined by the cubical contents of the auditorium and its acoustic properties. The present preferred practice is to use a special cloth screen which has good reflection powers and characteristics and which passes sound freely, with the horn or horns located immediately to its rear. These horns may be so mounted that they may be readily removed to make place for an act or other thing. This may be done by flying them or by another equally eflicacious method. In projecting the disc method the disc and the projector are both driven by the same motor. This insures perfect synchronization, provided the start be properly made (which is up to the projectionist) and that no parts of the film have been removed and not replaced. In projecting the film method the synchronism of sound and motion is automatic, provided the projector be properly threaded. The aperture through which the picture is projected is 14^^ inches (19 frames) above or, speaking as the film runs, back of the point of sound pickup. In other words the sound record at any frame will be the sound that will "fit" the frame 13 inches away from and back of the sound record as the film runs. The film is threaded over the aperture of the projector in the usual manner. It then is threaded into the projector sound gate so that precisely the right frame is over the sound gate to correspond with the picture frame over the projector aperture. * * * That sounds difficult. You might think there is plenty of room for error, but that is wrong. It is quite simple if you follo%y the rules. If you don't — well, if you don't do vour work right, of course the results won't be so good. The removal of any number of feet of the film does not affect synchronism. One thing more and I'll close this little talk. In projecting either method it is absolutely essential that you hold the projector EXACTLY at 90 r. p. m. In other words that you project exactly 90 feet of film per minute. This is taken care of by means of an electrical governing system which automaticallv regulates the speed of projection. In the projection department of Better The.\tres I will go far more into detail. I think vou will all find it interesting. I aril myself just now taking the regular installation engineer's course with the Western Electric Company in order to become more intimately familiar with sound reproduction and the apparatus. .\nd you may take it from me, it certainly is SOME course! The questions asked the "students" would turn the hair of a stuffed buffalo gr.-iy. One is expected to understand and expl.iin circuits that would. I thing, puzzle Marconi and cause even our beloved "Thomas -V. Edison to scratch his head with considerable vigor. What's that? Do I get stuck? I'm not answering — by ad\-ice of counsel!