The Motion Picture Almanac 1929 (1929)

1929 The MOTION PICTURE ALMANAC 115 in accordance with the variations in vibration of the microphone diaphragm. In both cases the procedure is essentially the same between the microphone and sound recording apparatus and in all cases the results at the horn or loud speakers are essentially the same, though of course each claims and probably has certain advantages and disadvantages. Still another method now giving promise of coming into large use is what is known as the "variable area" method of recording sound upon the film. It utilizes essentially the same procedure between the microphone and sound recorder, but there the similarity ceases, since whereas but one film is utilized in recording the sound upon the film by other methods, and both the picture and sound record is made in the camera by them all, by this method two separate films are used, the picture record being made upon one and the sound record upon the other; also the sound record is made by a separate machine, which is caused to run at precisely the same speed as the camera itself. By this method the light incident upon the film — the recording light — is constant in value, but the beam is focused upon a tiny mirror cemented to a oscillograph galvanometer consisting of a molybdenum wire loop through which the current from the microphone is made to circulate after it has been amplified 100,000,000 or more times. \\'hen the current is passing through this loop it does a shimmy — vibrates — and the vibrations are such that the mirror is made to move the light beam sidewise across the film sound track in exact accordance with the frequency and the volume of the sound waves which set the microphone diaphragm into motion. The net result is a series of exposures of a portion of the film sound track to the light in the form of sharp triangles, which are really not triangles at all, but "peaks" of greater or less base width and height. These exposures are developed out entirely opaque, so that the resulting sound track is half black (opaque to light) and half transparent, and when, in the course of projection, the sound track is made to pass under a slit of light about one one-thousandth of an inch high or "thick" by long enough to cover the whole sound track, the result is light variation intensities which may, by means of a photo-electric cell, be changed into electrical vibrations which will operate a loud speaker and send forth into the air sound waves which are almost magically perfect duplications of the waves which originally set the whole process into motion. Phew! There, I hope you can understand all that at least to some extent. It's no easy task to put it into even half-way understandable language. If you think it is, here is the typewriter. You may take my place and tackle the job. I'm very certain you're welcome to it! And now to get all that recording back into sound waves and into the horns or loud speakers, which won't be quite so hard — maybe. First, please understand that the recording methods I have described all result in two types of sound track, namely: the variable area and the kind that was first described, consisting of successive shadings of photographic silver salts upon the track, visible to the eye in the form of very fine lines running across the sound track. Both these widely variant types of sound track recordings may be reproduced bv exactly the same process. By that I mean that either one may be threaded into the same motion picture projector, in exactly the same way, and without any change in the apparatus, may be reproduced perfectly. Please don't ask me why that is so. I don't know, but it is the fact. Reproducing the sound from film is done as follows: Attached to the motion picture projector, in such position that its center is fourteen and one-half inches away from the center of the projector picture aperture, following the devious path pursued by the film, is what is called a "sound gate." This "gate" is merely a tiny opening, upon which the light from a small lamp giving steady, unvarying illumination, is concentrated after having passed through an appropriate train of lenses and a "slit" exactly the same as the one already described as being used in the recording. Thus we have the sound track illuminated by a tiny line of light extending clear across it, but only about onethousandth of an inch high or "thick." This means that only one one-thousandth of the length of the sound track is illuminated at a time, as it passes the aperture at the rate of ninety feet per minute. This light of course passes through the sound track, and there, by the shadings of the photography of either process described, its brilliancy is changed until we again have, in the resultant light beam, an exact reproduction of the microphone diaphragm vibrations in the form of light. This light beam now enters what is called the "photo-electric cell," which our fore daddies in Salem would certainly have picked up with a pair of very long tongs and burned in the very hottest fire they could create, for it is jusr plain witchcraft and black magic rolled into one. The interior of this witch (it is really a glass globe, air tight and fitted with a contact base the same as a radio vacuum tube) is lined with a thin coating of silver. This is merely to make electrical contact between the material with which the silver is, in its turn, coated and one wire of an electric circuit entering the witch globe, the other wire terminating in a round loop in the center of the globe. The material with which the silver is coated is a special form of metal potassium. The globe also contains a small amount of a rare gas, such as Argon, and that last is the key which unlocks the whole thing. We now have a globe lined with a material as described, in the center of which is a wire loop. From the globe all air has been exhausted, in its stead a small quantity of gas has been injected. The globe lining forms the terminal of one side of a circuit connecting with the first stage of amplification through a storage battery of considerable power. The wire loop forms the other side of this circuit. The gas, when the cell is dark, entirelj' insulates the lining material and the loop, so that no current can or does flow. And now comes the dirty work! When the light beam we have described is permitted to enter the cell, its action upon the metal potassium with which it is lined, serves to ionize the gas and make of it an electrical conductor IN EXACT PROPORTIOX TO THE AMOUNT OF LIGHT INCIDENT UPON THE MATERIAL .\T ANY SPLIT FRACTION" OF THE MILLIONTH OF A SECOND. And thus we have a circuit of current sent forward to the amplifiers which is an exact reproduction, in electrical form, of the fluctuations of intensity of the light beam from the sound track! This current is then sent forward through stages of amplification until it finally is strong enough to operate the horns or loud speakers, and presto changeo, we have sent forward into the air by their receiver discs an exact reproduction of the sounds which originally set this black magic train into action. It would, it seems to me, be rather futile to undertake a detailed description of the various apparatus itself. It is still being changed and improved too rapidly, but I have tried to tell you what makes the sound wheels go 'round. If I have succeeded even moderately well in that I think I've accomplished about all that could reasonably be expected from one man at one time. I might add, however, that even now I have been privileged to witness all "talkie" sound productions displayed in theatres which many present declared to be distinctly superior to the entertainment value that would have been supplied had the real actors appeared. This was because, due to magnification of both figures and voices, it was possible to both see and hear with vastly greater ease. However, this is not yet the general rule because of still existing faults in both recording and reproduction, which I prophesy will in the relatively near future all be ironed out. One thing is certain, however, it will be far easier to smooth out the recording into perfection than it will be the reproduction. The former is entirely in the hands of experts. The latter is too often in the hands of "that's good enough" projectionists and theatre managers. Sorry, gentlemen, but facts are facts. Reproduction of sound in synchronism with motion requires just as expert handling; just as careful, painstaking intelligent work on the part of the theatre manager and the projectionist as the recording demands from every one connected with it.