The international photographer (Feb-Dec 1929)

Thirty-two The INTERNATIONAL PHOTOGRAPHER August, 1929 "Vita vox -<lA £ound 'Recording System The commercial application of sound recording has grown up over a period of thirty years in the phonograph industry. However, its sudden application to the picture industry has given it an exaggerated importance which is not justified by the facts. The "medicine men" of the electrical industry have swept down on the "natives" of Hollywood with their little bag of mystery tricks and carried off the spoils. At the present time there are three methods of recording in use at the studios — variable area sound track on film, variable density sound track on film and disc or phonograph recording. The variable area system is used by R.C.A. and Vitavox; variable density by Fox Case, Western Electric, Powers and DeForest; Phonograph or disc is used by W. E., Victor, Telefilm, Qualitone and several others who are starting up. During the early stages of talking pictures all of these systems will flourish, however it will not be long before it is a case of survival of the fittest. Much has been written regarding the general theory and operation of these systems, but very little has been written about the troubles which have been encountered; it has all been verbal, but if it were written down it would make many volumes. As the phonograph or disc recording can only logically be considered as a temporary expedient in the talking picture industry, any further remarks will be confined to film recording methods. All methods of recording require a satisfactory amplifier. The space on the edge of the film allotted for the sound track is the same for both methods and has varied from time to time from as high as 125 mills down to 70 mills in width; any wiatn between these limits is satisfactory for either system. To obtain the variable density record a source of light is projected through a slit and focused on the film as a fine line of light covering the full width of the sound track. This light passes through a light valve which resembles the human cords. The electrical impulses which operate the light valve cause a fluctuation in the amount of light which passes. These fluctuations are photographed on the film as variations in light and shade. It will be seen that the tone to be produced will depend on the number of fluctuations per second while the volume will depend on the contract of light and shade. For good recording the light variations should be directly proportioned to the sound variations, but for tone variations it must follow an exponential function which is not unity. The conditions to be met in this recording system are very severe and BY T. A. MILLER, Sound Engineer, Vitaiox Corp. all factors must be perfectly co-ordinated. The natural frequency of the light valve must be above the recording range, the amount of light must Exterior lieu of the Vitavox Recording Unit. be exactly right for the correct film exposure, the development of the film must be brought to a definite limit both for the negative and positive print. The difficulties encountered <",re improper exposure, light refraction en the edges of the light valve, im Insnle of Vitavox Recorder showing the Light Beam proper characteristics for tone variations, film irregularities, variations in developing and printing and later the collection of oil and dirt on the sound track. In listening to the reproduction from the recording, the noticeable effects are distortion of the higher frequencies, described as fuzzy, raspy or harsh, lack of bass and change of tone or pitch from one scene to another, also increase of surface noise and impaired quality due to collection of dirt on the film after short use. The variable area recording is obtained by two methods, R.C.A. and Vitavox. In the R. C. A. method the light is taken through a slit onto a movable mirror and from there onto the film with proper lenses The source of light is not critical and can be set at any valve above that which will give full exposure of the film. The length of the line of light on the sound track is varied by the mirror and the record produced is of saw-tooth shape or an oscillograph record. There is nothing critical in the method except the rotating mirror which is supported by two fine wires which are very easily broken to produce satisfactory results for talking pictures. Five thousand cycles must be recorded; this requires that the light line must not occupy a space over one and one-half mills. Here we must also consider the refraction of the slit edges, the diffusion of the mirror and the revolving power of the lenses. These factors all militate against correct recording of overtones. In analyzing reproduction from these records note the perfect base but lack of distinction in characteristic overtones. There is nothing critical about the development and printing of these records and double printing offers no obstacles. The Vitavox method is the simplest and most direct of all. In image of the light source is forced directly in the film utilizing the maximum resolving power of the finest lenses. In addition to this the image is sliced obliquely in two by a razor edge giving a light line nearly twice as fine as it is possible to obtain by any other method. The light valve is the razor blade. There are no critical parts to this system and the light valve cannot be injured. It is the only system in which the percentage of overtones to fundamental can be changed in the recorder itself. On account of the over exposure at the sound track with the variable area method the collection of oil and dirt makes little difference, and a double print of this kind can be run hundreds of times with satisfaction; the sound track "■ill last as long as the picture.