Motion Picture Herald (Apr-Jun 1931)

74 Better Theatres Section May 9, 1931 Noiseless Recording {Continued from page 50) straight line part of the emulsion characteristic. Since this new method contemplates recording over the same part of the film characteristic, and within the limits of this characteristic previously utilized, there is no change in film technique. The processing which produced the best quality of reproduction with the former method gives the best quality of reproduction with this new method. Referring to Fig. 1, which is an approximate characteristic of the ground noise obtained from film of various densities, the point A indicates the approximate density other words, the spacing of the ribbons varies with the applied sound currents as illustrated in Fig. 2. It will be seen from this that for weak sound currents below a certain minimum amplitude the ribbon spacing is always the minimum, and the average spacing is unvarying. As the sound currents build up to near their maximum amplitude, it is seen that the average spacing of the ribbons (or their carrying capacity) is gradually increased up to a maximum which corresponds to that of the normal light valve. As the input is further increased, there is jio further in o o o o o Fig. 3. Koise r eduction amplijirr employed in normal recording. By shifting the ribbons to have something less than their normal spacing, we can increase the density during the quiet portions of the sound track to point B. This results, then, in a reduction of the noise in the quiet intervals. Then, as the sound currents are applied to the valve, its spacing automatically varies, so that it at all times has sufficient carrying capacity, as represented by the spacing between the ribbons, to carry the applied sound currents. A slight amount of margin is always established as a factor of safety, in order that a sound which builds up suddenly will not clash the ribbons. The manner in which the carr5dng capacity of the light-valve or, in crease in the ribbon spacing, and clash occurs precisely as it does in the normal lightvalve. It is entirely possible to continue the carrying capacity of the ribbons upward by allowing their spacing to exceed the normal spacing. No useful purpose is served by this, however, since the carrying capacity of the photographic emulsion would be exceeded by so doing and an effect equivalent to clashing of the light-valve would be obtained. Therefore, the device has been purposely arranged so that photographic overload and light-valve overload occur simultaneously, if the recording lamp has been set previously for entirely normal recording. Fig. 4. Noise reduction control unit COMBINING SOUND AND PROJECTION . . DEPARTMENTS In the next, the June 6th issue of Better Theatres, the departments, Sound in the Theatre, and Better Projection, will be combined. This is to be done in the belief that separation of editorial treatment of the two subjects is no longer tenable. Projection now is Sound — and Sound is Projection. It is hoped that readers will find that the single, enlarged department will serve their interests more conveniently. The general principles of noise reduction for sound records on film may be applied to other than the present form of light-valve recorders by making circuit changes as required by the particular type of equipments that may be involved in a specific method. Operation of the apparatus employed in this recording system is relatively simple, although considerable time and effort have been spent in its development. The equipment is divided into two units — an amplifier located usually at the location of the main amplifiers and a control unit fed by the amplifier and located at the film recorder. These units are shown in Fig. 3 and Fig. 4. Adjustment of these units is simple and means are provided for checking the adjustments quickly and at fairly frequent intervals. At the present time commercial recordings are being made with a reduction of ten decibels in the ground noise. It is expected that as more experience is gained in the use of this equipment, the noise reduction may be increased. Even ten decibels is a very noticeable reduction and permits an extension of the volume range to a point where sounds previously completely obscured in ground noise become definitely a part of the reproduction with a consequent considerable enhancing of the dramatic effect and naturalness. The practical elimination of this ground noise in the theatre gives to the audience a feeling of being present at the action and a removal of the mechanical from the sound. The average theatregoer's reaction seems to be one of finding the picture "easy to listen to" and possessing a naturalness which all but places it in the class of "original" instead of that of "reprdouction" of the recorded sound."