Exhibitors Herald World (Oct-Dec 1930)

46 EXHIBITORS HERALD-WORLD October 11, 1930 SOUND STAGE EQUIPMENT AND PRACTICE By L. E. Clark* TABORATORY equipment _ for faithfully -*— ' recording and reproducing sound is fairly easy to get and is capable of precise technical definition. On the other hand, equipment for recording sound in connection with photography in motion pictures is far less simple, as was disclosed as soon as sound recording equipment developed in eastern laboratories was brought to Hollywood to be put into actual production. Early talking pictures showed this very definitely. Many qualities of value in the silent picture were now sacrificed to obtain technically perfect sound recording, with the result that the first talking pictures were very poor photographically and their action stilted and unreal. The problem was immediately seen, however, and production attention focussed on relieving the situation. Great strides have been made toward restoring and extending the values which were developed in the silent motion picture. This process has been due in large measure to improvements not so much in the essential elements of recording — the microphone, the amplifiers, the disc or film recorder — but rather in the auxiliary equipment. The necessary auxiliary equipment is substantially the same for all the recording methods now in use in the Hollywood studios. These may be divided into three classes: sound recorded on wax discs; sound recorded on film by the variable density method and sound recorded on film by the variable area method. The essential differences between these systems lie in the method of placing the final record upon a receiving medium. In the first case, standard phonograph practice is used in cutting a wax record. In the second case, the intensity of a light is modulated to vary the exposure of the film and in the third case, the size of an optical image is varied in order to produce a similar variation in area of exposure. With the exception of these differences, which impose but slight limitations in response characteristics, the three types of recording equipment are identical, and accordingly the auxiliary devices which will be discussed in this article are equally applicable to each of the methods. SOUND STAGES In silent picture production no attention was paid to noise. The concentration of the actors on their work was so intense that the outside noises did not bother them. The microphone, however, is no discriminator of noises and the microphone's allabsorbing ear will add to the main theme the obligato of the carpenter's saw, or the rhythmic overtone of an airplane motor. The rush to produce the first sound pictures was so great that they were shot without sound stages. Work had to be done at night, or traffic stopped in the street outside. As soon as possible, however, sound stages were built. These have two primary functions: to keep all outside sounds from getting on to the stage and to keep sounds generated within the stage from reflecting from wall to wall and thus producing excessive reverberation. As the first of these requirements naturally means that no open doors or windows are permissible in the stages, artificial means of controlling air conditions and temperature must be provided. 'Technical Director of Sound, Pat he Studios. Eighteenth paper of Technical Dirje.it. . FIGURE 1 Motion picture studios can be readily identified from the air by the barn-like structures of the sound stages. This is a view of Paihe Studios. The sizes of these stages vary from 60x 80 feet, in the case of some of the first ones constructed, to as large as 150x225 feet in the large stages. Size was originally limited by acoustic conditions but recently has been governed by studio space and production requirements. It has cost many millions of dollars to build the sound stages with which all the studios are now equipped. To produce adequate soundproofing in general requires a double wall construction, virtually a building within a building, the inner structure being supported on separate foundations from the other one. Care must be taken to prevent telegraphing of sound from the outside structure to the inside through any contact of rigid material. The floor of the sound stage is a very important factor. It, too, must be soundproof and as a practical requirement, the top layer at least must be of wood to facilitate constructing sets. This wood can be laid over a concrete foundation, in the case of a stage whose floor is to be at ground level, or it can be floated upon a sub-floor filled with rock dust, cinders or sand. The purpose of these latter materials is to produce a heavy, non-vibrating base. SYNCHRONIZATION The coming of sound pictures immediately required a fixed speed for photography and projection. Silent pictures could be photographed over a wide range of speed, from as low as fifty feet a minute to over a hundred. Sound pictures must be photographed at a constant speed, a rate of 24 frames a second, which amounts to 90 feet a minute, being standard. Furthermore, the picture and sound negatives must run always at precisely the same speed and must also be in perfect synchronization. For obtaining this perfect synchronization of picture and sound, additional machinery was necessary. This equipment could be either mechanical or electrical, but from the standpoint of mobility of camera equipment the mechanical connection between sound and picture was immediately out of the question. Electrically there are two methods of keeping two machines operating in absolute step with each other. The first and simplest is by the use of the synchronous motor. Any number of synchronous mo tors when operated off the same power circuit will hold exactly the same speed relationship with respect to each other over long periods of time. The accuracy with which the speed is maintained is remarkable. Two synchronous motors can never get more than a very small fraction of a revolution out of step, even though they have been running for months or even years. A second and equally accurate synchronous method is by the use of interlocking or, as they are sometimes called, Selsyn motors which, due to their peculiar construction, constitute what may be known as an electrical gear. Both of these methods are in use and are quite satisfactory after having been adapted to studio needs. We now have mechanism of one type or another for driving our camera and our sound film or disc at the desired speed. In addition, it is necessary to provide a definite identification mark on both the picture and the sound negative to enable the two to be placed so that the prints from the picture and sound negatives can be readily matched. For instance, at the start and end of each take, a man may step in front of the camera and clap his hands or strike two pieces of board together. A somewhat more ingenious device is to wire up an electric lamp and a buzzer, place the lamp before the camera when desired and touch the key that sets off both lamp and buzzer. ACOUSTICAL CONTROL An entirely different set of accessories may be grouped together and classified as "Acoustical Control." First in this list comes the acoustic set, i. e., motion picture sets constructed of such materials that the recording conditions will be good in as much of the space within the set as possible. If a sound is generated between two solid parallel walls, a set of echoes is set up, resulting in what is known as a flutter echo. If the distance between the walls be exactly right, actual standing waves will be produced in the room. Most interiors have the property of preferential reflection, that is, of reflecting certain frequencies more than others. One way out of this difficulty has been to construct sets either of materials having uniform absorption characteristics or materials which are essentially porous. Use of cloth walls in certain studios is an example of what can be done along this line. Other studios have met the reflection problem by building sets with non-parallel walls. In this case very good results can be obtained with the oldfashioned set materials, but at the expense of artistic freedom. There are frequent cases, even in the best of sets, where, due either to considerable action or peculiar camera set ups, it is difficult to secure a good quality of sound pickup. The usual effect is an excessive reverberation, sometimes known as "boominess" and sometimes known as "liveness," depending upon the type of set. To remedy this, several devices have been used. If there is room, large flat soundabsorbing surfaces can be so grouped that they will kill most of the undesirable reverberation. In other cases, a small piece of sound-absorbing material, placed between the mike and the wall from which the reverberation is coming, will produce the same result. Another, and not as common, trouble comes from resonance with