International photographer (Jan-Dec 1934)

Twenty-four The INTERNATIONAL PHOTOGRAPHER March; 1934 Motion Picture Sound Recording HE physical aspects of the sound stages and the types of portable and permanent monitoring equipment employed on them for sound recording were described at length in the preceding chapters on monitoring. This chapter continues that discussion of monitoring by considering how the monitoring equipment is operated to produce pleasing and artistic recordings of music and dialogue. The technique of monitoring orchestrations is quite different from that employed for straight dialogue recordings. The "scoring" of music usually requires several microphones mounted before the orchestra in set positions that have been found to provide the most satisfactory blend of sound from the various musical instruments. (It must be mentioned here, however, that a few — a very few — monitor men still prefer to use one microphone for orchestrations.) The recording of dialogue and sound for routine picture production work usually is done with a single microphone that is moved during shooting to follow the actors ; although occasionally for involved shots two or more microphones are employed. Reverberation and Echo Sound is reflected when it strikes a hard surface, such as a wooden floor or wall. If the reflecting surface is close to the source of sound, as within the confines of a sound stage, and there are several such reflecting surfaces to cast the sound back and forth an acoustic condition exists that is known as reverberation. The sound that is thus reflected back is termed reverberated sound. If the reflecting surface is at such a distance from the source of sound that there is an appreciable delay in the return of the reflected sound, the reflected sound is called an echo, for it is a distinct repetition of the original sound. The chief difference between reverberated sound and echo is in the length of time that elapses between the creation of the original sound and the return of the reflected sound. Echo is not encountered when recording within sound stages, because their size is not great enough to cause sufficient delay in the return of the sound ; but sometimes the presence of too many hard surfaces causes reverberation to become so pronounced that it is almost as objectionable as echo. A certain amount of reflected sound is necessary to secure realistic sound recording; but if the reverberated sound persists in the stage for an excessive length of time after the generation of the sound, successive sounds will be confused by an overlapping caused by the persisting reverberations. Reverberation in Sound Stages Reverberation is measured by the length of time required for a tone of 512 double vibrations per second (one octave above middle C) to die to one-millionth of its initial intensity. It has been found that a time of reverberation in the order of three-quarters of a second or less is satisfactory for the interiors of sound stages. In other words, a tone of 512 dv should not persist in a stage longer than three-quarters of a second without its intensity becoming reduced to one-millionth of its original value. Sound stages have their interior surfaces covered with thick layers of sound-absorbing material, as previously explained ; so they do not reflect sound to an appreciable extent. If the stage was empty, a sound generated in it would die away almost the instant the production of sound ceased. That is the reason sound stages are said to be acoustically "dead." The amount of reverberation present Chapter VII By Charles Felstead Associate Editor can be tested by clapping the hands sharply and listening to the persistence of the reverberated sound. When motion picture sets are built in such a stage, their hard walls serve to reverberate sounds generated within the sets; and since there is practically no reverberation from the dead walls of the stage, it is, so far as acoustic conditions are concerned, as though the sets were built out in the open. Lack of "Depth" in Recorded Sound The microphone is a monaural hearing device ; whereas human beings have binaural hearing. The resulting flatness of "depth" in recorded sound is comparable to the lack of perspective in a photographed picture, which is due to the ordinary camera having monocular vision instead of our binocular vision. That is to say, the microphone represents just one ear, and human beings have two ears; the camera is like a single eye, and human beings have two eyes. These handicaps can be overcome to a certain degree by careful attention to the acoustic conditions existing within the set in sound recording, and by skillful lighting of the actors and their backgrounds in photography. The two eyes with which a human being is provided make it possible for him to determine the distance and direction of an object he sees; and his two ears provide the means by which he determines, but in less accurate degree, the distance and direction of the source of a sound. In other words, his two eyes and two ears acquaint him with the "depth" of the world about him; they give perspective to everything he sees and hears; they make the world appear three-dimensional and real. How a Source of Sound is Located The interval of time that elapses between a sound reaching one ear and the other ear permits a human being to judge the direction from which the sound came; and he subconsciously determines his distance from the source of sound by noting its loudness and the ratio of direct to indirect sound he hears. His experience aids him in these determinations of direction and distance. The closer the individual to the source of sound, the more direct and less reflected sound he hears. When he is at a distance from the source of sound, most of the sound that reaches his ears will have been reflected from adjacent walls and objects, and but little direct sound will be combined with it. This characteristic is employed in making the sound recorded for motion pictures seem natural. Locating the Microphone Effectively If an actor is in the rear part of a large set and the camera is equipped with a lens for making a long shot, the microphone should be placed facing partly toward the actor and partly toward some large, hard surface, such as a wall, so that it will receive mostly the reflected voice of the speaker. Then when the sound is reproduced in a theatre, the proper illusion of distance of the speaker back of the screen will be obtained. But if the camera is set for a close-up, the microphone should be hung in front of Please mention The International Photographer when corresponding with advertisers.