Patent GB-378963-A (GB)
Title: Improvements in or relating to sound picture recording and like arrangements
IPC: F28B3/02
Filed: 1931-05-21
Abstract: 378,963. Associated sound-recording and picture-taking; recording set acoustics. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Maxfield, J. P. ; 88, Jefferson Avenue, Maplewood, New Jersey, U.S.A.) May 21, 1931, No. 15087. Convention date, Feb. 27. [Classes 13 and 40 (ii).] A sound and picture-recording set is arranged to give the impression of naturalness in the recording of both " long shots " and "close ups," and for this purpose the distance from a sound source to the microphone and from the subject to the corresponding camera is proportioned according to the size of the recorded picture image of the subject. The ratio of the direct to the reflected sounds reaching the microphone is also controlled by the materials and construction of the recording set so that on reproduction the required illusion is given as to the surroundings from which the sounds are supposed to emanate. The diagram, Fig. 1, shows how the reverberation times should fall for single-channel recording of music in rooms of various sizes. The upper plotted line represents the maximum acceptable time and the lower line represents the minimum time and values lying between these lines will produce a pleasing effect. The sound recording is effected at volumes determined by the audibility curves of Fig. 2, which show the limits of audibility for sounds of varying intensity at different frequencies. The frequency absorption characteristics for the various materials of the set are determined by known reverberation measurements and the character of the set (i.e. whether live average, or dead) can then be ascertained by a curve such as shown by Fig. 3. The microphone placement is then found by reference to the curves of Fig. 4, which show the microphone placement factor for sound recordings corresponding to camera exposures with lenses of differing focal lengths in the cases of sets having various absorption characteristics. The curves of Fig. 4 are straight lines theoretically, but because of extraneous noises it is preferable when using lenses of short focal length to place the microphone closer to the source of sound than corresponds with theory, and the curve therefore is as indicated in full lines. Figs. 7 and 8, which show two views of the same recording set and action, illustrate the method employed. Fig. 7 indicates the camera and microphone positions for a " long shot " covering the general action of the scene, while Fig. 8 indicates the camera and microphone placements for close-ups of each of three dialogue scenes at 3J, 3K and 3L. The camera 20, Fig. 7, photographs the general action and, if for this purpose a 35-millimetre lens is used, reference to Fig. 4 shows that for a set of average absorption the microphone placement factor is 82 per cent, so that if the camera 20 is situated 25 feet from the mean position of the action the microphone 21 must be placed at about 21 feet from this position. In Fig. 8, the close-up cameras 50, 51, 52 are shown arranged to photograph images of the same size, so that cameras 50, 52 situated at about 14 feet from the relative action are each provided with a 75-millimetre lens. A 150- millimetre lens is used in camera 51 situated 28 feet from the scene at 3L. By reference to Fig. 4, it is found that for a set of average absorption the microphones 53, 54, 55 should, in each case, be placed 6¢ feet from the source of the sound. With this arrangement the sound, both direct and reverberative, is the same for all three " close-up " views. The individual picture films made by the separate cameras 20, 50, 51, 52 are afterwards assembled together by cutting and patching to form a composite picture film showing " close-ups " and " long shots " in the desired order. The sound record films recorded from the separate microphones 21, 53, 54, 55 are similarly assembled to form a composite record. The pictures and accompanying sound records may be recorded upon the same film.