Sound motion pictures : from the laboratory to their presentation (1929)

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STANDARD SOUND DEVICES 39 and reproducing of sound in conjunction with motion picture film (known as "Movietone''). Figure 1, page 41, shows cartoon diagram of Western Electric Sound Re- cording System. The sound record comes to the theatre either as a wavy groove in a composition disk, which is practically a phono- graph record; or as a marked track of varying density at one side of the picture film. It is the function of the ap- paratus to record and afterward to reproduce sound in perfect synchronization with the picture, so that the il- lusion of sound and motion picture are simultaneous, as I have said. In the Vitaphone method the sound is recorded and re- produced from a disk made of a hard composition used in the making of phonograph records. This is operated in synchronization with the film, which is timed with the projection machine that projects the film on the screen. The disk records do not differ essentially from those used in the ordinary phonograph, except that they are consider- ably larger and are run at a much slower speed. The pur- pose is that a single record shall play throughout an entire reel of film. The reproducer used is similar, in some ways, to that used on the ordinary acoustic phonograph, the needle holder being connected to a clamp of the diaphragm. The diaphragm itself is made of highly tempered spring steel. To it there is fastened an armature of an alloy which is of especially high permeability and which is so arranged that, as the diaphragm vibrates, the flux in the air gap of a permanent magnet varies correspondingly. Thus there are induced, in appropriately placed coils, currents which are the electric representation of the wavy groove along which the needle travels. With the disk method the first step in photographing and recording a scene is taken in a studio equipped with special facilities. These include one or more microphones