Projection engineering (Jan 1932-Mar 1933)

Page 16 PROJECTION ENGINEERING Wide sound track of variable density-fixed area type used with double film releases. of a loop of narrow duralumin ribbon held under tension in a frame, the two sides of the loop forming the two sides of the slit. The slit opens and closes and continually changes in width with variations in the speech currents flowing through the loop of ribbon. In the case of the Fox Movietone, the same type of track is produced by a light source that varies in intensity, or nickers, with variations in the speech currents. The lamp producing this light of varying intensity is known as an "Aeolight." The slit through which the light from this lamp shines on the film is of fixed and constant dimensions. In the Western Electric system, the light is focused directly on the varying slit ; but with the Fox Movietone system, the light is allowed to fall on the fixed slit and is not focused on it. An equivalent effect on the moving film is obtained with either arrangement. Variable Area The RCA Photophone is the only recording system that produces a sound track having an exposure on the film of fixed density and variable area. The overall w<dth of the track is slightly less that that of the tracks of the other systems — seventy mils instead of onetenth of an inch — but the portion that is actually exposed in this case varies in width with the instantaneous amplitudes of the speech currents. The track appears on the film as an irregular, black saw-tooth edge. The higher the frequency of the speech currents (the shriller the sound), the closer together will be the points ; and the greater the amplitude of the speech currents (the louder the sound), the higher will be the saw teeth. This variable area of exposure is produced on the film by light from a source of constant intensity that is reflected by a tiny mirror through a slit of fixed dimensions onto the film. The mirror is delicately suspended in an electromagnetic field of force, which reacts with the varying field of force set up by the changing speech currents flowing through a very small winding on the back of the mirror. This causes the mirror to vibrate, or swing, from side to side, exposing more or less of the sound track space on the film. When there is no speech current flowing, the mirror comes to rest in such a position that it exposes just one-half of the sound track width. In this system the light reflected from the mirror is focused sharply on the fixed slit. Sound records are released to theatres in three forms : on hard wax records, on film in composite, or "movietone," prints, and on film as a separate sound track print. The wax records have been described in detail and will not be taken up again, except to say that there is a start mark on the record and a start mark on the picture film accompanying it, and that these marks must be properly lined up when the projection equipment is started in order that the sound and picture will be in synchronism. The picture shown with a wax record is somewhat larger than the picture projected from a movie 1 1 1 u s t r ation of full-width picture released with disc recording and with double film. f tone print, because the space taken up on the edge of the film by the sound track subtracts just that much from the size of the picture. Also, the shape of the picture projected with a wax record sound release is generally considered more pleasing to the eye than is the nearly square picture on a movietone print. This difference in picture dimensions will be evident from an examination of the accompanying illustrations. In recording, the picture is photographed by a standard motion picture camera and the sound is recorded simultaneously with the picture on a recording machine generally situated at a little distance from the camera. The recording machine and the camera start and stop together and are kept running ar exactly the same speed by "interlocked" motors and a speed control arrangement. An exception to this is the Fox Movietone, because in that system the Aeolight is usually mounted directly on the picture camera. For projection, the picture and sound track are printed on a single piece of film, which is then given the name of composite, or movietone, print because it combines then: both. These two — hard wax record and movietone print — are the standard forms of releases for sound motion pictures. Separate Films On a rare occasion, however, the sound and action are released on separate films, which have start marks to permit proper synchronization. This form of release is not often employed because it necessitates the presence in the projection room of a "dummy" machine, which is ordinarily a standard sound and picture projection machine with the picture head removed. Slightly better sound quality can usually be obtained by this means, because the sound and picture films can be developed and printed separately without having to effect any sort of compromise between them in laboratory development. Another advantage of this arrangement is that a picture covering the full width of the film can be employed. Double film release is hardly worth the extra expense and labor involved, however, and is it never used except for "super" productions, and then only while they are being shown at the best theatres. It is sometimes employed when pictures in natural colors are released and it is not thought desirable to release them on wax, because the color stain on the film has somewhat of a derogative effect on the sound quality. Movietone Releases The motion picture companies using Western Electric recording equipment release their pictures on both film and wax ; but the companies using the other types of recording systems can release only on the 'medium on which their equipment permits them to record. The movietone form of release is coming more and more into universal use because it is less bulky and easier to handle than hard wax records, it is not so fragile, it does not wear out so quickly, the sound frequency and sound volume range that it will carry (Concluded on page 23) Sound track of fixed densityvariable area, ' 'saw-tooth,' ' type. 1 at >