Movie Makers (Jan-Dec 1948)

MOVIE MAKERS 117 PROBLEMS WITH OPTICAL METHODS More serious than the reduction in track width is the low 8mm. film speed. Table I compares the room available for storage of 35, 16 and 8mm. sound. A 35mm. sound film running at 24 frames per second, goes through the soundhead at 18 inches per second, and the track is 100 mils wide. If we multiply the film speed by the track width we get a sound-storage index number of 1800. The 16mm. sound on the same basis has an index number of 567, or roughly 31 percent as much. When we get to 8mm. film the index has dropped to 6 percent for a 24 frame speed, and to only 4 percent at a 16 frame speed. Experience shows that in going from 35mm. to 16mm. sound there is marked deterioration in quality. Considering that 16mm. sound with a rating of 31 percent is not too far above the borderline for high-quality sound, the possibilities for 8mm. with a 4 percent to 6 percent rating seem discouraging. If we choose to put the 8mm. sound track on the picture side, then we reduce the already limited picture area. Projectors would have to be modified for the smaller picture size. The possibility of adding tracks to old films would also be limited. We can avoid these difficulties by locating the track on the sprocketed side. If we try optical sound there are photographic troubles which are indicated in Fig. 2. Frayne and Pagliarulo have shown that film processing may cause uneven development of images that are as much as 30 mils from the sprocket holes. The uneven action of the developer at the edges of the sprocket holes has been represented by vertical shading. There is also the possibility of action at the the film edges, and this has been indicated by horizontal shading. Uneven development of this kind can cause sprocket hole modulation even when the drive system is perfect. Economic problems also must be considered. Eight millimeter photography has sacrificed quality in order to give the lowest possible cost. If sound can be provided only by critical and expensive equipment and processes, the average amateur will not be able to afford it. MAGNETIC METHOD Magnetic recording offers a fresh approach to the problem of sound for 8mm. projection. Instead of an optical track of varying density or area, a layer of a newly developed magnetic material is bonded to the film in the space between the sprocket holes and film edge. This magnetic material has high coercive force and remanence, so that it may be magnetized in accordance with variations of magnetic flux in the V2 mil gap of a recording head that rides against it. Fig. 3 shows one method for accomplishing this. With the selector switch in the record position shown, acoustic waves picked up by the microphone are amplified and fed into the magnetic head. Here they are changed into magnetic-flux variations which are recorded on the magnetic film track. The same head is used to translate the magnetic record back into electrical energy. With the switch in playback position, these waves are amplified and fed into a loudspeaker. Although the record is "permanent" and will last for the life of the film, it may be erased quite readily by switching to the erase position and running a high-frequency alternating-current demagnetizing flux through the head. It is apparent that magnetic sound has a number of special advantages for the amateur: (1) Recordings can be made in the home, without special equipment. (2) They can be played back immediately without processing. (3) Records may be erased and rerecorded. (4) Old films can be adapted for sound by adding a track. (5) Present silent equipment can be converted for sound. A HIGH-QUALITY 8MM. SOUND PROJECTOR To demonstrate the possibilities of 8mm. systems, some conventional 8mm. projectors were converted for sound. Fig. 4 is a photograph of the equipment that you now hear. A flywheel and damper arms were added to the silent projector. This gives essentially the same mechanical system used by the company on its 16mm. sound equipment. It should be noted that if Table I Sound Storage Index for Films Sound Film Storage Frames Speed, Track Index = Relative per Inches Width, Speed X Percent Type of Projection Second per second Mils Width Rating 35mm. sound 24 18 100 1800 100 16mm. sound 24 7.2 80 576 31 8mm. sound 24 3.6 30 108 6 8mm. silent (1) 18 2.7 30 81 4i/2 8mm. silent (2) 16 2.4 30 72 4 ^/esigned in Hollywood for the discriminating movie maker. Camera (less lens) priced from $1095.00, complete with amplifier, microphone, tubes, batteries, headphones and instructions. See your dealer or write today tor further information. 0?eotuneA . . . Records talking-pictures in black and white or color. Completely silent in operation, self blimped; no noise for recording microphone to pick up. Veeder-Root geared reset footage counter. Auto-Parallax View-Range Finder available. Synchronous motor driven. Rugged Auricon "Iron-Vane" sound track recording galvanometer, never needs adjustment. RCA Licensed High Fidelity 16mm Sound-On-Film Guaranteed One Year BERNDT-BACH,Inc. 7383 Beverly Blvd., Los Angeles 36, Calif. NANUFACTUBERS OF SOUND-ON-FILM RECORDING EQUIPMENT SINCE 1931