Home Movies (1943)

HOME MOVIES FOR OCTOBER 35101. BOOTH FILM Travels 90 Ft. per minute, allowing maximum latitude for recording sound frequencies. 16MK. SODHD FILM Travels 36 Ft. per minute, about two-thirls slower than 35cm., crowding sound frequencies closer together. • A comparison of 35mm. and 14mm. sound ♦ racks shows that frequencies on 16mm. film are crowded closer together due fo slower speed of film past recording light. Will this become a major problem in recording sound on still slower 8mm. film? IS 8MM. S.0J. JIST AROUND THE CORNER? ► NOT so many years ago when sound for 1 6mm. film was being talked about, many competent engineers in the field of 3 5 mm. sound declared acceptable sound for slower traveling \6mm. film was not feasible for the same reasons that many offer in argument against sound for 8 mm. film today. Eventually, of course, these men were proved wrong. Not only that, but the subsequent perfection of \6mm. sound led directly to still greater improvements in 3$mm. sound! We believe wide discussion on sound for 8mm. will not only benefit the work now going on in this field, but will hasten its development and we are glad of the opportunity to present here Mr. Arthur Hart's views on the subject. — Editor. I IN recent months, there has been a great deal of discussion among 8mm. cinefilmers on the subject of sound on film for 8mm. movies. Today, wherever 8mm. enthusiasts gather, 8mm. sound is one of the principal topics of conversation and speculation is generally strong as to what manufacturer will be the first to offer sound for 8mm. film; whether or not it is practical; and to what extent it would compare in quality to sound on i6mm. film. Most every amateur knows that both 35mm. and 1 6mm. sound film travels at the faster speed of 24 frames per second. They naturally reason why 8mm. film cannot be speeded up to 24 frames per second for the same purpose. But speeding up the travel of 8mm. film in the projector is not the only problem involved in achieving sound on this film. Now the term "24 f.p.s." expresses a certain meaning in sound terms, but it falls far short of being completely descriptive of the third dimension of the sound problem, namely mass or volume. It is as though someone said he had four dogs and we would accept the fact that the quantity is four and that a dog is a dog, regardless of his size or volume, and let it go at that. However, if he said he had four St. Bernard dogs, we would percieve the quantity plus mass and a fuller conception of the man's possessions would immediately be apparent. So it is in discussing sound on film. When we compare the area of film alloted for the sound track on 35 mm. film as compared to 8mm. it is apparent that there is a wide difference. And when we compare the area within that sound track available for registering a single cycle of frequencies according to the speed the film travels past the recording slit, then we begin to realize that mass and volume mean something in attain ing acceptable sound on film. Thirtyfive millimeter film travels at the rate of 90 feet per minute or one and onehalf feet per second. Eight millimeter film, speeded up to 24 frames per second for sound, would travel at the rate of 18 feet per minute or 3.6 inches per second — considerably slower than 35 mm. sound film. In order to illustrate the effect this slower rate of film travel would have on the recording of sound on 8mm. film, let us recall the penmanship exercises familiar to all of us in early grade school days. One of these exercises was a vertical movement of the pen consisting of up and down strokes gradually running out to the right. If the arm was drawn slowly from left to right as the strokes were made, the strokes were close together, often retraced one another. If the arm was moved faster from left to right, the strokes were farther apart and more distinct. The same result would be had by pulling the paper from right to left as the strokes were being made. Pulling it faster would cause the pen strokes to register farther apart. Now suppose while the paper was being pulled, frequency of the pen stroke was speeded up in order to keep the lines the same distance apart as when the paper was pulled slower. The faster the paper was pulled the faster the pen strokes would have to be made to maintain the same distance in spacing between lines. From this it may be seen that in order to make a given number of pen strokes per minute, and without retracing one line over the other, the paper must be pulled fast enough so there will be a small spacing between each stroke. If the strokes slow down, there will be more space between them. So it is in recording sound on film. The higher the sound frequency, the faster the film must travel in order to be able to record a reasonable facsimile cf the frequency. Sound frequencies register on the film as lateral strokes which vary in both length and width according to the volume and frequency of the sound recorded. This is demonstrated in the illustration on this page • Continued on Page 332 322