Home Movies (Feb-Dec 1939)

Authored by Dr. George Pasto Details far making As WE have already stated, the sound-on-film recording contemplated is electro-mechanical in nature and very much like that used in recording sound on a wax record. The essential difference is that the sound is recorded on the film itself. This immediately solves the problem of synchronization and, of course, does away with the use of records of any kind thereby eliminating any and all additional expense. Once the sound recording playback device is assembled, there will be no additional expense either in putting the sound on the film or playing it back. You have probably noticed that 8mm is mentioned repeatedly to the near exclusion of 16mm. The reason for that is not hard to find. Sound, as we have already stated, is made up of certain frequencies or cycles and good sound is sound having not only the easy-to-get low frequencies, but a good number of the not-so-easy-to-get high frequencies or high notes. Since 8mm film travels just half the speed of 16mm, the former film allows us but a mere two and one-half inches or so a second in which to record the sound. Thus, in recording a high note such as that of the flute or piccolo, which have frequencies of near 5000 cycles, the needle must make 5000 separate and distinct indentations in the two and one-half inches of film. That is almost 2000 to the inch. In other words, the spacing between the waves at 5000 cycles on 8mm film is, approximately, one two thousandth of an inch which, you will agree, is next to nothing. It all boils down to this: since we are able to record and play back on 8mm — the results with 16mm will be that much better due to its greater lineal speed on projection. Important things to understand and keep in mind in this method of recording are the following : 1. Steady, even film travel. 2. Shape, size and angle of needle. 3. Needle pressure. 4. Minimum side sway of recording head. 5. Correct film groove on recording drum. Constant film speed is the most important factor of all. As shown by the illustration (Figure A), the course of the film in this recording process is briefly as follows: On leaving the reel A, the film shiny side up, goes over recording cylinder B and under the recording head C. From there it goes under the stabilizer drum D to upper projector sprocket. E. F is a piece of spring metal which serves to keep the film in the groove of the recording drum and at the same time exerts a little drag on the film. Roller G and idler H keep the film tight around the stabilizing drum. To obtain steady even film motion we must start at the beginning with the supply reel A. This may be placed on a re-wind provided that the handle of the re-wind is of the type that disengages, otherwise the handle must be counter-balanced since any unevenness at this point will affect the film steadiness. The back tension spring F rides on the upper (shiny) side of the film but engages the film where there are no sprocket holes. This is important since otherwise a whirring sound will be generated here and transmitted by the film to the recording head and recorded as noise on the film. But a moderate pressure is necessary at this point —just so you can feel a drag when pulling the film between two fingers. The stabilizing drum D serves to filter out the jerky motion imparted to the film by the teeth of the projector sprocket E. The stabilizer may be omitted entirely if the recorder is • T urn to Page 208 • This sound recorder also acts as a playback pick-up in this system as explained in text FILM TO BE RECORDED KODALOID FIGURE B CUT-AWAY OF REC ORD/A/G DRUM HOME MOVIES FOR MAY PAGE 191