Movie Makers (Jan-Dec 1952)

175 FIG. 2: Sound head assembly shows the sturdiness of construction required by joint Army-Navy test standards. FIG. 3: Separate amplifier unit provides (lower right) connections for two projectors, mike and phono inputs. The chief engineer of this veteran projector company analyzes the application of magnetic sound to DeVry's Joint ArmyNavy (JAN) projection equipment. A "Movie Makers" exclusive Erasing of an old 16mm. magnetic sound track is accomplished automatically whenever new sound is recorded on the film. This high-frequency, alternating current blankets out the recorded magnetic signal; thus the magnetic stripe is left in a demagnetized state and new sound can be added to the film by the magnetic record head within the sound head assembly. THE AMPLIFIER COMPONENT The separate amplifier component of the DeVry JAN projection equipment (see Fig. 3) is a straightforward type of amplification system generally applicable to most types of film reproduction. Although separate mike and phono inputs are provided, a mixer unit is needed to record jointly voice, music and sound effects on a magnetic stripe. The frequency response characteristic of this amplifier alone is flat within ±1 decibel between 50 and 10,000 cycles, with a power output of 20 watts at less than 2 percent harmonic distortion over this pass band. THE SPEAKER COMPONENT The loudspeaker component contains a newly designed and perfected, high quality, heavy duty speaker capable of reproducing wide range, high fidelity, audio intelligence. To this loudspeaker component we have added a remote control unit (see Fig. 4), so that the operator can hear the sound as it is being recorded directly on the magnetic track. Portability dictated this very simple means of extending a control position to a distance sufficient to eliminate projector mechanism noises. PERFORMANCE SPECIFICATIONS Now let us discuss the performance of this equipment. The DeVry JAN projector is designed to operate at 24 frames per second only and (magnetically) to scan a 100-mil-wide stripe on single-perforated film. The equipment also will accept films with a standard optical sound track or films which combine both an optical track and a magnetic track. In the latter case, of course, each track is then reduced to 50 mils in width. Operating from a full-width magnetic stripe, the pro FIG. 4: The remote control unit, complete with microphone and monitor head-set, is housed in top of the newly-designed loudspeaker component. jector has an overall frequency response which extends from 80 cycles per second to well over 7500 cps at less than 2 percent harmonic distortion. The signal-to-noise ratio is 50 db. The location of the magnetic head within the sound stabilizer assembly is at a point where the film motion is steady and the flutter is at a minimum. No additional idlers or flutter-eliminating devices were added to maintain an overall flutter factor of less than 0.2 percent. THE FUTURE OF MAGNETIC And now a word about 16mm. magnetic practices. However fascinating this new sound medium may be, especially to the amateur movie maker, it is essential that I conclude this article with some pertinent comments regarding the current status of magnetic sound on 16mm. motion picture film. What is the current status of magnetic sound on 16mm. film? As this article is being written, the Societv of Motion Picture and Television Engineers is undertaking a study of magnetic-sound-on-film practices with a view to standardization. Officially accepted standards are approved by the American Standards Association (ASA) ; but they are suggested, created and submitted by the Society of Motion Picture and Television Engineers or the Motion Picture Research Council, or both. The factor of standardization is of prime importance, and it is one that must be resolved rapidly to make sure that 16mm. magnetic sound tracks will reproduce alike in various projectors. This, in the case of magnetic track, presupposes some conditions which to the amateur movie maker might be difficult to realize. First of all, how much energy [Continued on page 186],!