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possible by the present arrangement. As a matter of fact we do not change over our fourth track at all from projector to projector. This, as far as we are concerned, is a great simplification. We have had several phone calls suggesting turning it around the other way. We have, unfortunately, also had expressions of the idea that maybe the 12-kc control signal would turn on the left speakers, a 14-kc control signal would turn on the middle speakers, the lack of a control signal would turn on the right speakers and something like 13-kc would make the whole system dead. I trust that we will have a little time to develop this before we make any decision.
Mr. Hilliard: Do any of you have any recommendations on a higher frequency that might be used for this control or some other frequency that you think could switch it, other than the immediate area around 12-kc?
Mr. Athey: No.
Dr. Frame: I thought, perhaps, that you might be interested in how the prints were made on this system of recording. We were asked by Twentieth Century-Fox to develop what was called a magnetic printer. What we have supplied and what is being used to turn out the prints for The Robe consists of a master four-track reproducer, which reproduces from four master magnetic tracks. Each track is 150 mils wide on fully coated film. We had to design a special four-track head for this operation. This reproducer is equipped with complete reproducing facilities including equalization so that we get a 1 : 1 transfer as far as frequency characteristic is concerned. Then the output from this reproducer is fed to a battery of five quadruple-track recorders, running at normal speed and these recorders are in cabinet-type racks, or in a special cabinet, which contains complete recording and reproducing transmission facilities.
The film runs at standard speed, at 90 ft/min. It was originally considered to run the film at a higher speed, but because of the desirability of monitoring to permit the operator to monitor at will at any one track in any one machine, it was decided to retain the normal speed at 90 ft/min. These five machines are tied together in interlock, using a composite synchronous interlock type of motor
which does not require any distributor. Any one machine can be run individually for test purposes on the sync-motor basis or any group of machines can be tied together by simply throwing a switch on each machine to run in interlock. The five recorders will eventually be equipped with 60-mil heads to lay down a 60-mil track. Due to shortage of such heads, the present prints on The Robe are being made with 50-mil tracks, which is the same as the reproducing. Obviously, from the weave standpoint, it's desirable to have the recorder track wider than the scanning head in reproduction. This system is working very well. There are other bottlenecks in reproduction, but not in the printing operation.
Mr. Lewin: I've noticed in making distortion measurements on magnetic recordings that when you get up into the high frequencies you often get distortions that don't seem to show up on the meters, but your ear tells you they're there. Apparently they are heterodynes that are set up between the high frequency and the bias frequency, or possibly for some other reason; but for that reason I feel that you have to be very cautious about increasing the amount of high-frequency boost in your recording, because even though the frequency response might look as though you made an improvement and the noise measurement might tell you that you got less noise, you still might have a poor recording, because it just doesn't sound as clean on the high frequencies due to this heterodyning effect.
Mr. Hilliard: This problem has been considered at great length for several years, both from a radio-channel and recording-studio standpoint. The NARTB curve referred to 16 db of pre-equalization and then, in examining the frequency contents of the Academy Research Council test reel, it was found that the 100% modulation point in speech was repeated more often in the range between 2000 and 6000 than any other region ; and so I think that it behooves us to approach the degree of equalization that is proposed in a very cautious manner, because of the nearness of the microphone in the case of recording and the situation of sound effects and other frequencies that are well up in the spectrum of increased amplitude if you use the equalization characteristic.
Stereophonic Equipment Discussion
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