Journal of the Society of Motion Picture Engineers (1930-1949)

film for ten minutes' recording time. This method of retaining the 6.5-mm tape as a safety has an advantage in that this tape can be stored until the completion of the picture in case something happens to the magnetic film. At the same time the magnetic tapes can remain uncut and can be erased and reused after the completion of the film. For feature pictures the print-takes (i.e., approximately one-fifth of the length) are re-recorded again, this time on 17.5-mm magnetic film, immediately after the recording as it was done before on the optical sound film. For advertising, documentary and cultural films and for dubbing of foreign films it has been found that only a single recording was needed.* One magnetic film is sufficient for the working print, for the editing, for the review and for the final re-recording print. To simplify the cutting, the sound waves are registered visibly on the recorded magnetic film which is then forwarded to the editing room. After the recording, the magnetic film is cut and synchronized to the picture film and ready for daily running (review). After the first assembly of a dialogue reel comes the second cutting, after which it is ready for re-recording on the final negative. As already stated, in dubbing of foreign films the first magnetic film serves for the re-recording. Other magnetic film rolls contain the music and the sound effects. Optical sound reels, for example library music and sound effects, can, of course, be mixed in. Magnetic Sound Film Recording Equipment Figure 1 shows the magnetic sound recorder and Fig. 2, the (general) as * Dubbing of foreign films in German is done exclusively in Germany and now plays an important part in the film industry; up to 300 features are dubbed in one year in Germany. sembly of the recording equipment including monitoring. The mechanism of the magnetic sound recorder is driven by a 220-v, a-c, 50-cycle, three-phase synchronous motor. In Germany the picture camera and the sound recorder are supplied by the 50 cycles net. Synchronization is done by the old-fashioned clapstick (which has proved to be the best) . Also in dubbing work the picture projector and the sound recorder are supplied by the same 50 cycles net. In the sound track the commencement of the picture loop contains so-called bloops (blumpers, clicks) or short a-c signals. These are recorded and serve for synchronizing. When shooting on location the power supply for the picture camera and the sound recorder comes from an a-c-d-c unit or inverter. In the recorder (Fig. 1) the magnetic film is transported by a 32-tooth sprocket (1). Film stabilization is controlled by a filter of two pivoted rollers (2 and 3), a large flywheel on the shaft of the primary sound drum (4) and a small flywheel on the shaft of the secondary sound drum (5). In order to keep the film from becoming mechanically damaged, the large flywheel, which is at the start coupled with the motor, is driven until it has gained full speed and is then uncoupled automatically. The recorder and the pickup head are mounted between the two sound drums so that the recorder head is right next to the primary sound drum (4) with the playback head just behind it. The shields (6 and 7) are situated on the other side of the film. A special feature of this construction is that, when threading the film, only the head support (8) with the two magnetic heads will be lifted. During the process of reloading and rewinding, the withdrawal of the head support is not so far but that a certain amount of induction still takes place in the reproducer head so that when rewinding is in progress the signal can still be heard. This simplifies the refinding of different takes. Because the 412 April 1951 Journal of the SMPTE Vol. 56