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powders on a tape, but this was not, at that time, viewed as a fundamentally superior process of sound recording, and was only considered to be a better version of a dictating machine.
However, further developments during the war, mostly in Germany by Dr. von Braunmuhl and the late Dr. Weber, by introducing the H.F. bias method on the oxide tape, and also the work in the U.S.A. by Marvin Camras of the Armour Research Foundation and S. J. Begun of the Brush Development Co., raised the standard and quality of this new recording means to a very high level, so that it can now enter the field as one of our best methods of sound recording and reproduction. It has already resulted in equipment which, because of its versatility, is finding its way into broadcasting studios all over the world.
The film industry, which always has two main principles in view — the perfect picture and perfect sound accompaniment — watched these new developments with great interest, and it soon became apparent that consideration would have to be given to the use in the industry of the new improved magnetic sound method, side by side with the existing photographic sound methods.
Requirements of the Film Industry
Before magnetic sound can be introduced into the film industry, however, it has to fulfil several requirements.
Fig. 1 . 35mm. Magnetic Film, Type A
Fig. 2. 35mm. Magnetic Film, Type B.
Essentially, of course, perfect synchronisation must be kept between the magnetic sound record and the complementary photographic picture record. The simple application and use of the existing Magnetophon tape recorders and of the wire recorders is impracticable, because these two recording media do not present any method of achieving perfect synchronism, and normally run at a much higher speed than that of sound film. The only way, therefore, to achieve this desired result is to do the same to the magnetic sound track as had been done with the photographic track, namely, place it on a perforated carrier so that it can be run synchronously with the picture record.
Another requirement is that the magnetic sound must be at least of the same high standard in even' respect as the existing photographic sound. That is to say, it must be possible to record on, and reproduce from, the magnetic carrier at least the same frequency and volume range, with the same speed constancy and maximum permissible distortion as the existing photographic sound film records.
Many preparations and alterations to the film and equipment are therefore necessary before the magnetic sound-on-film can be put into practical commercial use.