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Magnetic Sound Film Developments in Great Britain
BY 0. K. KOLB
BRITISH ACOUSTIC FILMS, LTD., LONDON, ENGLAND
SUMMARY: The introduction of magnetic sound film recording and reproducing apparatus into Great Britain is described as well as the types and characteristics of magnetic film available. Details and the general circuit arrangement of the apparatus are given together with a description of special apparatus which has been used for adding a visible signal indication record to the invisible magnetic sound track. Apparatus which has been evolved for the bulk wiping of magnetic film stock is also described as well as experience gained with different types of magnetic film joints.
MOST PEOPLE are familiar with the Telegrafone, the name which Poulsen gave to his magnetic sound recorder and reproducer, in which a steel wire was run past a magnetic head to which signals were fed and thereby recorded on the wire, the signals being subsequently picked up again from the steel wire by means of the same or a similar magnetic head.
The steel wire recording system developed very slowly, mostly due to the absence of any large developments in the electronic field, but when, after World War I, thermionic valve amplifiers, good microphones and good loudspeakers were developed, the steel wire was again taken up but only for speech and signal (e.g., Morse) recording. It did not find its way into the motion picture industry chiefly for two reasons:
Firstly, the quality was not very good and could not compare with that of photographic sound.
Secondly, the speed of the steel wire was much too fast to allow it to be synchronized satisfactorily with the picture.
The Magnetophone: Successor to the Telegrafone
Some years before World War II, Pfleumer in Germany had developed the use of magnetic iron oxide powders on tapes as a magnetic sound recording medium and the Allgemeine Elektricitats Gesellschaft had marketed a machine for the use of it; but even this new apparatus, called the Magnetophone1 did not open the field of application to the motion picture industry, since the quality was still of the standard of a dictating machine.
A CONTRIBUTION: Submitted March 9, 1950
496 NOVEMBER 1950 JOURNAL OF THE SMPTE VOLUME 55