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July, 1951
19
THE MAGNETIC RECORDING AND REPRODUCING EQUIPMENT
FOR THE TELEKINEMA
G. F. Dutton, Ph.D., D.I.C*
THE equipment supplied by " His Master's Voice " is designed for use with standard 35 mm. perforated oxide coated film. The film is coated over the whole of the surface on one side and the four tracks shown in Figure 1 merely indicate the tracks recorded by the four recording heads, necessary for the production of stereophonic and panoramic sound effects.
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Fig. 1
Considerable development work was carried out to obtain the necessary un-formity of coating and choice of film base to meet the exacting demands of this equipment for the smooth running of the tape over the four sets of heads. Eventually, in order to meet the dimensional stability of the film and also
the uniformity of spread, high grade 5 thou, tri-acetate film was used. The thickness of the oxide coating spread on this film is .0005 inch ±.00005 inch. Even with this careful choice of film base and even spread and equally careful choice of compatibility in the lacquer of the oxide coating, it was found necessary to use pressure pads on the heads, as shown in a later paragraph.
The four tracks are recorded simultaneously side by side as shown in Fig. 1,
Fig. 2
Fig. 3
each track being about J inch wide (crosstalk between adjacent tracks being better than 36 dB), and run synchronously with the picture.
E.M.I. Engineering Developments, Ltd.