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MOTION PICTURE SOUND RECORDING BY WESTERN ELECTRIC METHOD
Dr. Donald MacKenzie*
The object of all recording is to furnish a sound which would be indistinguishable from the sound one would get from the real source if it were there. At best, it will be no better than direct transmission from the microphone which picked it up in the set, out to the horn which reproduces it in the theatre. From the point at which the recording device comes in, to the point where the photocell furnishes current for the amplifier, we have done nothing but introduce a delay circuit to stop the currents coming from the microphones and store them up until we want record will be nothing more than a delay circuit. The effort to them to actuate a loud speaker. You will see that the permanent give a complete illusion, then, is dependent upon the success of the transmission line and it is affected with all of the disadvantages of listening with one ear (one microphone) whereas you have two ears. The acoustical conditions which are favorable and give a fair illusion are discussed by Mr. Maxfield.
The recording method I wish to describe is used in the Western Electric system, and depends upon the light valve to effect modulation of the light on the sound negative.
The Photophone method described by Mr. Townsend is a variable area method. The method Mr. Hansen described is a variable density method, and I am about to discuss another variable density method. In Mr. Hansen's device we have a light source, whose intensity is varied, shining on the film through a slit of fixed width. The factors of intensity and time constitute the exposure and one or the other is varied. In the Fox device, the intensity is varied and the time of exposure is constant. In the light valve shown in Fig. 1, you have a shutter opening and closing. That shutter is focussed on the film to form a line % mil wide when undisturbed and varying from zero to twice its
^Technical Service Engineer, Electrical Research, Products, Inc.
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