The Prison Mirror

FROM SCRIPT TO SCREEN--IV
By H. L. H.

In sound recording the sound is impressed photographically upon a narrow band of the film at one side of the picture frames. Regardless of what system is used, the recording of sound in synchronism with motion pictures in itself presents great difficulties aside from the mere task of recording. That this is true you can readily see when it is considered that in recording productions, musical numbers, monologues, etc., it is essential to pleasing results that all sounds, except those the audience are supposed to hear, be excluded from the recording. This means, that since extraneous sounds would work harm when dialogue is used in a production, the studios must be as near sound proof as it is possible to make them. If located in a city, then all noises and vibrations caused by passing cars, trucks, etc., must be shut out. Even the noise incident to operation of the camera mechanism must be prevented from reaching the "mike."

In our explanation of sound recording we shall adhere to the method used by Fox Movietone, as it is the most successful at the present time. It is known as the Variable Density Method.

The negative film passes the camera aperture in the usual manner at a speed of exactly ninety feet of film per minute. The scene, not the sound, is then impressed upon it. The film then passes down, past the camera aperture, and is threaded into and passes through another "gate" in which there is a very much smaller aperture, and as the portion representing the sound track passes over the aperture it is exposed to a light from an "Aeo" lamp, which, acting just as the sunlight in an ordinary camera, impresses the sound upon the film.

The "mike" which is to receive the sound vibrations may be placed at any desired point, in close proximity, or far distant from the camera. The wires from the microphone connect directly with the main amplifying panel. The amplifying panel is in turn connected with the "Aeo" lamp, which, acting through a slit system, illuminates a space (on the film) approximately one one-thousandth of an inch by one-tenth of an inch in width. Put in a different form, the "Aeo" lamp projects to the sound band, through a special lens system and a slit, a ray of light of the dimensions as stated above. The illumination occurs just 14 1/2 inches from the center of the picture aperture, which means that the sound record accompanying any one picture frame is opposite the frame 14 1/2 inches.

As stated before, the current set up by the microphone, which is energized by a 220 volt storage battery, operates the Aeo lamp, affixed to the camera, after being amplified many times at the amplifying panel. The power of the current which operates the Aeo lamp fluctuates exactly with and in exact proportion to every sound picked up by the microphone, with the result that the sound band of the negative film is illuminated in exact proportion to the modulations of sound.

The Aeo lamp used in recording sound is not a filament lamp. It consists of a glass bulb in which are fixed a small metal plate and a loop of platinum wire coated with alkaline earth oxides. This bulb is filled with helium gas. The plate is positive, the loop is negative. When in action they are energized by a battery of about 350 volts, which causes the gas surrounding the plate to glow with a faint pink color, and the gas surrounding the loop becomes very brilliant, being of an extreme blue color. This light source is utilized for illuminating the film through the slit.

The circuit connected through the amplifier panel carries an alternating current, representing in its variations the sound wave frequencies, and is able and does impress those variations upon the Aeo lamp circuit in such a manner that the light brilliancy of the gas surrounding the plate varies in exact proportion or in exact frequency with the sound wave frequencies.

The hard thing for the reader to grasp is the fact that such an action can be set up with such perfection that all of the vast number of sounds can be faithfully impressed upon the film-sound band in photographic form.

Remember, that in the camera sound gate, the film runs continuously and this line of light is shining continuously upon the sound band, but with

SCRIPT TO SCREEN-IV
By H. L. H.
(Continued From Page One)

constantly varying brilliance. Of course; you all know that the amount of discoloration upon any point of a negative film will, after development, be dependent on the brilliancy of the light reaching it during exposure. That is just plain photographic lore. And it then follows, that when the negative film has been developed, the sound band will vary in density constantly and, since the time of exposure is fixed and constant, in exact proportion to the brilliancy of the light to which it has been exposed; in other words: in exact proportion to the brilliance of the Aeo lamp at any instant of time.

In concluding this discussion on sound in synchronization with motion, we will add that while there is a considerable similarity, in a general way, between it and radio, still the fields are wholly separate and their problems for the most part are entirely different.

That this is true you shall readily see as we discuss Sound Reproduction.

When the silent picture projectionist graduated into a sound projectionist, he still had all of the equipment and all the projection problems he had before. Nothing in any way changed with regard to picture projection. But in addition he is now called upon to produce and project sound, a task which involves the thorough knowledge of and careful use of complicated and highly sensitive equipment.

In the past the projectionist has been able to work great harm to the performance of those whose chief claim to "fame" has been to pose effectively, wear a minimum of drapes in public, or to vamp well, without serious protest from anyone. But with sound equipment, when it comes to outraging both the person and the voice of the artists, thus causing them to appear and sound foolish to their audiences, you may rest assured that it will not pass unnoticed or unrebuked.

Incidentally, a number of us make a practice of sharp-shooting for errors in every picture that is handled by our local projectionists, Harr and Morrie. To which we might reply that these boys are doing a splendid job and their work compares favorably with that of professional projectionists in many outside theatres, and we might add that it is superior to that of some theatres. Those of us who do not understand the duties of a projectionist should be slow in our criticism of men who are striving and who are delivering good projection results. Many little things enter into the projection of a picture which at times give us the jitters--but it is not always the operator who is at fault. Our local operators are to be commended for their work.

From any and every angle it is safe to assume that the advent of synchronized sound has resulted in the demand for more careful work in projection. Certainly, it sounds the doom of the "machine operator," because by no stretch of the imagination is it possible to regard synchronized sound projection as being merely the matter of "operating" a machine.

The projectionist of today must be more than a crank grinder. Intensive study and hard work are required of the projectionist who handles the modern equipment which reproduces life-like effects in both picture and sound projection upon the theatre screen. (To be concluded next week.)