US2095318A - Apparatus for and method of recording sound on film - Google Patents

Description

Oct. 12, 1937. G. L. DlMMlCK 2,095,318

APPARATUS FOR AND METHOD OF RECORDI NG SOUND ON FI LM I Filed Nov. 28, 1956 2 Sheets-Sheet l Oct. 12, 1937. s. 1.. DIMMICK 2,095,318

APPARATUS FOR AND METHOD OF RECORDING SOUND ON FILM Filed Nov. 28, 1956 2 Sheets-Sheet 2 Znwentor GMJW I (Ittorneg Patented Oct. 12, 1937 Glenn L. Diinmick, Erlton, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application November 28, 1936, Serial No. 113,128

3 Claims.

This invention relates to a new and improved apparatus for and method of recording sound on film.

The invention' relates particularly to the production of variable density sound records by what is commonly referred to as the penumbra method, and involves the application of that method to the making of push-pullvariable density sound records. In addition to this, it involves the" production of variable density sound records with ground noisereduction and variable density sound records wherein-each half of the sound o' t od f proflucifig variable density push pulljsoundrecords. I

*Another'object of the invention is to provide a novel optical system for-sound recording.

Another object of the invention is toprovide 36 a novel means forreducing ground noise in variable density sound records.

Another object of the invention is to provide a variable density sound record in which ground noise reduction is inherent.

Other and incidental objects of my invention will be apparent to those skilled in the art from a readingof the following specification and aninspection of the accompanying drawings, in

which Figure 1 shows an apparatus for making variable density sound records by the penumbra method, which is somewhat similar to the. apparatus described and claimed in my copending application Serial No. 745,793, filed September 2'7,

Figure 2'shows my improved optical system for making push-pull sound records,

Figure 3 shows the type of sound record produced by. the aperture of Figure 2, V

Figure 4 shows an aperture which may be substituted for the aperture shown in Figure 2, v

Figure 5 shows the illumination on the slit plate which is produced by the aperture of Figure 4,

Figure 6 shows the type of sound record pro: duced by the aperture shown in Figure 4, and

Figure"? shows the double ground noise reduc tion shutter which may be used in conjunction with the aperture in Figure 2.

In the apparatus shown in Fig. 1, the usual exciter lamp is indicated Ill, the light from which passes through a condenser lens II to a rectangular aperture [2. From theaperture the light beam passes the penumbra mask I3 and goes through the convex spherical lens M to the. galvanometer mirror [5. The condenser lens H and the lens it together serve to direct all image of the filament of the exciter lamp Ill onto the galvanometer-mirror I5. I

The positive spherical lens l6, in 'co'operation' with the lens l4, focuses an image of the rectangulart aperture l2 upon the slit plate H. The

mask I3 cuts 01f a portion of the light'at onev side of the beam andtherebycauses the image l2 of the aperture l2 to he graduated inbrig'ht ness from full'intensity at one'edge to practically zero ilfimination at the other edge, as described and claimed in my aforesaid application.

When the mirror [5 is vibrated about an axis more or less parallel to the slit l8 in the plate H, the rectangular image I2 is caused to move across the slit and thereby transmit a greater or less amount of light through the slit. An image of the slit I8 is formed upon the film F by the objective lens l9, which may be of the type of compoundlens usually employed as a microscope. objective, forming'an image I8 on the film.

It will be apparent that when the mirror I5 is actuated in accordance withsound waves, the brightness of the image l8 will changeto correspond, and as the'film is moved longitudinally. a sound record will be produced varying in density in accordance with the sound'waves.

In Fig. 2 the same general arrangement of elements is provided as in Fig. 1, and elements Y which are the same instructure and operation carry the same reference numerals in both fig ures. In this form of the invention, however, a plate 23, having two apertures 24 and 25, is substituted for the penumbra mask I3. Each of these apertures operates in the same manner on its half of the beam as the 'mask I3 operates on the entire beam. One aperture shades the lower half of the beam on its side of the axis and the other aperture shades the upper half of the beam on its side of the axis.

Instead of the lens M, a pair of lenses 26 and 21 are provided, 26 being a positive spherical lens and 21 being a positive cylindrical lens with its axle vertical; These lenses, together with the,

lens II, as in Fig. 1, focus light from the lamp I0 onto the galvanometer mirror 15, and an appropriate image of the mask 23 is focused by the lenses 26, 21, IS on the slit plate I1. However, in this form of the invention it is necessary that the vertical edges of the apertures 24 and 25 be sharply defined, in order to prevent overlapping of the two halves of the sound record, while at the same time the two effective horizontal edges of the apertures 24 and 25 must not be sharply focused, in order that they may produce a uniformly shaded image. The lenses 26, 21 and 16 are, therefore, so chosen as to focal length that a sharp image will be formed on the plate I! of the vertical edges of the apertures 24 and 25.

Due to the fact that the cylindrical lens 21 is efiective in the horizontal plane only, the system will not form a sharp image of the horizontal edges of the apertures, and therefore images 24' and 25' will be produced having sharply defined vertical edges and vertically shading gradually from maximum brightness at the outermost edges to a minimum brightness at theirinner edges. Images of the two portions of. the slit will be formed on the film F by the lens I9, as in Fig. 1, when the mirror I5 is oscillatedabout its axis, and the two shadows will traverse the slit and thereby produce oppositely modulated sound tracks on each side of the median line, as shown in Fig. 3.

If the aperture plate 33, shown in Fig. 4, be substituted for the aperture plate 23 in Fig. 2, then the shadows on the slit plate i I will take on the appearance shown in Fig.5, where the rectangular spots of light are of the minimum brightness at the slit I8 and maximum brightness at their outer edges; It will be apparent from this that when the mirror is actuated, one of these rectangular spots will move away from the slit,

l8, producing no exposure whatever, while the other spot will move across the slit, producing an exposure on its half of the sound track of gradually increasing density.

On the opposite movement of the galvanometer mirror, the reverse will occur, and there will thus be produced a sound track having alternate edges of the sound waves on opposite sides of the median line, with almost no exposure between the halves, as shown in Fig. 6. This type of sound track, where each half sound track operates only during one-half of the cycle, is generally referred to as Class B, as distinguished from the type of sound track before described where equal and opposite impressions occur at all times on each half sound track, which is generally referred to as Class A. It will be apparent that by properly choosing the size and placing of the apertures in the aperture plate, I may produce a sound track which partakes of the characteristics of both the Class A and Class B sound tracks, i. e., at low modulations equal records are produced with the two halves, while at high modulations one-half of the sound track will reach zero exposure before the other half reaches its maximum exposure. This type of track is referred to as Class AB, or as Class A.

In order to produce a Class A sound track with a minimum of ground noise, I may add the shutters shown in Fig. 7 to the aperture 23 in Fig. 2, or may substitute such shutters for that aperture. These shutters 43 and 44 are mounted on appropriately pivoted arms 45 and 46, which are adapted to be actuated by the magnets 41 and 48. These magnets may be connected either in series, as shown, or in parallel, and the shutters may be provided with such guides, stops and springs as may be necessary.- The magnets 41 and 48-are connected to an appropriate ground noise reduction amplifier, such, for example, as shown in McDowell Patent 1,855,197, and are thereby caused to move in opposite directions in accordance with the envelope of the sound waves. Thus at low sound intensities the shutters may overlap each other considerably and produce a minimum exposure on the film, while at the higher sound intensities they gradually withdraw toward the maximum position, in which they are shown, in accordance with the amplitude of the-modulation, thereby producing a sound record having an average exposure corresponding to the amplitude of the sound waves and having this exposure modulated in accordance with the sound waves.

I claim as my invention:

1. Apparatus of the class described comprising meansfor directing a beam of light in'the form of a fine line upon a record film, means for vibrating said beam of light in accordance with modulation to be recorded, a slit in the path of said beam of light between said vibrating means and said film, and opposed masking means in the'path of said beam of light producing opposed penumbras upon said slit, whereby separateportions of said beam-are varied oppositely in brightness by actuation'of said-vibrating means. 7 1

2. Apparatus as'defined in claim 1 wherein the masks areso arranged that only one-half of the said line is illuminated at one time.

3. Apparatus as defined in claim lwherein the masks are movable in accordance with the envelope of the sound waves.

GLENN L. DIMMICK.

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