US2271980A - Recording of alternating current impulses - Google Patents

Description

F125. 3, 1942. E. w.- KELLOGG i 2,271,980

RECORDING OF ALTERNATING CURRENT IMPULKSES K Filed Nav. s, 1939 @shwrs-sheet 1 Edward Wifellagg Feb.'3, 1.942. E, KELLQGG .2,271,980 l 'RECORDING 0F ALTERNATING CURRENT IMPULSES Fild Nov. 8, 19:59 2 sheets-sheet 2'.

' Imventot Edward Wllla Q vPatented Feb. 3, -1942 ULSES Edward W. Kellogg, Moorestown, N. assignor to Radio Corporation of America, a corporation of Delaware Application November 8, 1939, Serial No. 303,373

5 Claims. (Cl. 179-1003) invention relates to the recording of alternating current impulses such as those of audio frequency, and has for its principal object thev provision of an improved recording apparatus and method of operation for producing a class A `push-pull record having its diierent record f tracks registered in different or complementarycolors. -As is Well known, the recorded impulses are reproduced from such a record through the medium of color filters, prisms or the like.

A class A type of record is one wherein the positive and negative recordareas are so disposed as to simultaneously aiect a pair of pushpull connected photoelectric elements.v The positive and negative half cycle record areas, arranged to simultaneously affect the push-pull photoelectric elements,may be on the same .or different record tracks, the selection of the half cycle record areas being effected geometrically, by color, by carrier frequency, by polarization or by other suitable means. l

Color separation, for example, involves the employment of two reproducing elements, one of which is aected only by light of a certain color, and the other of which is affected only by light of another color. The sound track includes differently stained areas which will respectively absorb light of the two different colors. For example, the reproducing elements may be two photocells with two complementary color filters such as red' and blue in front of the rst and second cells, respectively, and the sound track may be recorded by the application of red and blue dyes or stains, each of which absorbs light; of its complementary color, but comparatively little light of its own color. Thus the photocell having the red filter receives light which is strongly modulated by the presence of blue dye in thesound track but is relatively little alected by the presence of red dye in the sound track.

This invention is related to those disclosed by United States Patent 2,102,695 of Giesking, by

` application Serial No. 196,554 .of Hullegard, and

by application Serial No. 287,324 of Dimmick, all assigned to the same assignee as the present application. As will appear, all of these inventions involve recording indifferent colors the positive and negative half cycles of a sound wave or other alternating impulse. One suitable recording material for this purpose is the multi-color motion picture nlm currently sold under the tradename Kodachrome, but if the only color requirements are for the sound track, a simpler film having only two emulsion layers, instead of three as in the case of Kodachrome, would suilice, 55

and the processing of the two color film would be correspondingly simpler.

The invention will be` better understood from the' following description considered in connection with" the accompanying drawings, and its scope is indicated by the appended claims.

Referring to the drawings: Figure 1 diagrammatically illustrates a device suitable for recording alternating impulses in the form of duplicate record tracks with their corresponding half cycles of Adifferent colors,

Figure 2 illustrates certain details of the device'of Fig. 1,

Figure 3 illustrates the record produced by the device of Fig. 1, Figure 4 illustrates a modification in certain details of the device of Fig. l, and

Figure 5 illustrates fthe record produced by the modified device.

Figure 6 illustrates an alternative method of obtaining ground noise reduction.

Figure 7 illustrates a sound lllm in which the unused areas are black.

The recording device of Fig. 1 includes alight source I0 from which light is projected through a" multi-colored mask II and lens I2 to'a galvanometer mirror I4, which is vibrated in accordance with the electrical impulses transmitted through its operating coil I5. Light is reflected from the mirror I4 through. the lens I3, a light slit I'I and lenses I8 and I9 to a film 20 upon which the impulses are recorded. 'I'he manner in which this recording system works to produce the photographic record of the sound is well understood, being the same as in the case of the recording systems now in commercial use in making variable area records.v

From a light source 2I, light is projected through an apertured mask, a slit 22 and lenses 23 and 24 to the record strip 20, for exposing toA white light the record area not required for modulatingthe light beam of the reproducer.

This is in accordance with the well known principle employed in ground noise reduction systems as applied to variable area photographic sound recording. In order to restrict this exposure to areas not occupied by the -record tracks, a V- shaped shutter 25 is arranged to be moved to and' fro transversely of the slit 22, in response to Variation in ther amplitude or volume of the recorded impulses. To this end, the operating coil A26 of the shutter 25 issupplied with a direct current which varies in accordance with the volume of the recorded impulses. Suitable means for deriving such current are so well known as to require no description here. 'I'he recording device so far described is substantially the same as that employed in the system for making direct positive, recordings described by G. L. Dimmick, copending U. S. application Serial No. 287,324, filed July 29, 1939 (RCV D-6030), except that in the system of Dimmick an opaque mask having a triangular opening, instead of the two complementarily colored filters shown at I I in my Fig. 1.

As shown more clearly in Fig. 2, the recording slit I1 and the shading or noise reduction slit 22 may be formed in the same mask 21; a stationary light beam is projected on the slit 22 from the light source 2|; the shutter 25 is vibrated transversely of the slit 22;v and the multi-colored light beam, or image 29 of the composite filter II, is vibrated transversely of the slit I1.

It will be noted the red and blue filter areas of the mask I I are separated bya diagonal boundary line, that the multi-colored image 29 contains similarly separated blue and red areas, and that the diagonal boundary line between the dif-A ferently colored image areas extends obliquely across the impulse recording slit I1. Vibration of the multi-colored image transversely of the slit I1 therefore causes the boundary between the record areas exposed to the differently colored parts of the beam to Vary transversely of the record in accordance with the impulses to be recorded. As a result of this, assuming that the film on which the record is being made is one wherein exposure to light of a given color results in dyed image of -the same color, there is produced a record which diers from the usual black and White variable area or variable width record only in that'the black and white areas are replaced, respectively, by red and blue areas.

In order to minimize the background noise otherwise incident to the playing of a photographic sound record, it is common practice to blacken the areas of the sound track which lie outside the envelope of the recorded waves. This has no effect on the useful sound as reproduced, provided the boundary of the blackened area has only gradual curvatures, but black film gives rise to much less random ground noise than -an equal area of clear film; hence .as much area is blackened in this manner as is compatible with avoidance of interference with the recording of the Waves. In a sound record of the type involved in this invention, wherein the light for operating two photocells in push connection, is separated by color filters, colorless film is almost as free from noise as black film, on account of the neutralizing action of the push-pull circuit for disturbances which affect both photocells equally. It is therefore almost as effective to make the unused areas clear as to make them black, the ground noise depending principally on the total area of colored film within the area scanned by the reproducing system. The ground noise reduction system employed in connection with a colored sound track system of the type illustrated herein may optionally consist in arrangements for making the unused areas either clear and colorless or black- I have chosen to illustrate the embodiment of my invention wherein the unused areas are clear. If the film on which the sound is recorded is of a type such as Kodachrome, wherein exposure to light of a given color, results in the xing of a dye of the same color, the complementary colored dyes being dissolved out, exposure to white light in suiiicient amount results in clear iilm. Thus the portions of the lm which receive white light exposure through the auxiliary slit 22 of Fig. 1 are clear, and this Iaccomplishes ground noise reduction. The shutter25 is moved transversely of the slit 22 in accordance with the volume of the recorded impulses, thus producing the clear areas indicated on the record illustrated in Fig. 3. This record may be played by any suitable type l of color separation reproducer, such Ias those disclosed by the aforesaid copending Dimmick application.

An alternative method of obtaining ground noise reduction is to @employ a shutter which obscures part of the recording beam, as shown in Fig. 6, in which the plate 21 is provided with only one slit I1 through which the light for recording the sound passes. The lamp 2I and lenses 23-24 are omitted. The filter II is imaged on the plate 21 as a red and blue light spot 29 which vibrates up and down in response to sound vibrations as in the case of the arrangement illustrated in Fig. 1. A shutter vane 33 having a V-shaped notch 34 obstructs the light 29 so that it does not pass through the slit I1, except for a small region near the middle of the slit where the boundary between the red and blue areas intersects the slit. As the modulation increases, the shutter vane is moved downward by a magnet corresponding to that shown at 26 in Fig. 1 and uncovers enough of the slit I1 to accommodate the modulation so that the vibratory movements of the light spot 29 never result in the exposed part of the slit being illuminated entirely with light of one color. At modulation, the shutter vane is completely out of the way and the full length of the slit is illuminated. The resulting sound record, if the film is of the same type already discussed, will be like that shown in Fig. 7, areas to the right and left of the modulation area being black instead of clear as in Fig. 3.

The form of apparatus shown in Figs. 1 and 2 has an advantage over that of Fig. 6 in that the use of an extra slit and light source for effecting the ground noise reduction permits a displacement of the position at which the noise reduction exposure is applied and that at which the sound waves are recorded. When there is a quick increase in the amplitude of the modulation, this displacementgives the shutter vane time to move the requisite amount so that none of the wave outlines are obliterated. In the arrangement of Fig. 6, overmodulation occurs if the shutter fails to move out of the Way fast enough.

If the type of film and method of processing the same do not have to be adapted to producing a colored picture of the usual kind, as, for example, when recording sound only, the apparatus of Fig. l may be used and a method of processing may be followed which will produce a track of the type just described wherein the unused areas are black instead of clear. The type of film represented by Kodachrome is what may be called a color positive in that the exposures makes the film transparent. The making of a colored sound negative, using, for example, the recording systemv illustrated in Fig. 1, would be substantial` ly as follows. Since only two complementary colors are required, a double emulsion lm will suflice.

Next the base would be a red-sensitive emulsion over which would be a thin layer of stained gelatine constituting a yellow-orange or red filter, and the outer layer would be an emulsion sensitive to blue light only. After exposure, the film would be developed without reversal, and

the :developedsilver imagesv in the two layers would` be transformed into colored images by toning or iixing of appropriate dyes. This is a well known photographic process. The under layer 'may be toned red and the outer layer toned blue, or vice versa, since the sound reproduction will be equally satisfactory in either case.v Areas which have not been exposed to light of either [color will come out clear, and areas exposed to? white light or both red and blue light will 'beblack. The color-'deposited inthe two vlayers' may be determined by depending on the vdierence in penetration in successive baths as is done while the records of Figs. 3 and 5 are in lsome respects similar tol those of the aforesaid patent Aand patent application, "they differ therefromv in that they include differentlycolored*areas separated by a common boundary'line which varies transversely of the record in accordance with the recorded. impulses. The outside-or noncommon .boundary lines of these diierently colored areas, of course,y vary in accordance with the volume -of recorded impulses. -Modulation of the reproduced light is thus effected by dii'- fercntly colored areas whichare interlaced. contiguous, mutually exclusive and restricted to the in Kodachrome orby incorporating in each layer, when the film is made, a suitable dye-cou- `pling agent which-will not dissolve outin the developing process, and which will take part in forming the appropriate stain. The last mentioned'process isy employed in a tem of the Agfa Company. y

A sound film in which the unused areas are color film sysblack, las in Fig. 7, has an advantage over one in which they are clear in that low ground noise is less dependent on balance between the two photocells and less impaired by lack o'f saturated colors in the film. A recommended procedure when a number of prints are needed is to use like Fig. 7, and to use this negative to print sound tracks o n the iinal or release prints, the pic-l tures being printed from a separate master color picture lm. The prints would then be processed with reversal development, as in the case of Kodachrome, to give a iinal iilm in whichthe color 'is the same as that of the light to which the print iilm was exposed. This mode of operating will be in accordance with the standard` method of making color picture duplicates on Kodachrome or similar film, while the sound track will have the two-color sound wave record, with the unused areas substantiallyopaque.

The modification of Fig. 4 differs from the preceding modification in that (1) the maskll is replaced by a mask which produces a multi-co1- ored image wherein the boundary line between the differently colored areas is V-shaped f and (2) the 'noise reduction shutter 25 is replaced by a W-shaped or multi-point shutter 3l. y

The record resulting from this modification is shown in Fig. 5. This is readily recognized as a multi-track or bilateral push-pull record which may be played by any suitable push-pull reproducer of the color separation type.

. the apparatus of Fig. 1 to make a sound negative minimum area required for modulation purposes. l5

I claim as my invention: I 1. AAn alternating current impulse record including differently `colored Aareas separated by a common boundary line which variestransversely of the record `in accordance with'the recorded impulses. 2. An alternating current impulse record including diiierently colored areas separated by -a' common boundary line which varies transversely .of the record in accordance with the recordedimpulses, and neutral areas which vary along the non-common boundary lines of said differently colored areas in accordance with the' volume of said impulses. i

3. An alternating current impulse record in cluding dierently-colored areas which are contiguous, mutually exclusive andl separated by a common boundary line of a contour dependent on the waveshape of the recorded impulses.

accordance with said impulses, and means responsive to the volume vof said impulses for restricting the recording eiiect of said differently colored light beams 'to such record area as is required to permit modulation of said impulses.

EDWARD w.

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