US2591045A - Sound recording system - Google Patents

Description

April 1, 1952 L. B. BROWDER 2,591,045

SOUND RECORDING )SYSTEM Filed Dec. 3d, 1948 lNVEA/TOR L, B; BROWDEH 6V4. n bc A TORNEY Patented Apr. 1, 1952 SOUNDRECORDING. SYSTEM Lewis B.'Browder, La Canada; ;G'alif.,- assignor to Western Electric Company, Incorporated, New York, N; Y., a corporation of New York ApplicationDecember 3Q, 1948', Serial No. 68,230

13 Claims.

-This invention relates to film sound recording systems and particularly to the recording of original or' direct positive variable area sound records with a light valve.

Inknown light valves, light is transmitted between the light valve ribbons onto a light-sensitive-film. When the film is developed the negative or originalsound track develops out into a black variable area record, the rest of the track being clear. :When the negative is printed, the soundtrack develops out into clear film, the rest of the track being dark. This print is called the positive.

The object of this invention is to produce an original or direct positive variable area sound recordwitha-light valve.

. Due-.to inhomogenities in the film, a certain amount of ground noise is produced during the reproduction of the positive sound record. If, however, the positive record is at all times as dark as possible, this. undesired noise will be reduced to a minimum. To produce this result,

[noise reduction bias is applied to the ribbons of conventional light valves in a well-known manner as shown, for example, in Patent 1,936,176 to R. R. Scoville, issued November 21, 1933. To obtain a positive record by the use of known light valves two developing operations and ajprinting operation are necessary.

. As produced with the presentinvention the original sound track is similar to the positive obtained with conventional light valves, thus producing an. original record with a minimum of ground noise.

In accordance with a preferred embodiment of this invention, highly polished, light-reflecting (o1. ire-100.3)

, 2 monitored by a photoelectric cell or other'suitable means with the advantage that the amount of light available is considerably greater than that obtained from a reflecting prism in the recording optical path.

With the application of noise reduction bias to the ribbons, the aperture between the ribbons is'made smaller and the percentage of clear area in the developed track becomes less and the ground noise in the reproduced film is correspondingly reduced. An original sound record exposed in this manner has the appearance of a positive, since in the present invention the area of the sound track which normally receives no exposure is exposed.

Although current-carrying light-reflecting wires have been previously used in oscillographs and'picture transmission devices, these wire conductors are not practicable in a light valve modulator for film sound recording systems. Mirror oscillographs which may be ,used to produce.

original or positive variable area records are also ribbons are used to intercept a recording light beam projected onto the ribbons and reflect back that portion of the light intercepted by the ribbons onto a moving light-sensitive film. There is thus formed by the polished ribbon surfaces image which the ribbons intercept.

a mirrored image of that portion of the filament Since the ribbons move laterally across the recording beam in response to electrical currents, the position of the 'reflected beam is constantly changing. The

reflected light is of uniform intensity but varies stantaneous displacement of the light valve rib- Q;

bons;

The light beam is also transmitted through'ir; the aperture between the light valve ribbons and iszmodulated by the ribbons in accordance with.

thereon. The transmitted modulated lighti's';

theglvariations in electrical currents impressed producesja variable area sound track in a new and efficient manner with attendant advantages which will be apparent from the description of a preferred embodiment shown diagrammatically on the drawing.

, In the drawing, light from the recording lamp l is directed off the aluminized front surface of the inclined slit mirror 2 into an objective lens 3. The inclined mirror by which the lightfrom the recording lamp is directed into the light valve objective lens contains a narrow rectangular. slit extending across its width. The width of this slit together with the reduction afforded by the objective cylinder lens determines the height of the recording image. The recording lamp isof the prefocussed type having a single helix, straight, horizontal filament. The axis of the filament is rotated at 45 degrees to the optical axis which has the effect of reducing the pitch of the filament helix to 'the point where there rents flowing lengthwise through the ribbons will,

cause them to move laterally in a common plane. The light valve of the present invention differs from that disclosed in the Wente patent by having the holes in the magnet pole-pieces pierced large enough to permit the light valve ribbons to be completely illuminated during their complete excursions when fully modulated by sound currents.

The ribbons may be connected to record either a. bilateral or a unilateral type of variable area sound track. For a bilateral sound track, the ribbons may be connected by wires 1 and to the recording circuit of a sound recording system as shown, for example, in the R, R. Scoville patent mentioned above. If desired, one of the ribbons may be connected to move in response to noise reduction currents while the other moves in response to speech currents. Obviously, in

cases where it is desirable, electrical currents may be applied to only one of the ribbons while the other ribbon or any suitable reflector may be used as a stationary reflectorto cooperate with the vibrating ribbon to produce a positive unilateral variable area sound track.

The ribbons may be made of polished and aluminized Phosphor bronze, beryllium copper, or any other suitable highly reflecting material. Extremely good results were obtained by using aluminum foil. It has been found that optical polishing of the rolled foil leaves occasional scratches which, since the ribbon surface is imaged on the film, appear as clear streaks in the sound track. Highly satisfactory results have been obtained by careful maintenance of the rolls with which the foil is worked. Excellent foil surfaces have thus been obtained having a very high reflectance. The width of the ribbons is considerably larger than the thickness. The thin, flat ribbons appear as a thin strip mirror whose surface is perpendicular to both the optical axis and the axis of the recording beam.

Thewidth of each ribbon strip is defined by the accurately space'd edges of the ribbon and is considerably less in extent than half of the width of the recording beam. The recording beam is sufliciently wide to completely cover the outer edges of the ribbons in their outermost positions when fully modulated by sound currents. There is thus formed by the polished ribbon surfaces a mirrored image of that portion of the recording beam which the ribbons intercept.

Since the ribbons move laterally across the recording beam in response to modulation currents, they reflect moving beams of light back toward the light valve objective lens 3. The light valve objective lens then picks up the reflected images and projects them through the slit in the inclined mirror. The light passes through the slit to a front surface aluminized mirror 9 whose function is to turn the recording beam through 90 degrees to a horizontal axis. A cylindrical lens ll located near the film gathers the beam of light from the slit and converges it to the narrow line required for the recording image and focusses it onto the film 8. The film 8 is moved at constant speed by the usual film drive (not shown).

A slit mask 16 is located at the cylindrical lens II to limit the extent of the exposed portion of the direct positive sound track so that the excursions of the outer edges of the ribbons are not recorded on the track. If the outer edges were recorded onthe film the varying outside. edges would introduce additional signal currents during reproduction and thus impair the fidelity of the reproduction A sound. track produced in accordance with this invention is suitable for reproduction in a standard film sound reproducing machine.

The modulated light also passes through the aperture between the ribbons upward through a slit in a mask [2. This mask is provided to prevent any stray light which may pass around the outer edges of the ribbons from reaching the condenser lens I3. The lens 13 focusses the modulated light onto a prism in alight conducting rod I4. The function of the prism is to turn the recording beam through degrees to a horizontal axis and direct the modulated light onto a suitable monitoring photoelectric cell l5. However, it is obvious that it is not necessary that the modulated beam be turned 90 degrees, for the modulated beam may be projected directly onto the photoelectric cell.

Recording of a negative variable area record is accomplished with the same light valve by interchanging the recording lamp and the photoelectric cell. With the recording lamp in position along the optical center line of the light valve, the beam is deflected downward by the prism in the light conducting rod to the condenser lens l3. An image of the lamp filament is focussed by the condenser lens slightly beyond the ribbon plane in order to further minimize the effect of the filament striations. The rear-illuminated aperture between the ribbons is then projected by the light valve objective lens through the slit and to the film. As in the direct positive set-up, the cylinder lens focusses the slit onto the film emulsion to define the height of the recording image.

Light for photocell monitoring in the recording of negative variable area sound records is obtained from the excess of the light over that passing through the slit of the inclined mirror and is directed to the photocell which has been placed in line with the reflecting surface of the mirror along a horizontal axis.

Thus, by interchanging the positions of the exciting lamp and monitoring photoelectric cell, either standard negative or direct positive recording may be accomplished.

What is claimed is: 1. In a sound recording system, a moving lightsensitive film, a source of light, a pair of spaced light reflecting current-carrying ribbons disposed in the light beam from said light source, means disposed between said light source and said ribbons for imaging the reflecting surface of said ribbons at said film and means for vibrating said ribbons to produce a record on said film.

2. In a sound recording system a moving lightsensitive film, a source of light, a pair of spaced light reflecting current-carrying ribbon conductors, means for directing said light onto said ribbons, means for vibrating said ribbons'transversely of said film, said ribbons in turn reflecting said light onto said film to produce a direct positive variable area record thereon.

3. In a film sound recording system, a moving light-sensitive film, a source of light, a pair of spaced current-carrying reflecting ribbons, a mirror having an aperture therein, said mirror being arranged to direct said light onto said ribbons, said ribbons in turn reflecting said light through the aperture of the mirror onto the lightspaced current-carrying reflecting ribbons, a mirror having an aperture therein, said mirror being arranged to reflect said light, means for focussing said light onto said ribbons, said ribbons in turn reflecting said light and redirecting it to said focussing means to project said light through the aperture of the mirror onto the light-sensitive film to produce a direct positive variable area record on said film in accordance with electrical currents impressed upon said ribbons.

5. In a film sound recording system, a source of sound modulated currents, means producing a beam of light, a pair of spaced light reflecting ribbons disposed in said light beam, a moving light sensitive film disposed in the path of light reflected from said ribbons, said ribbons being electrically connected to said source of currents and movable transversely of said film in response to variations in said currents to produce a direct 1 positive variable area sound record on said film.

6. In a film sound recording system, means producing a beam of light, a light reflecting ribbon, a source of sound modulated currents electrically connected to said ribbon to produce movement thereof in response to variations in said currents, a moving light sensitive film, a centrally apertured light deflecting means positioned in said light beam to deflect said beam toward said reflecting ribbon, and a single optical means positioned between said deflecting means and said ribbon for imaging said light beam at said ribbon and for imaging said ribbon at the plane of said film through the aperture in said light deflecting means.

7. In a system for photographically recording a direct positive unilateral variable area sound track, a source of sound modulated currents, means producing a beam of light, a pair of spaced light reflecting ribbons disposed in said light beam, a moving light sensitive film disposed in the path of light reflected from said ribbons, said source of currents being electrically connected to one of said pair of ribbons to produce movement thereof toward and away from the other of said pair of ribbons in response to variations in said current source.

8. In a sound recording system, a moving lightsensitive film, a source of light, a pair of spaced light reflecting current-carrying ribbons disposed in the light beam from said light source, means disposed between said light source and said ribbons for imaging the reflecting surface of said ribbons at said v film, means for vibrating said ribbons to produce a record on said film, and means disposed on the opposite side of said ribbons from said imaging means for monitoring that portion of the light beam which passes through the space between the ribbons.

9. In a sound recording system a moving lightsensitive film, a source of light, a pair of spaced light reflecting current-carrying ribbon conductors, means for directing said light onto said ribbons, means for vibrating said ribbons transversely of said film, said ribbons in turn reflecting said light onto said film to produce a direct positive variable area record thereon, and means disposed on the opposite side of said ribbons from said film for monitoring that portion of the light beam which passes through the space between the ribbons.

10. In a film recording system, a moving lightsensitive film, a source of light, a pair of spaced current-carrying reflecting ribbons, a mirror having an aperture therein, said mirror being arranged to direct said light onto said ribbons, said ribbons in turn reflecting said light through the aperture of the mirror onto the light-sensitive film to produce a direct positive variable area record on said film in accordance with electrical currents impressed upon said ribbons, and means for monitoring that portion of the light beam which passes through the space between the ribbons.

11. In a film recording system, a moving lightsensitive film, a source of light, a pair of spaced current-carrying reflecting ribbons, a mirror having an aperture therein, said mirror being arranged to reflect light, means for focussing said light onto said ribbons, said ribbons in turn refiecting said light and redirecting it to said focussing means to project said light through the aperture of the mirror onto the light-sensitive film to produce a direct positive variable area record on said film in accordance with electrical currents impressed upon said ribbons, and means for monitoring that portion of the light beam which passes through the space between said ribbons.

12. In a film sound recording system, a source of sound modulated currents, means producing a beam of light, a pair of spaced light reflecting ribbons, disposed in said light beam, a moving lightsensitive film disposed in the path of light refiected from said ribbons, said ribbons being electrically connected to said source of currents and movable transversely of said film in response to variations in said currents to produce a direct positive variable area sound record on said film, and means disposed beyond said spaced ribbons in the path of the light beam which passes therebetween for monitoring the sound being recorded on said film.

13. In a system for photographically recording a direct positive unilateral variable area sound track, a source of sound modulated currents, means producing a beam of light, a pair of spaced light reflecting ribbons disposed in said light beam, a moving light-sensitive film disposed in the path of light reflected from said ribbons, said source of currents being electrically connected to one of said pair of ribbons to produce movement thereof toward and away from the other of said pair of ribbons in response to variations in said current source, and a photoelectric cell disposed in the path of said light beam passing between said ribbons whereby the sound being recorded on said film may be monitored during recording.

LEWIS B. BROWDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS \Number Name Date 1,638,555 Wente Aug. 9, 1927 1,847,636 Taylor Mar. 1, 1932 2,101,940 Hansen Dec. 14, 1937 2,108,815 Gille Feb. 25, 1938 2,147,623 Wender Feb. 14, 1939 2,289,054 Dimmick July 7, 1942 FOREIGN PATENTS Number Country Date 370,422 Great Britain Apr. 6, 1932 498,394 Great Britain Jan. 6, 1932

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