US2322435A

US2322435A - Motion picture sound recording and reproducing system

Info

Publication number: US2322435A
Application number: US405239A
Authority: US
Inventors: Iri R Goshaw
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1941-08-02
Filing date: 1941-08-02
Publication date: 1943-06-22
Anticipated expiration: 1960-06-22

Description

June 22, 1943. l. R. GOSHAW MOTION PICTURE SOUND RECORDING AND REPRODUCING SYSTEM Filed Aug. 2, 1941 2 Sheets-Sheet l IE1. R @osHA W Ana/F152 OSCILLA 10,2

OSCILLAYI y R W m e m w v T m A of modulated tracks for various purposes.

Patented June 22, 1943 UNITED STATES PATENT OF Fi-CE MOTION PICTURE SOUND RECORDING AND REPRODUCIN G SYSTEM Irl R. Goshaw, Beverly Hills, Calif., assignor to Radio Corporation of America, a corporation of Delaware Application August 2, 1941, 'Serial No. 405,239

15 Claims.

in this area or areas for controlling the speed of a motor, while U. S. Patent 2,199,599, dated May 7, 1940, to Dawson, discloses a signal amplitude control track in this area. Copending application Serial No. 181,634, filed December 24, 1937, shows a type of control track system similar to Dawson's.

In each of these disclosures, however, the discontinuity of the sound track caused by the sprocket holes has been taken into consideration. For instance, in Patent 1,921,494 only the intermittent or absolute value of the light passin the photoelectric cell during the stationary periods of the film is utilized to operate a solenoid in a mechanical control system. This is perhaps the simplest form of utilization of the sprocket hole areas since the amount of light passing to the cell during the stopping time of the film controls the armature of the solenoid. It is obvious' that such a system will not produce a smoothly varying control current.

In Patent 2,199,599 and the above-mentioned copending application the sprocket holes have been utilized to produce a carrier frequency which is modulated by the varying opaqueness of the areas between the sprocket holes, it being necessary, of course, to pass the modulated carrier through a detector or rectifier before impression upon. an amplitude control element such as a variable gain amplifier in the signal current transmission channel. Such a system requires smoothing filters after detection or rectification. as is well known in the art. Furthermore, Patent 2,199,599 has emphasized the necessity of a filter network between the pickup photoelectric cell and the detector for reducing the wave to an approximately sinusoidal form. Similarly, inthe above-mentioned copending application the modulated carrier current is modified by the use of either selective circuits or a transformer-tuned to the sprocket hole frequency, the selective circuits and transformer being connected between the photoelectric cell and a detector or preamplifier. Furthermore, such systems are limited in the rapidity of their control action to less than 96 cycles per second, the sprocket hole frequency.

The present invention, however, utilizes this sprocket hole region of the film but with the regular sound recording and reproducing elements without the additional filters, networks, detectors or rectifiers mentioned above. In other words, thi sprocket hole area may be, recorded upon and reproduced in exactly the same manner as any solid or uniform sound track area not having discontinuities. Thus, a signal or control current as exactly recorded can be reproduced with a simple amplifying system without the above-mentioned additional elements.

This is accomplished by rotating the recording and reproducing slits at an angle which at all times impresses light on the same amount of recordable film area duringrecording, and upon the same amount of recorded film area during reproduction. That is,ithe invention may be used for film having othertypes of regular discontinuities such as a series of opaque areas, as well as-sprocket holes, it being necessary in every case that the slit see the same amount of recordable or recorded film at any instant. Thus, in the standard type of 35 mm. sound film, the slit will be positioned at an angle of approximately to its normal position 01' 30 to the direction of movement of the film, since the distance between similar points on the sprocket hole area longitudinally of the film is in the neighborhood of .187 inch, and the width of the sprocket hole is .110 inch, the tangent of this angle thereby being substantially 595. When 'while Patcnts 1,917,653 and 1,928,953 show rotated slits for recording normal sound track areas and claim certain advantages therefor. None of these disclosures, however, discloses the utilization of the sprocket hole region of the film as evidenced by the slit angles suggested therein. The principal object of'the invention, therefore, is to facilitate the recording of signals on motion picture film.

' Another object of the invention isto increase the utilization of a motionpicture film for signal recording.

v A further object of flieinvention is to utilize for signal recording a film region having a series of nonrecordable areas therein.

A further object of the invention is to utilize the areas between the sprocket holes of motion picture film without the use of any additional ap aratus other than that required for normal sound recording and reproduction.

A further object of the invention is to utilize the areas between the sprocket holes of motion picture film for one or more control records.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the appended claims, the manner of its organization and the mode of its operaflon will be better understood by referring to the following description read in conjunction with the accompanying drawings forming a part thereof, in which Fig. 1 shows a soimd track of the variable density type recorded in the areas between the sprocket holes of a motion picture film;

Fig.2isa =1 cofasoundrecording system for recording sound in the areas between the sprocket also showing how the system may be utilized for control track recording;

' light reaching the photocell is modulated by the r same amoimt of film at any instant.

Referring now to Fig. 2, a normal recording system is illustrated wherein light from a lamp I2 is collectedv by a lens l3, projected through aperture ll of a mask it past a,penumbra shutter II and through a lens II to amirror II of a galvanometer it. The light is reflected from the signal picked up by a microphone 28 and im- Fig. 3 isa c view of a recording system for a multiplicity of control signals;

Fig. 4 is a ditic arrangement of a reproducing system for a signal record and also showing how the sprocket hole record may be used for controlling the signal record; and

' r Fig.5 is a reproducing system for the recording system of Fig. 3.

Referring now to Fig. 1, this figure is a partial view of the sprocket hole and sound track regions of a sound and motion picture film 5 showing the sprocket holes 8 and the portions or lands 1 between the sprocket holes upon which a variable 1 density control track has been recorded. The regular signal record is shown at 8. To ilius-- tional to. the ratio of the film area between the sprocket holes-to the sprocket hole area. Aside from this reduction, this portion of the film may be treated as any solid film portion, the sprocket holesbeing ignored as far as recording and reproduction are concerned.

To further illustrate, the slit shown at ll extends across one hole and one land. when the film moves along .to a point shown by the dotted slit ll, itwill be observed that the same amounts of hole and land are across the slit but reversed.

pressed on the galvanometer I! through an amplifier 29. Such a recording system will provide a variable density sound track as shown in Fig. 1 when the slit ll, galvanometer mirror II, and silt ll are tilted to an angle of approximately to the direction of motion of the film 2i. cording in accordance with the invention may also be accomplished by leaving the optical recording element in their regular position for normal sound recording and rotating the direction oi film motion substantially 60. Furthermore, other types of light modulators and variable density recording systems may be used, such as lightvalves, glow tubes and the like.

If it is desired to record on this sprocket hole area a comparatively low frequency control track for various purposes such as the amplitude conin location along the slit. As the film is advanced "area at opposite ends of the slit. in positions It and It.

Thus, the recordable film area shifts back and forth across the slit but is always of the same length or value regardless of its position along the slit. In reproduction, thereior the trol of a signal record, it is only necessary to connect the galvanometer I! to a source of potential .30 which may be varied in its impression on the galvanometer by a rheostat II as shown by the dotted lines. The potential may be manually varied or automatically varied in accordance with the type of system employed. An-oscillator whose frequency is varied in accordance with the amount of control desired may also be used.

Referring now to Fig. 4,'there is shown a reproducing system for the simultaneous reproduction of the regular sound track and the sound track in the sprocket hole area. This system utilizes a lamp 3!, a lens 34, a slit mask ll, and

a lens 36 which projects a narrow beam of light transversely through the sound track area to a photoelectric cell 31 in a'manner well known in the art. The cell output is amplified by a standardamplifier 39 and may or may not be impressed upon a variable gain amplifier III before impression on a loudspeaker 2. This is the normal sound reproducing system well known in the art wherein the variable gain amplifier ll may be varied in amplification to control the output amplitude of the sound at 42.

For reproducing the signal track in the sprocket hole area, a similar optical system ineluding a lamp 5, a lens 46, a slit mask 41. and a lens 48 is utilized to project light through the sprocket hole region to a photocell 50. It is to be noted, however, that wherein the slit II 'scanning the regular sound track area is positioned transversely of the film, the slit l2 scanning the snrockethole region is at an angle, as described 'in Fig. l, which is the same as the angle of the slit 23 in Fig. 2. The output of the cell [0 is impressed upon an amplifier El and then to a loudspeaker 52. It is realized that a variable gain be the exact duplicate oi the regular signal channel portion of the system except for the angle of the slit 52. If the sprocket hole film region has been recorded as a control record for the ampli-' tude of the regular sound track signal by manipulation of the rheostat 3| in Fig. 2, it is only necthe control record are limited to control current variations below the frequency of the carrier current and also limited to the number of control currents which may be recorded and reproduced.

The present system is not so limited.

In Fig. 3, a multiple signal film recording system is illustrated wherein the same recording optical elements of Fig. 2 are shown. Since the sprocket hole area'now operates in the same manner as the solid film area,any type of track may be recorded on this portion of the film. Thus, it is possible to record a plurality of carrier frequencies on this area, each carrier being individually modulated for controlling a plurality of functions or characteristics of a signal. This is accomplished by the use of carrier frequency oscillators shown at 55, 55 and 51, each of which has a different frequency. The output of each oscillator may be modulated as diagrammatically shown at 58, 59 and 60, respectively. The modulation may be either by amplitude or frequency, as illustrated by the variable resistances (amplitude modulation) and variable condensers (frequency modulations), the output of each modulator being impressed upon the galvanometer la, the track thus recorded containing each modulated carrier frequency.

Referring now to Fig. in which the reproducing system for the recorder of Fig. 3 is illustrated, the same optical systems as shown in Fig. 4 may impression upon respective loudspeakers 64 and 85. Although this type of signal system is illustrated, it is to be understood that other combinations of controls for the signal output may be employed such as one wherein the control signals simply operate relays for connecting one or more speakers to the output of the variable gain amplifier 40.

Referring now to the control track system, the

output of the amplifier 5| is impressed upon a plurality of filters58, 59 and which are bandpass filters tuned to their respective oscillator frequencies and of. a band width sufiicient to take care of the modulation side bands. The output 01' each filter is impressed upon its respective detector and filter units I2, 13 and 14, these units fier 52 for individually controlling the amplitude of the signal current reproduced at loudspeaker 54. This reproducing system therefore provides a multiple system of control wherein the loudspeaker 84 may represent the center speaker or speakers in a theatre, and the loudspeaker 65 may represent the speakers located at the sides of the stage or along the sides of the listening area toenhance the reproduced sound. By manipulation of the modulator unit 58, .the volume of all speakers may be raised or lowered, while manipulation of modulator 59 may control the center speaker, and manipulation of the modulator 60 may control the side speaker separately from the center speaker.

The above-described recording method and system thus permits not only the recording of normal signals in the areas between the sprocket holes of a motion picture film, but'permits these areas to be used to record control signals without the use of filter networks. It is realized, however, that in case of mutilated film, random 96- cycleimpulses may be generated and although this would be immaterial in a carrier frequency control track system as shown in Fig. 5, it might be desirable to insert a 96-cycle elimination filter in an amplitude modulated system such as shown in Fig. 2, although it is not necessary as the amplitude of these impulses would be comparatively low whenever they occur. modulation of the control current mutilated sprocket holes will cause no deleterious effects.

be employed for scanning the signal and control It will be observed that a variable density track has been illustrated in the above system, but var- 5 iable area tracks may also be recorded and reproduced with, the slit tilted at the same angle, it being desirable in this event to increase the slit width so as to have its dimension lon itudinally of the film comparable to the sprocket hole height and the modulating shutters operating transversely of the slit.

What I claim as my invention is: I

1. A sound recording system for recording signal on a film having a series of discontinuities interposed along a recordable film area comprising means for producing a light beam, means for modulating said beam with a signal to be recorded, and means for impressing the same amount of recordable film area with light re-' gardless of the position of said discontinuitieswith respect to said light beam. v

2. A sound recording system in accordance with claim 1 in which said last-mentioned means includes a slit mask having a slit therein positioned at such an angle with respect to the direction of motion of said film pastsaid slit that the same amount of said recordable film area is including the required smoothing filters well I known in the art. The combination control system illustrated in Fig. 5 utilizes the output of detector 12 for controlling the gain of variable gain amplifier 40 over conductors 16, this control current simultaneously varying the gain in both loudspeakers 54 and 55. The output of detector filter unit 13 is impressed upon a variable gain amplifier 63 over conductors "and individually controls the amplitude 01' loudspeaker- 85. The output of detectorfand filter unit 14 is impressed over conductors 18 upon the variable gain amplibeing light-impressed at any instant.

3. The'method of sound recording on a film area having a series of discontinuities distributed along a recordable film area comprising modulating alight beam and impressing the same amount of recordable film area with said light beam.

4. The method of recording a continuous signal record on a series of recordable film areas separated by non-recordable areas comprising modulating a light beam in accordance with the signal to be recorded and light-impressing the same amount of saidrecordable areas at all times by said light beam.

5. The method of utilizing the areas of a film lying between the sprocket holes for the recording of a signal comprising forming light into a narrow beam, modulating said beam with said signal and impressing said beam on said areas be- With frequency 4 tw'eenssidsprocketholesatanangletothedirectionotmotionofsaidareassothatsaidbeam.

at each instant recording.

11. The method of utilizing a film area having a plurality of discontinuities distributed along a recordable film area comprising continuously lightim constant amounts of said film area and said discontinuities at any instant during said light impression. I

'1. a film sprocket hole area recording system inaccordancewithclaimfiinwhichsaidheam angle is approximately to the direction of motion of standard mm. motion picture film.

8. A sound reproducing system for reproduce ing a signal recorded on the film areas interposed between the sprocket holes comprising a source oi light, means for forming said light into a beam, means for translating said light into electrical currents, means connected to said translating means for amplifying said currents, means connected to said amplifying means for translating said currents into sound waves, and means for interposing the same amount of film area between said light beam and said light-to-current translater during passage of said film through said sys- 9. A sormd reproducing system in accordance with claim 8 in which said last means includes optical means for impressing said light beam at an angle of substantially 30 to the direction of v movement oi. said film.

10. The method of reproducing a signal re-. corded ln.the areas between the sprocket holes of a motion picture film comprising forming light into an elongated beam and impressing said light beam at an angle to the direction of motion of said film so that said beam impresses the same ammmt oi film area during passage of said film past said beam.

12. A multiple signal recording system for recording in the sprocket hole area of a film comprising a plurality of sources of signals of difierent' frequencies, means for individually modulating the signals from each of said sources, means for simultaneously varying a light beam in accordance with said signals, and means for impressing said beam on the sprocket hole areas of said film so that said beam impresses a constant amount of recordable film area.

13. A multiple signal recording system in accordance with claim 12 in which said film has recorded thereon a sound track, said signals bein g adapted to control the reproduced sound from said soimd track.

14. A system for translating signal records of difi'erent frequencies recorded in the sprocket hole area of a film into electrical currents comprising means for scanning said sprocket hole area with a beam of light, means for translating said light into electrical currents, means for dividing said multiple signals into separate electrical circuits in accordance with the frequencies of said signals, and means for interposing the same amount oi film area between said light beam and said translation means during passage of said film past said light beam.

15. A system in accordance with claim 14, in which means are provided for reproducing a sound track on said film simultaneously with the translation of said signal records into electrical currents, and further means are provided for controlling the reproduction of said sound track by said electrical currents.

IRL R. GOSHAW.