US2284731A - System for the recording of sound - Google Patents

System for the recording of sound Download PDF

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US2284731A
US2284731A US337191A US33719140A US2284731A US 2284731 A US2284731 A US 2284731A US 337191 A US337191 A US 337191A US 33719140 A US33719140 A US 33719140A US 2284731 A US2284731 A US 2284731A
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light
beams
recording
film
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Irl R Goshaw
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RCA Corp
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RCA Corp
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N9/00Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
    • G01N9/24Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity by observing the transmission of wave or particle radiation through the material

Description

June 2, 1942; l. R. GQSHAW 2,284,731
SYSTEM FOR THE nmconbme 0F scum) V Filed May 25,. 1940 q LIGHT TRANSM/Ssmu &
Patented June 2, 1942 2,284,731 sYs'rnM ron 'rnn nnooimmo OF SOUND Irl R. GoshamBeverly Bills, Calif, assignor to Radio Corporation of America, a corporation,
, of Delaware Application May 25, 1940, Serial No. 337,191
16 Claims.
This invention relates to sound recording systems, and particularly to the recording or sound film records consisting of a plurality of mutually related sound traces. Many types of sound film recording systems are known in the art, such as variable density, variable area, unilateral, bilateral, push-pull class A and push-pull class B, etc.
slit longitudinally disposed with respect to one another so that the apices of the beams 'just touch the slit or the center 01 the slit. In the 1 use of class B systems, an elongated extension is 1 the time that the other beam is effective.
The present invention is directed to a sound recording system for producing a record combining the characteristics of the records produced by certain of these types, such as push-pull class A with class B, wherein the advantages of each type of system are obtained and the disadvantages thereof eliminated.
Since the invention is directly related to the combination of push-pull class A with class B, it
might be well to state that the push-pull class 1 A system of recording on film consists in producing two mutually related tracks, either unilateral or bilateral, or variable density in which the modulations in each trace are 180 out of phase with respect to one another, each trace, however, containing the complete modulations of the signal. The usual method oi. obtaining a push-pull class A track is to project two light beams upon a slit passing light to the film from each beam, and as the light is decreased in one cut in the aperture mask producing the beams to provide a narrow light beam on the film during realized that the construction of the class B recording system necessitates an accurate azimuth adjustment of the slitwith respect to the apices of the lightbeams inorder to insure that both positive and-negative cyclesoi the sound waves are properly impressed upon the film. Also, because of the substantial elimination of one of the .beamsduring the' negative and positive cycles or the signal, greater care must be taken in the exposure and processing of such records. I
The present invention is therefore directed to I the combining of the push-pull class A and class B type of systems to eliminate the difilculty oi slit orientation and adjustment and to provide inherent noise reduction.
Combination push-pull class A and class B systems are known in the art, one such system be- 7 ing disclosed and claimed in copending applicaof said beams, it is equallyincreased in the other,
light always reaching the film from each beam during the entire amplitude range-oi the signal. In the variable area type oi! system the position of the tapered light beams at times of no signal is midway between the vibration limits of the beams, and considerable light is therefore impressed upon the film. This condition requires the introduction of noise reduction to class A recording in order to produce a quiet film during times of no signal, noise reduction generally consisting in the blocking oi! of an amount of light dependent upon the amplitude of modulation oi the light beam. However, the orientation or azimuth adjustment '0! the slit with respect to the light beams and the film is not critical with this arrangement, nor is any substantial difiiculty encountered with process distortion since the light from each beam is on the, film at all times.
Referring now to the class B type oirecording,
. which has the great advantage of having inherent noise reduction, this system employs two, light beams similar to the push-pull class A system, exceptthat at times of no signal, substantially no light reaches the film. In variable area class B recording, tapered light beams are positioned at times of no signal on each side of the tion of C. H. Cartwright, Serial No. 168,565, filed October 12, 1937. This disclosure points out that a certain definite relationship must exist when going from the class A type of recording to the combination type, this fundamental and basic relationship being that each beam must be made twice as effective when the other beam is eliminated; or, in other words, that the light transmission reaching the cell must double in effectiveness at the point of changeover. This fundamental relationship is, of course, retained in the present invention, while securing all the boneficial features of push-pull class A recording and of class B recording.
The principal object of this invention, there-- fore, is to facilitate the recording of sound on film.
Another object of the invention is to combine push-pull class A and class B recording systems i to eliminate the disadvantages of each and to secure the essential advantages of both.
A Iurther object of the invention is to produce a sound track, the low levels of which are recorded as class A, and the upper amplitude levels of which arev recorded as a combination of class A and class B. j
A further object of the invention is to produce a soundtrack, the low levels of which are recorded as pure class A at one value of light intensity,
It'is and the upper amplitude levels of which .are recorded as a combination of class A and class B at a difierent light intensity or as a combination 01' a plurality of light intensities.
A further object of the invention is to produce a combination class A and class B sound track having both variable area and variable density components.
Although the novel features which are believed to be characteristic of this invention are pointed out with particularity in the claims appended herewith, the manner of its organization and the mode of its operation will be better understood by referring to the following description read in conjunction with the accompanying drawing forming a part thereof, in which Figure 1 is a diagrammatic view of a sound recording system embodying the invention;
Figure 2 is an enlarged detailed view of the slit Referring now to Fig. 1, a light source illustrated by a filament 5 produces light which is collected by a lens 6 and projected on an aperture mask 1 having apertures 8 and 9 therein. The light passing the apertures is projected by a lens ll upon a mirror of a galvanometer I2. light is then reflected to a slit mask it having a slit l5 therein, the light'beams passing-the apertures 8 and 9 being shown at l! and ill on the mask. The light from the beams passing the slit I5 is projected by lenses l9 upon the sound track portion 2| of a film 22 advanced in any well known manner.
In the above mentioned copending application,
'the shape of the apertures 8 and 9 was such that the width of the light beams reaching the film increased twice as rapidly for amplitudes of the signal above a certain level, which level represented the cross-over between pure class A recording and combination class A and class B. The present invention permits the'use of normal triangular-shaped apertures normally used in push-pull class A wherein they are overlapped so that the apex of one triangle lies in the same horizontal plane as the base of the other triangle. In class B systems the same shaped equilateral triangles are employed, except that the apices of each lie in the same horizontal plane, and the apices of the light beams lie at the center of the slit. In the present invention the equilateral apertures are overlapped, the amount of overlapping representing the proportion of class A track signal. However, it will be noted that a certain portion of eachtriangle adjacent the apioes is v shaded, this shading representing a lesser light intensity at these portions caused by the introduction, in the apertures 8' and 9 of mask I, 01' neutral light filters II and I3. The position The of the light beams l1 and I8 on mask ll is shown for a no signal condition, and it will be noted that the light passing through the film is represented by the width of the beam impressed on the slit 15. As the light beams vibrate normally to the slit and an amplitude of vibration is reached which is greater than the distance between the slit to the edge of the filter shadows and 26, the full intensity of the light beams will be impressed upon the film 22.- In other words, when one of the shadows 25 or 26 is eliminated from reaching the film except for the tail sections 28 and 29, the light intensity of the other beam reaching the film increases.
To conform to the fundamental relationship required to produce a direct proportionality between input and reproduced output, it is necessary that the light intensity be increased in an amount such that the final print will produce a decrease in light reaching the reproducing photocell. Thus, the processing of the negative and positive should provide the print with twice the light transmission in the class A region of the track than for the pure class B region. Thus, the density of the class A modulations of the final print will not approach opaqueness, but will lie substantially midway between transmission and zero transmission. A certain amount of noise reduction will, of course, be represented by this opacity of the film at times of no signal but this opacity is insumcient for the amount of noise reduction desired in modern sound track recording. Furthermore, a gray opacity introduces noise because of its graininess, thus producing a certain hiss. Thus, it is preferable to provide the trace of the class A region with a greater opacity. Of course, the use offine grained film will reduce the grain noise to a minimum.
Referring now to Fig. 3, a variation in the apertures has been shown wherein the class sections 3! and 32 of the light beams are shown considerably darker to represent lower light transmission filters. Thus, for the class A portion of the recording, a very high degree of noise reduction is introduced, this noise reduction being that of the order obtained in normal variable density recording systems. However, it is necessary, in the modification shown in Fig. 3, to retain the fundamental relationship at the points of cross-over between pure class A and combination A and B. To obtain this relationship, there have been inserted in the remaining portions of the apertures 8 and 9 gray filters having a transmission similar to those used in Fig. 2, asshown by the gray regions 33 and 34. However, this carrier film density introduces undesired ground noise.
To overcome all difliculties, however, the modification of the aperture mask shown in Fig, 4 is employed, this figure showing the light mask l4 and slit IS with the light beams shown thereon at -times of no signal. Itwill be noted that the light beams are identical in symmetry and in construction and have the same relative position as those of Figs. 2 and 3. In this modification, the filters used in the pure class A section represented in the beams at 35 and 36 have the density of those of- Fig. 3 to produce a high degree of noise reduction in the pure class A region. However, the remaining portions of the light beams are at full intensity as shown at 3'! and 38, these portions of the aperture not having any filters. This change in light intensity between the beam portions 35 and 36 and the beam portions 31 and the pure class A portion of the traces.
. 2,284,781 38 does not conform to the fundamental relaadvantages of class A and the advantages of class.
B are obtained.
To further explain the operation of this type of recording system, reference :is made to Fig. 5, wherein galvanometer deflection is plotted against light transmission through the final sound record. With the type of filter shown in Figs. 3 and 4 for the classA region, the light reaching the film at times of no signal maybe represented i at slightly above zero light transmission. Then,
over. the class A portion, a linear relationship ex-,
, ists between galvanometer deflection and light transmission, since these portions of the. apertures have straight lines. However, at the point of cross-over, as represented by the point e, the
light transmission will increase tothe point I, at
which point the light transmission will vary along a straight line for further galvanometer' deflection. The class A section is represented by the distance x, the remaining abscissa being combination class A and class B. To conform to the fundamental cross-over relationship, the
distance 'a must be equal to the distance I). If a larger class A portion is desired, such as repreborhood of 5 or 6 used for variable area films. Thus, the filters will produce the proper density on the final print with the normal variable processing. It is to be understood that other shapes of apertures may be so related to the filter densities as to produce other variations such as compression or expansion. Furthermore, the separation between sections and 36 and sections 31 and 38 may he graduated in density, the change in dimensions of the beams being similarly graduated by curving the sides of the apertures at the point where they change in slope.
- What I claim as my invention is:
1. A sound recording system comprising means for obtaining a, plurality of light beams, and
means for varying the light values of said beams in accordance with a signal, said light beams having a certain intensity and varying in dimensions as a class A recording for amplitudes of saidsignal within a. certain amplitude range of said signal, and varying similarly in dimensions as a combination class A and class B recording for another amplitude range of said signal, said. beams having a different intensity when varying as a combination class A and class B recording, the variations in said light beams corresponding to the amplitudes of said signal at all amplitudes thereof.
2. A sound recording system comprisin a pinrality of light beams, means for vibrating said beam in accordance with a'signal to be recorded,
' and a film upon which said light beams are impressed, said light. beams having sizes, shapes and one variation in intensity to produce a class A record'on said film, and other sizes, shapes and another variation in intensity to produce a comsented by the distancey, it may be obtained by making the distance 0 and the distance d equal to one another, and a light transmission curve, such as shown bythe dQt-and-dash line, is ob tained. Another curve is shown by the dotted line showing a case where the light transmission is higher for the class A portions, such as might be obtained with filters giving an intensity as shown at 25 and 26 in Fig. 2. 1
The form of negative track producible with this type of combination class A and class B system is shown in Fig. 6, wherein the gray portions 40 and ll represent the no signal condition, while the modulations 42 and 43 represent the pure class A section, which, of course, will have the same density as the sections 40 and II. For higher levelsof cross-over, the wider the traces shown at 40 and 4|. At higher amplitudes represented by themodulations H and 45, two density components are found, the higher amplitudes being, completely opaque, while the intermediate sections have a density corresponding to that of The print of this negative of course, will have reversed densities, the entire unmodulated areas being completely opaque, the areas 40 and 43 having a very low light transmission, and the peak areas oi modulations M and 45 havingsubstantially bination class A and class B sound record on said film, said variations being proportional to the respective amplitudes of said signal.
3. In combination, a source of light, means for accordance with a signal, and afilm upon whichthe emergent light beams from said slit are projected, said light beams having sizes, shapes and variations in intensity such that for amplitudes, of vibration up to a predetermined point, said emergent beams produce a push-pull class A track of one density upon said film, and for amplitudes of vibration above .said predetermined point, said emergent light beams produce a combination class A- class B track having a plurality of densities upon said film, the variations in said light beams corresponding in a linear manner to all the amplitudes of said signal. I
4. In a sound recording system, means for producing a plurality'of light beams, means for projecting said beams uponan elongated slit, a film having a motion transversely of said slit, and means for vibrating said light beams in the direction of movement of said film, said light beams having a shape and variation in intensity and so positioned with respect to said slit that parallel beams of one intensity are projected sibeing proportional at all times to a signal being recorded.
5. In a sound recording system, a sourceof light, a mask for producing spatially disposed light beams, and a mask having an elongated slit therein upon which said beams are projected, said first mentioned mask having spatially disabove acertain level as combination class A and class B, all 01' said amplitudes corresponding to g the respective amplitude of a recorded signal.
posed apertures therein with overlapping portions with respect to different portions of said slit, said overlapping portions containing a filter for decreasing the light intensity of certain respective portions of said beams.
6. A light defining mask having a pair of substantially triangular-shaped apertures therein horizontally disposed with respect to one another, and oppositely opposed vertically, the width of said apertures in a vertical direction increasing in a predetermined proportion over a certain length and varying in a different proportion over the remainder of their length, one portion of each aperture containing a neutral light filter.
7. A light defining mask in accordance with claim 6 in which the change in width of the remaining length of said apertures varies in accordance with the density value of said filters.
8. A film sound track having two substantially parallel continuous traces of a certain density extending longitudinally of the film for signal amplitudes below a certain predetermined amplitude level, and having two substantially parallel discontinuous traces of difierent densities for amplitudes above said certain predetermined level.
9. A push-pull film sound track having traces, each trace containing continuous modulations of one density for amplitudes below a predetermined level, and each trace containing discontinuous modulations of a plurality of densities for amplitudes above said level, all of said modtudes above said point, all or said modulations corresponding to the respective amplitudes of the recorded signal.
11. In a sound recording system, the method of recording a sound track which comprises recording at a definite lightintensity amplitudes below a certain level as class A, and recording at a plurality of light intensities amplitudes 12. In a sound recording system, the method of producing a combination class A and class B sound record comprising recording at one light intensity signals below a certain predetermined level as pure class A signals, and recording at said one light intensity and another light intensity all amplitudes of said signals above said certainlevel as combination class A and class 3, all recorded amplitudes corresponding in a linear manner to all amplitudes of said signals.
13. In a sound recording system, the method of recording a sound track which comprises recording amplitudes within a certain range at one light intensity, and amplitudes within another range as a combination of said one light intensity and another light intensity, all of said amplitudes'corresponding to the respective amplitudes of a recorded signal.
14. In a push-pull sound recording system, the
. method of recording a combination class A and class B sound track comprising simultaneously varying the lengths of spatially disposed light beams such that the decrease in length of one beam is proportional to the increase in length of the other of said beams for signals up to a predetermined amplitude, said beams having a certain predetermined light intensity, and for signals above said predetermined amplitude, said light beams having a diiferent intensity, the variations in the length of each of said beams being at a rate in accordance with the difference in the intensities 01' said beams.
15. A push-pull variable area sound recording system in accordance with claim 14 in which the variations in the length of said light beams for a signal having amplitudes above said predetermined amplitude occurs at mutually exclusive time intervals.
16. A sound track having a plurality of traces,
at least one of which has a constant density and contains the complete variations of a recorded signal for amplitudes below a predetermined amplitude value, said trace havinga plurality of densities and containing only a portion of the variations of said recorded signal for amplitudes above said predetermined amplitude value, the remaining portion of said variations of said recorded signal within the amplitude range above said predetermined amplitude value being contained in said other trace or traces and having a plurality of densities.
' IRL R. GOSHAW.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2519194A (en) * 1946-06-03 1950-08-15 Maurer Inc J A Method of and means for recording electrical impulses and impulse record produced thereby

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2519194A (en) * 1946-06-03 1950-08-15 Maurer Inc J A Method of and means for recording electrical impulses and impulse record produced thereby

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