US2102777A - Photophonographic apparatus - Google Patents

Description

Dec.`21, 1937. J, O, BAKER ET AL PHoToPx-IONOGRAPHIC APPARATUS Filed May 29, 1956 2 Sheets-Sheet l (Ittomeg Dec. 21, 1937. .1. o. BAKER ET AL 2,102,777

PHOTOPHONOGRAPHI C APPARATUS Filed May 29, 1936 2 Sheets-Sheet 2 Bnventors Patented Dec. 21, 1937 UNITED STATES PHOTPHONOGRAPHI APPARATUS Judd 0. Baker, Westmont, and Cecil N. Batsel,

Haddonlield, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application May 29, 1936, Serial No. 82,596

7 Claims.

The present invention relates to sound recording apparatus, and more particularly to sound recording apparatus of the type adapted to record sound photographically upon film.

The recording of sound on film by what is known as the variable area method has been known for a number of years and is described, for example, in Fritts Patent No. 1,203,190. In the reproduction of the earlier variable area and 'variable density sound records, there is present what is known as ground noise, due to imperfections in the lm and to noise produced in the photo-cell. In these earlier records the volume of this noise was constant, as the average light transmission was constant, and accordingly, it was very objectionable at low sound volumes. It was accordingly proposed, as, for example, in

Robinson Patent No. 1,854,159, to reduce the transparent area of the positive lm at low sound amplitudes, thereby decreasing the ground noise as the volume of sound was decreased, and correspondingly improving the quality of the sound at low amplitudes.

It was proposed in McDowell Patent No. 1,855,-

197 to use a shutter in the sound recorder to cover, and thereby render transparent, the unused portion of the sound negative, which in turn rendered the corresponding portion of the positive film opaque, in order to reduce ground noise.

Our invention is an improvement on the said McDowell apparatus.

One object of our invention is to provide a sound record which is symmetrically arranged in relation to the sound track area.

Another object of our invention is to provide an improved ground noise reduction shutter.

Another object of our invention is to provide an attachment for conventional recording apparatus which will serve to convert it to produce our improved record.

Other and incidental objects of our invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawings, in

which:

Fig. 1 is a schematic representation of a sound recording apparatus built in accordance with our invention,

Fig. 2 is a horizontal section through our improved optical system and shutter arrangement,

Fig. 3 is a vertical section thereof,

Fig. 4 is an end view looking from the right hand side of Figs. 2 and 3,

Fig. 5 shows details of the construction,

Fig. 6 shows a positive print of the improved sound record produced by our apparatus,

Fig. y'7 is an enlarged view showing the relation of one form of the ground noise reduction shutters to the recording aperture, and

Fig. 8 is a schematic diagram of a second form of the shutters.

Referring rst to Fig. 1, the sound recording microphone is indicated at l and the microphone amplifier at 2. From this microphone amplier a portion of the current is fed to the main recording amplifier 3, which in turn actuates the gal- Vanometer 4, thereby causing the galvanometer mirror 5 to oscillate about a horizontal axis.

A portion of the output from the amplifier 2 is fed to the ground noise reduction amplifier 6, which may be constructed in accordance with the said McDowell patent. This amplier 6 amplifies the current fed to it, then rectiiies the amplied current and passes the rectified current through a low pass filter, thus providing a varia-- ble direct current output, the instantaneous Value of which corresponds tothe average value of the sound input to the galvanometer. Such a current is commonly termed an envelope current, as it corresponds to the envelope of the sound waves.

In the recorder, light from an exciter lamp I is passed through a condenser lens 8 and an aperture 9 to the lenses l0 and I I. These lenses I0 and Il concentrate the light on the galvanometer mirror 5 and also serve to focus an image of the aperture I2 in the plate 9 on the slit plate I3. This slit plate is provided with a narrow slit I4 which serves to select the desired portion of the image I2', which is then focused on the film I5 by the lenses I6 and I'I. As shown in the drawings, the aperture I2 is in the form of an elongated rectangle with two triangular extensions on one side and a smaller rectangular extension on the other side. When this aperture is imaged on the plate I3, as indicated at I2', the triangular portions fall on the slit I4 and produce two areas of illumination of the slit. When the galvanometer mirror 5 is oscillated about a horizontal axis, these triangular areas move up and down across the slit I4, thereby causing the slit to intercept portions thereof of different lengths and correspondingly producing two separated sound records, each corresponding to the sound being recorded. Light from the rectangular extension in the aperture I2 is deected by the prism I B and is again reiiected by the prism I9 onto the screen 20, where the movement of this portion of the spot of light permits the operator of the apparatus to see the manner in which the4 galvanometer is operated.

Current from the ground noise reduction amplifier 5 is passed to a magnetic means 2l, which may be of any desired type, where it is caused to deflect a movable member 22 in accordance with the amplitude of the envelope current. As the member 22 is deflected it pulls upon a flexible resilient member 23, thereby causing the shutters 24 and 25 to move about the pivots 26 and 2 against the tension of the spring 28. It will be apparent that the ampliiier unit 5 may be so connected as to cause an increase in the envelope current when there is a decrease in the output of the amplifier 2, thereby causing the shutters 24 and 25 to be moved toward each other and masking off a corresponding portion of the aperture i2. Alternatively, the shutters 24 and 25 may be mechanically adjusted to remain in their most nearly closed position, and when there is an increase in output from the microphone l, the output from the amplifier and rectiiier 5 would then be so connected as to cause the shutters to lbe opened by the increasing current.

We prefer, however, to have the shutters mechanically adjusted, so that when their circuit is open they are in the position shown in Fig. l; to adjust the amplifier and rectier 6 so that, when the circuit is closed, the shutters 2li andY 25 are pulled to their closed position when there is no input; and when modulation is applied to the amplifier 2, and the rectiiying amplifier t, to cause the current through the magnetic means 2i to decrease, thereby permitting the shutters to open in accordance with the amplitude of the sound to be recorded. It will be apparent that the selection of any one of these three methods can be accomplished by merely a reversal of connections either between amplifier 2 andthe rectifying amplier 6, between amplifier 5 and the magnetic means 2l, or of magnetic means 2l to the arm 22. Similarly, if it is desired to cause a decrease in the output of the amplier 6, or an increase in the output of the amplier 2, it is necessary that the output of the amplier 2 increase the negative grid bias in the rectifying ampliiier 5, while to produce the opposite result, the connections are so made as to cause a decrease in the grid bias.

Referring now to Figs. 'l' and 8, the aperture plate 5 is located quite close to the shutters 2t and 25, and when the shutters are in the closed position, i. e., when there is no sound being recorded, each covers approximately one-fourth ol the aperture l2. When the image of this covered aperture is projected on the slit plate i3, onlyV narrow tips of the image i2 coincide with the slit, thereby producing only a very narrow record such as indicated at Si) in Fig. 6. When, however, modulation is applied to the amplifier 2, the shutters 2li and 25 are withdrawn toward the position shown in Fig. l, a distance corresponding to the amplitude of the sound to be recorded, and when the shutters are completely withdrawn, for recording maximum amplitude, the image I2 on the slit plate i3 presents the appearance shown in Fig. 1. it will be apparent that when the image l2 in Fig. l is moved vertically by oscillation of the mirror 5, it will swing between two extreme positions, in the lower-most position only the tops of the triangles of the image coinciding with the slit and producing a very narrow record portion, as indicated at 3l, and at the uppermost position substantially the entire slit being filled with light,

thereby producing the peaks indicated at 32 in Fig.

6. As a consequence of the described movement of the shutter in accordance with the modulation, a negative record will be produced from which a positive may be printed having the appearance shown in Fig. 6, from which it will be apparent that the record has an outer envelope corresponding with the envelope of the voice currents and an inner outline corresponding with the sounds themselves, the outer envelope being produced by the shutter and the inner outline being produced bythe galvanometer. It will be apparent that each of the halves of this record corresponds with the McDowell record, but that two records are symmetrically arranged with relation to the sound track, thereby preventing the cutting off of peaks at high amplitudes if the reproducing aperture is slightly out of alignment, and preventing the cutting out of the sounds under similar circumstancesy at extremely low amplitudes which might follow with such sound records, as for veziample that of Hanna` Patent No. 1,888,724.

Referring more specifically to the shutter mechanism, a base member et is provided, which may be the base of the recorder. Upon this base member is mounted a support member di, on

which the portion of the optical system including the condenser 8, the lens l5, and the intervening shutter mechanism is mounted. On this is mounted an appropriate carriage e2. .es shown in Fig. 4, this carriage is mounted for lateral4 movement on the member l being shifted by the screw 43 provided with the jam nut fifi and being held firmly in position by the compression spring l5 which produces a pressure opposing that eX- erted by the screw d3. This carriage 42 includes a cylindrical upper portion it in which the barrel il of the optical system is fitted.

In order to position the optical system with the aperture l2 accurately parallel to the slit i4, the

optical barrel is slitted at d3 and into this slit is iitted an eccentric pin d@ on a screw It will be apparent that rotation of the screw 56 will cause the pin l5 to move laterally of the member l5 and to thereby rotate the barrel together with the aperture plate 9. The barrel may not only be rotated but may be slid longitudinally within the limits prescribed bythe slot fit1, and it can then be clamped in piace 'by the screw El, which passes through the slit ring 52 and forms a portion of the member 45.

As shown in Fig. 2, the shutters 24 and 25 are pivoted on the knife edges 26 and 21, being held thereagainst by the spring 28. These shutters 2li and 25 are adjustably secured on the arms 53 and 511 by the screws 55 and 56 in order that i they may be adjusted to the proper distance from the aperture plate 9. It will be apparent that, although the ends of the shutter blades must clear the aperture plate 9, they must, at the same time, be so close thereto that a properly focused image of the edges of the shutters will be formed on the slit plate i3 in the same focal plane with the image of the aperture I2. The individual shutter blades are adjustable laterally by means of screws 5l and 58 as shown in Fig. 5, these screws passing through V-shaped blocks 59 and Sli, Figs. 3 and 5, which are held into the correspondingly shaped slideway 6l by the spring members 62; It will be apparent that rotating the screws 57 and 58 will shift the blocks 59 or til longitudinally in the guideway, thereby shifting the pivots of the shuttersand correspondingly shifting the opposite ends of the shutter blades in the opposite direction to the movement of the pivots.

As before described in connection with Fig. 1, a resilient member 23 is connected froml the arm 22 to the arms supporting the shutters, and when this arm is actuated by the magnets, the shutters are pulled closer together or moved farther apart, as the case may be.

In the preferred form of the invention, as shown in Figs, 2 to 5, the arm 23 is provided with a rectangular armature 63, as shown in dotted lines in Fig. 3, and moves in a plane passing through the axis of the lenses between the poles of the pairs of magnets 64 and 85. 'Ihe coils of the several magnets 84 and 65 are connected to the ground noise reduction amplifier 6, and in such a manner that the pairs of poles longitudinally of the device are of opposite polarity, thereby causing movement of the arm 23 in accordance with the energization of the magnets, and correspondingly moving the ends of the shutters 24 and 25.

As shown in Figs. '7 and 8, I prefer to use an exciter lamp having a helical filament curved toward the aperture, in order to secure more uniform illumination than could be secured from a straight helical iilament as described and claimed in the application of L. T. Sachtleben, Serial No. 76,316, filed April 25, 1936,

In the modified form of the invention illustrated in Fig. 7, the shutters are supported on movable pivots 15 and 16, which in turn are supported on screws 'l1 and 18 which are fitted into bosses on the laterally slidable member 19. The pivot members are held against the screws by the tension springs 80 and 8|. The member 19 is adjustable laterally against the force of the compression spring 82 by the screw 83. Instead of the spring member 23 of the form of the invention before described, there are provided links 84 and 85 which are connected to the armature 86. This armature 86 is of the same type and is actuated in the same manner as the armature 22. The shutter blades 24 and 25 are held toward each other, at their ends farthest from the aperture, by the coil spring 81 which serves to hold the shutters against the pivots 15 and 16 and to exert a force in opposition to the magnetic force exerted on the armature 86,

The modication shown in Fig. 8 diiers from that shown in Fig. 7 in that flexible links 90 and 9| are provided, which are connected to a very small pulley 92 which is rotated by a magnet arrangement similar to that provided for the forms of the invention before described, but with the armature connected to the member 92 so as to move it about its axis instead of longitudinally of the optical system.

Having now described our invention, we claim:

l. Apparatus of the class described comprising means for forming a spot of light tapering from the middle to both ends, means for selecting a narrow line of light from said spot, means for vibrating said spot across said selecting means in accordance with sound waves to be recorded, and a pair of pivoted shutters for masking the ends of said spot in accordance with the volume ofthe sound to be recorded.

2. Apparatus of the class described comprising means for forming a spot of light tapering in width from the middle to both ends, means for selecting a narrow line of light from said spot, means for vibrating said spot across said selecting means in accordance with sound waves to be recorded, a pair of pivoted shutters for masking the ends of said spot in inverse accordance with the volume of the sound to be recorded, magnetic means for actuating said shutters, and link means connecting said shutters to said magnetic means.

3. Apparatus of the class described comprising means for forming a spot of light tapering in width from the middle to both ends, a slitted member for selecting a narrow line of light from. said spot, a galvanometer for vibrating said spot across said slitted member in accordance with sound waves to be recorded, and a pair of shutters pivoted for movement about axes parallel to said means and movable to mask the ends of said spot in inverse accordance with the volume of the sound to be recorded.

4. In sound recording apparatus, an optical unit comprising a condenser lens, a mask having an aperture with one side V-shaped, and a pair of shutters pivoted. for movement about axes parallel to said mask and adapted to obscure the ends of said aperture in accordance with the volume of sound.

5. In sound recording apparatus, an optical unit comprising a condenser lens, a mask having an aperture with one side V-shaped, a pair of shutters pivoted for movement about axes parallel to said mask and adapted to obscure the ends of said aperture in accordance with the volume of sound, and magnetic means for actuating said shutters.

6. In apparatus of the class described, a pair of movable shutters, magnetic means for moving said shutters, and links similarly connecting said magnetic means to both of said shutters whereby said shutters are simultaneously and similarly moved by said magnetic means.

7. Sound recording apparatus including an aperture plate, a pair of shutters adjacent to said aperture plate and movable about axes at their ends r-emote from said aperture, means for moving said shutters across said aperture inversely as the volume of sound to be recorded, and means similarly connecting said moving means to said shutters between their axes of movement and the said aperture plate.

JUDD O. BAKER. CECIL N. BATSEL.

Images