Title:
Reproduction of sound
United States Patent 2462263


Abstract:
This invention relates to the reproduction of sound from photographic sound records or the like, and more particularly to the provision of an improved sound reproducing apparatus and method of operation whereby a sound record made without noise reduction may have sound reproduced from it with...



Inventors:
Haynes, Harold E.
Application Number:
US57588545A
Publication Date:
02/22/1949
Filing Date:
02/02/1945
Assignee:
RCA CORP
Primary Class:
Other Classes:
250/202, 250/549, 369/44.11
International Classes:
G06E1/00; G11B7/00
View Patent Images:
US Patent References:
2347084Noiseless sound system1944-04-18
2277502Line tracker1942-03-24
2121211Automatic line tracker1938-06-21
2017901Electrooptical system1935-10-22
1974900Photophonographic apparatus1934-09-25



Foreign References:
AU810832A
GB434936A1935-09-11
Description:

This invention relates to the reproduction of sound from photographic sound records or the like, and more particularly to the provision of an improved sound reproducing apparatus and method of operation whereby a sound record made without noise reduction may have sound reproduced from it with less background noise than that heretofore involved in the reproduction of sound from such a record.

The present invention is related to that disclosed by a copending application of John R.

Cooney, Serial No. 530.415, filed April 10, 1944.

The two inventions are similar in that they both involve scanning of the sound track by a light spot which originates at the fluorescent screen of a cathode ray tube and tends always to be driven by means including a feedbiack circuit toward the opaque area of a variable width sound track so that thegh t is maintaiined astride1tEe boundary line between the transparent an opauears o suc arecord. The two inventions differ in that the present invention (1) dispenses with the light wedge of the aforesaid copending application and relies altogether on the movement of the sound boundary track with respect to the light spot for deriving the audio modulation, and (2) high frequency oscillations are applied to the control grid of the cathode ray tube or to the phototube for providing the audio impulses with a carrier which simplifies the problem of amplifying the output of the phototube.

In the ordinary sound film reproducing system, the instantaneous value of light transmitted through the film is measured and the variation of this light with time constitutes the audio wave contained in the record. In the case of the variable width record, it is the position of the boundary between the opaque and transparent areas which is the inherent measure of the instantaneous voltages recorded, and not the light-transmitting property of the transparent area. The present invention provides an improved means of reproducing sound from a variable width sound track by recognizing the position of this boundary from instant to instant.

The principal object of the present invention is to provide an improved apparatus and method of operation whereby a sound record made without background noise reduction may have sound reproduced from it with less background noise than that heretofore involved in the reproduction of sound from such a record.

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 is a diagrammatic representation of a preferred embodiment of the invention, and Figure 2 is an explanatory diagram illustrating the path followed by the light spot as it is moved transversely of the sounRrack n rispo0e to the ariatiosin the amplitude 9 e od ed audio g . The sound reproducing apparatus of Fig. 1 includes a cathode ray tube 10 which has the usual electron gun or beam producing means such as a cathode 11, a grid 12 for controlling the intensity of the beam, a first anode 13 and whatever other electrodes are required for properly focusing the beam. At its enlarged end, the tube 10 is provided with a fluorescent screen upon which a spot of light is produced by impingement of the beam on the screen. The tube 10 may include a second anode 14 and a pair of deflectors 15 and 16 for moving the beam transversely of a sound record 1 . A voltage divider or other suitable meaiiii(i ot illustrated) is provided for maintaining the various electrodes of the tube 10 at such potentials as are required for proper operation of the tube 10. A high frequency oscillator 18 may be connected to the grid 12 for varying the potential of the grid 12 at a superaudible frequency or may be associated with a phototube 19 which receives light modulated by the record 17. If the oscillator 18 is connected to the grid 12, it is desirable that the tube 10 be of the short-persistence type so that the spot intensity itself will be modulated. If it is connected to the phototube 19, the fluorescent screen of the tube 10 may be such as to permit somewhat longer persistence of the light spot.

The light spot which is indicated at x on the fluorescent screen can move only in the path L-R as indicated in Fig. 2. An image of this path is formed on the record 17 by a cylindrical lens 20 which is positioned parallel with the record 17 and at right angles to the motion of this record as indicated by the arrow adjacent to the edge of the record.

With the oscillator connected to the control grid 12 of the tube 10, the spot x is modulated in intensity at a frequency well above the highest audio frequency recorded on the record 17. The light thus modulated is passed through the record 17 to the phototube 19. The output of the phototube 19, which is a high frequency alternating voltage (or "carrier") amplitude-modulated by the audio signal, is amplified by the amplifier 21. 66 Since the signal is analogous to an ordinary amplitude-modulated radio signal, the amplifier 21 may be a tuned amplifier similar to the intermediate frequency amplifier of a radio receiver.

Thus, the modulating signal is detected by the detector 22, and any of the carrier passed by the detector is dissipated in the filter 23.

This fluctuating unidirectional potential is applied (1) through a coupling capacitor 25 to a utilization device such as an audio amplifier and a loud speaker and (2) through a lead 26 to the deflector 15 in such a phase relation that it tends always to drive the image of the bright spot x toward the opaque area of the record 17.

If the spot x moves over into the opaque area, however, the signal received by the phototube drops to zero and no voltage is available to keep the spot so deflected. In other words, if the overall gain is very hligh so that only a small fraction of the light contained in the spot is sufficient to produce voltage high enough to deflect the spot the full width of the track, then the spot will follow the contour of the recorded wave faithfully with only a small portion of it spilling over into the clear area to provide deflecting voltage.

Since the spot deflection on the record 17 is proportional to the voltage applied to the deflecting plate 15, providing beam deflection in the cathode ray tube is proportional to the voltage difference between electrodes 15 and 16 and providing that the spot movement at the film is a replica of the spot movement on the screen (except for size), this voltage necessarily is the audio voltage contained in the sound track of the record and appears at the terminal 24 at a quite high level.

A source of bias potential 28 may be provided in the lead of the deflector 16 for biasing the spot x to any desired point in the path L-R of Fig. 2.

Another way of utilizing the carrier wave principle is to omit the intensity modulation of the electron beam of the tube 10 and apply as a polarizing voltage to the phototube a carrier frequency potential. In this case, the fluorescent 4 screen of the tube 10 need not have such short persistence as in the previous case since the spot x is required only to follow the highest frequency recorded on the record 17. In either case the beam applied to the record is subjected to a car- 65 rier frequency. Appended claims calling for this feature are therefore intended to cover either case unless otherwise limited.

I claim as my invention: 1. In a device for reproducing sound from a 5y variable width sound record, means for producing a light spot which varies in intensity at a superaudible frequency, and means responsive to light transmitted through said record for moving said spot in accordance with the contour of the boundary between the opaque and transparent areas of said record.

2. The combination of means for producing a light spot which varies in intensity at a superaudible frequency, a light sensitive device responsive to light transmitted from said spot through a sound record having adjacent opaque and transparent areas, an amplifier tuned to said superaudible frequency for amplifying the output of said light sensitive device, means for eliminating the superaudible component of said amplified output, and means responsive to the remaining component of said output for moving said spot in accordance with the contour of the boundary between said opaque and transparent areas.

; 3. The combination of means for producing a light spot which varies in intensity at a superaudible frequency, a light sensitive device responsive to light transmitted from said spot through a sound record having adjacent opaque and transparent areas, an amplifier tuned to said superaudible frequency for amplifying the output of said light sensitive device, means for eliminating the superaudible component of said amplified output, means responsive to the remaining com-0 ponent of said output for moving said spot in accordance with the contour of the boundary between said opaque and transparent areas, and means for supplying a part of said remaining component to a utilization circuit.

:*:; 4. In a device for reproducing sound from a record wherein transparent and opaque areas are defined by a boundary having a contour which varies in accordance with said sound, the combination of means for applying a beam of light ::' to said record, means for varying the intensity of said beam at a frequency which is high with respect to the frequency of said sound, and means responsive to light transmitted through said transparent area for maintaining said beam at 3r said boundary.

5. In a device for reproducing sound from a record wherein transparent and opaque areas are defined by a boundary having a contour which varies in accordance with said sound, the combination of means for applying a beam of light to said record, means for varying the intensity of said beam at a frequency which is high with respect to the frequency of said sound, and 5 means responsive to light transmitted through said transparent area for maintaining said beam at said boundary, and means responsive to said transmitted light for deriving an audio frequency current dependent on the position of said beam.

3 HAROLD E. HAYNES.

REFERENCES CITED The following references are of record in the file of this patent: UNITED STATES PATENT-S Number 1,974,900 2,017,901 2,121,211 2,277,502 2,347,084 Number 8108/32 434,936 Name Date Shoup __ ... __._ Sept. 25, 1934 Huffman ---------- Oct. 22, 1935 Padva et al. -------- June 21, 1938 Padva -.--... _ -___ Mar. 24, 1942 Cooney -- _____- _ Apr. 18, 1944 FOREIGN PATENTS Country Date Australia ------- July 5, 1933 Great Britain .-- . Sept. 11. 1935 V 0