US2144749A

US2144749A - Sound reproduction

Info

Publication number: US2144749A
Application number: US47289A
Authority: US
Inventors: James R Balsley
Original assignee: United Research Corp
Current assignee: United Research Corp
Priority date: 1935-10-29
Filing date: 1935-10-29
Publication date: 1939-01-24
Anticipated expiration: 1956-01-24

Description

Jan. 24, 1939. J R. BALSLEY I SOUND REPRODUCTION Filed Oct. 29, 1935 PIE. 3.

INVENTOR. JA/WES AP; BALSLEY PIE. 2.

Patented Jan. 24, 1939 UNITED STATES PATENT OFFICE SOUND REPRODUCTION Application October 29, 1935, Serial No. 47,289

14 Claims.

This invention relates to sound reproduction and particularly to the reproduction of sound from a moving transparent carrier having a sound record thereon.

In the recording of sound from a sound record film the upper and lower limits of volume range recordable are dependent upon the sound record or track itself. That is, in the case of high level sounds the upper level limit is determined by the width of the sound track in a, variable area type of track or by the amount of variation between the opaque and transparent striations in a variable density type of track. The lower limit of volume range recordable on either type of sound track is determined by the ground noise level during the reproducing, most of which is produced by the apparently clear portion of the sound track as it passes across the sound translating light beam. It is apparent therefore that the latent sound recorded on the film is restricted to a certain volume range. Heretofore, arrangements for increasing the volume range of the sound reproduced from a sound record have included complicated electrical circuits.

One object of the present invention is to obtain a controlling effect which varies in accordance with the volume of the sound recorded on the sound record without the useof complicated electrical circuits. In this invention I take advantage of the fact that in anti-ground noise type of records the average print transmission varies in accordance with the volume of sound recorded on the sound record.

I accomplish the above object by passing through the anti-ground noise sound record a beam of light which is longer in the .direction of film motion than one wavelength of the lowest recorded frequency. The emerging beam of light will thus vary in intensity in accordance with the average volume of the recorded sound wave representation passing across the light beam.

Another object of my invention is to obtain an increase in the range of useful volume levels reproduced from an anti-ground noise type of sound record.

This is accomplished by projecting a sound translating beam of light through the sound recrd, the intensity of the beam varying in accordance with the average volume of the recorded sound in the manner above described. On low level sounds the intensity of the translating beam is decreased causing a lower level sound to be reproduced which is not proportional to the sound level on the record. On reproducing from a normal type of biased sound track the reproduced volume range will be greater than the volume range recorded upon the film. Therefore, an expansion or a greater contrast will be produced between the various reproduced sound levels thus creating a pleasing and dramatic effect.

As the noise level due to scratches or graininess of the apparently clear portions of the sound track is proportional to the intensity of the translating light beam projected therethrough it will be seen that the signal to noise ratio remains substantially the same throughout the entire volume range of the sound. On low levels the decrease in intensity of the translating beam decreases the ground noise level correspondingly thus allowing the lower level sounds to be reproduced. I

Other objects and advantages of the invention will be apparent upon reference to the following description taken in connection with the accompanying drawing in which:

Fig. 1 is a diagrammatic View of a sound reproducing system embodying the invention.

Fig. 2 is an enlarged fragmentary view of a variable area type of film which is adapted to be used in the system illustrated in Fig. 1.

Fig. 3 is an enlarged fragmentary view of a variable density type of film adapted to be used in the system illustrated in Fig. 1.

Referring to Fig. l, the film I may have either a variable area or a variable density sound track thereon of the noise reduction type wherein the sound wave representations are biased or shuttered. However any type of record may be employed in which the average amount of opacity at any particular point along the sound track is substantially proportional to the average volume of the latent sound on the film at that particular point. Light from an exciter lamp 3 is passed through a condenser lens 4 and a mask 5 to pass a beam of light 2, rectangular in cross section, (Fig. 2) through the sound track portion of film 1. Although the beam 2 is shown and described as being rectangular in cross section, it is to be understood that various other cross sectional shapes may be employed if desired. The light thus passed through the film I is reflected on the opposite side by mirrors 1 and 8 into lenses l6 and I! or a slit assembly 9 from whence it is focused as a sharp line of light on the film at the point of sound translation F, preferably in the center of the beam 2. The emerging translating beam of light as modulated by the sound track portion of film l passes into a photo-electric cell It). Electrical impulses corresponding to the modulated light beam thrown upon the photoresponding amount.

electric cell I 0 are passed through amplifier I I and thence into the loud speaker I2.

When variable area type of sound records are employed, a cylindrical lens I8 may, if desired, be inserted in the beam of light between the lens I1 and the film I so as to image the spherical lens I! upon the film 59. The addition of this lens I8 produces on the film I a slit of light having an intensity which is uniform along the length of the slit but which varies in direct proportion to the amount of light passing through the slit 9. When employing a variable density type of sound record the lens I8 may, if desired, be allowed to remain in the path of the translating beam.

Preferably, the height of the beam 2 as indicated by the dimension H (Figs. 1, 2 and 3) is such that it includes several sound wave cycle representations on film I; at least it should be sufficient to cover one cycle representation at the lowest frequency to be recorded. It will therefore be seen that the beam 2 upon emerging from the film I will have an intensity which varies substantially in accordance with the envelope of the sound wave representations passing across the point F. This beam as reflected and focused at the point F upon the sound track will therefore produce a fine line or slit of sound translating light L (Figs. 2 and 3) which varies in accordance with the average transmission of the film passing across this line L. In using a biased or other noiseless type of sound track, this average transmission, of course, will depend on the volume of the sound or, in other words, upon the envelope of the sound waves at any particular point along the length of the film. When sounds of low intensity pass the beam of light L the aver age print transmission will be low. Therefore, the sound reproduced by the low level portions of the sound track as at I3 and I4 will be further decreased due to the decrease in intensity of the line of light L. This not only allows the low level sound limit to be additionally lowered but it also decreases the ground noise, due to the film, a cor- When high level sounds are being reproduced, as at the point I5, the average transmission will be at its highest value and therefore the light beam L will have its highest intensity allowing for full amplitude of current to be set up by the photo-electric cell ID.

The fact is that the arrangement shown in Fig. 1 provides means for multiplying the effective noise reduction in reproducing sound from the film I for the following reason. Assume that the film I has 10 db. noise reduction and therefore an average transmission which varies 3 to 1. In the reproducing arrangements according to the prior art, the average light for translating a noise reduction record such as film I would in the assumed case also vary as 3 to 1. In the case of Fig. 1, however, the average light for translating the record varies as the product of the film transmission variation and the translation light variation, each of which is 3 to 1, the product being 9 to l or 20 db. effective noise reduction. The noise reduction is therefore multiplied.

Upon reproducing from the normal type of noiseless sound record, this system provides a method whereby greater contrast of sounds may be obtained. However, where the so-called compressed type of sound record is used in which the lower volume levels are raised and the upper volume levels attenuated, the invention may be em.- ployed to expand the volume range and thus produce a normal reproduction of the sound as originally received in the recording microphone.

In any event, however, the signal to noise ratio will remain substantially constant, thus preventing the ground noise, due to imperfections in the apparently clear portion of the sound track, from being reproduced.

Method and means for varying the generation of sound currents in accordance with the variation in the volume thereof are generically claimed in my co-pending application Serial No. 47,287, filed Oct. 29, 1935, for sound reproduction.

Having thus described the invention, what is claimed as new and desired to secure by Letters Patent is:

1. The method of reproducing sound from an anti-ground noise sound record occupying a single sound area strip which comprises passing a beam of light not greater than one sound wave cycle through the sound record and varying the intensity of said beam by said record as said beam passes through said record of a width greater than one sound wave cycle in accordance with the envelope of the sound waves of the sound to be reproduced.

2. The method of reproducing sound from an anti-ground noise sound record occupying a single sound area strip which comprises passing a beam of light of a height to cover at least one sound wave cycle representation on said sound record through said sound record, transforming said beam into a narrow beam of light and passing said narrow beam of light through said film within the same area as said beam first passed through said record.

3. In sound reproduction, the method of modulating a beam of light which comprises passing a beam of light through a single-track sound record for modulating said beam in accordance with the average print transmission of a sound record, the height of said beam covering at least one sound wave cycle representation on said record, and again passing said beam through the same sound record for modulating said beam in accordance with the frequency of said sound record.

4. The method of reproducing sound from a sound record which comprises passing a beam of light through the sound record, and reflecting said beam of light back through said record at the point of first passage of said beam through said record and into a light receiving device.

5. The method of reproducing sound from a sound record which comprises passing a beam of light through the sound record and reflecting said beam of light back through said record within the area that said beam first enters said record.

6. The method of reproducing sound from an anti-ground noise type of sound record which comprises passing a beam of light of a height to cover at least one sound wave cycle representation on said record through said record, reflecting and focusing said beam upon said record as a narrow line of light at substantially the center of the area on said record that said beam first entered.

7. In an apparatus for reproducing sound from a single sound track moving sound record, means for projecting a sound translating beam of light through the record, means before the entry of said beam in said record for varying the intensity of said beam in accordance with the intensity of sound being reproduced said varying being produced by said record as said beam is passed therethrough and a photo-electric device for receiving said beam after double passage through said record.

8. In an apparatus for reproducing sound from a. moving sound record, means for focusing a sound translating slit of light upon the sound record, said record varying the intensity of said translating slit in accordance with the form of the sound beng reproduced, said means comprising a light source for passing a beam of light through said sound record and means for directing said beam upon emergence from said film again through said sound record.

9. An apparatus for reproducing sound from a single sound track moving sound record comprising a light source for projecting a beam of light of substantially constant intensity through the sound record, reflecting means for reflecting said beam upon emergence from said record back through said record and a photo-electric device for receiving said beam after the second passage of said beam through said film.

10. An apparatus for reproducing sound from a sound record comprising the combination of means for passing the sound record across a light beam of substantially constant intensity, said beam having sufficient cross sectional area to cover at least one sound Wave cycle representation on said record, an optical system for focusing said beam upon emergence from said record and reflecting means for directing said focused beam upon said record within the area that said first mentioned beam first entered said record.

11. An apparatus for reproducing sound from a sound record film comprising a source of light, means for projecting a beam of light of substantially constant intensity from said source through the film, said beam being of suflicient cross sectional area to cover a plurality of sound Wave cycle representations, a slit assemly, deflecting means for deflecting said beam after emergence from said film into said slit assembly, said slit assembly being adapted to focus said beam on said film within the area of said film that said beam first enters said film.

12. The method of expanding the reproduced sound from a normal sound record comprising first modulating a light beam by the variations in the average light transmission through said record longitudinally of said film and then again modulating said beam by the variations in Wave form of said record.

13. The method of expanding the reproduced sound from a normal sound record comprising modulating a beam of light by the wave form of said record and simultaneously modulating said beam by the average transmission of said record,

the volume of said reproduced sound varying in accordance with both the Wave form and average transmission variations.

14. The method of reproducing sound from a normal sound record so that the higher level sounds are higher than normal and the intermediate level sounds are proportionately higher than normal but lower than said highest level sound comprising increasing and decreasing the intensity of the beam being modulated by the wave form of said record in accordance with the increase and decrease in the average print transmission of said sound record.

JAMES R. BALSLEY.