US2064665A - Photographic sound recording - Google Patents

Description

Dec. 15, 1936. E. w. KELLOGG 2,064,655 I PHOTOGRAPHIC SOUND RECORDING Filed Nov. 2e, 1929 Hg.' ll.

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Patented Dec. 15, 1936 UNTED S FICE Edward W. Kellogg, Schenectady, N. Y., assigner to General Electric Company, a corporation of N ew York Application November 26, 1929, Serial No. 409,954

21 Claims.

My invention relates to the photographic recording of sound and particularly to the making of a variable width record of sound which as the recording progresses undergoes considerable variation in loudness or volume.

In any system of recording sound it is a desideratum that in the reproduction of the sound the ratio of useful sound to back-ground noises shall be such that a listener shall at no time be conscious of the presence of such noises much less to have his attention diverted thereby. When the sound recorded is of relatively large or even normal volume the back-ground noises usually are not noticeable but when the volume is small, as for example, during a weak musical passage they often become quite apparent and under certain conditions may detract from the enjoyment of the music. One method of overcoming this objection, to which resort has been` had to some extent in the commercial recording of music, is to preserve the desired ratio between the usei'ul sound and back-ground noises by increasing the amplification in the recording system, whereby the sound waves at times oi relatively small sound volume may be recorded with a greater amplitude. This practice, however, is objectionable in that it robs the music of its proper expression when the record is reproduced in the ordinary manner.

It is one object of my invention to provide an improved method of making a photographic sound record as a result of which the advantages of decreased ground noises are obtained, without sacrificing the expression, or proper relation between the loud and soft passages. Another object of my invention is the provision of an improved apparatus ior carrying out this method and a further object of my invention is the provision of an improved sound record which is the product of the same method.

If a photographic sound record were made in the manner just described, namely by increasing the amplication during the recording of faint passages, the proper musical expression could be restored by turning down the amplification in the reproducing system in the proper degree, just as the place is reached where the recording amplier was previously increased. With the reduced amplification in the reproducing system, the loudness of the ground noise will be reduced as well as that of the music, and since a satisfactory ratio was secured by recording at large amplitude, the desired result is secured, namely the soft passages are reproduced softly, as in the original playing, and the ground noise is always (C1. 179-1ii0.3)

kept low enough to be unnoticeable. Instead of turning down the amplification in the reproducing system to reduce the loudness, the same effect may be accomplished by decreasing the amount of light which is directed upon the sound record and which passes on into photo-electric cell in the reproducer. Such variation in the light reaching the film may be effected in various ways, for example, by interposing a colored or dark glass in the light path or by reducing the 10 brightness of the lamp as by inserting resistances in its circuit. All such methods of reducing the loudncss of the reproduced sound require the services of an attendant or else require elaborate auxiliary equipment, controlled for example by 15 notches or special perforations of the film. In accordance with my invention, the desired result is accomplished without the intervention of any attendant and without the employment of any complicated controlling apparatus. Briefly stated, I record the softer passages of the sound at a greater amplitude and at the corresponding portions of the record from which reproduction is to be made I produce a darkening or fogging of the record. 25

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 shows in a 30 diagrammatic manner a form of apparatus forming a part of my invention by which the method, also forming a part of my invention, may be carried out; Figs. 2 and 3 represent portions respectively of a negative film and a positive print having sound of varying volume recorded thereon in the usual manner; Figs. 4 and 5 represent portions respectively of a negative lm and positive print having sound of a similar nature recorded thereon in accordance with my inven- 40 tion; Fig. 6 is a View similar to Fig. 1 illustrating a modication; and Fig. '7 shows a portion of a negative made with this modified apparatus.

For a better understanding of my invention reference is had first to Figs. 2 and 3 which are intended to show respectively a negative, and a positive print of the same, illustrating a variable width sound record as produced in the usual manner. The sound recorded on the left portion of negative I is of relatively large volume 50 hence the amplitude of the record waves 2 is large, the waves extending nearly the entire width of the sound track 3. Near the center of the negative the sound volume decreased and continued at relative low volume producing the 55 low amplitude Waves 4 at the right portion of the negative shown.

In the making of variable width photographic sound recordings, the intensity of the exposing light usually is such that the exposed portion of the negative is black or opaque while the unexposed portion is substantially transparent or clear. In the negative I have shown the opaque portion 5 of the record on the side of the sound track toward the center line of the film and the clear portion 6 toward the adjacent margin thereof. The positive l, shown in Fig. 3, being a print oi the negative I has a similar record but with the opaque and clear portions 8 and 9 respectively reversed. Whether the negative made in accordance with the method now in general use and illustrated in Fig. 2, or the print of the same, illustrated in Fig. 3 is used for the reproduction of the sound in the usual manner in which a narrow transverse beam of light is projected through the sound record into a photo-electric cell, it will be seen that during those portions of the record corresponding to low sound volume there is a substantially unobstructed passage of light through approximately one-half of the sound record track. The back-ground noises which are objectionable during faint passages are due to shot effect in the photo-cell, and to modulation of the light by specks of dirt and scratches on the film. Both of these sources of noise are decreased by decreasing the light which passes through the film to the photo-cell. In accordance with my invention I reduce these noises during the times of less sound volume by rendering the normally clear portion of the Sound track less transparent and compensate for this change by increasing the amplitude oi the record waves, thus illuminating the photo-cell with a small amount of light almost completely modulated instead of with a large amount of light only slightly modulated. Specifically I obtain the sound record just described by reducing the intensity of the light beam falling upon the film in the recorder, by increasing in a denite correlated manner the amplitude of vibration of the light beam, and by printing the negative so made in the usual manner.

In Figs. 4 and 5 I have shown respectively a negative film record and a positive print thereof presumably of the same sound as is recorded on the lrns shown by Figs. 2 and 3 but made in accordance with the method forming a. part of my present invention. The sound record at the left end of the negative l0 is not different from that of the corresponding end of Fig. 2. Beginning at the middle and extending to the right end the record differs from that of Fig. 2 in two respects, namely, the normally opaque portion li is gray or semi-transparent and the amplitude of the record waves l2 is larger than that of those shown at 4 in Fig. 2, being substantially the same average height as those at the left end of the lrn I0. As a result of printing, the positive I3 made from film l0 has its left end similar to that end of nlm 'l in Fig. 3 but the normally clear portion I4 of its right end is gray or Senn-opaque, the amplitude of the Waves being the same as in the negative l0 of Fig. 4. Thus when the lm i3 is passed through the usual reproducer less light enters the photocell during the periods when faint sound is desired. The reduced light results in a reduction of background noise, yand offsets the increase in amplitude of the record Waves, in such a manner that the music is reproduced in the proper volume at all times to maintain the same expression as was in the original playing.

In Fig. 1 I have shown diagrammatically one form or apparatus by means of which the above described method may be carried out. I have used for illustration an apparatus for the most part like that now in commercial use -or making variable width photographic records of speech and music. The sound to be recorded is received by a suitable pick-up device, for example, the microphone 2) connected by the wires 2l with the amplifier 22 where by means of suitable thermionic amplifying devices the feeble current variations from the microphone are amplified to the extent desirable for the operation of the recording galvanometer 2G shown connected to the amplifier by the wires 24. The recorder structure includes a light tight box 23 Within which the film is moved steadily past the point where. it is exposed, the electric lamp 25 which is the source of exposing light, and the oscillograph galvanometer 26 on the vibratory mirror of which a light beam from the lamp is focused. The recorder is provided with an optical system 2l by which the reflected beam is focused to a very narrow band on the sensitive lm and by reason o its transverse vibration the beam produces a Variable width record of the sound waves picked up by the microphone. In carrying out my invention I decrease the amount of light reaching the nlm during those periods when, owing to the aintness of the sound reaching the microphone, the amplification between microphone 2i) and galvanometer 26 has been increased and I increase the light again during periods of normal or large sound volume, when the degree of amplification has been reduced to normal. Various means may be provided for so varying the quantity of light reaching the nlm. In the drawing I have shown by way of example the rheostat 28 having the adjustable contact arm 2Q and connected in circuit with the battery B and lamp 25. Movement oi the rheostat arm Z9 in one direction inserts resistance in series with the lamp and thus decreases its intensity of illumination while` the opposite movement causes an increase in the i1- lumination. I have shown the amplier 22 as having two controls, a primary volume control 3l and a compensating volume control 32, the construction of which controls may be of any well known form. Both controls as shown effect an increase in the amplification upon movement thereof in a clockwise direction and a decrease thereof when moved in the opposite direction. The normal procedure would be to set control 32 for minimum amplification, and then adjust control 3l by trial so that the loudest sounds cause the light beam to swing to the maximum permissible amplitude, or in other words so as to just prevent overshooting. The lamp will then operate at full briiliancy during recording of loud passages. During the remainder of the recording the control 3l would not be changed, but control 32 would be adjusted from time to time in accordance with the loudness of the music so as to keep the amplitude of movements of the light beam at all times as near the maximum permissible as possible. Control 32 is connected by the rod 33 to a rear extension of the rheostat handle 29 and the parts are so proportioned that as the amplification is increased the illumination of the lamp is decreased by such an amount that the volume of the reproduced sound is substantially unchanged. In Figs. 4 and 5 the amplitude of the 75 sound waves `l5 is shown-approximately thesame for the rightv or soft portion of the record as` for the left or loud portion thereof, however, upon the reproduction of the recorded sound from the print record, Fig. 5, the desireddiminution in volume ofthe right portion is eiiected principally by the decreased amount of light reaching the photocell through the darkened lm instead of by small amplitude of the recorded waves. The variation in light intensity preferably is made in small steps andthe relation of these steps to the compensating volume control is based upon the development of the negative and print to certain contrast ratios or gamma values. The appa- -ratus being so constructed, the operator is able to vary the volume control at pleasure so as to keep the amplitude of the recording light spot well up toward the maximum permissible (in other words to just prevent over-shooting) without affecting the loudness of the reproduced sound and therefore without impairingthe expression of the music.

While I have described by way of illustration the application of my invention to the making of a variable width sound record, the same principles may be applied to a system for making variable density records, the only difference being that in the latter case special care must be taken to avoid underexposure of the negative. The variable density system requires, if distortion is to be avoided, that exposure of both negative and print be kept between certain limits and that the development of both be so controlled as to give a product for the two gammas of approximately unity. The application of my invention toa variable density system will somewhat increase the range of exposures employed, but it will still be possible with proper care to keep the exposures within the non-distorting limits of exposure, and if this is done the full benets of the invention will be secured.

When my invention is applied to a variable width recording system, it will be necessary to determine in advance the gamma product of negative and prints, and to adhere in practice reasonably close to the developments so determined upon, but it is not at all necessary that the gamma product be unity. The variable width recording system calls for only two degrees of exposure, and of these only the maximum exposure of the negative and the minimum exposure of the print need be within the range of normal exposure. Within the range of normal exposure and with any degree of development of negative andv print, or gamma values, and with a known value of printing light, there will be a deiinite and reproducible relation between the exposure of the negative lm and the transmission, or fraction of incident light transmitted through the corresponding part of the print. This relation can be calculated in advance for emulsions of known characteristics. The data required for the design of the equipment shown in Fig. l would include the characteristics of both emulsions and the gamma values to which each is f' to be developed, the printing exposure, the negative exposure with lamp at full brilliance, and the reduction in negative exposure resulting from Various amounts of resistance in series with the recording lamp. With this information it will be possible to calculate for each step of volume control 32, the increment of resistance in the rheostat 23 which will just compensate, or reduce the light transmitted through the print in the same ratio as the voltage applied to the recording galvanometer 'i2-tisincreased. A movable light wedge` interposed in the path of the recording light beam might b-e employed instead of controlling the exposing light by means of the rheostat 28. The transmission characteristics of the wedge would need to be known for the design of the apparatus, but the design in this case might be somewhat simpler than in the case of the rheostat, and less dependent on the characteristics of the lamp 25.

In practice it would be necessary to always use the kinds of lm for which the apparatus was designed, and to standardize development. If this is not done, changing the settings of control 32 will not leave the final sound volume entirely una-iected, but even though there be considerable departure from the ideal relation, the results, employing my invention, will be much better than from present practice in which the recording volurne control is varied without any compensating factor.

My invention, in the form in which I have so far described and illustrated it, applies to the making of an original or negative recording, and making a print therefrom, using either an optical or a contact printer, the print being used for the reproduction oi the sound. cumstances be desired to use the original recording to control the light reaching a photo-electric cell, for purposes of reproducing the sound or for reproducing electric current waves correspondingr to the recorded sound. An example of this would be the case in which re-recording is employed as a substitute for printing. Under these circumstances the procedure would need to be modified so as to produce in the original recording, a sound track resemblingr that of Fig. 5, in that the normally clear portion of the film is fogged as shown at i4 to compensate for the increased amplitude of the recorded waves.

One m'eth'od of obtaining such a record as I have just described would be to expose the lm in the apparatus shown in Fig. l, just as though a print were to be made, but instead of developing the film in the ordinary manner, to reverse it, making it into a positive instead of a negative. The method of reversal is well known and has long been employed in making amateur moving pictures. If re-recording is to be done on a oommercial scale, it would be preferable to avoid the extra film processing involved in the reversal. This can be accomplished by a slight modification in the recording arrangements such as I have shown for example in Fig. 6.

In this form of the apparatus, the recording lamp 25 would burn at full brilliancy, the lamp being shown connected directly across the battery 3U although a suitable switch and rheostat may be employed in the connection if desired. An additional lamp is used whose brilliancy is controlled by the volume control 32 to produce a suitable degree of fogging of the sound track over its tire width. The fogging light may be applied to the film either before or after the sound is recorded thereon.- In Fig. 6 l' have shown the recorder box 23 provided with an auxiliary optical system 35 in front of which is arranged the small fogging lamp 36. Light from this lamp is thrown on the lm in a band covering only the sound track. I have shown the auxiliary lamp 38 connected to the battery Sil through the rheostat 2S in such a manner 'that as the volume control 3E is turned to increase the amount of ampliiication the amount of resistance in series with the lamp is decreased, hence producing an increase in the illumination. An example of a. negative sound record made by this apparatus is shown in Fig. 7. 75

It may in certain oir- As in Figs. 4 and 5, the amplitude of the recorded sound waves remain substantially constant even though the sound volume changes from loud at the left end of the gure to soit at the right end thereof. The normally clear portion of the sound record, however, is ogged as shown at 3'! where the recorded sound is soit. It will be understood that the graduations of the iogging light must correspond With the steps of the volume control 32 in such a manner that when the amplification is for example doubled the fogging exposure Will be just surcient to reduce the light transmitted through the record, after development of the same, to one half, or to use photographic terms to produce a density oi 0.3. The above described apparatus is merely illustrative of how the amount of fogging light may be varied in accordance with the degree of amplication. The same result may be accomplished for example if the lamp 36 be maintained at a uniform brilliancy and the amount of light passing through the optical system 35 be varied by the use of a suitable light wedge or a diaphragm Whose position is controlled by a connection with the volume control 32. Other means than those illustrated may be used for varying the light intensity reaching the lm. I may even effect the regulation of the amount of light reaching the iilm' and the electrical ampliiication by means automatically responsive to the volume of the sound being recorded. It will therefore be apparent that many modications may be made without departing from the spirit and scope of my invention, which modifications I aim to cover by the appended claims.

I desire it to be understood. that when my invention is applied to the making of a variable Width record, the effect of increasing the amplication during recording is to produce Waves of greater visible amplitude or deeper serrations, thus producing a greater percentage modulation of the transmitted light during reproduction. If on the other hand the record is one of the variable density type, an increase in amplification during recording results in an increase in contrast between the dark and light areas, thus again causing a greater percentage modulation of the transmitted light during reproduction. Thus contrast, in` the variable density record corresponds to the visible amplitude of the Wave in the variable width record, and if the contrast is high the waves may properly be spoken of as having large amplitude. A large amplitude is entirely compatible with small average transmission although to the eye it might seem that the very dense nlm had small contrast. The dense iilm with high contrast or amplitude, transmits only a small amount of light but modulates this light by a high percentage.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In photographic sound recording, the method which comprises exposing a light sensitive member to a light beam varied in accordance with the sound Waves being recorded, varying the intensity of the light of said beam in accordance with the volume of the sound extending over a plurality of successive waves and varying the relation between the amplitude of the recorded Waves and said volume.

2. In photographic sound recording, the method of recording on a light sensitive member sound having passages which diier in volume, which method comprises varying an exposing light beam in accordance with the sound waves, varying the intensity of light of said beam in accordance with the sound volume and varying the amplitude of the recorded Waves inversely in accordance with said volume.

3. In photographic sound reco-rding, the method of recording on alight sensitive member sound having loud and soft passages which comprises varying an exposing light beam in accordance With the sound waves being recorded, decreasing the intensity of the light forming said beam and increasing the amplitude of the recorded Waves during the soft passages of the sound being recorded.

4. In photographic sound recording, the method which comprises exposing a light sensitive member to a light beam varied in accordance With the sound Waves being recorded, maintaining the amplitude of the variations of said beam substantially constant independently of variations in the volume of the sound, and varying the intensity of said light beam with the volume of the sound.

5. The method of photographically recording sound on a moving light sensitive member which comprises vibrating a light beam laterally of the member in accordance with the sound Waves being recorded, maintaining a substantially constant amplitude of vibration of the light beam during the loud and soft portions of the sound and simultaneously varying the intensity of the light beam in accordance with the volume of said portions.

6. The method of photographically recording sound on a sensitive film employing a light source and a galvanometer arranged to reflect on said film a light beam from said source and to vibrate it laterally of the film, which method comprises supplying to said galvanometer a current varied in accordance with the sound Waves being recorded, regulating said current to cause the amplitude or" its variations to remain substantially constant irrespective of the volume of the sound, and modifying the intensity of light received from said source to cause a less exposure of said iilm during the periods of less sound volume.

7. In combination, means for making a photographic record of sound and means comprising simultaneously' actuated members for varying inversely to each other the amplitude of the recorded vibrations and the intensity of the recording light.

8. In combination, means for making a variable Width photographic record of sound, means for varying the amplitude of the recorded vibrations, means for varying the intensity of the recording light, and a connection between said means whereby they vary in a predetermined relation to each other.

9'. Apparatus for photographically recording sound on a light sensitive member comprising means for directing light on said member varied in accordance with the sound waves to be recorded, means by which the amplitude of the recorded Waves may be maintained substantially constant irrespective of the volume of the sound, and means arranged for simultaneous operation therewith for varying the exposure to which said light sensitive member is subjected by said light.

10. Apparatus for photographically recording sound on a sensitive film comprising means for converting sound Waves into current variations, means for variably amplifying said variations, means responsive to said variations for directing light on said film, means for controlling the exposure of said lm by varying the intensity of said light, and a connection between said amplifying means and said exposure controlling means whereby they operate simultaneously.

11. Apparatus for photographically recording sound on a sensitive lm comprising a sound pick-up device, an adjustable amplier connected therewith, a galvanometer connected with said amplifier and arranged to reflect a light beam on said film, means for varying the intensity of said light beam and means connected therewith for simultaneously varying the adjustment of said amplifier.

12. Apparatus for photographically recording sound on a sensitive lm comprising a sound pick-up device, an adjustable amplifier connected therewith, a light source, a galvanometer connected with the amplifier and arranged to reflect on said Iilm a light beam from said source, a rheostat in circuit with said source, and a connection between said ampliier and rheostat whereby when the rheostat is operated to decrease the amount of light from said source the amplifier is operated to increase the amount of amplification produced thereby.

13. The method of recording sound which comprises producing a sound-track having a constant amplitude Variable area record of the sound tone being recorded .and varying the density of the clear portions of said sound-track in accordance with the amplification necessary to produce said constant amplitude.

14. The method of recording sound which comprises producing a sound-track having a variable area constant amplitude sound record of the sound being recorded, and varying the density of said record in accordance with the amplication necessary to produce said constant ampliture.

15. The method of producing a sound record on a single sound record track which comprises amplifying the sound to be recorded to produce a constant amplitude current, recording said current in one sense upon said reco-rd track, and recording the volume of said sound in a different sense upon the same record track.

16. The method of recording sound which comprises producing a variable area record of the sound being recorded, and varying the density of said variable area record in accordance with the average volume of said sound.

17. The method of recording vsound'which comprises producing a sound-track including a variable area record of the sound tone being recorded, and varying the density of the clear portions of said sound-track in accordance with the average volume of said sound.

18. A lm having thereon a photographic record of sound of Varying Volume, those parts of the record corresponding to the sound of less volume having waves of greater amplitude relative to the sound they represent than that of the waves of those parts corresponding to the sound of greater volume, and the less volume parts of the record having less contrast than the greater volume parts.

19. A lm having thereon a variable width photographic record of sound whose volume varies at dierent parts of the record, the waves of those parts of less volume being recorded with greater amplitude relative to the sound they represent than the waves of those parts of greater volume and the normally clear portion of the record being less transparent at the parts of less volume than at the parts of greater volume.

20. A lm having thereon a Variable width photographic record of sound of varying Volume, the amplitude of the record waves being substantially the same for all portions of said record and the contrast between the light and dark portions of the record being variable in accordance with the sound volume corresponding with that part of the record.

2l. A iilm having thereon a Variable width photographic record of sound of varying volume, the amplitude of the record waves corresponding with large and small volume sound being substantially the same and the normally clear portion of the record being darker at those parts thereof at which the small volume sound is recorded than at those parts at which the large volume sound is recorded.

EDWARD W. KELLOGG.

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