US1971181A - Ground noise elimination - Google Patents

Description

Aug. 21, 1934.

C10. GREENTREE GROUND NOISE ELIMINATION Filed April 12. 1930 RECTIFIER DUUUDUUU Fig.5.

Invent o1":

Greentvee,

His Attorneg.

Patented Aug. 21, 1934 PATENT orrics 1,971,181 (mom NOISE umrmn'nox crimes 1). Greentree, Schenectady, N. r., aaelgnor to General Electric Company; a corporation or New York Application April 12, 1930, Serial No. 443,875

1 Claims. (Cl. ire-no.3)

My invention relates to the making of photographic sound records which are adapted for use in the reproduction of the recorded sound. In the reproduction oi sound from a photographic film record as heretofore made, whether the record be of the variable density type or the variable width type, there is usually in addition to the recorded sound a certain amount of so called ground noise". Such noise being of a substantially constant intensity of volume is not noticeable as long as the recorded sound'is of the usual volume but whenever the sound volume reaches a low value the ground noise in comparison becomes the more prominent. Ground noise is particularly noticeable, lor example, during very soft passages in musical reproductions and also before the recorded sound comes on and after it ceases. It is known that a considerable part of the ground noise heard when a film record is reproduced is a result of striations, scratches and dirt on the relatively clear portions of the record where the light passes freely into the photo-electric cell. Various arrangements have been proposed for reducing the ground noise irom film sound records by the use of supplementary apparatus applied to the sound recorder for modifying the record in the original recording. In certain cases it is found to be objectionable to add anything to the recorder which will add oomplication thereto or require any additional attention by the operator, this being particularly true in the case oi portable instruments. It is the object of my invention to provide an improved method and apparatus ior reducing, not eliminating, the cause of the objectionable ground noise in a copy of the sound record.-

My invention will be better understood iroin 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. l is a diagrammatic view of one term of apparatus embodying my invention; Figs. 2 and 3 are detail views thereof and Figs. c and 5 are enlarged views of fragments respectively or an original sound record iilm and a copy 'thereoi'msde in accordauce with my invention.

In illustrating my invention I have shown apparatus ior making the photographic copy lrom a previously made photographic film record which record may be an original sound record or a duplicate thereof suchd'or example as that made by printing or by ire-recording 1mm 1 him, a phonographic or a magnetic rec- 0rd. Moreover the sound record to be copied may be of either the variable density type or the variable width type.

In Fig.1 I have shown the film '1 being unwound from the roll 2 and being wound up on the roll 3, which film for example, may be an original negative soundrecord film, a fragment of which appears in Fig. 4. At 4 is shown the sensitive film being unwound'irom the roll 5 and wound up on the roll 6 upon which film u the sound record on film 1 is being printed. The particular form of printing apparatus employed forms no part of and is immaterial to my present invention. Various well known film. printers may be used. For convenience of illustration I have shown in a diagrammatic manner a printer of the contact type wherein the two films 1 and 4 pass in contact beneath the printing light. In this printer. the two films are shown moved by engagement with the common sprocket wheel 8 while p sing between members 9 and 10. Light from the source 11 passes through the opening 12 'to the films. The two films are shown led to the printer by a common sprocket 14 and are withdrawn from the printer by the sprockets 15 and 16, the

driving means for the sprockets being omitted from the drawing. Between sprocket blend the printer suitable friction rollers 17 are shown by means oi which the films are given the 35 proper tension upon entering the printer.

Between the film roll 2 and the sprocket 14 film 1 passes a gate shown for example as the curved member 19 having the opening 20 arranged opposite the sound record track on the At one side of the gate is the light source and optical system 21 by means of which a narrow light beam is projected through opening so on the ills. the beam forming a line of light men the him, see Fig. 2. Behind the film is the photo-electric cell 24 in a position to receive the light beam as modified by the sound record. Connected with the cell 24 is the amplifier 25,

the lull wave rectifier 26 and the filter :l'l i i-om there is received a direct my the latter of which current which varies substantially with the am plitude of the sound waves recorded on film 1. Between film roll liand sprocket 14, film e passes a gate whichis shown for example as the curved member 29 having therein the opening 30 arranged opposite the sound track oi film 4. By means of the light source-and optiaystem 31, which for example may or may not be similar to thatnhown at 21, a light beam uprolectedthrough the openinzwontctbe no sound track 01 him 4, The light thus projected on the film is controlled to give a supplemental exposure of the sound track in accordance with the output of the filter 27 whereby said exposure shall be a minimum when the amplitude of the waves recorded on film 1 have a given maximum value and shall be a maximum when the amplitude of the recorded waves are a minimum. Various means may be employed thus to control the supplemental exposure of the sound track. In the form of my invention illustrated, the sound record being printed is of the variable width type and the amount of supplemental exposure is controlled by the use of a shutter arranged in the path of the light beam and movable transversely of the film in accordance with the output of the filter 27. Referring to Figs. 1 and 3, the shutter 33 is mounted on the arm 34 attached to the coil 35 which is connected with the filter 27 through switch 28. Coil 35 is mounted on pivots 36 within the field of a magnet having pole pieces 37. The small stop pin 38 projecting from the member 29 is posltioned in the path of movement of the arm 34 which is yieldinglv held agaimt the stop by the coil spring 39. In this position ofthe shutter substantially one half of the sound track is exposed, or ii preferred more than one half may be exposed. Energization of the coil 35 effects a counter-clockwise rotation oi the shutter as viewed in Fig. 3 whereby more and more light is cut 0!! depending upon the degree of rotation. In Fig. 4, the negative film 1 has the sound record 40 which in the region indicated by 41 has a very large amplitude and in the region indicated by 42 has zero amplitude corresponding to no sound, the sound track in the latter region being exposed for substantially one half of its width. The positive print 43 made from this negative and illustrated in Fig. 5 shows at 44 the eiiect oi! the supplemental exposure. From this figure it will be seen that where the amplitude of thesound waves is a maximum the amount of supplemental exposure is a minimum and where the sound volume is very small or is of zero value the supplemental exposure is the greatest. I prefer to have the two exposures slightly overlap at those times when there is no sound on the record, however, under certain conditions it may be preferable to have them Just meet at such times or even to come not thus leaving a narrow clear cen- Inasmuch as the filter circuit introoertain electrical time lag in the response of the shutter the supplemental exposing apparatus is spaced from the printer along film 4 a distance which is less than the correspondin: distance along him 1 or the optical system This diflerence in spacing is suflicient, takmay also be varied, ii desired,

convenient, hence I arrange close as practicable to the member 29. In'makin: a variable density record with this apparaswitch 28. Such may tus, however, I prefer that the shadow shall not be sharpbut rather be as uniform as possible across the sound track. For this purpose the shutter would be arranged as close as practicable to the optical system 31 and for maximum effectiveness it obviously would be adjusted to have a swing suiiicient substantially to completely cover and uncover the light opening in the end of the optical system. Instead of the shutter construction which I have illustrated for varying the supplemental exposure I may in certain cases prefer to use a well known form of oscillograph or reflecting galvanometer such as is commonly employed in the recording of sound of the variable Width record type and as shown for example in the Dimmick Patent 1,820,785, Aug. 25, 1931. For the making of record copies of the variable density type I may also in certain cases prefer to use instead of the shutter apparatus illustrated a light valve such as shown for example in the Wente Patent 1,638,555, August 9, 1927, to produce the desired variation in supplemental exposure of the film copy. It is to be noted that the purpose of the filter 27 is to iron out the waves and to provide for a relatively smooth line of the supplemental exposure. In the event that the light controlling device employed has a low natural period of vibration or period below the audible range, I may dispense with the filter and rely entirely upon such device to give the desired smooth line.

By providing for the elimination of ground noise at the time of making a copy of the sound record, I not only avoid unnecessarily complicating the recording apparatus but I am able to take any sound record with which there is an objectionable amount of ground noise and by making a copy thereof in accordance with my invention to greatly reduce it not to entirely eliminate the ground noise heard when the copy is used to reproduce the sound. In the event that the operator desires to render inoperative the supplemental exposing means at any time he simply opens the circuit by means of the be found convenient when the record includes sharp or irregular sounds such as pistol shots. Ii. desired the record film itself may be arranged to control the switch automatically in any well known manner, for example, by the use of notches cut in the edge of the film.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various modifications may be made without departing from the spirit and scope of my invention which modiilcations I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent 0! the United States, is:

1. The method of making a sound record copy whichis relatively free 01' the cause oi ground noise from a previously made sound record making a contact print or the sound record, producing a current which varies in accordance with the average amplitude of a number of successive waves of said record and variably exposing the normally clear portion of the print in accordance with said current.

2. In apparatus for making .a print 111m from ord film, means for directing a light beam on the print film to expose the same and means including a shutter responsive to said current for varying the amount of said beam reaching the print film at portions thereof unexposed by said printing means.

3. In apparatus for making a print film from a sound record film, means for printing the sound record on the print film from the record film, means for producing a current variable in accordance with the average amplitude of a number of successive recorded waves or the record film, means for directing a light beam on an unexposed part of the print film, a, shutter in the path of said beam and means responsive to a decrease in said current corresponding to a decrease in said amplitude for moving said shutter in a direction to exposea greater part of said print film unexposed by said printing means.

4. The method of making a sound record copy which is relatively free from the cause of ground noise from a previously made sound record which comprises exposing a light sensitive strip in accordance with the waves of the sound record, producing a current which varies in accordance with the average amplitude of a number of successive waves of said record, exposing an unexposed part oi the strip to light of a uniform intensity and varying the exposed area of of the strip in accordance with said current.

5. The method of making a sound record copy which is relatively free from the cause 0! ground noise from a previously made sound record film which comprises printing the sound record from the record film at successive points thereof on current.

6. Apparatus for making a copy of a previously made sound record which copy is relatively free from the cause of ground noise which light sensitive strip in accordance with the variations of said sound record, means for producing a current which varies in accordance with the average amplitude of a number of successive waves of said previously made soundrecord and means for exposing portions of said strip otherwise unexposed in accordance with said current.

7. Apparatus for making a copy of a previously made sound record which copy is relatively free from the cause of ground noise which-comprises means Ior progressively exposing a light sensitive strip in accordance with the variations of said sound record, means including a light sensitive device associated with said record for producing a current which varies in accordance with the average amplitude of a number of successive waves of said sound record, a source of light of uniform intensity arranged to expose portions of said strip otherwise unexposed and a shutter responsive to said current for controlling the exposure of the strip by said light. 1

CHARLES D. GREEN'I'REE.

comprises means for progressively exposing a

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