US2196735A

US2196735A - Sound recording

Info

Publication number: US2196735A
Application number: US168779A
Authority: US
Inventors: John H Mcleod; Walter K Grimwood
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1937-10-13
Filing date: 1937-10-13
Publication date: 1940-04-09
Anticipated expiration: 1957-04-09
Also published as: GB519282A

Description

April J. H. MCLEQD El AL 2,196,735

SOUND RECORDING Filed Oct. 13, 1937 John hf McLeod INVENTORS Mil-W lmxbwz- ATTORNEYS Patented Apr. 9, 1940 PATENT "OFFICE.

SOUND RECORDING John H. McLeod and Walter K. Grimwood,

Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application ctober 13, 1937, Serial N6. 168,779

3 Claims.

This invention relates to sound recording and particularly to push-pull sound-on-film record- It is an object of the invention to provide a so-called noiseless or class B push-pull recording system using variable area.

t is a particular object to provide a toed-in variable area class B push-pull sound record and a method of producing such a record.

It is a further object of the invention to provide a ribbon type light valve of extremely simple construction capable of producing the abovementioned sound record.

According to the invention, a ribbon type light valve consisting of a single ribbon in the usual magnetic field and an aperture at least as wide as the ribbon, is connected to an'input circuit carrying the signal to be recorded. An optical system including a source of light and suitable spherical and cylindrical lenses projects a shadow image of this ribbon to a sensitive film on which the record is to be made. The optical system must besuch thatthe edges of this shadow image are sharp (i. e., the image must be longitudinally sharp) and the image should exactly fill the sound track area for zero input signal. Furthermore, a

mask exactly overshadowing the remainder of the film is placed as nearly as possible in the plane of the ribbon or of a real image thereof, such as at the film itself or at any intermediate image. Positioning the mask near an intermediate image is preferable since otherwise, the mask would tend to interfere with the vibration of the ribbon or the motion of the film when placed near enough to either to insure exact and sharp masking.

For zero input signal, no light reaches the film since the shadows of the ribbon and that of the mask are exactly supplementary to each other.

On the introduction of a modulation, the positive duced from the two sides in accordance with the,

negative and positive amplitudes respectively.

The usual advantages of class B push-pull recording as discussed in a copending application, Serial Number 168,777, patented June 6, 1939, No. 2,161,369, filed concurrently herewith by McLeod, one of the present inventors, and

Morse, are thus obtained in a unique and convenient manner requiring relatively simple light valves and in the preferable embodiment, a simple uni-axial optical system. The positive sound track printed from the above negative sound track consists of a succession of transparent areashavin'g widths varying in accordance with the input signal and alternately, according to the positive and negative halves of each cycle, bordering on the sides of the area assigned to the sound record. As is the case with all class B push pullrecordings, the positive sound track approaches a maximum density for small input signal. 1 i

Other objects and advantages of the invention will be apparent'from the following description when read inconnection with the accompanying drawing, in which: 7

Fig. 1 is a schematic drawing of a sound recording system incorporating the invention. Fig.2 is aplan of the optical system employed in.Fig.l., v c

Fig. 3 schematically shows a recordingsystem incorporating a preferred embodiment of the invention.

Fig. 4 is a plan of the optical system employed in Fig. 3.

Fig. 5 is an elevation of this optical system.

In Fig. 1 an input signal picked up by a microphone I0 is passed through its accompanying amplifier H to any suitable input circuit shown as a transformer having a primary l2 and a secondary [3. A ribbon type light valve comprising a ribbon M in the usual magnetic field (not shown in Fig. 1 but portions it of the pole pieces appear in Fig. 2) is connected across the input circuit. An optical system comprising a source of light 20. spherical lenses 2| and 23, and a cylindrical lens 26 projects a sharp shadow image of the ribbon l4 onto a film 30 having the usual picture area 3|. Any suitable optical system may be used provided the shadow image of the ribbon l4 exactly fills the area 32 provided therefore on the film. That is, the edges of the ribbon 14 must be exactly imaged by the lens system shown as the spherical lens 23 and the cylindrical lens 26 along the

lines

33 and 34. This is clearly shown in Fig. 2.

The height of this shadow image is limited by a mask 24 having a slit 25, preferably positioned near the lens 23 and arranged so that the cylindrical lens .26 projects a sharp image of this slit 25 onto the film. This is the usual expedient for providing sharp resolution.

According to the invention, a mask 22, shown approximately in the plane of the ribbon I 4 is positioned to exactly overshadow the remainder of the film not covered by the shadow image of the ribbon l4 itself. As discussed in the general case above, this mask 22 may be in the plane of the ribbon hi, the plane of the film or in the plane of any intermediate image of this ribbon l 5.

The preferred embodiment of the invention wherein the mask is in the plane of an intermediate image is shown in Fig. 3, wherein a lens system shown as a simple positive lens 21 projects an aerial image of the ribbon M at the position indicated by the broken lines 14. Themask 22 is replaced by a mask 22' which together with the shadow image Hi just cuts out all the light when no input signal is present.

Figs. 4 and Bindicate clearly how the lens 21 forms an exact image M of the ribbon I4 in the plane of the mask 22 and further how this image is projected by the lens 23 onto the film 30. How the cylindrical lens 26 and slit 25 perform their function of exactly determining the height of the recording beam as it strikes the film 30 is also clearly shown.

In Figs. 1 and 3, the single aperture in the magnet of the light valve is indicated by broken line Hi. In Figs. 2, 4, and 5, this aperture is shown by indicating the magnet I 6 in cross section. The mounting and tensioning of a ribbon in the magnetic field is well known in the art and need not be discussed in detail here. The aperture l5 must be at least as wide as the ribbon 4. In fact, it is conceivable that it could be arranged to be exactly the same width and to act as the mask for this ribbon H, but from a practical point of view it is not convenient to do so and hence the only arrangements shown include the introduction of an

extra mask

22 or 22.

Having thus described our invention and the manner in which it may be practiced, we wish to point out that it is not limited to the specific embodiments shown, but is of the scope of the appended claims.

recording system comprising an input circuit carrying the signal to be recorded, a single ribbon, single aperture light valve across the input circuit, a sensitive film having a portion adapted to receive the sound record and an optical system including a source of light, for projecting a longitudinally sharp shadow image of the ribbon onto the film, said image exactly covering said portion for zero input signal and stationary masking means in a plane other than that of the ribbon exactly overshadowing the remainder of the film.

2. A variable area push-pull sound-on-film recording system comprising an input circuit carrying the signal to be recorded, a single ribbon light valve having an aperture at least as wide as the ribbon which is connected across the input circuit and an optical system including a source of light for projecting a longitudinally sharp shadow image of the ribbon in the plane adapted to be occupied by the sensitive recording medium and stationary masking means for limiting the width of said plane to exactly the width of said shadow image, whereby, at zero input signal said shadow image and the shadow of said masking means are exactly supplementary.

' 3. A variable area push-pull sound-on-film recording system comprising an input circuit for carrying the signal to be recorded, a single ribbon single aperture light valve across the input circuit and an optical system including a sourceof light for illuminating the valve, lenses for projecting a longitudinally sharp intermediate shadow image of the ribbon between the valve and the plane for the film and for reimaging this shadow image in the film plane and stationary masking means in the plane of the intermediate image exactly supplementing its width at zero input signal only.

JOHN H. McLEOD. WALTER. K. GRIMWOOD.