Optics: motion pictures – With sound accompaniment – Common picture and sound record carrier systems
Reexamination Certificate
2000-05-11
2002-02-26
Adams, Russell (Department: 2851)
Optics: motion pictures
With sound accompaniment
Common picture and sound record carrier systems
C352S037000, C369S125000
Reexamination Certificate
active
06351302
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to motion pictures and more specifically to an analog sound track digitizer for motion pictures.
The best prior art analog sound track digitizer is described and illustrated in the Carlsen U.S. Pat. No. 5,526,075. This earlier version of the inventors scanner was found difficult to adjust for the variations in errors in film sound tracks. Some of these included variations in the location of the sound track or weave, the minimum width of the tracks when there was no modulation, changes in film density, scratches, blotches and the inability to deal with very large noise transients caused by breaks in the film and splices.
The present standard for sound-tracks imaged on motion picture film dates back to 1967 wherein the location on, and the area covered by stereo sound tracks on film was specified. This standard describes the dimensions of the track and the related standards used today. This method places two tracks along one edge of the film which are of two types, variable density and variable area, the last of which is used almost exclusively. Inherent to this method of reproducing sound is the undesirable effect of background noise and rumble due to the nature of the plastic medium and residue of the film emulsion passing through the light beam of the photo sound detector. Dolby Corporation with its Dolby B,C,H, etc has pretty much dominated the industry both with its noise reduction systems for movie film and those for magnetic tape. However even with the best system Dolby can offer, the sound suffers distortion and amplitude variations caused by the extreme processing needed to remove random noise from between the normal sound peaks.
The introduction of the compact disk or CD with its almost perfect sound reproduction ability has stimulated interest by several companies to try and incorporate digital-quality sound on film.
This has proven to be a formidable problem because of the immense amount of digital information required to produce the multiple channel digital formats while keeping the old stereo sound tracks intact for general use by most movie theaters. Also the cost of the digital reader-heads to decode the new digital sound tracks is very high. Dolby Laboratories has recently developed its Theater Digital System that is currently being tested in a number of theaters. Sony Corporation also has introduced their digital system. It should be noted that these systems are expensive and complicated. Also the economics of necessary maintenance and the actual working-life of a digitally-encoded film sound-track is yet to be established.
None of the new digital sound systems that are being developed by these major corporations at great expense, does anything to improve old analog film sound-track that remain on the film.
The background of the present invention relates to the reproduction of sound from motion picture film. Two of the biggest hurdles to overcome in the effort to improve sound from the movie film are the increase of high frequency response and the reduction of background noise. Filters to reduce background noise also reduce high frequency response which forces the user to use compression and dynamic filter techniques. These lead to unwanted distortions and complexity.
Present analog sound track readers used in moving picture theater projectors read the variable width sound tracks on motion picture film by back lighting the sound track portion of the film with a focused slit of light which is arranged perpendicular to
1
l the direction of travel of the film and just wide enough to span both tracks of the normal stereo print. A dual photo detector is placed on the opposite sides of the film to intercept the light which passes through the sound track portion of the film. The two tracks, which are transparent to light, vary in width as the film moves past the slit light source. The thickness of the slit light source and the instantaneous width of the sound track as it passes the photo detector determines the total amount of light falling on the photo detector and in turn the amount of electrical output from the detector. As the film continues to move past the detector the sound information which modulates the width of the tracks is converted to an electrical audio signal. Present photodiode detectors are linear devices and any change in the amount of light falling on the detector causes a corresponding electrical output. Electrical output changes due to different changes in the width of the sound tracks cause useful output. However changes due to residual emulsion, scratches, dirt and light aberration through the film plastic medium cause unwanted light modulation and are perceived as background noises in the electrical output.
The frequency response of present systems, irrespective of the noise limitation, is ultimately limited by the recording camera response. In reality, the limitation is based on the thickness of the slit light source used during playback. The best of the slit lenses produce about a 0.5 mil slit thickness which produces a high frequency limit of about 5 KHZ. These wide band slit lenses are usually used in special playback systems such as Dolby stereo or Surround Sound and are followed by dynamic noise filters high frequency boost amplifiers and expanders. These require that the film be specially recorded with compression techniques to improve signal and noise ratios. Generally slit sizes are used which produce high frequency limits of about 9 to 16 KHZ.
It is an object of the invention to provide an improved analog sound track digitizer having the highest accuracy and having a minimum amount of noise and distortion.
It is also an object of the invention to provide an improved analog sound track digitizer having a novel weave tracking circuit.
It is another object of the invention to provide an improved analog sound track digitizer having a circuit which allows the scanner to track minimum width tracks that are as little as
{fraction (1/4+L )}the minimum standard set by the industry.
It is an additional object of the invention to provide an improved analog sound track digitizer having an automatic gain control (AGC) that was added to the video amplifier circuit which allows for changes of 10 to 1 in light density and/or film density.
It is a further object of the invention to provide an improved analog sound track digitizer having a new method for comparing the video signal with a reference signal.
It is another object of the invention to provide an improved analog sound track digitizer having novel noise canceling circuits which work independently to remove the effect of breaks or scratches as large as 1/10 of an inch on the film and blotches of any size.
SUMMARY OF THE INVENTION
The novel analog sound track digitizer for motion picture projectors has been designed to be retrofit to existing sound head housings but the system can also be incorporated in newly manufactured sound head housings.
The present invention includes structure for linearly scanning a light beam of appropriate dimensions and intensity perpendicularly across the movie film sound tracks. A photo detector is placed on the opposite side of the film to intercept the light beam such that when the light beam is directed on the dark or emulsion portion of the film there is no output from the photo detector. When the light beam is directed on the transparent portion of the film the photo detector is saturated. The resulting output of the photo detector is a group of electrical pulses each having a width proportional to the width of the related transparent portion of the film sound tracks and all having a fixed amplitude. Continuously scanning the light beam at a fixed rate and frequency across the films sound tracks produces a continuous stream of pulses each changing in width at a rate related to the instantaneous changes in the width of the transparent portions of the sound track. The scanning frequency of the beam is chosen to produce the desired high frequency response of the system, usually twice the desired frequency.
The
Carlsen, II George D.
Vale Ronald W
Adams Russell
Fuller Rodney
Logan II Charles C.
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