Note: Descriptions are shown in the official language in which they were submitted.
SPECIFICATION
This invention relates to a movie film with dual
optical sound tracks, methods for reoordi~g and reproducing audio
information and to a scanning apparatus for reproducing the audio
information.
BACKGROUND OE' THE II~VENTION
_ _ _ _
Movie films with dual sound tracks are often used~ for
example, in a bilingual production or to provide stereophonic
sound. Dual sound tracks have not normally been available
except on 16 mm. or 35 mm. film. There are situations where the
smaller size and weight of an 8 mm. projector and film make it
preferable. As an illustration, in-flight movies shown on commer-
cial airlines commonly use 8 mm. equipment. However, many flightson which movies are shown are international, and often carry
passengers who do not speak the same language. The ability to
utilize bilingual sound tracks would enable more viewers to
enjoy the film.
A standard 8 mm. movie film does not have a provision
for a second optical sound track. The Super-8 film format,
however, has an image location which leaves a margin along one ~-
edge that is used for a primary optical sound track. There is
also a margin, although narrower, between the sprocket holes
and the other film edge.
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THE PRIOR ART
It has been proposed to utilize dual magnetic sound
tracXs with the Super-8 film, see Ha$1er 3,452,161. Film with
magnetic sound track is more expensive to produce than that with
an optical sound track, and the magr~etic materîal on the face
of the film adds to its thickness, increasing the size of the
reels which are necessary. Lewin 2,950,971 shows a dual sound
track film having an infrared optical track on one surface and
a magnetic sound track on the other. Michelson 3,502,398,
3,502,399 and 3,502,404 illustrate multiple sound track config-
urations on 16 mm. or 35 mm. film.
THE INVENTION
The present invention provides for recording and
reproducing a second optical sound track in the narrow margin
between the sprocket holes and the film edge of the Super-8
film, with fidelity at least comparable to that afforded by the
primary sound track in the larger margin. The use of the terms
"primary" and "secondary" herein differentiates between the ~`
sound track in the usual location, the wide margin between the
images and the film edge, and the sound track in the narrow -
margin between the sprocket openings and the other film edge
which is made feasible by the present invention. The fidelity
of the secondary sound track is not inferior to that of the
primary sound track. j -
One feature of the invention is the provision of -
a Super-8 mm. film with both primary and secondary optical sound `
tracks thereon. More particularly, the primary sound track is
in one margin and has a nominal dimension for 100 percent -
modulation of .020 inch. The secondary sound track is in the
other margin of the film and has a nominal dimension for 100
percent modulation of .010 inch.
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Another feature is the method of optically record-
ing audio information on a film by directing a light beam on
the film which has a beam dimension in the direction of move-
ment of the film of the order of 0.2 of the wave length on
the film of the maximum frequency to b~ recorded, and vary- `
ing the other dimension of the light beam in accordance with
the audio information.
A further feature is the method of reproducing sound
so recorded on a motion picture film by establishing a light
beam and directing it on the sound track of the film, having a
fixed beam dimension in the direction of movement of the film
of the order of one-half the wave length on the film of the
highest recorded frequency to be reproduced.
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Yet another feature is the provision of apparatus ;
for establishing a scanning beam for the audio sound track and ~ '
for focusing and aligning the beam with the sound track. More ~ ;
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particularly, the light beam is projected on the film through
a cylindrical lens which is movable axially of the light beam --
to focus it on the film surface and is rotational about the -
axis of the light beam to align the beam at right angles to the
sound track. ~--
Further features and advantages of the invention will ~ -
be seen from the following specification and the drawings,
in which: -
Figure 1 is a view of the film Qhowing the general `-
format of the Super-8 mm. film with dual optical sound tracks
in accordance with the invention;
Figure 2 is a block diagram of a dual channel sound .-
reproducing system illustra~ing the invention;
Figure 3 is a perspec*ive of the scanning apparatus
of the invention;
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Figure 4 is an elevation of the film and scanning
head; ~;~
Figure 5 is an enlarged fragmentary view of the lens
carrier and adjusting means;
Figure 6 is a fragmentary plan view of the lens, lens
carrier, mask, film and photocells;
Figure 7 is a diagram illustrating the scanning of
the primary sound track; ~ -
Figure 8 is a diagram illustrating scanning of the
secondary sound track;
Figure 9 is a block diagram of an apparatus for
recording the audio information on the film, and
Figure 10 is a curve illustrating volume compression
of the audio signals to be recorded.
A section of the film 15 with the Super-8 mm. format
is illustrated in Figure 1. A serîes of images 16 occupy the
center portion of the film. The images are spaced from the
edge 17 leaving a margin for the primary sound track 18. As
is common with optical sound tracks, there is an opaque back- `
ground and a transparent center portion, the width of ~hich rep-
resents the audio information. Primary sound track 18 occupies
a longitudinal ba~d .030 inch wide and for 100 percent modu- ~`
lation has a transparent dimension of .020 inch.
Sprocket holes 20 are spaced from the film edge 21
leaving a margin of .020 inch in which the secondary sound track
22 is located. The nominal transparent dimension of sound
track 22 for 100 percent modulation is .010 inch.
A syste~ for optically scanning the sound tracks
and reproducing the audio information is illustrated in Figure
2. A light source 25 generates a two light beams 26 and 27 `
which are directed through lens systems 28 and 29 and masks 30, -
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31 to the sound track on film 15. The light beams 26 and ~7
have a narrow di~ension in the dire,tion of movement of the film
and a dimension transverse to the f;lm which is no greater than
the maximum width of the sound track so that it does not over-
lap the film edges, the images 16 or the sprocket holes 20. The
beams are modulated by the audio information of the sound track
3~
and the modulated light is received by photocells ~3~-~4 which '
convert the varying intensity of the light beams to a corres-
pondingly varying ~lectrical signals. The signals are connected
w;th amplifiers 36, 37 and the amplified outputs are connected
with speakers or individual earphones. The two sound tracks
may provide bilingual audio for the movie so that the viewer ~ ~;
can select which language he wishes to utilize. Alternatively, -
the dual sound tracks may be used to provide stereophonic sound
to accompany the film. The nature of the audio information re-
corded is not a part of the present invention. ;
The small size of the secondary sound track re- -
quires that the scanning means provide for precise contral
of the geometry of the light beam. This enables the develop-
ment of a high fidelity audio signal with a minimum of noise and
distortion.
The preferred form of the optical scanning apparatus
for the two track film is illustrated in Figures 3-6. A lamp
40 is a source for light which is directed through an aperture
41 in a mask plate and an infrared filter 42 to two bores 43,
44 in a body 45 Nhich carries the focusing lenses and further
beam masks, as will appear. `The mask plate aperture 41 adjacent
lamp 40 has a length corresponding to the length of the filament
of lamp 40. This keeps reflected light from the bores 43, 44
and prevents the development of secondary images of the sound
track. The wid~h of aperture 41 contributes to the establishment
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of the dimension of the light beams in the direction of the
movement of the sound tracks 18, 22 and prevents the development
of secondary images from reflected light. The infrared filter
42 removes the infrared light compo~ent which might penetrate
the opaque portions of the sound track. The filtered light
passes through a cylindrical lens 47 from side to side in a
direction transverse to the axis of the cylinder. The lens
focuses the light providing a sharply defined beam with its
narrow dimension in the direction of movement of the sound ~
track, Figure 6. ~- -
Each lens 47 is mounted in a tubular carrier and the
carriers are received in the bores 43, 44 of the body 45. The
carriers may be adjusted in poSitioD both axially and
rotationally to focus and align the light beams.
Photocells 34, 35 are located in housing 50 carried
by an adjustably mounted bracket 51. The electrical signals `~
are derived through cables 52, 53.
The lateral dimension of mask opening 41 and the
focusing effect of the cylindrical lenses 47 establish the
dimension of the scanning beams in a direction longitudinally `
of the sound tracks. Mask plate 55 has aperatures 56, 57 which
establish the dimension of the light beams 26, 27 transverse
to the longitudinal extent of the sound tracks. A film guide
60 engages film edges 17, 21 to ma~ntain the position of the
film with respect to mask openings 56g 57 as the film passes
the scanning head to avoid interference which would be caused
by misalignment o-E the sound tracks and light beams.
Figures 3, 5 and 6 illustrate the adjustment of the
lens 47 to focus and align the light beam. Lens carrier 4~ ` :
is a tubular metallic element received in the bore of body
43. The carrier has longitudinal cutouts 62 w~ich allow the
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carrier to fit the bore. An actuating arm 64 is secured to the
wall of the carrier and extends outwardly through a hole 65 in
the body 43. Hole 65 has a dimension larger than that of arm
64 to accommodate limited movement of lens carrier 48. A first
screw 67 threaded in the body 45 bears on the upper surface of
the arm. A second screw 68 threaded in the body 45 has an
eccentric extensioD 69 at its inner and which bears against the
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front surface of arm 64 to move the carrier axially of the bore
of body 45 and thus axially of the light beam. A spring 70
held by a screw 71 bears against the surface of arm 64 urging
it against screw 67 and extension 69 to hold the carrier 48
in position. Adjustment of screw 68 moves the lens carrier
back and forth to focus the light beam while adjustment of screw -
67 rotates the carrier to align the light beam at right angles
to the sound track. Figures 5 and 6 illustra~e the lens carrier
for the primary sound track beam in bore 44. The lens carrier ;
for the secondary sound track beam is a mirror image with the
actuating arm extending in the opposite direction.
Adjustment of the screws to optimize the lens position
is prererably done while scanning a test film and observing the
output of the photocell on an oscilloscope. Both the focus and
alignment of the light beam are adjusted for maximum output froM
the photocell.
Typical sound tracks and scanning beam dimensions are
illustrated in Figures 7 and 8. The primary sound track 18
of Figure 7 has a width of .030 with the peak-to-peak dimension
of the audio information for 100 percent modulation being .020.
The scanning beam 27 has a dimension of .024 inch laterally of
the sound track, established by mask opening 57. The secondary
sound track 22 has a width of ~020 inch and a peak-to-peak
dimension for 100 percent modulation of .010 inch. Light beam
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26 has a lateral dimension of .012 inch determined by mask open-
ing 56. In each case the narrow dimension of the light b~am,
in the direction of movement of the sound track is determined
by the highest recorded frequency to be reproduced and the
fidelity which is desired. In a typical system having a maximum
audio frequency of 5000 Hertz and a film speed of 4 inches per
second, the longitudinal beam dimension is one-half wave length
or .0004 inch. The half-wave length beam dimension results in
cancellation of second order harmonic distortion in the sound
track. -~
A system for generating the audio sound track on film
15 is illustrated diagrammatically in Figure 9. A signal from
an audio source 75 is connected with a volume compressor 76,
the output of which is connected to a film modulator 77. The ;
film modulator generates a light beam which has a fixed dimension
in the direction of the ~ongitudinal movement of the film sound
track and a variable dimension at right angles thereto or
transverse to the movement of the sound track. The variable ~;
dimension is controlled in a suitable manner, as by a light
valve or a galvanometer and mirror (not shown) to vary in accord- ~`
ance with the audio signal.
In order to achieve the desired fidelity, the fixed
dimension of the recording light beam is preferably of the order
of .2 of the wave length of the highest frequency to be recorded
on the film. With a frequency of 5000 Hert~ and a film speed of
4 inches, the fixed dimension of the light beam is .00016.
This relationship optimizes recording of the fundamental and
reduces the second harmonics which result from the aperture
effect of optical recording.
The volume compression of the audio signal prior to
recording is particularly important because of the restricted
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dynamic range of the sound tracks, and particularly of the second-
ary sound track with its very narrow width. Volume compression
amplifies the low level audio signals and reduces the high level -
signals. In Figure 10, linear amplification, solid curve 80 is
compared with volume compression, broken line curve 81, both
plotted on a logarithmic scale. The primary sound track 18 may
have a dynamic range of 20db while the secondary sound track
22 has a dynamic range of 14db.
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