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Патент USA US2136724

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_ Nov. 15, 1938.
5. F. MILLER
“
2,136,724
SOUND RECORDING
Original Filed June 24, 1935
I 2 Sheets-Sheet 1
PIE. 3. 23
INVENTOR.
Burn-0N F.’ M/LLEI? ‘
ATTORNEY.
Nov. 15, 1938.
'
B, F, WLLER
SOUND
2,136,724
RECORDING
I
Original Filed June 24, 1935
2 Sheets-Sheet 2
INVENTOR.
BUQTON i’.- M/LLEQ
BY
ATTO
_
Y.
Patented Nov. 15, 1938
2,136,724“
UNITED STATES PATENT OFFICE
2,136,724
SOUND‘ RECORDING
Burton F. Miller, Hollywood, Calif., assignor to
‘United Research Corporation, Burbank, C'alif.,
a corporation of Delaware
Original application June 24, 1935, Serial No.
28,109. Divided and this application April 4,
1936, Serial No. 72,730
2 Claims. (Cl. 179-1003)
This invention relates to light valves for photo
has a tendency to weave sideways when passing
graphically recording sound upon a moving light
a
sensitive ?lm.
,
On'e object of the invention is to record on a
5 moving ?lm a graphic representation of sound
waves in such a manner as to have the graphic
representation of as large an amplitude as possi
ble with a relatively small movement of the speech
101
current carrying conductor.
This is accomplished by providing an aperture
through which a beam of lightiis projected upon
a uniformly moving light sensitive ?lm. The
aperture is in the form of an isosceles triangle
having a very small height in comparison to its
15: base. A speech current carrying conductor is
placed over thetriangular aperture parallel to
itsbaseso as to cover part of the aperture when
no current‘ is‘ flowing.
When a modulated al
ternating current ispassed through the conductor
20. the interaction between the magnetic force‘ set up
by the modulated currentand a strong magnetic
?eld provided adjacent the aperture causes the
conductor to vibrate in accordance with the am
plitude and frequency of the sound being recorded.
25, This vibration allows a greater or‘less' length of
the aperture to be exposed to the ‘beam of light.‘
Another object of the’ invention is to keep the
zero line or center of ‘modulation of the wave
forms always in the center of the sound track.
302 Another object of the invention is to reduce
the ground noise due to‘ the‘ grain of the emul
sion, or to dirt, oil, etc., adhering to the clear
portions of the sound track (positive ?lm) .
Heretofore; sound recording devices of the
variable areaj type obtained ground noise reduc
tion either by biasing the current carrying vibra
tory conductor or by the use of auxiliary shutters
which were automatically controlled to follow the
envelope of the wave forms and thus allow only
40, the areas between the successive wave forms to
‘
be exposed. Both of these‘methods have inherent
disadvantages; ‘the use of shutters entails rather
complicated and sensitive apparatus which, due
to electrical or mechanical lag or 'to faulty ad
45, justment, ‘may cause clipping of the sound peaks.
Especially is thistrue in the case of stacatto type
sounds where the rise in amplitude is practically
instantaneous. When biasing of the conductor
is employed, the zero or center of modulation is
50. moved as close as possible to the edge of the clear
‘ ‘ portion of the sound track; that is, ‘all the peaks
of both the high and low level sounds are as
close as possible to one edge of the track. Due
the point of sound translation; this weave is at
times su?icient to allow one end of the light slit
to cut off some of the wave peaks; although the
peaks of the high level sounds may be cut off a a
substantial amount without any apparent dis
tortion of the reproduced sound, this is not true
of the low level peaks.
By keeping the center of modulation always in
the center of the sound track, there will be no 10
chance of clipping the low level peaks.
The present application constitutes a division
of my co-pending application, Serial No. 28,109,
?led June 24, 1935. The above co-pending ap—
plication discloses and claims the light valve per 15
se which is shown and described herein.
Referring more particularly to the drawings,
Fig. 1 is an enlarged fragmentary view of the
triangular aperture and its accompanying opaque
speech current carrying conductor.
20
Fig. 2 is a sectional view taken along the line
2——2 of Fig. 3 showing my improved form of ligh
valve for recording variable area.
‘
Fig. 3 is a sectional view taken along-the line
3--3 of Fig. 2.
Fig. 4 is a schematic view showing the appli
cation of noise reduction to my improved form .
of light valve.
Fig. 5 is an enlarged fragmentary view of the
section of sound ?lm showing a double edged 301
variable area sound track as recorded by my
improved light valve.
Fig. 6 is an enlarged fragmentary view of a
section of sound track on a negative ?lm.
Fig. 7 is an enlarged fragmentary view of a sec 35:
tion of sound track on a positive ?lm.
Fig. 8 is a diagrammatic view showing the
method of regulating the noise reduction.
Referring now to-Figs. 2 and 3, the light valve
I comp-rises an upper magneticframe 2 having
a pair of depending legs 3 and 4. A lower base
plate 5 is secured'to the legs 3 and 4 as by screws
6. The frame 2 has a hollow core 1 comprising
one of the pole pieces and is provided with a mag
netizing coil 8. Direct current of as constant a 45)
value as possible is passed through the coil 8 to
produce the high magnetic flux between the core
1 and a pole piece 9 secured to the base plate 5
in substantial alignment with the core ‘I. The
pole piece 9 and also the base plate 5 are provided
with an aperture ID to allow a beam of light to be
projected therethrough.
The triangular aper
to the shrinkage of the ?lm or inaccuracies in
ture l I comprising the light slit is formed by
means of three plates I2, l3, and I4, (Figs. 1
55‘. the reproducing machine, the ?lm thus biased
and 2) which are secured to the upper surface
m.
.27
2,136,724
of the pole piece 9 by means of a pair of clamping
pieces I5 and I6. Clamping screws I1 serve to
is passed through the ampli?er and recti?er
combination 56 and 51 but when high level sounds
clamp" the pieces I5 and H5 in position. The
aperture I I is of very small height in comparison
to its base, being, in this instance, about 11/2 mils
high and about 140 mils long. A pair of bridges
are recorded, a correspondingly greater amount
I8 and ‘I9 is provided,’ one on either side of the
pole piece 9 parallel to the base of the aperture
II. These bridges I8 and I9 are preferably com
10 posed of an insulating material such as Bakelite
or hard rubber and are secured to the base plate
5 as by screws 29 and 2|. The forward edges of
the bridges I8 and I9 have plates 22 and 23 se
cured thereto as by screws 24 and 25. These
15 plates 22 and 23 project above the‘surface of the
bridges I8 and I9 and serve as supports on which
a vibratory conductor 21. is placed. Clamping
pieces 28 and 29 are secured‘ to the plates 22 and
23 as by screws 39 and 3| (Fig. 2). Each of the
20 bridges I8 and I9 is provided with a pair of ad
of current is passed through the ampli?er 56 and
recti?er 51. The resulting recti?ed current is
passed through the conductor 21 in a direction
opposing the steady biasing current from the
battery 6I thus neutralizing the biasing effect,
Thus the center of modulations for high level
sounds is moved to a position shown by the full 10
lines 21 (Fig. 1).
The biasing of the conductor 21 may also be
obtained by applying the recti?ed current from
the recti?er 51, which varies in accordance with
the amplitude of the sounds being recorded, di 15
rectly to the conductor 21. In this case, the
normal position of the conductor at low level
recording would be mechanically adjusted so that
it would cover a greater part of the slit II as
indicated by the dot and dash lines 55 (Fig. 1). 20
justing jaws 32 and 33. These jaws are p-refer- ' With the increase in amplitude of sound recorded,
ably of a spring material and are secured to the
rear ends of the bridges as by screws 34 and 35.
The forward ends of the jaws 32 and 33 are en
gaged by adjusting screws 36 and 31. Adjustment
of the conductor 21 is accomplished by rotating
either of the adjusting screws'36 and 31. When
the proper adjustment has been effected, the con
ductor 21 is clamped in position by means of
3.0; the clamping pieces 28 and 29. Theends of the
conductor 21 are secured to windlasses 39 and 39
which are rotatably secured within insulated
blocks 40 and 4|. Beforereaching the Windlass
39, the right hand end of the conductor is looped
351 over a spring pressed arm’ BI which is pivotally
mounted to the base as at 62. The arm SI allows
for easier adjustment of the tension of the rib
bon and prevents undue'tensionfrom being ap
plied. The blocks 49 and M are secured'to the
base plate 5 by means of screws 42. Each of the
windlasses 38 and 39 is electrically connected to
terminals 43 and 44 (insulated from the'base
plate 5) which in turn are adapted to be con
nected‘to a suitable sound amplifying system.
Referring to Fig. 4, I will now describe the
application of noise reduction to the above men
tioned type of valve. The sounds to be recorded
upon a light sensitive ?lm 45 are received in a
microphone 46 and ampli?ed by a suitable am
pli?er 41.
The speech currents thus ampli?ed
are passed through a transformer 49 and thence
by means of conductors 49 and 59 are passed
through the vibrating conductor 21. Interaction
between the magnetic force set up by the modu
553 lated alternating current passing through the
conductor 21 and the strong magnetic ?eld set
up between the pole pieces 1' and 9 causes the
conductor 21 to vibrate in accordance with the
amplitude and frequency of the sound waves and
thus vary the length of the triangular aperture
II (Fig. 3) exposed to a beam vof light from an
exciter lamp 52.
Light from the exciter lamp
52 is collected by means of a condenser lens 53
and is focused at a point adjacent the slit II
65 from whence it is projected onto the moving ?lm
45 by means of an objective lens 54.
Noise re
duction is obtained by holding'the center of
modulation of the conductor 21 in a position as.
shown by the dot and dash lines 55 (Fig. 1)
701 when no or little‘ sound is being recorded. This
is accomplished by passing a biasing current
from a battery 6| (Fig. 4) through the conductor
21. An ampli?er 56 and recti?er 51 are shunted
across the conductors 49 and 50. In recording
low level sounds, a very small amount of current
the corresponding increase of the recti?ed cur
rent from the recti?er 51 would shift the center
of modulation of the conductor 21 toward the
position shown by the full lines (Fig. 1).
25
The amount of biasing of the conductor is gen
erally dependent upon the kind of sound being
recorded. When recording dialogue or music in
which the volume is low or where the change in
volume is gradual the mean biasing position of 30
the conductor may be brought nearer the apex of
the triangular aperture than in the case of re
cording staccato sounds such as are produced by
a harp or piano. In recording the latter type of
sound, more leeway has to be given to the con 35
ductor to prevent the higher level wave forms
from being clipped before the conductor has a
chance to be moved toward its unbiased position.
This change in biasing position of the conductor
is accomplished by means of suitable potentiom
eters as at 58 and 59 (Fig. '1) and may be effected
during the recording wherever the tempo of the
sound is changed. The amount of biasing is gen
erally determined by the amount of margin de
sired between the opposite depressions of a wave
form, for example, D1 and D2 (Fig. '1) . ' Referring
to Fig.‘ 8, the margin may also be determined by
the distance from the apex of the triangular aper
ture to the position of conductor 21 at the upper
limit of its excursions as shown by the dotted 50
lines 60. In setting the biasing position of the
conductor 21, the potentiometers 58 and/or 59
are manipulated until the distance X, represent
ing one-half the amplitude of the conductor ex
cursions, is allowed to reach a certain percentage 55
of the distance D; this, of course, depending on
the type of sound being recorded. In recording
soft sounds, the distance X may be allowed to
cover as much as ‘75% of the distance D.
In the example shown in Fig. 8, the potentiom 60
eters 58 and/or 59 is set so that X will equal one
half D when the conductor is in its biased posi
tion. Thus the margin for low level sounds is
indicated by the dimension M. When X exceeds
one-half of D the change in biasing current causes 65
the mean position of the conductor to be moved
downward so as to maintain the same ratio of
X to‘ D. This ratio is kept constant until the
conductor 21 reaches the unbiased position as
shown by the dotted lines 21' at which point the 70
mean position of the conductor 21 will lie half
way between the apex and the base of the tri
angle. Here the margin M’ will be seen to be
considerably larger allowing for an increase in
ground noise. This is, however, negligible due to 75
2,136,724
the ‘fact that the sound level ‘is higher in pro
portion. As higher amplitudes are recorded, the
center of modulation of the conductor 2'! remains
the same while the margin again becomes smaller
as at Mh to accommodate these higher ampli
tudes.
Referring to Fig. 5, the center of modulation
for each edge of the positive sound track is in
dicated by the center lines BI and 62. Where no
‘10 sound is‘recorded on the ?lm, only a narrow path
of transparency 63 traverses the center of the
sound track.
As modulations are recorded and
increased, the centers of modulation 6! and 62
corresponding to the mean biasedposition of the
15 conductor 2'! are spread apart until they reach
their unbiased position.
I
Due to the fact that the edges of the sound
‘ tack are formed by the acute angle between the
conductor, 21 and the trangular aperture ll these
20 edges will not form sharp lines but will gradually
pass from clear transparency to opacity as
shown in Figs. 6 and 7. In the negative ?lm 65
(Fig. 6) the sound track starts with a faint out
line at 65 and gradually darkens until it is pure
26 black at the core. Whenvthe negative is printed
onto the positive print 61, the latter is given a
rather hard development, that is, the positive is
‘made extremely sensitive to the shading of the
negative so that except for a small zone 68, the
30 clear portion 69 will be entirely transparent. The
‘amount of distortion produced by the shaded
zone 63 is negligible due to the fact that its di
mension as measured transverse of the direction
of ?lm travel remains constant and thus is un
35 able in itself to effect a varying change in light
.
3
passing therethrough; it being understood, of
course, that the reproduction of sound is‘depend
ent upon a change in the amount of light ema
nating from a slit placed transverse of the ?lm
travel.
Having thus described the invention .what is
claimed as new and desired to secure by Letters‘
Patent is:
1. Means for recording an anti~ground noise
type of variable area sound record comprising a 10
single electrical conductor, means forming a tri
angle aperture and cooperating with said, con
ductor, means for directing a beam of light
through the opening between said aperture and
said conductor, means for vibrating said con
ductor across said aperture in accordance with
sound modulated current and means for varying
said opening in accordance with the average vol
15’
ume of said current.
2. An apparatus for recording an anti-ground 20
noise type of sound record comprising means
forming a triangular aperture, a single' vibratile
electrical conductor, vibratile at the frequencies
to be recorded, said conductor being positioned
adjacent said aperture forming means and adapt 25
ed to vibrate across said aperture, means for di
recting a beam of light through the opening be
tween said aperture and said conductor, means
for simultaneously vibrating'said conductor in
accordance with both sound modulated current 30
and current varying in accordance with the aver
age amplitude of said modulated current, and
means for moving a light sensitive ?lm across
said light beam modulated by said conductor.
BURTON F. MILLER.
35
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