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Патент USA US2136723

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Nov. 15, 1933. y
. Filed Sept. 25, 1955 V
5 Sheets-Sheet 1
FIG. 1.
Burro/v FM/LLEQ
Nov. .15, 1938.
Filed Sept. 25, 1955
< < <°
3 Sheets-Sheet 2
Nov. 15', 1938.‘
Filed Sept. 25, 1955
s Sheets-Sheet 5
Patented Nov. 15, 1938
Burton F. Miller, Hollywood, Calif., assignor to
United Research Corporation, Long Island City,
N. Y., a corporation of Delaware
Application September 25, 1935, Serial No. 42,116
(Cl. 179-4003)
11 Claims.
a consequence of this method of recording, the
reproduced volume of the lower level sounds is
reduced below that of the higher level sounds by
an amount correspondingto that at which they
were increased above their original levels, thus 5
likewise reducing the ?lm background noise dur
ing periods of low level sound reproduction and
during silent intervals. It will be shown later
thatthe amount of this reduction is greater than
that now commonly obtained with usual Well 10
This invention relates to the recording and
reproduction of sound and particularly to the
recording of sound on light sensitive material to
‘ produce a diapositive record having varying light
5 ‘and dark areas or intensities and the reproduc
tion of sound therefrom.
In recording, sound on ?lm, the minimum
volume level recordable and satisfactorily repro
Hduceable, which may be considered the minimum
10 ‘variation in light and shade areas or intensities,
is that which is not less than the variations pro
known circuits.
,When ‘using this anti-ground noise system,
duced by the nature of the ?lm, such as graini
ness and varying degrees of inherent trans
Mparency» or the so-called ?lm background noise
15‘"level. The upper or maximum variations record
able are those controlled by the width of the sound
track which ‘is of ?xed dimensions or'the greatest
variation obtainable between a transparent and
opaque section. Both limits represent the
go‘ boundaries of sound levels recordable on ?lm,
the minimum being perhaps more troublesome,
‘since the cause creating this minimum level is
also present in reproduction at the time of' no
there is automatically obtained a greater range
of volumes within the limits of the ?lm than
formerly could be recorded and faithfully re- 15
produced without the use of the invention.
.Another object of the invention, is to‘ increase
the volume range of reproduction and reduce
ground noise from a sound record previously
made according to any of ‘the well known methods v20
of noiseless recording, viz shuttering a variable
area track,’ orbiasingqa galvanometer mirror or
lightv valve strings according to the amplitude of
the recording.
This is accomplished by using the reproduc- 25
ing portion of this system to reproduce standard
An object of the invention is to automatically
increase the range of volume levels recordable
upon the sound track of motion picture ?lm and
non-compressed "anti-ground > noise
sound '
faithfully reproduceable therefrom, and thereby
records, the total noise reduction being the sum
to obtain more effective noiseless recording than . of the noise reduction of the record and of the
30 ‘is obtainable with noiseless recording systems now reproducing system, the latter being determined 30
in common use.
by the maximum volume expansion employed. In
this instance, however, the reproduced volume
This is accomplished according to one feature
of the present invention by a method of and means
for reducing the minimum volume level of the
35 original sounds which may be recorded and re
produced and thus increasing the range of re
corded volumes.
The method involves the
expansion _ of
volume levels along ‘a predetermined character
40 istic between the minimum and maximum points
which the record is capable of handling. That is,
for the lower portion of the range of volume in
reproduction, a certain volume expansion is pro
range is greater than that of the record range,
this'belng‘ accomplished by reducing the repro
duced volumes of the low level sounds and conse- 35
quently the ?lm background noise. This, of
course, entails expanding the upper level sounds
abnormally, which produces dramatic and other
presentation eifects of ‘considerable value. When
reproducing a non-compressed track, the inci- ‘10
dental electrical .and mechanical noises which oc-‘
curred in‘the recording thereof and those origi
45 ferent over the upper portion of the volume range.
The changes in volume expansion may be uni
nating‘ in any portion of the reproducing equip
ment precedingthe expander are reduced in level
by an amount equal to the total‘degree of volume
form otherwise. By compressed recording and
expanded reproducing of the sound on the ?lm,
silent intervals, the reproducing system noises
vided, while this volume expansion may be dif
expansion during low level reproduction or. at ‘
the record range of levels will be less than the
50 original range of levels but the reproduced range
also being reduced when reproducing compressed
will be preferably equal to the original range.
In recording, the lowest volume sounds are ampli
A further object of the invention is to more
?ed to such an extent as to be recorded at a level
equal to or above that corresponding to the ?lm
volumes, when said sound volumes are in the
form of electrical currents.
This is accomplished by similarly impeding the 55 ‘
55 background noise level during reproduction. As
opposite half waves of the currents in accord
ance with the amplitude thereof.
Other objects and advantages of the inven
tion will be obvious and the details of the inven
tion more fully understood by reference to the
following description read in conjunction with
the accompanying drawings, in which:
Fig. 1 is a schematic drawing of a sound on
?lm recording system involving the invention.
Fig. 2. is a schematic circuit diagram of a
sound on ?lm reproducing system embodying the
Fig. 3 is a graph illustrating the relationship
between the input and output’ of each of the
systems in Figs. 1 and 2; and,
Figs. 4a and 4b are block diagrams showing
the transmission level at various stages in the
recording and reproducing systems.
Referring now to Fig. 1, the light modulation
20 portion of the recording circuit includes a source
of light 5 of constant intensity, a condensing lens
6, a light beam forming mask 1, a galvanometer
8, having a movable re?ecting mirror, a light
slit mask I0, an objective lens II and a ?lm I2.
through those tubes and the resistance 26 is
therefore added to minimize the effect of the
tube impedances on the time constant. All of the
vacuum tubes above mentioned have their ele
ments polarized from a power recti?er unit 32
in the usual manner. This recti?er, however, has
a variable tapped potentiometer resistance 33,
the function of which will be explained herein
The output of ?lter 30 is connected in series 10
With the grid-cathode circuit of impedance tubes
I6 and I1 across the potentiometer terminating
resistance 29 of the ?lter 30 and in series with a
resistance 36. This connection provides tubes I6
and I"! with a grid bias and therefore a cathode.— 15
to-anode impedance determined by the amplitude
of the current output of ?lter 30. The static
value of this grid bias is determined by the
potentiometer resistance 33, which is given a
value in accordance with the characteristics of 20
the tubes used and the function thereof. Filter
condensers 34 and 35 are employed across the
terminating resistance of the power supply cir
cuit. By the use of resistance 36 of the desire-d
25 The operation of this portion of the system is .
value, any tendency for the grids to be driven
well known in the art and operates in the usual positive by high signal levels will be counter 25
manner; that is, the beam of light is moved longi
acted by the voltage drop across this resistance
tudinally of the slit in mask Ill, thus varying caused by grid current ?ow. Thus a lower im
the quantity of light striking the ?lm. The gal
pedance limit for tubes I6 and I1 is thereby es
vanometer 8 is connected to the output of an am
tablished. Tube I6 is shunted by a series ar 30
pli?er I4, the input of which may be from ter
rangement of resistance 38 and a condenser 39,
minals 9 connected to the output of tubes I6 while tube I1 is shunted by a similar resistance
and I1 which transmit sound currents there
40 and condenser 4|. These elements are sub
through serially with the line, or to terminals I3 stantially non-reactive and function to provide
35 connected to conductors I5 which eliminate tubes
an upper impedance value by preventing an ef
I6 and I1 from’ the circuit. The input of tubes I 6 fectively open circuit through tubes I6 and H. 35
and I1 is connected to the output of an ampli?er
The reproducing circuit of Fig. 2 is substan
20,. over terminals I8, the input thereof being
connected to a microphone 2 I, or other sound-to~
40 current translator.
The output of ampli?er 20
may also be connected to terminals IQ of con
ductors I5. Shunt resistances 22 and 3| func
tion to match the impedances of input and out
put transformers with their connecting circuits.
The output of tubes I6 and I1 is impressed
upon. a three stage ampli?er including vacuum
tubes 23, 24 and 25, with the usual inter-con
necting circuits. The output of this plural stage
ampli?er is impressed upon a full wave vacuum
tube recti?er 21, 28. The recti?ed current is
?ltered by a low time constant ?lter 30, including
resistance 302 and condenser elements 30I and
303 having values such that, together with ter
minating resistances 26 and 29, the time con
55 stant thereof is not greater than about .01 sec
ond and preferably as'low as .008 sec. The pur
pose of this low time constant is as follows: ?rst,
to insure that on increase of signal strength the
audible ampli?cation will reach its ?nal value
in so short an interval of time that no improper
‘variation in signal level occurs, and second, to
insure that on decrease of signal strength the
background ?lm and system noise will not be
unduly ampli?ed afterthe signal has ceased. In
order to insure that the rates of growth and
decay of voltage across resistance 29 are sub
stantially the same, resistance 26 having a value
comparable to the ‘minimum impedance of either
of tubes 21 and 28, is connected in shunt to the
?lter input circuit between those tubes and the
?lter 30. This will be apparent from the fact
that the time constant of the ?lter circuit, for
currentpassing through the tubes 2‘! and 28 de
pends'in part on the impedance of those tubes.
Current cannot pass in the reverse, direction
tially identical to that of Fig. 1, except that the
input circuit to the ampli?er-recti?er circuit is
now not connected to the output of tubes I6 and
I‘! but is connected to their input circuit which 40
comprises a photo-electric cell 45 or other light
sensitive device upon which light from a constant
intensity source 46 is varied in intensity by a
sound record on ?lm 41. The output of cell 45
is ampli?ed by an ampli?er 52 to which tubes
23, 24 and 25 are connected while the output
of the system terminates in a loud speaker 49
or other sound reproducer connected to the out
put of an ampli?er 50. The remainder of the
circuit contains all the same elements of the 50
circuit of ‘Fig. 1 but has the connections of the
output of ?lter 30 to the grids and cathodes of
tubes I6 and I‘! now reversed while a di?erent
staticpotential is applied to tubes I6 and I ‘I by
potentiometer 33 as will be explained herein—
after. The same by-pass switches with conduc
tors I5 are also employed in this circuit. Also
in this system a unilateral device such as a push
pull ampli?er having tubes 42 and 03 is inserted
between the output of ampli?er 52 and the input
to impedance tubes I6 and I ‘I to prevent unbal
ance impedance relations in the circuit of tubes
I 6 and I‘! from reacting on the control circuit.
The coupling between the tubes I6 and I1 and
tubes 42 and43 is shown as a resistance-con
denser circuit but these tubes may also be trans
former coupled.
The impedance control of the above described
recording and reproducing circuits, by means of
impedance tubes I6 and I1, is the same except
that the polarity of the recti?ed current from
recti?er 30 is reversed in Fig. 2 from that in Fig.
1. The transmission characteristic of each cir
cuit, or the relationship between input and out 75
3 ,
put current variations is shown in the curves of
Fig. 3 where the recording characteristic is shown
extended to the point c,‘which is approximately
circuits, it is believed desirable to refer to Figs.
to the point D on the reproducing curve, the
minus 55 db. since we are still not below the re
by the solid line plotted between input record- ' produced noise level limit of minus 35 db. This
means that the recordable input range has been
ing level and output recording level, and the re
producing characteristic shown by the dotted line materially increased over that recordable with
. plotted between the record level and‘ reproduced the systems now in use.
' Now in reproduction the point a is transferred
level. Before describing the operation of the
4a and 4b, in which the ranges of levels in each . input level now corresponding to an output level 10
between zero and minus 55 db., this minus 55 db.
10 element of the circuit are shown. In Fig. 4a the
level being below the ?lm background noise level.
input microphone 2| is shown feeding a micro
phone ampli?er and mixer 55, the output of
which has a level of approximately 40 db. range
extending from minus 40 db. to minus 80 db. A
15 second ampli?er 56 increases this range of levels
from minus 40 db. to zero still maintaining the
same original range. The degree of uniform am
pli?cation is arbitrary and is controlled by at
tenuation and the usual circuit factors. We then
20 reach compressor 51, which includes the re
mainder of the circuit of Fig. 1 between the am
pli?ers 20 and [4, this circuit variably decreasing
the upper and lower level limits so that the
lowest level of minus 40 db. is now minus 45 db.
25. and the upper level is now at minus 20 db., the
difference constituting a range of 25 db. as com-.
pared with 40 db. The subsequent ampli?er M
then uniformly ampli?es this range to levels be
tween zero to minus 25 db., at which point it is
30 impressed upon the galvanometer .8 to produce
variations in.the light impinging on the ?lm 12
in accordance therewith.
This degree of am
pli?cation is also dependent on the load. It is
thus seen that the original range of minus 40 to
35 minus 80 db. is impressed on the ?lm as a range
extending from zero to minus 25 db., this range
being within the limits of the ?lm track, the
lowest sound level, however, being above the ?lm
background level.
The reproduction of this record is shown in
Fig. 45 wherein the reproducer 60 translates the
record range of 25 db., but in view of losses in
recording, this range now lies between minus 50
db. and minus 75 db; However, the expander
circuit 6| which is that part of Fig. 2 existing ~
between ampli?er 52 and ampli?er 50,. extends
this 25 db. range to the original range of 40 db.
This means that this background noise may not
be reproduced at the loud speakers 49 with suffi
cient volume to be audible. In fact I have ob
tained with this invention of Figs. 1 and 2 a noise 15
reduction of 20 db. better than the average ob-v
tained with standard noise reduction arrange
ments well known and in common use. Not only
is the ?lm background noise reduced but also
the electrical and mechanical noises incident to 20
reproduction are eliminated. In brief, therefore,
the ratio between the variations in levels occur
ring in the original sound has been reduced for
recording and the ratio between the variations
in level occurring in the recorded sound is in 25
creased in reproduction.
The reproduction system of Fig. 2 may also be
used to increase the volume range reproduced‘
from a standard noise reduction sound track, this
reproduction also following the broken line re 30
producing curve in Fig. 3. Thus, this‘type of
track will be reproduced without the present ob
jectionable ?lm background noise since the low
levels reproduced are below the noise level. This‘
means that ‘the ratio of level variation is in 35
creased to bring the upper levels to zero db. By
this variation, special effects such as louder pistol
shots, siren noises, etc., will be accentuated.
To preventundue modulation of voice repro
duction, the ratio of variation between levels may 40
be changed between the upper and lower volume
limits as shown by the curves in Fig. 3 thus pro
ducing a different ratio of volume variation at
particular portions of the level range. This will
be further described later.
The volume compression and expansion above
described are accomplished by the circuits of
Figs. 1 and 2 and particularly by varying the im
by reducing the higher volumes to 52 db. and the
lower volumes to 92 db. A subsequent ampli?er ’ pedances of tubes I6 and H in accordance with
52 may bring this range to any desired level such the envelope of the soundcurrents impressed on 50'
as plus 10 db. and minus 30 db. for impression the tubes I6 and I1. As mentioned above, these
constitute series impedances in the line
on loud speakers 49, which translate the currents tubes
inter-connecting ampli?ers 52 and 50 in Fig. 2
to sound energy. The range, therefore, im
and ampli?ers l4 and ‘20 in Fig. 1. By the use
pressed on the loud speakers, extends over 40 of
two of such tubes arranged in a parallel series
db., the same as the impressed range which orig
arrangement, both halves of the sound currents
inally extended from minus 40 to minus 80 db. at are equally impeded, the amount of impedance
increased level limits dependent upon the output
being a function of the current of recti?er tubes
volume required for any particular area.
21 and 28, which is a function of the envelope of
Reference to graph in Fig. 3 may further ex
plain the general operation of the two circuits the sound currents. [While the relationship be 60
in which it will be noted that the relationship tween the input and output current of tubes 21
between the recording curve and reproducing and 28 is linear, the relationship between the in
curve appear as re?ections of one another, about
an axis which represents a one to one translation
or ampli?cation ratio between the input and out
put levels of the compressor and expander cir
That is point a represents a minus 35 db.
level for both input and output, this point also
being the level of the ?lm background noise. At
this point, the signal to noise ratio is unity. This
' put and‘output current for impedance tubes l6
and I1 is non-linear and varies in accordance
with a power function dependent upon the rela
tionship between the impedance of the tubes and
their terminating load. To obtain the various
degrees of compression and expansion at dif
ferent portions of the volume range and to pre
vent the impedance of the tubes from becoming 70
70, ,also means that no lower input levels may be re- _ too high, shunt resistances 3B and 40, of ap
corded on the record than those between minus proximately 100,000 ohms are employed, these
35 and zero levels, otherwise they are masked values also determining the points at which the
by noise during reproduction. However, with
759 the present invention, this input level may be
changes in impedance of tubes l6 and I1 is more
effective. Thus the steepness, of the recording 75
and reproducing curves between output and in
put levels which represents the ratio of com
pression and expansion is controllable. . In order
to prevent the transmission impedance from drop
pin'g to an extremely low value approaching zero,
a 100,000 ohm resistance 36is placed in the gird
circuit, which will prevent the grids becoming
positive, as any tendency to draw current ine
creases the drop across the resistance. This
10 means, of course, that the impedance of tubes
I6 and I‘! cannot be materially lowered beyond
this point. The general range of variation may
be determined and controlled by the position of
potentiometer 33. In recording, a small bias is
15 placed on the tubes, the recti?ed currents in~
creasing this bias in accordance with their ampli
tudes, and thus varying the transmission loss
through tubes l6 and H. In the reproducing cir
cuit of Fig. 2, a high initial bias is employed, the
20 recti?ed currents decreasing this bias and thus
decreasing the transmission loss as the envelope
of the sound currents increase.
Having thus described the invention, what is
claimed as new and desired to secure by Letters
25 Patent, is:
1. In a sound on ?lm reproducing system, the
combination of a carrier for a sound track hav
ing noise reduction, means for translating the
modulations of said track into electrical currents
corresponding thereto, an ampli?er circuit, and
a series-parallel impedance circuit connected in
series intermediate said translator and said
ampli?er circuit for varying the amplitude trans
mission therebetween in a ratio different from
that existing upon said carrier, said impedance
circuit including the cathode-anode circuits of
a pair of thermionic devices having a common
of thermionic devices in shunt to said ?xed im-'
pedances whose bias is controlled by said recti
?ed currents and whose input and output cir
cuits are in series with the cathode and anode
of said devices.
6. A system of sound recording and reproduc
tion comprising a source of current having a
certain range of volume levels, a light sensitive
medium for recording light variations in ac
cordance with sound variations as a single track 10
record, a light modulation system, an electrical
circuit inter-connecting said source of electrical
currents and said light modulating system, said
means including a ?xed impedance and variable
impedance in parallel,- said variable impedance 15
being a pair of thermionic vacuum tubes con
trolled by the envelope of said electrical currents
for compressing the ratio between the original
volume levels a predetermined amount, means for
translating the single track record so produced 20
into corresponding electrical currents, means for
amplifying said currents, and means inter-con
necting said translating means and said amplify
ing means for expanding the ratio between the
volume levels of said record currents, the amount 25
of expansion corresponding to the amount of
compression produced during recording.
7. A variable impedance circuit comprising a
thermionic device having cathode, grid and anode
elements, input and output circuits of said device
including said cathode and anode elements, a
resistance shunt circuit to said cathode and an
ode, and a resistance in series with the grid
to cathode circuit of said device, the impedance
of said cathode to anode circuit varying in a
manner and between limits determined by the
grid circuit.
grid to cathode circuit.
2. A sound recording system comprising a car—
8. An electrical circuit comprising a transmis~
rier for a sound record, said record having a
sion path, a control circuit for controlling the
certain percentage noise reduction, means for , transmission of electrial currents over said path,
translating said record into electrical currents
a recti?er, a ?lter, said recti?er and ?lter being
having volume levels corresponding thereto, an connected
intermediate said control circuit and
ampli?er for amplifying said volume levels pro
portionately thereto, and a series-parallel im
pedance circuit intermediate said translator and
said ampli?er for varying the ratio between the
volume levels of said transmitted electrical cur
rents, said variations differing at different por
tions within the range of said volume levels, and
said impedance circuit including ?xed impedance
elements in parallel.
3. A recording system‘ in accordance with claim
2 in which said last mentioned means includes
thermionic vacuum tubes in shunt to said re
spective ?xed impedance elements, each of said
tubes and associated elements transmitting oppo
site cycles of said currents with substantially
equal variations.
4. In a sound reproducing system, the combi
nation of a ?lm carrying an anti-ground noise
sound record, means for translating the varia
tions of said record into corresponding electrical
currents, an ampli?er, a balanced impedance cir
cuit inter-connecting said translator and said
ampli?er, said circuit including ?xed impedances
in parallel, a recti?er inter-connecting said
translator and said impedance, and means in
cluded in said impedance responsive to the recti
?ed current from said recti?er for variably
changing the value of said transmission im
pedance, said change in impedance di?ering for
said transmission path, a ?lter output terminat
ing resistance and a ?lter input terminating re
sistance element intermediate said recti?er and
said ?lter, said ?lter input terminating resistance
element having a value approximating the mini
mum impedance value of said recti?er to pro
vide said ?lter with substantially equal rates of '
voltage growth and decay across said ?lter out
put terminating resistance.
9. An electrical circuit comprising a plurality
of ampli?ers, means having impedance and con
necting said ampli?ers, a control circuit for vary
ing the impedance characteristics of said con
necting means, a recti?er intermediate said con
trol circuit and said connecting means, a ?lter
in the output of said recti?er having a low time
constant, said ?lter having an output terminat
ing impedance, connections whereby the voltage 60
across said terminating impedance is adapted to
be applied to said transmission means, and a re
sistance intermediate said recti?er and said ?lter
and in shunt thereto for providing the time con
stant of said ?lter with substantially equal rates
of growth and decay of the voltage across said
terminating impedance.
10. A system of sound recording comprising
means for generating electrical currents cor
responding to sound waves to be recorded, a re
cording device for translating electrical currents
changes in recti?ed current of different values.
into modulated light, and an impedance circuit
5. A' reproducing system in accordance with’ interconnecting said current generating means
75 claim 4 in which said impedance includes a pair
and recording device, said impedance circuit in 75
eluding a pair of thermionic devices having re
spective cathode, grid and anode elements, the
input and output circuits of said devices in
cluding said respective cathode and anode ele
ments, resistance elements in shunt to each
cathode and anode circuit and a resistance in
series with a common grid circuit, the impedance
of said cathode-anode circuits varying between
the limits determined by the values of said shunt
v resistance elements and said grid circuit resist
11. A system of sound recording comprising
means for generating electrical currents cor
- responding to sound to be recorded, a recording
device for translating electrical: currents into
modulated light, and impedance circuit intercon
necting said current generating means and said
recording device, said circuit comprising a pair of
thermionic devices having a common grid cir
cuit and having their cathode-anode circuits con
nected in series with each other and with said
generating means and said recording device, and
an ampli?er-rect?er circuit having its input con
nected to the output of said thermionic devices
and its output connected to the common grid
circuit of said thermionic devices.
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