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Патент USA US2124150

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July 19, 1938.
»
IMRmHI/IRDI‘
2,124,150
METHOD AND DEVICE FOR RECORDING SOUND
Filed March 27, 1957
2 Sheets-Sheet 1
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July 19, 1938-
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P. c. RICCHIARDI
2,124,150
METHOD AND DEVICE FOR RECORDING SOUND
Filed March 27, 1937
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Patented July 19, 1938
2,124,l50@1
iJNlTED STATES BIA-TENT‘ OFFEQE
2,124,150
METHOD AND DEVICE FOR RECORDING
SOUND
Pier Carlo Ricchiardi, Paris, France
Application March 27, 1937, Serial-N0. 133,455
4 Claims. (Cl. 179—100.3)
My invention. relates to sound recording and
reproducing devices.
It is known that in existing sound recording
and reproducing systems, although the recorded
5 .sound may be pure as regards the ?delity of the
frequencies that are recorded, it nevertheless ap
pears to be ?at and colorless in comparison with
the sound source. This is due to the fact that
the range of volume variations as electromag
10 netically recorded on a ?lm, disc or band is limited
Fromv this compression, there results a ?nal
curve C, which‘ shows the variations of the vol
ume that is actually recorded. By comparing
curve A, which corresponds to the original sound,
with curve C, which corresponds to the recorded 5
sound, it is visible not only that the recording
fails to maintain the levels of the sound source,
which destroys colour and power, but also that
there is introduced a sound level distortion which
may be as high as 100%, since curve C has noth- 10-‘:
ing whatever in common with the original curve
to about 40 decibels whereas the power or volume
range of an. average orchestra is around '10 or 75
A.
decibels.
In order to avoid this distortion, electronic de
vices are employed which apply to recording on
The limiting of this power range cor
responds to bringing down the volume of a large
15 i orchestra to the sound level of a human voice.
It is therefore obvious that, under these con
ditions sound recording and reproduction can
never be an accurate image of the original sound
because the various proportions of volume or
20 power are not maintained.
The sound being limited in the recording to
maximum variations in power of 40 decibels,
when a sound strikes the microphone with higher
power or volume the practice is to effect a com
25 pression by means of either a manually operated
or an automatic attenuating device, in such man
ner as to reduce the original volume of the sound
source to the maximum of 40 decibels which is
allowed for recording.
30
An examination of the diagram of Fig. 1 shows
how this compression is effected during record
ing. Curve A represents the power variations
of the sound source, the variations in decibels of
which can be observed in ordinates. It is found
35 that these variations oscillate between 5 decibels
and '72 decibels. When the sound level of the
source exceeds 30 decibels, a compression is
effected by acting upon an attenuating device
associated with the ampli?er. The action of this
40 attenuating device is illustrated by curve B,‘ the
attentuation values of which, reckoned in deci
bels, are plotted on the right hand side abscissa.
It is found that when the sound source ex
ceeds the 30 decibels above mentioned, the ac
45 tion of the attenuating device is called into play,
in order to keep the record inside the range of
these 30 decibels. Thus, at point 8 of the hori
zontal axis, curve A has reached 40 decibels and
attenuating device B has produced a correspond
50 ing attenuation of 10 decibels. At l l,the curve A
discs as well as on ?lms.
These devices, which 15 Y.
are commonly called “volume-expanders” are in
tended to increase the power range by bringing
it up to a level of 70 and even 80 decibels. There
is thus obtained a volume variation the maximum
level of which approximates the original, but the 20 "
very principle of these devices merely further in
creases the distortion. above mentioned.
Thus double recording devices have been util
ized,'one of these recordings corresponding to the
modulation and the other to the variations of the 25
level of this modulation. This second recording
acting upon the factor of ampli?cation of the
ampli?er, adds to the 30 decibels recorded with
the modulation a supplement of 40 decibels or
even more, thus increasing the range so that it 30
becomes equal to the necessary minimum, 70 deci
bels.
But
this supplement of
ampli?cation
merely proportionally increases the rate of dis
tortion, because the second recording, which con
trols the volume variations, being taken at the 35
output of the ampli?er, can but correspond to
the shape of the volume variations of the modu
lation that is recorded.
And, as compression. has
been effected during the recording, the variations
of thesound level have been modi?ed by this 40
operation, and no longer correspond to the volume
variations of the sound source.
As above stated, this distortion is observed by
examining the form of curve A, as compared to
that of curve C.
The second curve intended for 45
the “volume expander” in question can therefore
but have a form proportional to that of curve C.
Finallyywhen reproducing sounds, the result of
the action of said “volume expander” is illus
trated .by curve D, the characteristics of which 50
of the sound, source has reached '70 decibels and
are worse than those of curve C, while corre
the attenuating device produces a reduction of .
sponding to the desired range of 70 decibels.
40 decibels.
other words, the action of the attenuating device
(curve B, Fig. 1) is. exerted ‘as well upon the
At l4, curve A drops 20 decibels and
reaches 40 decibels, at the same time the atten~
55 nation is reduced by 20 decibels, and so on.
modulation as upon the “volume expander.”
In
55;v
2
2,124,150
My invention has been developed with the
above considerations in view and has for its ob
jects to provide sound recording and reproducing
means which will accurately record and repro
duce the volume variations of the recorded sound;
and to produce a sound record which may be
reproduced or read by means of standard exist
ing apparatus Without necessitating any impor
10
tant modi?cation thereof.
For this purpose, the sound recording is double.
In the case taken by way of example, I will refer
io photo-electric records on a ?lm, but it is ob
"vious that the invention applies as well to records
‘Paced on discs and to all forms of electro-me
.ical recording on bands or other means.
‘clone, in what follows the term “sound band”
'i be employed for the sake of simplicity, but
clear that the invention is not limited to
*ording on bands but applies to any other form
20 of record or means.
According to the invention, which includes
a double recording, one of the elementary records
carries the modulation, with its variations of
normal volume after compression, whereas the
25 other one records level variations which have
nothing in common with the variations of volume
of the sound source or of the modulation but
which are proportional to the compression action
the function of which has been above explained.
30 Therefore, the difference between the system ac
cording to the invention and the “volume ex
panders” lies essentially in the fact that the sup
plement of ampli?cation of the “volume ex
panders” is controlled by the variations of volume
35 of the modulation or of the sound source, whereas,
in the system according to my invention, the
supplement of ampli?cation is controlled by the
compression action exerted upon the modulation
for effecting the recording.
40
The advantages of the system according to
the present invention, and also the manner in
which it is working, are illustrated by the dia
gram of Fig. 2. In this diagram, the curve of
the variations of the level of the sound source is
45 A; C shows the variations of volume such as they
are normally recorded in a normal recording
after the action of the compressing device, the
action of which is illustrated by curve B. It will
be seen that these three curves are identical to
50 those of the diagram of Fig. 1, above described.
In the diagram of Fig. 2, there is shown a fourth
curve, E, which illustrates the recording that
pilots the second volume control, the action of
which is analogous to that of the ordinary
55 “volume expanders”.
'
By examining curve B, of the attenuating de
vice acting as compressing means, it is found that
it is proportional to the curve E of the expander
control. This record, which pilots the power of
60 ampli?cation of the ampli?er, acts simultaneously
with the modulation either on the same reading
means or on separate reading means.
Therefore,
to the variations of level of the modulation (curve
C, Fig. 3), I add the variations of level of the ex
65 pander control (curve E). The recording ampli
?er and the reproducing device are arranged in
such manner that the variations of the expander
control act in opposition and proportionally with
the attenuating action of the compressing means.
70 The sum of the volume variations of the modula
tion and of those of the expander control is then
illustrated by curve AB. When comparing this
curve with curve A of Figs. 1 and 2, it is found
that they are wholly identical, which shows that
75 any distortion introduced by the level compression
when recording is automatically eliminated by
the second recording of the expander control.
When comparing the results obtained with a
normal volume expander, that is to say the curve
D of Fig. 1, and those obtained with the system
according to the present invention, that is to
say the curve AB of Fig. 3, it is found that the
difference between the two systems involves con
siderable advantages for the system according to
the invention.
10
The difference between the two systems lies in
the fact that the records of the ordinary volume
expanders are proportional to the sound level
variations of the source, or of the modulation,
Whereas the variations of the expander control 15
according to the invention have nothing in com
mon either with the variations of the sound source
or with those of the modulation, but are merely
proportional to the compression action exerted by
the attenuating device upon the modulation, when 20
recording.
A preferred embodiment of the present inven
tion will be hereinafter described, with reference
to the accompanying drawings, given merely by
way of example, and in which:
25' 1
Figs. 1 to 3 are diagrams showing explanatory
curves above referred to;
Fig. 4 is a diagrammatical view of a device
according to the invention;
Fig. 5 shows a sound band.
30.
The embodiment of the invention which is
shown by way of example, corresponds to the
case of photo-electric records on ?lms, but it is
clear that the same principle applies to the case
of recording on a band or disc through electro
mechanical means, since it su?ices to change the
recording system to obtain the same results.
Besides, even in the case of photo-electric record
35 “
ing means, the circuits, the type of recording de
vices and the like can be changed or modi?ed
without departing from the principle of the in
vention.
In the example illustrated by Fig. 4, reference
character E designates a microphone and F an
ampli?er. The sound caught by the microphone
E is ?rst ampli?ed by the pre-ampli?er. The
sound level is then controlled by the gain control
A. B. and then ampli?ed by ampli?er G. Through
the coupling transformer L, it is fed to the re
cording device M. The light rays that come from
50
lamp N through the optical system 0 are re
?ected by device M through the usual optical
system P Q S, so as to be impressed upon the
?lm Z. By acting upon attenuating device AB,
I therefore exert the necessary compression when
the sound level from F exceeds the limit, so as
to keep it within the range of 30 decibels that is
allowed for recording. The action of this at
tenuating device is illustrated by the curve B
of Fig. 1.
A rod K connects the handle of attenuating
device B with the handle C of a rheostat D. Any
action exerted upon attenuating device AB is
therefore reproduced on rheostat DC.
The current flowing through this circuit there
fore varies as a function of the resistance value
of rheostat C. D.
Reference character I desig
nates an apparatus for measuring this current,
whereas A1, acting as an ammeter, will vary the
position of
sity of the
Plate U is
emitted by
plate U proportionally to the inten
current flowing through the circuit.
capable of stopping the light rays
lamp B1 and condensed by optical
means X. The light rays which act upon the
band of the expander control at V are more or 75
3
2,124,150
less stopped by plate U, according to the
value of the current flowing through the cir
cuit of rheostat DC, and, ?nally, the ac
tion of said plate will be exactly proportional
to that of the attentuating device AB.
With
this arrangement, I therefore produce upon the
band of the expander control, a sound track
the form and appearance of which are analogous
to the disclosure of Fig. 5 and in which the
10 variations of amplitude will be piloted by the
action of the attenuating device AB, which
corresponds to carrying out into practice the dia
gram illustrated by Fig. 2 and above described.
By varying the recording systems, it is possible
15 to obtain other arrangements which are within
the scope of the invention.
The band of Fig. 5 includes a variable area
record B for modulation, and a variable density
record C for the expander control. This ?gure
20 also shows, at D, a variable area record of the
triangular type, for modulation, and at E a ?xed
density record for the expander control. The
' same principle is applicable for instance to a
variable density record for modulation and a
25 ?xed or variable density record for the expander
control. Thus, at F is shown the modulation and
at T the expander control.
However, another characteristic feature of the
present invention lies in the fact that the width
30 of the two bands is equal to the width of a normal
band, in order to permit reading by means of the
standard optical means of the existing appa
ratus, without necessitating any important modi
?cation.
In a general manner, while I have in the above
description, disclosed what I deem to be prac
tical and e?icient embodiments of the present
invention it should be well understood that I do
not wish to be limited thereto as there might
40 be changes made in the arrangement, disposi
tion and form of the parts without departing
from the principle of the present invention as
comprehended within the scope of the appended
claims.
What I claim is:
1. A sound recording device which comprises,
in combination, modulation recording means for
tracing a sound track on a ?lm, an attenuating
device associated with said means for exerting a
50 compression action on the sound level so as to
keep it inside the permissible range, and a sound
level recording means operatively connected with
said attenuating device for tracing on said ?lm
a sound level track showing variations propor
55 tional to the compression actions exerted on the
modulation when recording, said means being
adapted to form parallel and adjacent sound
tracks the total width of which is equal to the
width of an. ordinary sound track, whereby both
of the ?rst mentioned sound tracks can be read
by means of a single reading device, without
necessitating any modi?cation in existing appa
ratus.
2. A sound recording device which comprises,
in combination, modulation recording means for
tracing a variable area sound track on a ?lm,
an attenuating device associated with said means
for exerting a compression action on the sound
level so as to keep’ it inside the permissible range, 10
and a sound level recording means operatively
connected with said attenuating device for trac
ing on said ?lm a variable density sound level
track showing variations proportional to the
compression actions exerted on the modulation 15
when recording, said means being adapted to
form parallel and adjacent sound tracks the
total width of which is equal to the width of
an ordinary sound track, whereby both of the
?rst mentioned sound tracks can be read by 20
means of a single reading device, without neces
sitating any modi?cation in existing apparatus.
3. A sound recording device which comprises,
in combination, modulation recording means for
tracing a variable density sound track on a ?lm, 25
an attenuating device associated with said means
for exerting a compression action on the sound
level so as to keep it inside the permissible range,
and a sound level recording means operatively
connected with said attenuating device for trac 30
ing on said ?lm a variable area sound level track
showing variations proportional to the compres
sion actions exerted on the modulation when
recording, said means being adapted to form par
allel and adjacent sound tracks the total width 35
of which is equal to the width of an ordinary
sound track, whereby both of the ?rst mentioned
sound tracks can be read by means of a single
reading device, without necessitating any modi?
cation in existing apparatus.
40
4. A sound recording device which comprises, in
combination, modulation recording means for
tracing a variable area sound track on a ?lm, an
attenuating device associated with said means
for exerting a compression action on the sound
level so as to keep it inside the permissible range, 45
and a sound level recording means operatively'
connected with said attenuating device for trac
ing on said ?lm a variable area sound level track
showing variations proportional to the compres
sion actions exerted on the modulation when re 50
cording, said means being adapted to form par
allel and adjacent sound tracks the total width
of which is equal to the width of an ordinary
sound track, whereby both of the ?rst mentioned
sound tracks can be read by means of a single 55
reading device, without necessitating any modi?
cation in existing apparatus.
PIER CARLO RICCHIARDI.
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