Патент USA US2124150код для вставки
July 19, 1938. » IMRmHI/IRDI‘ 2,124,150 METHOD AND DEVICE FOR RECORDING SOUND Filed March 27, 1957 2 Sheets-Sheet 1 Fig. 1 I I’ I l I | I I l IIII‘I I I I I 1 II l IIIIII 7 _2 3 4‘ 5 6 7 8 9 70 7/ I2 I3Ill151677787.9202177237425262726’ 700 July 19, 1938- . P. c. RICCHIARDI 2,124,150 METHOD AND DEVICE FOR RECORDING SOUND Filed March 27, 1937 v 2 Sheets-Sheet 2 Fir g. 4 k M; @Wi/W W‘ 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.