Патент USA US2107135код для вставки
Feb. 1, 1938. W. WILSON 2,107,135 ' MEANS FOR NEUTRALIZING SOUND DISTORTION Original Filed April 24, 1923 AMPLIFIER T ‘ EINPuf ’ AMPLIFIER 5' LIGHT CONTBI. 3 Sheets-Sheet 1 LOUD SPEAKER § 6’ LlGHT [ONTRUL AMPLIFIER 7/ AMPLIFIER > wzzzvroza. gram.’ V I ?nk/PW A TTORNEYS. Feb. I, 1938. w. WILSON 2,107,135 MEANS FOR NEUTRALIZING SOUND DIS'I‘ORTION ' Original Filed April 24, 1929 51Sheets—Sheet 2 .37 _ . I; IN PUT ' ' 39 J AMPLIQFIER . /"f' - AMPUFIER @ v k , ‘ . 2a’ A+5 . ~1 % B E“; 7 "1' _ ' 1? - A ? IN PUT ANPLIFIEL ‘ . 1 I *4 \ ’ ‘ g 7) ‘ E 'NPUT EINPUT ' AMPLIFIEk AMPUFIER - ' I ‘I AMPLIFIER I L0 v g AMPLIFIER 1 VENTOR. ' , BY - _ -' " I 3PM Wand/MUM ' ATTORNEYS. Feb. 1, 1938. w. WILSON ' 2,107,135 ‘MEANS FOR NEUTRALIZING SOUND DISTORTION ' Original Filed April '24, 1929 Q i /0% 3 Sheets-Sheet 5 I 2,107,135 Patented Feb. 1, 1938 UNITED STATES PATENT OFFEQE 2,107,135 MEANS FOR NEUTRALIZING SOUND DIS TOR-TION _Wesley Wilson, Chicago, Iii. Application April 24, 1929, Serial No. 357,861 Renewed August 13, 1937 9 Claims’. (Cl. 179—-100.3) My invention relates to translating devices duced apparatus counteracts the effect of the dis (such as electrical sound reproducers, trans tortion produced by said part. It will be understood that the following de scription relates more to this example of the practice of the invention and that the invention will be de?ned in the appended claims. This invention is particularly adaptable to elec Further objects will appear from the descrip trical circuits and energy transformers of sound 7 formers, microphones, light control valves, etc.) and more particularly it contemplates the coun 5 teraction of distortion arising therein. recording and reproducing apparatus in which the permanent record is made on photographic 10 ?lm. These ?lm records can be so made as to tend to counteract distortion arising within the recording and reproducing apparatus. This is not only an advantage in reducing distortion which can not be overcome by the methods of 15 construction in vogue but also where a saving or simpli?cation in the construction of the appara tus would be effected if it were not necessary to _ In the drawings, in which several embodiments Figure 1 is a diagrammatic view showing ap paratus for making a sound record on photo graphic ?lm and counteracting the e?ect of the distorting characteristics of the reproducing and recording apparatus; Fig. 2 is a face View of a portion of the photo graphic ?lm showing diagrammatically the direct sound record and the counteracting sound rec This invention is also adaptable to radio broad casting and television, in which case the electrical ord; Fig. 3 is a view similar to Fig. 2 but showing 4 impulses or waves could be distorted reversely at diagrammatically a different type of sound rec the broadcasting station to the distortion arising ord; Another possible method of utilizing this in vention is in secret communication such as te lephony and the transmission of pictures by radio. In this method it would be necessary to arti?cially cause distortion in the receiving ap paratus to such an extent that the reverse dis SO vtortion necessary in the sending apparatus (to counteract the distortion in the receiving appara tus) would be so great that the signal would be unintelligible if reproduced on apparatus not having the proper distortion. Among the objects of my invention are to re duce the degree of distortion arising within translating devices by distorting the electrical waves (which operate or are operated by said devices) in the reverse direction to the distortion produced in the waves by the translating device; to tend to neutralize the distortion arising vwith in sound or picture recording and reproducing apparatus by deliberately distorting the records (which are made and reproduced by this appara ' tus) in the reverse direction to the distortion arising within said apparatus. A further object of my invention is to provide a method of correcting the effect of distorting char acteristics in part of a sound controlling appara ‘ tus, comprising the introduction into the sound 10 of my invention are shown— reproduce the record with perfect ?delity. within the reproducing apparatus. 40 tion and claims. Fig. 4 is a view showing diagrammatically the manner in which the two sound records of Fig. 2 may be combined in a single record at the side 25 of the ?lm; Fig. 5 is a face view showing diagrammatically how the two sound records of Fig. 3 may be com bined in a single record, at the side of the ?lm; Fig. 6 is a diagrammatic view showing appara tus for reproducing the sound from photographic ?lm similar to that shown in Figs. 2 and 3; Fig. '7 is a diagrammatic view showing appara tus for counteracting at the broadcasting station the e?ect of distorting characteristics in the audiofrequency ampli?er system of a radio re ceiving set; Fig. 8 shows apparatus for counteracting the eifect of distorting characteristics in‘ amplifying and reproducing apparatus in which the counter action or reverse distortion is effected electri cally; . Fig. 9 shows apparatus for counteracting the effect of distortion arising within a loud speaker in which the reverse distortion is effected by energy dissipation; and Fig. 10 is a chart showing curves plotted from the table at the end of the speci?cation. ' The basic idea underlying the various form of my invention shown is a method of correcting - the effect of distortion arising within translating controlling apparatus of additional apparatus devices (such as electrical sound reproducers, having distorting characteristics similar to ‘the distorting characteristics of said part in such manner that the distortion caused by the intro transformers, microphones, light control valves, etc.) by utilizing additional apparatus having ap proximately the same distorting characteristics 2 2,107,135 as the device producing the objectionable distor tion, in such a manner that the distortion caused by he introduced apparatus will have a counter acting eifect with respect to the objectionable dis tortion. For example, if a ?lm record is made ofa violin solo by recording apparatus which produces distortion in the record in varying degrees and at certain de?nite frequencies itis obvious that this distortion will be reproduced in the reproducing 10 apparatus. Now, if there is distortion. also in the reproducing apparatus it is also obvious that this distortion will also show up in the reproduced violin solo. That is, there will be a variation in torted the most will have the greatest difference between their equivalent value on the primary and secondary records. If the notes or frequen cies recorded on the secondary record are made to partially neutralize the corresponding notes on the primary record and the resultant effect recorded on a third ?lm it will be found that this third ?lmwill be distorted in the proper direction to at least partially neutralize the effect of distor tion arising within the said apparatus. By 10 varying the degrees of neutralization between the original (primary) and secondary record when solo that is reproduced from the ?lm record. If this same recording apparatus is used to make a making the neutralizing record, it is possible to ob tain the most advantageous degree of neutraliz ing distortion. Bearing in mind that the equiva lent value of corresponding notes on the primary (original) and secondary records are identical record of the sound that is reproduced by passing the original record through the reproducing ap when there is no distortion in the apparatus it becomes apparent that the notes that will be the equivalent value of the corresponding notes or frequencies in the original violin solo and the 20 paratus, it is obvious that in this second record, which we will call the secondary record, the equiv; alent value of the notes will vary from the cor responding notes in the original record at all points where there was distortion in the reproduc 25 ing apparatus or in the recording apparatus as it was making the secondary record, If in either the reproducing or recording ap paratus the ,e?iciency is very low when handling notes of one particular frequencyv it will result in 30 the recording of this note on the secondary record at an equivalent value below that of the original record. Now, if the e?iciency at this frequency was, lowered in the recording apparatus it would mean that the equivalent value of the note on i the original record would be lowered by this dis tortion and would again be lowered on the sec ondary record. If all of the distortion were in the reproducing apparatus at this frequency it would me'anthat on the original record this note neutralized the most will be the ones that were 20 weakened the least by distortion within the said apparatus. In actual practice this method is quite impractical and is of value only as a means of explaining the theory of the invention: In stead the electrical waves from the pick-up 25 apparatus receiving the original sound waves are divided and made to flow through two parallel channels. One is provided with additional ap paratus for producing distortion similar to the objectionable distortion and controls alight . valve. The other channel also controls a light valve but has no additional apparatus for de liberately producing distortion. (This is similar‘ ~ to the system shown in Fig. l of the drawings.) The light ?uctuations from these valves are re- . corded on the same ?lm, either side by side (as shown in Figs. 2 and 3) so as to make two sepa-. rate records (which would correspond to the 40 would not have its equivalent value lowered but original and secondary ?lm records and‘ which could be made to partially neutralize each other would be lowered on the secondary record.v Therefore, in either case the equivalent difference between the two records would depend upon the distortion in ‘the reproducing apparatus‘ or in the in the reproducing apparatus as. in Fig.6)v or the two records could be superimposed (as shown. in Figs. 4 and 5) if care were. taken to insure that the recorded light from one valve neutralized the ‘ recording apparatus when recording the sec ondary record. Or another way of saying it is that the equivalent differences between corre-, sponding notes on the original and secondary rec ords are similar to the equivalent differences be tween the notes of the original violin solo and the corresponding notes of the reproduced solo. Now, a way to neutralize this effect of distortion arising within the recording and reproducing apparatus is to distort the ?lm record in the reverse direc ,, tion to the distortion arising within said ap paratus' That is, if the equivalent value of a particular note or frequency is lowered by distor tion in either the recording or reproducing ap paratus the ?lm record should have this note recorded at a higher‘ equivalent value in order to neutralize it. As the distortion recorded on the original and secondary records is in the same direction (but in different degrees) as the distor tion arising within said apparatus, it follows that (3.“ the desired ?lm record (which will be called the neutralized record) should be distorted reversely to the distortion in the, original and'secondary record. ' Now, as the equivalent value of notes on the secondary record have been lowered below the sound reproducing quality of the recorded light from the other valve,‘ to such an extent as to produce the proper degree of reverse distortion. The electrical waves from the two channels can be made to partially neutralize each other direct (as shown in Fig. 8) if a means is provided’ _ for maintaining the time lags in the channels identical. Such an arrangement would'be adapt able to public address systems, radio telephony; the making of wax records for phonograph re production, etc. . . - , Referring to the drawings in detail, and ?rst to the apparatus shown in Figs. 1 to 3, inclusive, this comprises in general, apparatus'for produc ing sound records on photographic ?lms, which ?lms, after having the sound record made there 55 on, may thereafter be used in the sound reproduc ing apparatus in Fig. 6. The apparatus shown in Fig. 1 comprises sound pickup which may be‘ of any usual or suitable type, including input means I and, amplifying means 2, a light control ap 65 paratus 3 controlled by the microphone, for pro ducing a sound-record onrthe ?lm 4 correspond ing to the received sound, and a corrective circuit for counteracting the effect of the distorting char equivalent value of corresponding notes on the original record to the extent resulting from dis acteristics of the apparatus shown in Fig‘. 6 and 70 also input I and ampli?er 2. It is well known that reproducing apparatus, such 'as shown in tortion caused by passing once through the re producing and recording apparatus it follows that notes or frequencies which have been dis Fig. 6, almost necessarily possesses distorting characteristics which will distort certain portions of the sound record more than it will‘ distort 75 3 2,107,135 other portions; that is to say, certain frequencies may be reproduced well and with little loss of volume, while other frequencies may be repro duced poorly; that is, with considerable loss of CL volume. It is with a view to equalizing this dis tortion or loss of volume that the present ap paratus is designed. In order to effect this equal izing or counteracting effect, certain apparatus is introduced into the recording apparatus of Fig. 10 1, including an ampli?er 5 and speaker 6 (which should be identical with or similar to the arm pli?er ‘l and speaker 8 of the apparatus of Fig. 6), receiving means 9 for sound transmitted by the speaker 6, which should have characteristics similar to input i, amplifying means II! (which should be similar to 2) for the receiver 9, and light control apparatus H for causing a sound record to be made on photographic ?lm 4 which can be made to correct the effect of distortion due to the distorting characteristics of the re producing apparatus of Fig. 6, and also input I and ampli?er 2 of Fig. 1. In order to take care of the time lag caused by the fact that the receiver 9 is necessarily placed an appreciable distance from the speaker 6, the recording point A2 of the light control ap paratus I! of the corrective circuit may be ad— vanced a slight distance in the direction of ?lm movement from the recording point I?» of the light control apparatus 3 of the direct circuit, the distance “A” having such a relation to the distance “B” that it will counteract the time lag due to the spacing between the receiver 9 and the speaker 6. Bearing in mind that the ampli?er 5 and speaker B of the corrective circuit have distort ing characteristics substantially the same as the distorting characteristics of the ampli?er l and speaker 8 of the reproducing apparatus of Fig. 6 40 and that the receiver 9 and ampli?er ID of Fig. 1 are similar to the input means I and ampli?er 2 of Fig. 1, and also that the record made from light control 3 will correspond to the direct (pri mary) record, while the record made from light control II will correspond to the secondary rec ord (which will be recorded in opposite phase). Recording in opposite phase may be accomplished by reversing the electrical connections, as shown clearly in Figs. 7, 8, and 9. Fig. 1 has a re versed connection between receiver 9 and am pli?er ID in that the upper conductor becomes the lower conductor on making the bend. It will be seen that there can be effected a partial neu tralization of the direct record by the secondary record by properly adjusting light sources 25 and 26 of Fig. 6 which will produce the counteracting (reverse distorting) e?ect. Thus those parts of the record which would otherwise be reproduced with too great a volume will have this volume automatically cut down by the corrective circuit to a considerable extent, while those parts of the record which are relatively poorly reproduced in the apparatus of Fig. 6 will have their volume cut down comparatively little, by the corrective cir cuit of Fig. 1. By recording these two records on the same ?lm no trouble should be encoun tered in permanently maintaining them in the proper phase relation. If recorded on separate recording medium this would be practically im 70 possible to do. If the primary and the second ary records are made side-by-side, either as a variable density record as shown in Fig. 2, or as the variable width method as shown in Fig. 3, it will not be necessary to accurately control the 75 relative intensities at which the two records are recorded. All that is necessary is that the two records be 180° out of phase. Fig. 2 shows one type of ?lm record (known as the variable density type) which might be made by the apparatus shown in Fig. 1. The direct primary undistorted record 14 is alongside the secondary distorted record 55 with the cor responding portions in opposite phase (that is, one record passing the most light where the other record passes the least light). By using the en 10 tire Width of the ?lm for these records, the ef i'ect of ?lm noises (caused by the granular struc ture of the photographic emulsion) is reduced. This ?lm record is adaptable for use on re producing apparatus of Fig. 6. With such an 15 arrangement the degree of reverse distortion is adjustable, it being necessary only to change the relative amount of light passing through the two records to vary the degree of partial neutraliza tion. This is due to the fact that the sound re 20 produced in speaker 8 is dependent only upon the ?uctuating component of the light striking the photoelectric cell and not upon the total quan tity, the non?uctuating component of light being of zero frequency. ' Fig. 3 shows a different type of record known as the variable width type in which the amount of iight transmitted through the ?lm is propor-. tional to the width of the transparent portion ll of the record. Otherwise it is the same as Fig. 2. 30 Fig. 4 shows a ?lm in which the direct and sec ondary records Ill- and I5 of Fig. 2 have been superimposed or combined into- a narrow record 18 at the side of the ?lm, leaving the rest of the ?lm to be used for motion picture reproduction. 35 With such an arrangement the degree of reverse distortion is ?xed at the time the ?lm is made and, therefore, must be accurately controlled in the making. , Fig. 5 shows a ?lm in which the direct and 40. secondary sound records of Fig. 3 have been com bined into a single narrow sound record l9 at the side of the ?lm leaving the rest of the ?lm for the reproduction of motion pictures and is similar in characteristics to that of Fig. 4. 45. Fig. 6 shows the use of the sound record ?lm t which is similar to the ?lm shown in Fig. 2 or 3 produced by the apparatus of Fig. l in a sound reproducing apparatus having light apertures 20 and 2! for the direct and secondary sound record, feed apparatus 22 for the ?lm, and a lens 23 for bringing the light which passes through the sound records into proper relation to a photo electric cell controlling the ampli?er ‘! and speaker 3. Light from sources 25 and 26 is di rected against apertures 25! and 2i, respectively. Thereby having a separate light source for the direct and secondary records and thereby making it possible to manually vary the degree of reverse distortion continuously during the reproduction of a record so as to obtain the best results at all times. Fig. '7 shows a method of reversely distorting a radio broadcasting signal so as to effectively neu tralize the distortion in all receiving sets using a particular type of ampli?er, ampli?er 21 to be as nearly perfect as possible and to correspond to the direct circuit while ampli?er 28 to be the same as that used in the said receiving sets, and to correspond to the secondary or corrective cir~ cuit. The output from ampli?er 28 is made to partially neutralize that of ampli?er 21 and thereby obtain this reverse distorting e?ect elec trically. Ampli?ers 2i and 28 may be of the push pull type so as to eliminate harmonics, etc. 2,107,135 Figi 8 shows how ‘it would be possible to ac‘ complish this reverse distortion for neutralizing the distorting characteristics of a loud speaker ‘ without ?rst permanently recording the sound. verse distortion as practiced by this invention. The values for this curve are arbitrary and have conveniently been assumed to vary from 100% perfect reproduction to 10% perfect reproduc The fundamental difference between this circuit tion. ' t should be understood that any point and the previous ones is in the way of avoiding on this curve may represent a large number of the time lag encountered by the air gap “A” diiferent frequencies that may happen to be re between speaker B and microphone C‘. This is produced with the same degree of e?iciency. accomplished by having two pick-up mi The line P of Fig. 10 is assumed to represent the desired energy level at which all frequencies 10 10 crophones D and Er located at different distances from the source of vsound. Microphone D picks ' should be reproduced in order to give the proper up the sound for the circuit having the arti?cial volume of undistorted sound under a given condi distortion and which would correspond to the circuit used forthe making of the secondary The curve R of Fig. 10 represents the amount record of Fig. l. Microphone E (which is lo of distortion correction that may be effected by cated at a greater distance from the sound source the practice of this invention when using appa than D) operates the circuit having no arti?cial ratus similar in its distorting characteristics to distortion and which would correspond to that . the apparatus used to obtain curve Q. part of Fig. 1 which records’ the direct record. 7 At the end of the Specification is a table show-7 By properly adjusting the distance of microphone ing how ‘the arbitrary values for curve R have tion. been obtained. phone Dv it will readily be seen that the time lag between speaker B and microphone C will be balanced out. When the sound which is to be Column 1 denotes the various frequencies which are so distorted in the recording and reproduc ing apparatus as to produce curve Q. Column 2 gives the arbitrary values in percent necessary that the mouth pieces of the micro phones D and Ev be located side-by-side or even converge into one in order to obtain the proper time lag between the two microphones. This is In this table'— ' for the distortion arising within the recording apparatus. 1. Column 3 gives the relative percent of energy recorded on the original or primary ?lm, and accomplished diagrammatically in the ?gure in which are the same as the values of column 2. the form of a tube F which has the proper Column 4 gives the arbitrary values in percent for the distortion arising within the reproduc acoustical properties and extends from micro phone E to a point adjacent to the mouth piece of microphone D. CO Cl . E‘ from the sound source in relation to micro . picked up comes from many different points it is 30' . 30 . ing apparatus. Column 5 gives the resultant relative reproduc Fig. 9 shows a still different way of carrying V tion in percentage reproduced from the sound 35 out the objects of this invention and consists of record of column 3 by the reproducing appara two parallel circuits, energized by the same tus column 4. source, which may be similar to each other with the exception that in one of the circuits a loud 40' speaker is inserted (having characteristics similar to that of the speaker which is to do the ?nal reproduction) in such a way as to dissipate the electrical energy impressed upon it in the form of sound energy. Now the frequencies at which the speaker operates most e?iciently at will will also be the ones that have the greatest amount of energy dissipated. The result will be that the distortion produced in this circuit by this energy dissipation will be in the desirable direction. ‘ However, it will not be suiiicient to produce the most advantageous results and, therefore, it will be necessary to partially neutralize by the rela tively undistorted energy of the other circuit in order to increase this reverse distortion suf ?ciently. Referring to Fig. 10, this is a diagram exhibit ing the relative distortion correction that may’ be effected by the practice of my invention, as, for example, when using apparatus similar to 60 that of Fig. 1.- The vertical lines denoted by the letters “A to J”, represent various frequencies handled by the apparatus and which correspond to the sound frequencies which are to be re produced. The horizontal lines represent the 65 relative energy levels at which the said various frequencies are reproduced, the scale of which is logarithmically shown to the left as the “rela tive energy levels shown in percent,” while to the right are shown the corresponding values in TU 70 (transmission units, de?ned by the equation TU=1O log. [P1132] when [P1P2l is the power ratio.) The linear relation shown by curve Q represents the relative reduction in volume of the various important frequencies of a recording and 75 reproducing apparatus. when employing nov re~ V . The values in this column correspond to curve Q of Fig 10. Column 6 gives the relative percentage of the 40 reproduction of column 5 that is recorded on the secondary record, when using recording appa ratus having characteristics similar to that of column 2. 7 Column 7 gives the relative percentage of the recorded energy that is to be reproduced on ap~ paratus similar to that of Fig. 6, when the energy recorded on the primary record of column 3 is partially neutralized by subtracting 80% of the secondary record of column 6. ' . Column 8 gives the relative percentage of re production obtainable for the various frequencies, when the partially neutralized record of column '7 is reproduced on apparatus similar to that of Fig. 6 and having characteristics similar to that 5.5 of column 4. These values correspond to curve B of Fig. 10. The comparison of curve Q and curve R of Fig. 10 shows quite clearly the result obtained by subtracting 80% of the secondary record from 60 the direct record. This partial neutralization of one record with another has the effect of re ducing the volume of the reproduced sound as well as tending to correct for distortion. There fore, additional ampli?cation will be required in 65 the reproducing apparatus to overcome this re duction in volume. Curve R2 shows the result obtained by increasing the ampli?cation approx imately four fold over that used in obtaining curve R. If the reduction in volume, caused by distor tion of the various important frequencies were such as could be represented by the letters A to F, and there were no frequencies reproduced as poorly as those represented by the letters G to 70 5. 2,107,135 J, it would be necessary to subtract only about 70% of the secondary record from the direct record in order to obtain the most advantageous results. Column 9 and column 10 show the re sults-obtained under this condition. Curve “S” of Fig,'10 which corresponds to the values given in column 10, shows clearly that the relative im provement is greater in this case than that of bining synchronously the products of two input apparatuses in parallel with each other, one of which input apparatuses is corrective and has distorting characteristics over said band of fre quencies similar to the distorting characteristics of the reproducing apparatus, and applying said combined products to said reproducing apparatus. curve B and leads to the conclusion that the 10 less the distortion within the apparatus, still greater will be the improvement effected by the 5. A method of obtaining faithful reproduc tion of sound from sound-reproducing apparatus including an ampli?er and a loud speaker, both 10 having distorting characteristics over a substan tial band of frequencies, which method comprises present invention. Direct1 reciirtgi neutra ize y . so% of SecOéld- m’éfg‘fve ary recor , 15 . - glglfgyggggé Relative % oi Fre- by the direct energy record- energy passed qucncy a recording circuit ed on direct record Relative % oi by the reproducing circuit Sound Relative "/aoi Relative % of g?glggllgfvtggé sound repro- energy record- mt is t'h‘gsame duced dueed for 500ondary record ed on secondmy record 1 for both mi_ mmy and Sec_ from neiiggrial 20 ondary circuits when operating at fre quency “A” repro 20 direct record _,__.___ ______ _, Percent100 Percent l00 Percent 100 100 90 70 ‘i0 75 100 60 80 100 90 70 90 75 100 60 8O 90 90 100 66 66 40 50 25 Percent 90 81 70 (‘:0 50 (i0 30 20 90 73 49 51 37 40 18 16 0 28 31 31 ‘i7 116 (‘v8 46 67 100 100 l0 l0 10 92 I claim: 1. Sound recording means comprising a sound recording circuit for making a permanent record corresponding to the sound waves energizing said circuit, a sound reproducing circuit energized by the output of said recording circuit, and a sec ond sound recording circuit having distorting characteristics similar to the distorting charac teristics of said first recording circuit energized by sound reproduced by said reproducing circuit for making a second permanent record on the same recording medium as used for the record ing from said first recording circuit. Percent 100 30 09 having distorting characteristics over said band of frequencies similar to those of the ampli?er and loud speaker, respectively, of the reproduc ing apparatus, and applying said combined prod— nets to said sound-reproducing apparatus. 6. Apparatus for obtaining faithful reproduc tion of sound from sound-reproducing apparatus band of frequencies which method comprises combining synchronously the products of two sound input apparatuses in parallel with each other, one of which input apparatuses is cor rective and has distorting characteristics over said band of frequencies similar to the distorting characteristics of the reproducing apparatus, and applying said combined products to said sound reproducing apparatus. 3. A method of obtaining faithful reproduc— tion of sound from sound-reproducing apparatus including a loud speaker having distorting char acteristics over a substantial band of frequencies, which method comprises combining synchronous ly the products of two sound input apparatuses in parallel with each other, one of which sound input apparatuses is corrective and includes a loud speakers having distorting characteristics over said band of frequencies similar to those of the loud speaker used in the reproducing appa ratus and applying said combined products to said sound-reproducing apparatus. 4. A method of obtaining faithful reproduction of sense~affecting waves from reproducing appa ratus having distorting characteristics over a sub stantial band of frequencies, which method com- - prises applying said waves to said apparatus com 25 28 31 31 ‘i1 27 23 17 other, one of which input apparatuses is correc CC Cr tive and includes an amplifier and loud speaker ing distorting characteristics over a substantial 70 Pcrcem‘2 combining synchronously the products of two sound input apparatuses in parallel with each 2. A method of obtaining faithful reproduction of sound from sound-reproducing apparatus hav 60 Percent 40 having distorting characteristics over a substan~ tial band of frequencies, which apparatus com prises two sound input apparatuses in parallel With each other, one of which input apparatuses is corrective and has distorting characteristics over said band of frequencies similar to the dis torting characteristics of the reproducing ap paratus, and means for combining synchronously the products of said two sound input apparatuses. 7. Apparatus for obtaining faithful reproduc tion of sound from sound-reproducing apparatus including a loud speaker having distorting char acteristics over a substantial band of frequencies, which apparatus comprises two sound input ap paratuses in parallel with each other, one of which sound input apparatuses is corrective and includes a loud speaker having distorting char— acteristics over said band of frequencies similar to those of the loud speaker used in the repro ducing apparatus, and means for combining syn chronously the products of said two sound input apparatuses. 8. Apparatus for obtaining faithful reproduc tion of sense-affecting waves from reproducing apparatus having distorting char-acteristics over a substantial band of frequencies, which appa ratus comprises two input apparatuses in p.ar— 70 allel with each other, one of which input appa ratuses is corrective and has distorting charac teristics over said band of frequencies similar to the distorting characteristics of the reproducing apparatus, and means for combining synchro 6 s ‘ 2,107,135 nously the‘products of said two input apparatuses. 9. Apparatus for obtaining faithful reproduc tion of sound from sound-reproducing apparatus, including an ampli?er and a loud speaker, both having distorting characteristics over a substan~ tial band of frequencies, which apparatus com prises two sound input apparatuses in parallel with each other, one of which input apparatuses is corrective and includes an ampli?er anda loud speaker having distorting characteristics over said band of frequencies similar to those of the am pli?er and loud speak-er, respectively, of the re producing apparatus, and means for combining 3 synchronously the products of said'two sound ' input apparatuses. ' WESLEY WILSON.