US1713039A - Phonograph recording and reproducing - Google Patents

Description

May 14, 1929. L.. :sPENscl-nso 1,713,039

rnonosluru RECORDING Ann nnrnonucluo V Filed Hoy. 15, 1919 3 Sheets-Shasta l eyueuy, Q/e'ks per Sesma W' INVENTOR.

ATTORNEY May if, 1929.

L. EsPENscHlr-:

PHONOGRAPH RECORDING AND REPRODUCING Filed Nov. 15, 1 919- 5 Sheets-Sheet` 2 20'00 Freyung, @cles per Jaco/d $520@ Mxw INVEN-IOR.

" ATTURNEY MW 1 4,- 1929. L. ESPENSCHIED 1,713,039

PHONOGRAPH RECORDING AND REPRODUCING Filed Nov. 15, 1919 3 Sheets-Sheet 3 INVENQR.

A TTORNEY Patented4 May i4, 1929.

" UNITED STATES PATENT OFFICE.

IiLOYD ESPENSCHIED, OF QUEENS4 VILLAGE, YORK, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY; A CORPORATION OF- NEW 'YORK PHONOGRAP RECORDING AND RZEPRODUCING.

Application led'November 15, 1919. Serial No. 338,211.

The invention relates to phonographic delvices and provides methods and means for improving the recording and the reproduc-` ing of sound Waves.

' -The broad object of the invention is to improve the clarity and fidelity of sound reproduction. More specifically the objects tion Will be evident from the following description taken in conjunction Wit-li the ac companying figures.

A comprehensive understanding of the 1nvention Will be facilitated by first yconsidering briefly the causes of the imperfect operation of phonographic devices. discussion of the principles involved and in a the descriptive matter, the ordinary mechanically recording phonograph Will be referred to, but-it will be understood that the broad features characterizing the present invention apply equally Well to all types of phonographs, such as those employing magnetism oi' light as the recording agent.

The disagreeable scratchingsound of ordinary phonographs arises from extraneous variations or irregularitiesin the Wave as represented in the recording medium. caused inthe case of the ordinary mechanicaltype of record byphysical imperfections and ir'- regularitiesin the surface of the record, and by the presence of dust particles, etc. on the record surface. 'These irregularities cause the reproducing needle in tracing the surface of the Wave to be thrown off from its true course in an irregular manner and\ to give rise to diaphragmmovements representing noise.

Another limitation of the ordinary phonograph resides in its characteristic of not reproducing with equal efficiency all of the frequencies which constitute the f frequency spectrum of sound.' The ordinary phono; graph, in fact, reproduces at maximum effi ciency only a smallV part of the tot-al frequency range involved and transmits inefli- `lciently the greater part vofthe frequency In this range necessary for good quality in the reproduction of music or speech. This inequality in the efficiency of reproduction of the broad band of frequencies involved in sound waves is hereinafter referred to as distortion. It is this effect which causes the monotonous twangv so characteristic of the ordinary phonograph. The distortion is caused very largely by the inertia of and by resonance effects in the various translating devices employed. The phragm, for instance, vhich is used in the recorder and also in the reprod'ucer or phonograph proper, has a natural period or several natural periods of vibration and therefore responds much more readily to some component frequencies present in the original sound than to others. Resonance effects also occur in the acoustic cliambersof horns, such as those employed in directing the original sound to the recording diaphragm and in distributing the Vibrations of the phonograph diaphragm throughout a room. These resonance effects are frequently so `pronounced and selective in their afi-- tion as to substantially suppress frequency components of 'the original sound other than those in the region of the natural periods.

In accordance with the present invention the difficulty first enumerated above, that of scratching, is ameliorated by amplifying the original sound wave energy 4and using the enhanced energy in obtaining a greater ratio between the amplitude of the desired record Waves and of the undesired deviations in the true Wave caused by the record irregularities. The second difficulty nientioned, that of distortion, is corrected by introducing compensating .distortions which when added to the previously existing distortions gives a resultant substantially dis- .tortionless These compensating distortions are illustrated as introduced electricallybut it- Will be understood, may be also introduced otherwise, as mechanically. The distortions, being due to the enhanced efficiency of reproduction atfrequeiicies corresponding to the resonant periods of the instrument, are offset by similar resonance effects so inserted in the system as toprol duce a maximum loss in efficiency instead of gain in eiciency at the resonant periods.

ordinary Adiaillustratingl thevariation in the efficiency Thereby the two resonance effects or sets of resonance effects are made to offset each other. Such an arrangement, of, course, lowers the over-all efficiency of the system, but this is not a serious objection, since the amplitude of the currents representing' the original sounds may be increased to any desired extent b distortionless amplification. The method ofyearrying out these operations and likewise the means therefor are more fully explained in the following disclosure taken in conjunction with the figures forming a part of this specification.

Figure l illustrates an arrangement for increasing the amplitude of the waves available for 'recording upon t-he masterrecord -and has for its object minimizing scratching and interference effects. Figure 2 illustrates an arrangement for introducing into the phonographic process an anti-distortion in accordance with the method of improving the quality of reproduction as outlined broadly above. Figure 3 presents curves with which the differentfrequencies constituting sound are reproduced in the ordinary phonograph, together with curves illustrating the characteristics of the anti-distorting means and illustrating also the resultant characteristic after amplification. Figure 4 illustrates the ca'se o ffproviding .a plurality of anti-distorting means and shows a variation in the specific anti-distorting means gfemployed. Figure 5 presents curvessimilar to those of Figure 3, but for the' case where correction'for a plurality of resonant periods is involved. vFigure 6 illustrates a further development of means for correcting for a.plurality Iof natural periods causing distortion. I I y The above figures illustrate the application of the anti-distorting means in the process of making the original record. Figure 7 illustrates` the application of the same means in the process.of`reprodueing the record in the ordinary phonograph, as distinguished from the process of making the original record. Figure 8 shows the invention appliedto thereproducing or multi-l plying of phonograph records.

Referring to Figure l, l represents a telephone transmitter provided with an enlarged mouth-piece tov facilitate thecolleethe dipahragm. The transmitter is connectcd through the usual battery and the battery-supply transformer 2 to the input transformer 3 of a vacuum tube amplifier indicated as of two stages of amplification and including the input transformer 3, the audion amplifier. bulbs 4 and 6 related by the transformer 5 and the terminating output .coil 7. These amplifiers are provided with their usual battery supply circuits and being of a well-known audion or vacuum tube type, need not be described in detail. The output transformer 7 is connected with an electromagnetic device 8 which is simila'r electrically to the ordinary telephone rcceiver. Its diaphragm 9 is attached to an arm which is pivoted at l0, the outer end of which carries a record scribing needle' 11.

This general arrangement constitutes a means for amplifying substantially without distortion the energy available for making the impression on the original or master record 12. Sound waves falling upon the telephone transmitter 1 are converted into electric current waves of corresponding frequency, the currents are amplified, the amount of which may be adjusted by the potentiometer 13, and are impressed upon the device 8 for conversion into energy of mechanical vibration in diaphragm S). The scribing needle 11 undergoes undulations corresponding in frequency to the original sound Waves which undulations are cut or otherwise impressed upon the record 12. The enhanced energy thus obtained is ,used for overcoming extraneous record noises in either of two ways as follows: (n) by causing the scribing needle 11 to undergo undulations larger in amplitude than otherwise possible without'the amplifying means, and to thereby eut in the master record w'aves of correspondingly larger amplitude. In this manner the ratio of the amplitude of the desired wave undulations of the record to the amplitude ofthe undesired variations in such undulations caused by record irregularity, dust, etc. is made so large that the extraneous noises are lost in comparison with the desired sound, when the record is reproduced in the phonograph. The other method of using the enhanced energy' (b) is that of using the increased force ofthe excursions of the needle ll to inscribe the record wave upon the record with no greater amplitude than normal but with much greater precision of wave shapeI is employed the amplitude of the engraved tion and concentration of sound waves .upon

waves may, to advantage. be made smaller than that which is ordinarily used. In order to obtain the same or-even a greater volume of sound when the record is played on the reproducing machine, a stiff and more tightly pressing needle should be einployed. Owing to the stronger biasing force of such a needle it will be caused to vibrate with greater power and thus to produce an enhanced sound outputawhieh is greater for the desired sounds than for the undesired noises, because of the improvement initially effected in the qualityr of the record. Furthermore, it is obvious that the enhanced energy obtained by amplification offers the further advantage of permitting a Wide degree of selection -in the materials employed in a master record and' in the manner of taking and of Working such record. For example, a number of master records may be simultaneously inscribed. Bly thus amplifying the sound waves before or in the recording process, as distinguished from amplifying in the reproducer or phonograph proper, and incorporating in the record the effect of the increased energy by either producing record undulations of greater amplitude or by employing the increased force in executing recordgraphs of cleaner cut and greater perfection of Wave shape. the improvement is propagated into all of the record output andu is realized in the reproducing phonographs Wit-hout the addition thereto of supplementary apparatus.

Figure 2 illustrates the inclusion in an amplifying system of the type of Figure 1,

of distortion-correcting means. i In this case the device 14 for converting the sound Waves into electric current waves is indicated as a i 'telephone receiver, the actuation of the diaphragm of which causes a current to flow in the windings and in `turn to Vinput transformer 31.' This current is amplified in the vacuum tube 41, is passed through output transformer 51 and into a circuit across Which is connected a shunt 14;, consisting of three elements in series, inductance 15, condenser 16, and resistance 17. The current is then transferred by transformer 51 to amplifier 61 and actuates the recording,

mechanism as described above. The shunt circuit is' lin effect a tuned circuit bridged across the transmission path and designed to introducein the path a large loss in transmission efliciency at a frequency corresponding to the predominant natural period of the phonograph system, preferably including in'tlie system the recording as well as the reproducing devices. The-frequency at 'which the maximum lossin efficiency of the anti-distortion network occurs and the frequency range over which it extends and also the absolute magnitude of the loss in efficiency are all designed to correspond in inverse manner to the similar 'characteristics of the phonograph system itself. The frequency 'at which this loss occurs is determined by the formula- N r w/tr y tra Where L is the inductance of the coil 15, C is the capacity of the condenser 16 and R is the resistance of the shunt indicated as localized in 17. The avidth of the band over whichv the transmission `loss occurs, correspending inversely to thesharpness of tunfrequency.

ing, is controlled by theresistance 17. That is, the damping factor is preferably adjusted to correspond to that of the distorting device the effect of which it is desired to offset. When the distortion correcting device is arranged to counteract the distortion of the entire phonograph system, i. e., both the recording and reproducing phonographs, as above noted, thc record thus made will have the sound waves recorded thereon in a distorted manner, this distortion being such as to correct Ifor the distortion Which Will be encountered when the said record is played on a reproducing phonograph. record and the record itself, may, therefore, be appropriately termed predistorted to designate that the distortion therein is not inherent or undesired but of predetermined character, being designed to compensate entirely or partially for the distortion which `the phonographic system, With change in Frequency is plotted as ab-' scissas and efficiency of reproduction as ordinatejs. By efiiciency of reproduction is here meant the ratio of the energy output tothe energy input of the phonographsystem including both the recording and reproducing steps. Curve A illustrates the manner in which the eiciency of reproduction rises to a relativelyhi-gh value at some frequency corresponding to a resonant period in one or more of the devices involved, and then rapidly falls off and maintains a relatively loW value vup through the higher frequencies. The curve indicates a predominant period at about 500 cycles. This means that the 500 cycle component of the music or speechinvolved will be over-emphasized in the reproduced sound and will thereby distort the reproduced sound as compared with the original sound. effect is often much larger than that indicated by the curve A. Curve B represents the performance of the shunt network 14: of Figure 2. As indicated by the curve, it transmits very inefficiently at the resonant frequency of say 500 cycles, and progressively more efficiently at frequencies divergent therefrom. The resultant overall characteristic obtained by. the combination of the anti-distorting characteristic B with the natural distorting characteristic A of the system is indicated bycurve K. The peak corresponding to thereonant point of the original system haslbeen taken out bythe The sound Waves on the` ilo` Such distorting Nreduced and would be so low as to seriously reduce the volume of sound obtainable from' the phonograph. This 1otherwise serious limitation is overcome by amplification of the resultant current by means of the vacuum tubes of Figure 2. These amplifiers are in themselves substantially distortionlcss so that the currents of all frequencies are amplified alike and the line K is shifted bodily upward to line L which indicates the restoration 'of the efficiency of reproduction. The volume or efficiency of reproduction ma f be increased to any desired value above or below that obtainable without the distortion-correcting feature, by merely controlling the amplification effected by the vacuum tube circuits in some such manner as is indicated by the potentiometer 13,.

A further development of the single network 14 of Figure 2, is indicated by Figure 4 which illustrates the use of a plurality of distortion-correcting networks. The network 14 of Figure 2 is connected in shunt across the circuit. It is possible to introduce a similarly functioning network suitably designed forinclusion serially in the circuit, as indicated at 18 in Figure 4. This series network comprises the inductance 19 connected in series with the circuit, said inductance being shunted by capacity 20 and resist-ance 21 mutually in series. This is the so-called anti-resonant network, and is the electrical equivalent in the circuit of the shunt resonant circuit 14 of Figure 2, which is here reproduced as 142. These two distortion-correcting networks may be both designed for the same resonant frequency or may be designed for different frequencies corresponding to a plurality of natural periods in the phonograph system. Likewise further networks may be added to the circuit corresponding to additional periods of resonance in the phonograph system and these Jnetworks may be distributed as between the series and shunt type in any desired manner. v

Figure 5 illustrates in curve form the operation` of the circuit arrangement of Figure 4 in compensating for the distortion effect of two natural periods in the same manner as do the curves of Figure 3 illustrate the arrangement of Figure 2 in the case of one such resonant period. The curve A, representing the reproduction efficiency ofthe phonograph system, has in it two humpsk or points of maximum efficiency' corresponding to two natural periods somewhere in thev phonograph system, one perhaps in the recording mechanism, and one in the reproducing device or phonograph proper. These resonance effects are compensated by individual anti-distorting networks', the network 142, for instance, introducing an efficiency -loss 'in the system corresponding to curve B and compensating for one of said resonance effects, and network 18 compensating for the other of said resonance effects as indicated by curve C.

The summation of these effects results in a much more uniform frequency-efficiency curve, as indicated b curve K1, corresponding to curve K of" Figure 3. The amplification of the vacuum tubes raises the over-all volume of reproduction to any desired value as indicated .by curve L1.

Figure 6 illustrates a further developlnent of distortion-correcting means. Where distortion is caused by a considerable number of devices not necessarily coincident as to their natural periods,.but all occurring in some limited range of frequencies, it may be desirable to compensate for them as a group. This is accomplished in Figure 6 by the network 19 and the element 20 which together insert in the system a transmission loss throughout a band or range of frequencies corresponding to the band in which the resonance effects occur. Network 19 is a selective circuit of the socalled Gr. A. Campbell band filter type, now well known in electric communication engineering. It excludes all frequencies lying without a certain band of frequencies and transmits freely the frequencies lying within said band. The currents within this frequency band are transmitted to element 20 which may be merely a resistance as illustrated and which is designed in conjunction with filter 19 to give the transmission loss necessary for offsetting the abnormal efficiencies of reproduction which would be caused by the predolninant periods of the phonograph devices. It is preferable to insert the anti-distortion networks in between amplifiers rather than directly with the distorting device under correction, such as a diaphragm-actuated recorder, in order to prevent reactions between such devices and complications of the natural periods involved. It is, however, permissible for the major purposes of the invention to connect the distortion-correeting elements between the amplifier taken as a whole and either the air-electric or the electric-record translating devices.'

In the adaptation described above the' distortion correcting means and the amplifying means are shown applied in .the recording process of making the master record. They may, of course, be as well applied in the process of -reproducing the original sounds; that is, in the reproducing phonograph itself. This condition is illustrated in Figure.7 where 21 indicates the record being played, 22 the reproducing needle, 24, 25 the pivoted diaphragm and telephone receiver device corresponding to 9 and 8 F igure 1, forexample, but used here on the input instead of the output side of ythe amplifying and distortion correcting stage@ Transformer 34 corresponds to input transformer 3 of Figure 1 or 31 of Figure 2, etc., and output transformer 74 to the corresponding output transformer of the other gur'es. In between these input and output transformers any of the means for amplifying and correcting distortion previously described in connection with Figures 1, 2, 4 and 6 may be employed. In this instance the current from the output transformer 74 actuatcs an electromagnetic reproducing device 25 similar to a telephone receiver which iii turn actuates the diaphragm 26 and transmits the reproduced sounds out through the horn 27.

In the above the devices employed in translating between the soundvvaves and the electric Waves of the circuit are of the electro-magnetic type. These devices may be of the Well-known electrostatic type, as shown in Figure 8. This ligure illustrates the further feature that the general distortioncorrecting-amplifying system may be ap-J plied in the reproduction or duplication of phonograph records. The electrostatic translating devices 28 and 29 are condensers consisting of two plates or sets of plates one of Which is stationary and the other of which is capable of displacement. The displaceable member isattached to the phono'- graph needle. In the case of the transmitting condenserv 28, the rotation of` the record causes the" needle vand attached plate or plates to vibrate and'to thereby vary the capacityi'of the. condenser and in turn the potential impressed thereon by the polarizing battery 30." These potential variations cause corresponding current variations in the input coil 35. These variations are amplied and their distortion correctedl as before, and are impressed upon and cause' mechanical vibration of the output condenser-translator 29. These vibrations are copied upon the second record in any Well known manner.

Figure 8 illustrates alsoV the possibility of transferring 'the matter recorded on one -record, such as a master record 211 simultaneously to a plurality of other records 124 and 125. This is made possible by the increased energy resulting from the amplification of amplifiers 45 and 65. Thetranslating devices 29 andv Blfor the respective new records are connected together and to the output circuit of the last amplifier 65. Obviously by increasing the amplification of the system the number ofthe new records which can be thus simultaneously produced may be increased indefinitely.

In respect to the distortion-correcting feature of this invention, it Will be under-.v stood that although the means illustrated are electric circuit networks it is the intention to cover suoli means broadly as applied to phonographs, lirrespective of Whether they are electrical, mechanical or acoustical in their operation.

`While the invention has been broadly set forth in the initial outline, the disclosures of it have been necessarily limited to specific. embodiments. It therefore Will be understoodthat many variations from these arrangements and amplilications of them are possible Without departing from 'the spirit of the invention. y

What I claim is K 1. The method of reducing extraneous noises in phonographic reproduction Which consists in amplifying the original sound Waves, then impressing the amplified Waves upon a record and finally. reproducing the record upon a phonograph of reduced sensitivity.

2. The method of reducing extraneous sounds in phonographic reproduction which .consists in amplifying the sound ,Wave energy, then impressing the -amplified sound `Wave energy upon a record, producing thereon undulations of Ienlarged amplitude and finally of operating from such a record a phonograph reduced in sensitivity by an amount corresponding to the amplification of the record.

3. The method of reducing extraneous sounds in -the reproduction of sound which Consists in amplifying the sound Wave energy before recording, impressing the amplilied sound Wave energy upon a record of material having compressive or shearing strength large as compared With Wax and finally of actuating by such record or copyl thereof a relatively tightly-pressing needle member of a phonograph.-

l. In a recording system, an electric circuit comprising means for converting soundv waves into electrical Waves, an electromagnetic recording device, avacuum tube ampli- Iier for augmenting said electric Waves before recordation, said circuit having the characteristic of passing different frequencies imequalIy, compensating means for equalizing the transmission of the circuit over a Wide range of frequencies, and means in said circuit for governing the amplitude of current applied to the recorder so-as to @permit of the control of the amplitude of` the recorded Wave independently of variations in loudness of the original Waves..

5. A' phonograph record having the ulidulation thereon distorted substantially' opposite to the distortion entailed when the record is played on a reproducing phonograph, so that the emitted sound. energy is free from said distortion. y

6. The method of ob aining faithful reproduction .of sound, .W ich consists in subjecting the sound energy prior to its recordation to distortion substantially opposite to that of the reproducing device so as to compensate for the distortion of the said device.

7. The method herein described which consists in modifying the undulations of the sound waves before they are recorded substantially in accordance with the distortion entailed in the reproducing process, so as to neutralize for the distortion entailed in the saioll process.

8. The method herein described which consists in excluding from the record the distortion inherent inthe recording process and introducing into therecord distortion tending to neutralize the distortion entailed in the reproducing process.

9. The method of obtaining improved reproduction of sound which consists in constructing the reproducing phonographs to have distortion of predetermined character, making records With distortion of opposite character, and operating said records in said phonographs so` that said distortions tend to cancel each other.

10. In combination, a reproducing phonograph arranged to distort the sound reproduced thereby, and a record therefor having sound recorded thereon in distorted manner, the distortion of said phonograph and record being such as to tend to compensate for each other.

11. In combination, means for `forming a record of sound. means associated therewith for diminishing the amplitude of recordation of such components of the sound waves as are augmented relatively to the other components during the reproduction of the record, and means associated with said firstmentioned means for amplifying the amplitude of recordation of all of said components of said sound as to offset the loss caused by said second-mentioned means in the volume of the sound When reproduced from the record.

12. The method of correcting distortion in phonographs which consistsin moulding the records with a predistortion the opposite of that caused by the phonograph itself.

13. The process of making phonograph records which consists in moulding in the record a predistortion which compensates for the distortion in the phonograph itself.

14. The method of recording and reproducing sound Waves, which consists; first, in accurately determining the acoustic transmission properties of the reproducing machine; second, in similarly accurately lixing the transmission properties of the recording system in a manner such as to compensate for distortion effects in the reproducing machine; third, in producing by said recording system a predistorted record; and fourth, in playing the record so formed, or copy thereof, upon said reproducing machine.

15. A phonograph system comprising a recording machine including an electrical circuit, a reproducing machine for playing records originated by thc recording machine, and meansin said electrical circuit for causing a distortion Which is greater than is necessary for neutralizing any distortion which may exist in said recording machine, thc distorting means being of such character that the distortion caused thereby in excess of the distortion natu ally existing in the recording machine will tend to oisct the distortion entailed in the reproducing machine. l

16. rlhe method of recording sound vibrations which consists in distorting the vibrations to be recorded inversely tothe predetermined distortive elects of a given reproducing system and recording the modiiied vibrations.

17. The method of recording sound .vibri tions which consists in converting sound vibrations into electrical vibrations, attenuating vibrations of such frequencies as are overemphasized by the elements of the rccording system, further attenuating vibrations of such frequencies as are overeniphasized by the elements of any given reproducing system and recording the modified vibrations.

In testimony whereof, I have signed my name to this specification this 12th day of November, 1919.

LLOYD ESPENSCHIED.

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