US2230949A - Automatic sound picture dubbing system - Google Patents

Description

Feb.` 4, 1ML H, sul-{ELLER ETAL 2,230,949

AUTOMATIC SOUND PICTURE DUBBING SYSTEM Original Filed Jan. 18, 19.37 Sheecs-Shee'I l AUTOMATIC SOUND PICTURE DUBBING SYSTEM Original Filed Jan. 18, 1937 2 Sheets-Sheet 2 MST @Sv s kl I Patented Feb. il, 1941 uNrrsEo srA'rEs AUTOMATIC .SOUND PICTURE DUBBING SYSTEM Herman S. Heller, West Los Angeles, and Frank M. Kennedy, Los Angeles, Calif.; said Kennedy assigner to said Heller Application January 18, 1937, Serial No. 121,100 Renewed July 1, 1940 11 Claims.

This invention relates generally to the art of dubbing motion picture sound records, and deals more particularly with automatic dubbing systems for motion picture sound records.

The expression dubbing as applied to sound pictures contemplates three varieties of operations, namely, scoring, or adding incidental music to an existing sound record, synchronizing, or adding background sound effects at appropriate places in the originally taken sound record, and simple re-recording, that is, recording an original record for instance at a dilierent volume level, or with desired volume modifications. rlhese three classes of dubbing operations may of course be performed singly or in combination.

In practice, an original or existing sound record is run synchronously with a sound record or records having the incidental music or sound eieots to be dubbed in, the electrical sound currents reproduced from such component records, are mixed at the desired volume levels by a mixer, and the resulting composite electrical sound current is recorded on the new record. An operator, called a mixer, operates a series of volume change devices or faders controlling the relative amplitudes of the several electrical sound currents combined Within the mixer. This operator is furnished with a loud speaker or monitoring horn from which the resultant composite electrical sound current is audibly reproduced simultaneously with recording on the new record, and by listening to this reproduction and simultaneously operating his controls, the mixer attempts to control the amplitudes of the several input currents in such manner as to combine lthem at proper relative amplitudes to produce the desired combination sound record. If a mistake in judgment is made, and a sound is recorded at too high or too low volume, the whole operation must be performed over again. The Work is highly tedious, and is in reality impossible to complete to satisfaction. Many retakes are made, with. a resultant wattage of iilm, and the iinal product .is invariably no more than a rough compromise with the actual result Wanted.

t is the object of the present invention to provide an automatic dubbing system, enabling the desired volume levels or changes to be individually predetermined for each component or dummy record before any recording on lm is done, after which the component records may be run simultaneously and their output mixed and recorded under automatic mixer control.

The system in one aspect may be considered as a pantograph, wherein a series of executed motions of the fader may be repeated or reproduced at any time in the future. In other Words, the system of the present invention reproduces automatically the movements of the mixer made While he is manipulating his mixing or volume controls, but this reproduction is accomplished at any desired time in the future. This reproduction in fact is a play back of the original movements of the mixing or volume control members which, thereby, causes the same degree of volume control as the operator or mixer originally effected. In other words, the play back is an accurate replica of the original movement of the mixing or volume control settings.

The invention in all its aspects, including its various objects and corresponding accomplishments, will be best understood Without further preliminary discussion by referring now to the following detailed description of a present illustrative embodiment thereof, reference being had to the accompanying drawings, in which:

Fig. 1 is a schematic diagram showing a typical dubbing system; and

Fig. 2 is a schematic diagram of an illustrative automatic control unit in accordance with the present invention, it being understood that the mixer unit indicated in Fig. 1 is to be provided with one such control unit as is shown in Fig. 2 for each component record of the complete dubbing system.

Reference is rst directed to Fig. 1, showing a typical dubbing or 1re-recording system. A plurality of sound records l0, here indicated as of the motion picture film type, are indicated as 5 synchronously driven by synchronous motors ll fed from a common three Wire distributing system l2. The records IG may contain different sounds to be combined on the final film; for instance, one may contain the original talking record, another may bear incidental music, another sound eiects, such as the `sound. of a closing door, a pistol shot, etc. These several records are of course so prepared and driven as to synchronize with one another. The synchronizing system here indicated, comprising motors ll and distributing system l2, may be of a type well known inthe art, it being understood that each motor Il connected across distributing system I2 will run in exact synohronism With each other such motor so connected. f

Optical and photo-electric means for producing electrical sound currents from the records contained on films l 0 are diagrammatically indicated at l5, and the electrical circuits which conduct 55 such sound current to the mixing unit are indicated at I6.

Circuits I6 are connected into a mixer I1, which as heretofore knowny comprises a system for combining the electrical sound currents carried by the several input circuits into a single output circuit, together with individual manually controllable resistors, known as faders, for regulating the amplitudes, and therefore the Volume level characteristics, of the input currents received from circuits I6. 'I'hese resistors,'which are of well known type and need not be illustrated in Fig. l, thus serve to regulate the volume level characteristics of each input sound current, and after such regulation, the several currents are combined in a conventional manner within the mixer and are delivered to a common output circuit I8.

Output circuit I8 is shown as going to amplier I 9, and the output of amplifier I0 is conducted by way of circuit 20 to an electro-optical recording means at ZI which records the composite electrical sound current on final film 22. This final film 22 is indicated as driven by a synchronous motor 23 also connected across distributor system I2.

A monitor horn 25 enabling the operator controlling mixer I 'I to hear the result of the volume changes which he imposes is indicated as connected via circuit 26 to amplifier output circuit 20.

It will be understood that, in accordance with prior practice, the mixer operator maintains a constant manual control over the faders controlling the amplitudes of the several component sound currents which are combined within the mixer and delivered to the single output circuit going to the final recorder. It will also be understood that in the event this operator should make a mistake in judgment as to the volume at which one sound current should be mixed with the others, that mistake will not show up until the new record 22 has been developed, a print taken therefrom and that print reproduced.

The present invention provides means whereby the successive positions and changes of positions of each mixer fader during the manually controlled run may later be automatically reproduced.

Fig. 2 shows one of the input circuits I6, which will be understood to carry the electrical sound current produced by reproduction of one of the lms I0, and shows said circuit IS going to the terminals of a fader 30 of conventional type. The fader is shown provided with the usual control arm 3l adapted to wipe over fader contacts 32, and the output circuit 34 leading from the fader is connected as usual across one side of input circuit IE and fader arm 3I. It will be understood without further description how resistor or fader 30 controls the amplitude of the electrical sound current carried by circuit 34 leading from the fader in accordance with the setting of fader arm 3l on contacts 32. It Will be understood that the fader and its connections may be of any suitable or conventional nature, so long as its operation controls the attenuation of the sound current delivered to circuits 34 and I8.

It is to be understood that there is one fader, such as 30, controlling each input circuit I6, and a unit or system such as shown in Fig. 2 for automatic control of each such fader 30. It will also be understood that the circuit 34 leading from each fader 30 is so connected within the mixer to the corresponding circuits 34 leading from the other faders as to combine the several fader controlled sound currents within the single output circuit represented at I3. Such mixer circuits are well understood in the art and need not here be shown in detail, though in Fig. 2 I conventionally indicate several fader circuits 34 as connected into a common input circuit I8 leading to amplifier I9.

The automatic control unit of Fig. 2 will now be considered in more detail. Fader arm 3l is mounted on a manually rotatable shaft 40, which also carries the arms 400 and 40| of resistors 402 and 403, respectively. A low frequency oscillator 405 and a high frequency oscillator 40B are provided, the frequencies of which may typically be 50 cycles and 500 cycles, though it is to be understood that this illustration constitutes no limitation on the invention. One terminal of low frequency oscillator 405 is connected by lead 401 to the arm 400 of resistor 402, and one terminal of high frequency oscillator 405 is connected by lead 408' to arm 40| of resistor 403. The other terminals of oscillators 405 and 406 are interconnected by a lead 409, which is in turn connected by lead 4m to a center tap on the primary winding 4II of a transformer 4I2. Non-corresponding terminals of resistors 402 and 403 are connected by leads 4I4 and 4I5, respectively, to the outside terminals of transformer winding 4l I. That is, resistors 402 and 403 are so connected that as resistor arms 400 and 40! rotate in the same direction as shaft 40 is turned, the resistance in the circuit of one oscillator is decreased as the resistance in the circuit of the other oscillator is correspondingly or complementarily increased. Rotation of fader shaft 40 therefore causes the low frequency oscillator current input to transformer winding 4II to increase as the high frequency oscillator current input to said winding decreases, and vice versa, said currents varying always complementarily to one another.

The secondary winding 4I8 of transformer 4I2 is connected to the input terminals of an amplilier 4I9. The output terminals of amplifier 4I9 are connected by leads 420 and 42| to stationary contacts 422 and 423, respectively, of a control switch 424. Movable switch arms 425 and 426 are adapted to make with contacts 422 and 423, respectively, when moved toward the left, as viewed in Fig. 2. Connected to these switch arms 425 and 420 are circuit wires 42'! and 428 leading to a recording means, preferably of the magnetic tape type, and are here shown as going to recording and reproducing magnets 420.

The magnetic recording tape 430 passes between recording and reproducing magnets 429 in the usual manner, the tape running from a supply reel 43| to a take-up reel 432, the latter being understood to be driven by a synchronous drive motor (not shown) powered from distributor system i 2, while the supply reel is adapted to be driven by any suitable re-wind motor (not shown).

It will be evident that, switch arms 425 and 426 being moved ove!` to the left, the low and high frequency oscillator currents, which are complementarily varied as the fader shaft is rotated, are mixed within transformer H2 and recorded together on tape 430.

The tape as here shown is provided with a separate erasing coil 434 adapted to be energized by an alternating current supply circuit 435 including a control switch 430. This circuit may be utilized to clean all or a portion of the magnetic record oif the tape.

Switch arms 425 and 426 when moved to the right, as seen in Fig. 2, make with stationary switch contacts 440 and 44|, which are connected across a circuit 442 leading to the input side of an amplifier 443. Thus, when tape 430 has been re-wound on reel 43|, and is again run forwardly to reel 432, the complementarily Varying (complementary amplitude) oscillator currents recorded on tape 430 are reproduced within coils 429, and are amplied at 443. The output leads `444 and 445 of amplier 443 are connected across a circuit `449, which interconnects corresponding input terminals of a low-pass filter 441 and a high-pass filter 449. Low-pass filter 441 and high-pass filter 448 are thus both fed from the output of amplifier 443. Low-pass filter 441 is designed to pass substantially exclusively currents of a frequency corresponding to low frequency oscillator 495 and high-pass filter 448 is designed to pass substantially exclusively currents corresponding to high frequency oscillator 496. Such low and high-pass filters are well known in the art,`and will require no explanation here.

Low-pass lter 441 is connected by leads 450 to the input winding 45| of a transformer 452, while high-pass lter is connected by leads 453 to the input winding 454 of a transformer 455.

The output of transformer 452 is amplified by a vacuum tube amplifier, generally designated at 459, and then rectified by a rectifier designated at 46|, while the output of transformer 455 is amplified by a Vacuum tube amplifier indicated at 452, Vand then rectified by a rectifier indicated at 453. As here shown, amplifiers 450 and 462 are of the push-pull type. Considering amplier 459 in detail, the secondary winding 454 of transformer 452 is connected at its Vends through leads 459 and 491 to the grid elements of two Vacuum tubes 459 and 459, respectively, while the center tap of transformer 454 is connected by lead 410 to the heater elements 419e of tubes 468 and 469, as indicated. Theplate leads 41| and 412 of tubes 458 and 459 are connected to the end terminals of the primary winding 413 of a transformer 414, while the center tap of winding 413 is connected by lead 415 to positive B voltage, as indicated.

Lead 419 includes a condenser 480, and connected to lead `479 between said condenser and transformer winding 454 is one end of a resistance element 45|. The opposite end of resistance 48| is connected by wire 492 with one end of a second resistance 483, the other end of which is connected to lead 41,9 between condenser 480 and the heater elements of tubes 458 and 469. A condenser 494 is shunted across resistance483.

rIhe outside terminals of secondary winding 488 of transformer 414 are connected by leads 489 and 499 to the plate elements 49| and 492 of a pair ofrectifier tubes 493 and 494, respectively. ' I'hefilainent elements 495 and 496 of tubes 493 and 494 are connected in parallel, as indicated and connected across such filament elements is a resistance element 491, to the center of which is connected an output lead 498. The other output lead 499 is connected tothe center tap of transformer winding 488, as indicated.

It will be understood that the low frequency current passed by filter 441 will be amplified by amplifier 469, and that the resulting amplified low frequency current is rectified by tubes 493 .and 494, so thatoutput circuit `498, 489 carries an amplied, rectified low frequency (50 cycle) current.

Amplifier 462 and rectifier 453 are the same as amplier 460 and rectier'46 I respectively, members of amplifier 452 and rectifier 453 being identied with the saine reference characters as have been applied to amplifier 430 and rectifier 46|, but with primes annexed. Accordingly, output circuit 498, 499 carries a rectified 50 cycle current, while output circuit 499', 499' carries a rectified 500 cycle current.

Output circuits 498, 499 and 498', 499 are provided with 1r net works 50|] and 59|, respectively, each consisting of a pair of shunt connected condensers 502 and 593 and an intervening series connected inductance 504. These net works or filters are designed to take out the 50 and 500 cycle oscillation frequencies, passing only a uni-directional current wave bounded by the complementary envelopes of the 50 and 500 cycle waves received from the rectifiers, which envelopes will be understood of course to be determined by the movements of resistor control arms 459 and 49| during the making of record 430.

Circuits 498, 499 and 499', 499' are connected to a motor unit 5| 4. This unit, in the illustrative form here shown, comprises a .pair of opposed series connected field windings 5H and 5I2, connected in series with leads 499 and 499, and a pair of series connected field windings 5|3 and 5i4 connected in series with leads 498 and 499. As here shown, .the pairs of eld coils 5| |-5|2, and 5|3-5M are disposed at 90 from one another, all being radially disposed with reference to the axis of rotation O of the motor armature. As here shown, adjacent coils 5|2 and 5|4 are wound and connected so that their north poles are at their inner ends, while coils 5H and 5|3 are so wound and connected that their south poles are at their inner ends.

The motor armature A consists of a winding 529, wound to provide a north pole at one side of the armature and south pole at the other, as indicated. Opposite ends of the winding are connected yto direct current supply leads 524 and 525. The motor armature is normally positioned with its north pole side mid-way between the north poles at the inner ends of coils'5l2 and 5|4, and with its south pole side between the south poles at the inner ends of coils 5| I and 5|3.

It will be evident that the motor armature will tend to rotate in a clockwise direction under the inuence of the fields produced by coils 5I2 and 5| and will tend to lrotate in a counter-clockwise direction under the influence of the fields produced by coils 5|3 and 5|4. The armature will accordingly under all conditions seek and take a position dependent upon the relative strengths of the currents flowing in said two pairs of field coils.

The armature of motor 5|!) has a range of operation of something less than 90 of rotation; accordingly, since a rotation of as much as perhaps 300 is desired to 'be imparted to the fader shaft, step-up gearing arrangements are ernployed. Thus, as here indicated, a gear 530 on motor shaft 523 drives a smaller gear 53| on a shaft 532.

Shaft 532 is adapted to be drivingly connected by magnetic clutch 533 with fader shaft 40. The winding of magnetic clutch 533 is connected by leads 534 and 535 to the 4movable arm 536 and stationary contact 531, respectively, of control switch 424. Contact is made between said. arm 536 and contact 531 when the switch is moved toward the right, to take position. A battery 538 is included in one of the leads leading to magnetic clutch 533, as indicated.

The operation Kof the system may now be understood. It is assumed that a series component 4sound record films I0 have been prepared, and that the speech, sound effects, or music recorded on said films have been so synchronized that when the several films are synchronously driven, the sounds recorded thereon may be reproduced in proper synchronous relation to one another. These lms I are then run in the system of Fig. 1, each film being driven by its synchronous motor energized from the central distributing system I2. Switch 36 is open, so that nothing will be recorded at this time, switch 424 is moved to the left, to select position, and the magnetic recorder is operated so as to drive tape 430 from supply reel 43| to take-up reel 432 in synchronous relation with the drive of the sound films l0. The sound records on the several sound lms |0 are now all reproduced as electrical sound currents within circuits I6, and these currents fiow by way .of fader controlled circuits 34 and common mixer circuit I8 to amplifier I9, the output of which is reproduced by monitor horn 25. 'I'he mixer operator listens to the sound coming from the records |0 as reproduced by horn 25, and from time to time rotates the fader shafts 40 by means of knobs 39a, so as to adjust the fader `control arms 3| of the several faders 30 and thereby change the volume level of the several components of the reproduced sound as he may think desirable.

The rotation of each shaft 40 turns the corresponding arms 400 and 40| of resistors 402 and 403, respectively. As previously described, rotation of a fader shaft 40 in one direction increases the resistance of one of the resistors 402 and 403 as it decreases the resistance at the other, so that the amplitudes of the low frequency and high frequency oscillation currents flowing from oscillators 405 and 406 are simultaneously varied in opposite directions. That is, said currents are varied complementarily to one another.

Switch arms 425 and 426 being moved to the left, or to select position at this time, the two oscillator currents as thus complementarily controlled by resistors 402 and 403, are amplified at 4|9, and then fiow by way of switch 424 to recording coils 429, the two currents, both low and high frequency, thus being recorded on magnetic tape 430.

At the end of the run, tape 430 is wound back from take-up reel 432 to supply reel 43|, and switch 424 is shifted over to the right, to take position. Oscillators 405 and 406 are then out of the circuit, and coils 429 are connected by way rof' switch 424 to input amplifier circuits 442. Contact is also made between switch arm 536 and contact 531, energizing magnetic clutch 533, thus coupling motor shaft 523 with fader shaft 40.

The films I0 of Fig. l are run back to starting position, and film I0 and tape 430 are then synchronously driven in a forward direction, care being taken that the films I0 and tape 430 start synchronously. The run now to be made is simply -for the purpose of checking the correctness of the amplitude changes which were manually effected duringthe preceding run, and recording switch 36 is therefore still left open at this time.

The high and low frequency complementarily varying current waves recorded on the tape 430 of each automatic unit are now reproduced within coils 429, are amplified at 443, and are divided at filters 441 and 448, so that the low frequency current wave flows exclusively in circuit 459, and the high frequency current wave flows exclusively in circuit 453. These current waves are amplified at 460 and 462, respectively, are rectified at 46| and 463, respectively, and fiow in circuits 498, 499 and 498', 499 as complementarily varying direct current waves, the 50 and 500 cycle oscillator frequencies being removed at net works 500 and 50|. It will be evident that these current waves represent the complementary resistance changes at resistors 402 and 403 during the manual control run vof sound films I0.

'Ihese complementary varying currents then fiow in the opposed pairs of motor field coils 5|2 and 5| 3, 5| 4, so that the opposing rotative forces on motor armature A likewise vary complementarily, with the result that said armature shifts its position first one way and then the other from its mid position between said sets of eld coils. For each pair of values of the complementary currents fiowing in the opposing eld coils, there is a position at which the opposing forces on armature A are in balance, and the armature therefore rotates back and forth under the control of the complementary current waves.

This movement of motor armature A is transmitted by way of shaft 523 and 532 and magnetic clutch 533 to fader shaft 40, the drive ratio at gears 530 and 53| being such that the rotation of fader shaft 40 so received from the motor armature duplicates the original manually effected rotations or movements of shaft 40 during the initial manually controlled run of sound films I0.

It will now be evident that as sound films |0 are audibly reproduced by way of circuits I6, 34, |8, amplifier I9 and circuit 26, the volume level of reproduction of the several records will be controlled by faders 30 under the automatic control of the records on the magnetic tapes 430. The volume changes manually effected during the initial manually controlled run may therefore be checked by the mixer before any recording on film is made. It will be evident that a single sound film I0 may thus be reproduced and checked in the manner here described, or a plurality of such sound films |0 may be run together with their several faders all under individual automatic control and the composite effect noted by listening to the reproduction from horn 25.

If a given sound is recorded at an undesirable volume level, the corresponding section of the record on tape 430 may be modified. To do this, the tape is rewound until the record portion to be modified is just before erasing magnet 434. Switch 436 is then closed, and the tape run forwardly, the erasing current flowing in the magnet 434 erasing the previously made record on the tape. The tape is of course stopped when the section of the record to be modified has passed the magnet 434 and been erased. Switch 424 then being thrown to select position, and the tape having been rewound the proper distance, a

new position or set of positions of fader arm 3| may be recorded on the tape. Thus by this procedure the record on the tape may be modified in parts to correct earlier mistakes.

When the records on the tapes of all automatic fader control units are deemed to be satisfactory, the recordation on nlm 22 may be made. The several sound recordfiilms l0 are then to be synchronously driven with the fresh negative nlm 22 on which the new composite sound record is to be recorded. Switch 36 is closed, switch 424 of each automatic unit is again in take position, and the magnetic tapes 430 having been rewound and the films I0 and 22 all being at their starting positions, the main switch controlling the synchronous motor distributer system is closed. This run is carried out in the same way as the previously described trial run, except that theswitch 36 is closed and the final recording on nlm 22 is accordingly made. Thus the sound records on the several sound lms l0 are reproduced-as electrical sound currents Within circuits I6, and these currents flow by way of fader circuits 34, and common mixer circuit I8 to amplifier I9. The output current from the amplier flows to recording means 2l, producing a composite sound record on film 22. 'I'he sound current flowing in each mixer circuit 3d is controlled in amplitude by its corresponding fader 30, which in turn is under the automatic control of the pre-estab-` lished fader-position recording on tape 43E). Thuseach component sound current going into mixer circuit I8 is controlled in volume by its own automatic control unit in exact accordance with the manual volume level adjustments which were previously made during the fselect run for the corresponding sound iilm Il), and which are represented on the fader-position record of that automatic control unit.

The automatic system thus duplicates each manual volume level adjustment which was made during the select run, eliminating the possibility of mistakes in judgment in effecting volume level changes in the nal recording on film, and therefore eliminating entirely retakes on lm.

It will thus be understood that a record is made on the record element 430 of each automaticunit of the manually eected movements of thevolume control fader 30 of that unit during the manually controlled run of sound films I0, and that in vsubsequent runs of lms IIJ, both for trial purposes (withswitch 36 open), without recording on nlm, and in the nnal run duringwhich a final recording is made on iilm22, said record 43)` produces electrical currents which control an electric motor device drivingly connected to the same volume control fader for automatic duplication of the manual volume adjustments made during the initial or manually controlled run of sound lms I0.

We have now illustrated and described certain specific illustrative means for carrying our invention into effect; it is to be understood, however, that the disclosure given is for illustrative purposes only, and that various changes, modifications, and substitutions may be made Without departing from the spirit of our inventionlor of the appended claims.

We claim:

l. The herein described method, that comprises producing an electrical sound current-from an original sound record, audibly reproducing said sound current, manually effecting desired amplitude modicatons in said sound current by reference to such audible reproduction, making a record of suchamplitude modifications, again producing an electrical sound current from said original sound record, repeating the same amplitude modifications in said electrical sound current under the control of said amplitude modication record, and making a sound record of said Mamplitude modified electrical sound current.

2. The herein described method, that comprises producing an electrical sound current from an original sound record, audibly reproducing said sound current, manually controlling the amplitude level of the sound current as desired by reference` to such audible reproduction, simultaneously making a record of the manually effect- -ed control operations, again producing an electrical sound current from said original sound record, effecting a control of the amplitude level of said sound current by use an electrical current produced by simultaneous reproduction of said last mentioned record, and making a sound record of said amplitude controlled sound current.

3. In a sound record dubbing system having a fader involving a movable manually operable control member adapted to control the amplitude of an electrical sound current, means for automatically controlling said fader comprising means for recording manually effected movements of the fader control member, and means controllable by the record so made for subsequently automatically effecting similar movements of said fader control member.

4. In a sound record dubbing system having a fader involving a movable manually operable control member adapted to control the amplitude of an electrical sound current, electric circuiting carrying two separately controllable electric currents, means for complementarily varying said currents in accordance with manually eiected operation of said fader control member, means for recording said electric currents', means for subsequently reproducing said electric currents from the records so made, and electromagnetic means controlled by said two currents for operating the fader control member to reproduce the previously effected manual control operations of saidmember.

5. In a sound record dubbing system having a fader involving a movable manually operable control .member adapted to control the amplitude of an electrical `sound current, electric circuiting 4carrying two separately controllable electric currents, means for complementarily varying said currents in accordance with manually effected operation of said fader control member, means for recording said electric currents, means for subsequently reproducing said electric currents from the records so made, and electromagnetic means controlled by lsaid two currents for operating the fader control member to duplicate the previously `effected manual control operations of said member, said electromagnetic means comprising a field winding adapted to carry one of said currents and another field winding adapted to carry the other of said currents, said windings being disposed with the like magnetic poles in opposition to one another, a movable armature having a current carrying winding and arranged with one of its poles between and acted upon by said field winding poles, and a coupling between said armature and the movable control member of said fader.

.6. In a sound record dubbing system having a faderinvolving a movable manually operable control member adapted to control the amplitude of an electrical `sound current, electric circuiting carrying two separately controllable electric currents,means for complementarily varying said currents in Yaccordance with manually eiected operation of said fader control member, means for recording said electric currents, means for subsequently reproducing said electric currents from the records so made, and electromagnetic means controlled by said two currents for operating the fader control member to duplicate ther previously effected manual control operations of said member, said electromagnetic means comprising a field winding adapted to carry one of said currents and another field winding adapted to carry the other of said currents, said windings being disposed with like poles in opposition to one another, a movable armature having a magnetic pole between and acted upon by said field winding poles, and a coupling between said armature andl the movable control member of said fader.

7. In a sound record dubbing system having a A fader involving a movable manually operable control member adapted to control the amplitude of an electrical sound current, a pair of oscillators, one of higher frequency than the other, electric circuiting carrying electric currents generated by said oscillators, means for complementarily varying said oscillator currents in accordance with manually effected operations of said fader control member, means for recording said oscillator currents, means for subsequently reproducing said currents, means for rectifying said currents, and electromagnetic means controlled by the rectified currents for operating the fader control member in a manner to reproduce the previously effected manual lcontrol operations of said member.

8. In a sound record dubbing system having a fader involving a movable manually operable control member adapted to control the amplitude of an electrical sound current, a pair of oscillators, one of higher frequency than the other, electric circuiting carrying electric currents generated by said oscillators, means for complementarily varying said oscillator currents in accordance with manually effected operations of said fader control member, means for making a single record of said oscillator currents, means for reproducing an electric current from said record, a pair of filters for separating the current corresponding to the higher frequency oscillator from' the current corresponding to the lower frequency oscillator, means for rectifying each of the resulting currents, and electromagnetic means controlled by the rectified currents for operating the fader control member in a manner to reproduce the previously effected manual control operations of said member.

9. In a sound record dubbing system having a fader involving a movable manually operable control member adapted to control the amplitude of an electrical sound current, a pair of oscillators, one of higher frequency than the other, electric circuiting carrying electric currents generated by said oscillators, means for complementarily varying said oscillator currents in accordance with manually effected operations of said fader controlmember, means foi` making a single record of 'said oscillator currents, means for reproducing an electric current from said record, a pair of filters for separating the current corresponding to the higher frequency oscillator from the current corresponding to the lower frequency oscillator, means for rectifying each of the resulting currents, means for filtering out the oscillator frequencies from the rectified currents, thereby producing a pair of unidirectional complementarily varying electric currents, and electromagnetic means controlled by the last mentioned currents for operating the complementarily varying said oscillator currents in accordance with manually effected operations of said fader control member, means for making a single record of said oscillator currents, means Y, for reproducing an electric current from saidy record, a pair of filters for separating the current correspondingrtothe higher frequency oscillator from the current corresponding to the ilower frequency oscillator, means for rectifying each of the resulting currents, means for filtering out the oscillator frequencies from the rectified currents, thereby producing a pair of uni-directional complementarily varying electric currents, and electromagnetic means controlled by the last mentioned currents for operating the fader conf trol member to duplicate the previously effected manual control operations of said member, said electromagnetic means comprising a field winding adapted to carry one of said rectified filtered currents and another -iield winding adapted to carry the other of said rectified filtered currents, said windings being disposed with like poles in opposition to one another, a movable armature having a current carrying winding and arranged with one of its poles between and acted upon by said field winding poles, and a coupling between said armature and the movable control member of said fader.

1f1. In a sound record dubbing system having a fader involving a movable manually operable control member adapted to control the amplitude of an electrical sound current, a pair of oscillators, .one of higher frequency than the other, electric circuiting carrying electric currents generated by said oscillators, means for complementarily varying said oscillator currents in accordance with manually effected operations of said fader control Ymembenmeans for making a single record of said oscillator currents, means for reproducing an electric current from said record, a pair of filters forV separating the current corresponding to the higher frequency oscillator from the current corresponding to the lower frequency oscillator, means for rectfying each of the resulting currents, means for filtering out the oscillator frequencies from the rectified currents, thereby producing a pair of unidirectional complementarily varying electric currents, and electromagnetic means controlled by the last mentioned currents for operating the fader control member to reproduce the previously effected manual control operations of said member, said electromagnetic means comprising a field winding adapted to carry one of said rectified filtered currents and another field winding adapted to carry the other of said rectified filtered currents, said windings being disposed with like poles in opposition to one another, a mov- -able armature having a magnetic pole between and acted upon by said field winding poles, and a coupling between said armature and the movable control member of said fader.

HERMAN S. HELLER.

FRANK M. KENNEDY.

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