US2247554A - Method of recording and reproduction of sound and apparatus therefor - Google Patents

Description

y 1, 1941- w. E. GARlTY ETAL 7,554

METHOD OF RECORDING AND REPRODUCTION OF SOUND AND APPARATUS THEREFOR med April '12, 1939 s Shasta-Sheet 1 A ORNEY.

IN VENTORS J y w. E. GARITY Em. 2.247554 METHOD OF RECORDING AND REPRODUCTIONOF SOUND AND APPARATUS THEREFOR Filed April 12. 1959 5 sheets-sheep 2 j! as (4,4 0 F2 3 j sa E3 E3 I 1| s ,/F 1 '5- 36 E E ATTORNEY.

July'l, 1941. w. 'n' ETAL 2,247,554 METHOD OF RECORD ING AND REPRODUCTION. OF SOUND'AND APPARATUS THEREFOR Filed April 12, 1939 5 Shuts-Sheet 3 Our/ ur Mumiml1ummwils imm.

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' A ORNEY.

INVENTORS July 1, 1941; w. E. GARITY EVTALI" 755 METHOD. OF RECORDING AND REPRODUCTION OF SOUND AND APPARATUS THEREFOR 5 Sheets-Sheet 4 Filed April 12, 1939 WILLIAM E GAR/TY Jo/m' N. 6'. Hnw/v/vs INVENTOI.

ATT RNEY J y 1 1 w. E. GARITY arm. 2,247,554

METHOD OF RECORDING AND REPRODUCTION OF SOUND AND APPARATUS THEhEFOR Filed April 12, 19,59. 5 Sheets-Sheet 5 SPEAKER INVENTORJ (2? M% I ATEORNEY.

Patented July 1, 1941 METHOD OF RECORDING AND REPRODUC- TION OF SOUND AND APPARATUS THERE- FOR William E. Garity and John N. A. Hawkins, Los Angeles, Calif., assignors to Walt Disney Productions, Los Angeles, Calif., a corporation 01' California Application April 12, 1939, Serial No. 267,416

23 Claims.

The present invention is directed to means and methods of manipulating the transmission characteristics of networks or circuits used in recording and reproduction of sound. In its simplest form it may be stated that the method of this invention contemplates the introduction of attenuation into one or more circuits or channels of a system and in simultaneously decreasing attenuation in other channels or circuits of such system, whereby the sum of the attenuations in the circuits or channels, at any given time, when attenuation is expressed as power ratio, is a constant. Means are provided whereby attenuation can be introduced or removed in a facile manner and accomplish the desired results. When, for example, two or more inputs contribute equal power or level, then the method or means permit smooth fading or transition from one to the other of said sources without change in the output power or level. In the event differences in level exist between two or more sources, then the present invention permits the smoothest possible transition from one to the other of such sources with change in level smoothly distributed over the entire fade or transition.

In the recording, rerecording and reproduction of sound, occasions often arise where it is highly desirable to fade from one source to another or from one reproducer to another. Attempts to accomplish this in the past have involved the use of separate mixing gain control devices, or attenuators. Since equal and inverse linear or rotational movements of either linear or logarithmic types of variable attenuators can not effect constant level transition from one sound source to another, it is virtually impossible for the operator to produce a transition or fade Without change in level. For example, inserting an attenuation loss of 0.6 decibel (between 0.6 and 1.2) requires a corresponding reduction of loss in the other leg of the network of 2.7 db. (from 8.9 to 6.2) in order that the output level be maintained constant, while a further insertion of ad-- ditional 0.6 db. loss requires a reduction of only 1.5 db. in the other leg. These difiiculties are overcome by the methods and devices of this invention, as will become apparent from the detailed description given hereinafter. Various adaptations and novel uses are made possible by the methods and devices embraced by this invention and examples are embodied in such description.

One of the objects of the invention, therefore, is to provide a method of manipulating the electrical transmission characteristics of networks,

channels or circuits whereby two or more sources or inputs can be supplied to a single output, either singly or together in any desired proportion, without appreciable change in level or power.

Another object is to provide a method of manipulating the electrical transmission characteristics of networks, channels or circuits whereby a single source or input can be supplied to one or more outlets, selectively or concurrently, without material change in level or power.

A further object is to disclose and provide methods of manipulating electrical transmission characteristics of junction networks or circuits whereby a number of diiierent eifects can be obtained.

An object, also, is to provide means and combinations of elements adapted to introduce and remove attenuation into a channel or channels in such manner that the level is not materially altered.

Other objects will become apparent to those skilled in the art from the following detailed description of illustrative forms of apparatus and modes of operation.

In the appended drawings:

Fig. 1 is a diagrammatic representation of one arrangement of elements in which the methods and devices of this invention may be employed.

Fig. 2 is another diagrammatic representation of an arrangement of elements which may be used in carrying out the method of this invention during recording.

Figs. 3 and 4 are diagrammatic representations of arrangements in which the method of the inventions may be used during reproduction of sound.

Fig. 5 is a diagrammatic representation of an arrangement of elements for use in rerecording sound.

Fig. 6 is a wiring diagram of one form of device embodying the inventions herein disclosed.

Fig. 7 is a wiring diagram of another form of device embodying the inventions.

Fig. 8 is a front view of a device embodying the wiring diagram of Fig. 7.

Fig. 9 is a rear view of the device shown in Fig. 8.

In Figs. 10 and 11 are plan and side elevations (partly broken away) of the device shown in schematic form in Fig. 6.

Figs. 12 and 13 are wiring diagrams of circuits embodying the devices of this invention.

Fig. 14 is a wiring diagram of another arrangement of elements embodying the invention.

Fig. 15 is still another simplified diagram of an arrangement adapted for use in the methods of this invention.

Reference will be had hereinafter to attenuators or networks whose insertion loss preferably remains constant with changes in frequency or whose attenuation loss varies with frequency in some desirable manner. Attenuators may be of the series impedance type, shunt impedance type, full series type, full shunt type, T type, bridged T type, lattice type or ladder type. For use in sound recording and sound reproducing networks or channels it is desirable to employ attenuators of substantially constant impedance in both directions and the T, bridged T, lattice and ladder types are preferred for this reason. The ladder type will be specifically referred to hereinafter as splendid results have been obtained by its use. Moreover, attenuation can be obtained by varying either a resistance, inductance or capacity, or bya combination thereof. In the specific examples given hereinafter, attenuators of the bridged T and ladder types will be described, these atenuytors employing a varying resistance.

Moreover, it is to be understood that the type of attenuator employed will vary somewhat with the conditions under which the attenuator is used. If, for example, attenuation is being accomplished at low levels (where power is not expensive), the ladder type is eminently suited.

The bridged T type is often more effective where the operation is being carried out at higher levels.

By referring to Fig, 6 of the appended drawings, a simple form of device embracing this invention will be seen in circuit or diagram form. Input terminals of one channel are indicated at l and l and the input terminals of another channel are shown at 2 and 2'. Output terminals are indicated at 3 and 3. A ganged differential attenuator of the double ladder type is generally indicated at 4. Each attenuator comprises a sequence of series impedances or resistances indicated at Z1, Z2, Z3, etc., provided with contacts .or taps generally indicated at 5 and adapted to be connected with a switch arm 6 attached to the line 1 leading to the input terminal I. A fixed impedance or resistance Z is carried in the line 7. Shunt impedances,v generally indicated ,at 8, are also provided, these shunt impedances being connected to a grounded line 9 which con- :i'

nects terminals l and 2. The input terminal 2 is connected as by line 10 with the switch arm 6 which is selectively and controllably movable into contact with the various contacts 5'.

The attenuator output may then be connected as by leads II and [2 to a transformer T whose output is connected to the output terminals 3 and 3.

single control, impedance is introduced into one .a

circuit or leg of the network and simultaneously eliminated or removed from the other leg of the circuit. For example, attenuation may be added to the input I and decreased in input 2 and when the taps 5 and 5' are properly arranged, the sum of the attenuations in the completed circuit, expressed as to power ratios, will be maintained a constant at all times. In the event the power input through terminals I and l is equal to the power input through the terminals} and 2, then the power output can be maintained constant while a gradual change is made from I to 2. At any time during the change an approximate hyperbolic relationship will exist between the attenuations in the two legs of the network, and

ator contacted by arm 6.

the two losses in the two ganged variable attenuators are related by the formula:

where A and B are the respective losses in the two variable legs of the differential mixer network of this invention, expressed in decibels.

The above equation may be graphically represented by a hyperbolic curve symmetrical about the 3 decibel loss-point. In one extreme position of the attenuators the loss through one of the variable attenuators is at a minimum while the loss through the other network is infinite. In the other extreme position, the reverse is true. Half way between the two extreme positions the loss through each of the two attenuators equals the minimum attenuator loss plus 3 decibels. The following table gives the relationships, assuming that there are eleven steps or taps 5 on an attenuator made in accordance with the above disclosures:

E En PA lu Stop Loss A Loss 13 E Db. Db.

0 Infinite 1.0 0.0 1.0 0.0 0.6 8.9 .93 .30 .87 .13 1.2 6.2 .87 .40 .76 .24 1.8 4.7 .81 .58 .60 34 2.4 3.7 .76 .65 .58 .43 3.0 3.0 .707 .707 .5 .5 3. 7 2. 4 65 .76 .43 .38 4.7 1.8 .58 .81 .34 .60 6.2 1.2 .49 .87 .24 .76 8. 0 0. 0 36 .93 l3 87 Infinite 0 0 1. 0 0 l. 0

The above table does not include any fixed and constant insertion loss, such as the minimum insertion loss of approximately 6 decibels occurring in a ladder attenuator. When and if minimum insertion loss is present, it merely adds a constant to loss A and loss B, the sum of whose attenuations, expressed as power ratios, is also a constant.

It is to be noted that in the above table equal decibelincrements of 0.6 db. occur between 0 and -3 db. The increments between 3 and infinity are not equal decibel increments but are correlated to the increments between 0 and 3. The column entitled Loss A represents the loss in ,one of the attenuators such as, for example, the

one operated by the switch arm 6, whereas the column entitled Loss B represents the corresponding loss which is introduced by the attenu- The two arms 6 and 6 are mechanically coupled together so that insertion of attenuation into the line I automatically removes a predetermined amount of attenuation from the line H). It is to be noted that the sum of the power ratios at any given time equals a constant, namely, 1.

In certain forms of devices made in accordance with this invention the increments might be equal power steps or equal voltage steps and ,the specific form referred to hereinabove and expressed in tabularform is simply illustrative. Since in most instances two or more inputs (oroutputs) are-connected by means of the differential mixer or attenuator with but a single output (or input), the present invention may be stated to pertain to a four terminal network or circuit, since terminals I and'Z are grounded,

leaving active terminals l, 2,3 and 3.

In Fig. 7 another form of arrangement is shown. Input terminals are again identified as I and I and 2 and 2. An input gain control device is connected to the terminals such input gain control device being generally indicated at I4. A similar input gain control device is connected across the input channel 2-2' as indicated at I5. The devices I4 and I5 as diagrammatically shown in Fig. 7 are ladder type attenuators which supply the terminals 2|, 2|. 22 and 22' of a differential mixer network of the character shown in Fig. 6. The output of the transformer T is connected to a master gain control device, indicated at 16. The switch arm 6 is shown as moving between the terminals 5 and a ring II.

By referring to Figs. 8, 9, 10 and 11 it will be seen that the wiring diagram of Fig. 7 embodied in physical form comprises a panel carrying the differential mixer network 4, the input gain control devices I4 and 5, the transformer T and the master gain control device It. Input contacts, together with associated cables, are indicated at I and 2. The output terminals are contained within the output plug I9. A knob 24 operates the brush arms 6 and 6' within the diiferential' mixer. The knob 26 operates the switch arm of the master gain control I6 whereas the knob operates the switch arm of the input gain control device I5. The knob 24 is connected to the shaft 2'! (Figs. 10 and 11) which carries a brush block 28. The brush block carries the brush arms 6 and 6', thereby permitting both brush arms to be moved simultaneously.

It is to be noted that the brush arm 6 has one end 6a. contacting the contacts 5 whereas the ent by considering some of the uses therefor. For I example, as shown in Fig. 1 a camera, generally indicated at 30, may be directed upon a scene, sound from such scene being picked up by microphones M1 and M2 connected by lines I and 2 to amplifiers. These amplifiers supply current to an arrangement such as: is shown in Fig. 7 and including the gain control devices I4 and I5 and the differential mixer network generally indicated at 4. A master gain control device is indicated at I6 and supplies current to a recording device R. During the taking of the scene, it may be desirable to first photograph the entire scene and during photography perambulate or truck the camera toward a smaller portion of the scene immediately under the microphone M1 so as to obtain a close-up of the action taking place in that particular portion of the scene. During the taking of the general scene, sound from both microphones M1 and M2 should be uniformly combined and recorded whereas during the later sequence When a close-up of action under the microphone M1 is being taken, all of the sound should be collected by M1 and none by microphone M2. The level should be the same, however. It will be obvious to those skilled in the art that this can be maintained by manipulation of the differential network 4 since attenuation loss may be introduced into the circuit 2 while simultaneously attenuation is eliminated from circuit the output level being maintained constant. The manipulation of but a single dial or knob thereby creates a fade without change in output level. Thus the change in acoustic perspective matches the change in visual perspective obtained by the movement of the camera, Without affecting the recorded level.

By referring to the diagram of Fig. 3, it may be desired to reproduce sound from two recordings carried by F1 and F2 and to fade from one to the other. These circuits, again indicated by the numerals I and 2, may include amplifiers, variable attenuators I4 and I5, a differential mixer network 4, a master attenuator I6, a power amplifier, and the reproducing horn 3|. After the attenuators |4, I5 and I6 have been set, manipulation of the differential mixer network'4 permits gradual fade in from one sound source to another without change in level of the speaker or reproducer 3|.

In another adaptation of this invention, it may be desired to produce a sound record and emphasize sound from one source, as forexample where a symphony orchestra is being recorded and it is desired to emphasize the work of a soloist with such orchestra. A plurality of microphones may be arranged for the purpose of picking up sound from the orchestra whereas a separate microphone, such as M2 (Fig. 2) is used for the soloist. The various input circuits leading to the orchestra microphones may be combined and fed into a differential mixer network indicated at 4, which is also connected to the cir cuit leading to the soloist microphone M2. Manipulation of the differential mixer network 4 will permit emphasis upon the soloist without change in output level supplied to the recorder R.

Very often during rerecording a number of separate sound records are combined, desired modulation being introduced for the purpose of blending the various sound records. In some instances it is desirable to introduce reverberation as, for example, to create the effect of distance or large halls. The differential mixer network of this invention can be used to advantage in such rerecording and Fig. 5 illustrates one form of arrangement embodying such mixer. Sounds may be reproduced from records F1, F2 and F3. The record on F3 may be the only one which at given points should be modified to introduce reverberation. The output of the corresponding amplifier, therefore, is divided into the lines 32 and 33. An additional amplifier 34 may be introduced into the branch circuit and supply a reproducing unit or horn 35 positioned in a reverberation chamber 36 also containing a microphone M associated with an amplifier, a gain control device I5 and the differential mixer 4. The output 33 may also pass through an attenuator I4 and then into the differential mixer 4. Outputs from records F1 and F2 may be suitably amplified and then supplied as by lines 38 and 39, suitably attenuated as by variable attenuators 40 and 4| to the main recording channel 43 having a master gain control 44. In the arrangement shown, adjustment of the differential mixer 4 permits the recording of either altered or unaltered sound from. the record F3 and any desired proportion of the sound recorded on F3 can have reverberation or brilliance added thereto without causing undesired changes in output level.

Figs. 12 and 13 are wiring diagrams representing additional arrangements of elements in which a differential mixer can be employed to advantage. In Fig. 12, for example, input terminals 5| mixers 4 and 4".

and represent one channel whereas input terminals 52 and 52' represent another channel. Input terminals 5i and 52 may lead as by lines 54 and 55, respectively, to switch arms 6 and 6 of a differential mixer 4 whose output, indicated by the lines 5 may pass through a transformer and then be supplied to a reproducing unit attached to the terminals 53 and 56. The lines 54 and 55 may also be connected to the switch arms of another differential mixer 4' whose output is supplied to the terminals 5'! and 51' of another speaker or reproducing unit. By means of the arrangement here shown, both speakers may be caused to reproduce from either one of the input channels or from both of said input channels. One of the reproducing units may be reproducing from one input channel while the other is reproducing from the other. The two differential mixers 4 and 4 may be mechanically coupled if desired. Either speaker can smoothly fade between either sound source.

A rather similar arrangement in simplified form is shown in Fig. 13, the arrangement in Fig. 13 differing only in that the common side of each differential mixer faces a sound source and not a speaker. Either input can smoothly fade between the two outputs. The inverse coupling of the attenuators is graphically indicated, and although T pads are shown, any type of attenuator may be used.

It is to be remembered that the terms inpu and output as used herein are exemplary only and in many instances the arrangement shown can efiectively operate in reverse, 1. e., current can be supplied at the so-called output terminals.

Fig. 4 of the drawings is a diagrammatic representation of a method of selectively directing the output of a record F1 from a reproducer to any one or more of a plurality of reproducing heads or horns and in switching from one horn to another or from one set of horns to another in a gradual and smooth manner without change in level. Numerous novel effects can be obtained in this manner. The various horns or reproducing elements may be located at different points in the theatre. For example, reproducers R1 and R2 (Fig. l) may be located on left front and left rear positions in a theatre whereas R3 and R4 may be located on the right front and right rear portions of a theatre. Sound could then be reproduced from the front horns only (R1 and R3) or from the rear horns (R2 and R4), or both pairs. In order to create another effect, R1 and R2 representing the left side of the theatre, could carry the brunt of the load, or in order to create the effect of sound moving from left to right, the output could be gradually switched from the horns R1 and R2 to the horns R3 and R4. All of the horns could be employed at certain points in the photoplay, if the nature of the subject matter makes it desirable. In order to emphasize ac tion or a rapidly approaching sound source, the output of the record F1 could be directed from the two front horns R1 and R3 into the rear horns R2 and B4. In order to create the effect of a sound floating around the theatre, the output of the record F1 could be made to travel from E1 to R2, to R4 to R3, thereby completing a circuit of the entire theatre.

These effects as shown in Fig. 4 could be obtained by the use of a differential mixer indicated at 4, the output of such differential mixer being then again modified by the differential The controls on the mixers.

4' and 4" can bemechanically interconnected so as to cause simultaneous modulation by both ofthem.

Fig. 14 is a wiring diagram which involves a further development of the general system indicated in Fig. 4. 6| indicates the input from an audio amplifier circuit. The unit generally indicated at 64 is a differential mixer or differential dividing network which, as shown, conarms on all of them move simultaneously. Such mechanicalcoupling is indicated by the dotted lines 62, and simultaneous movement is illustrated as an up and down movement. In Fig. 14 the differential dividing network 6-? shows the switch arms in intermediate position, namely, on the three decibel loss step. As a result, the audio input is being supplied in equal increments to the transformers T1 and T2. By moving the contacts of the differential mixer network downwardly, the entire audio input would be directed toward the transformer T2 whereas infinite loss would be introduced into the circuit leading to transformer T1. Exemplary resistance values are given in Fig. 14.

The elements 65 and 6B consist of two dividing differential networks which, as shown, are also of the bridged T type. Each of these two mixer devices includes two variable pads, each pad having two sets of steps or contacts, suitable in number. Again, the diagram shows only the three decibel step between zero and infinite loss on each set of contacts. The four contacts on each of the devices 65 and 25 are mechanically coupled together so as to move in unison as indicated by dotted lines 83 and 83. In the position shown, infinite loss is introduced into the upper channel of 65 and into the upper channel of the device 66 whereas zero loss is being introduced into the lower channels of each device.

The diagram of Fig. 14 is capable of selectively supplying signal current to an arrangement ofsix horns or reproducing units. For purposes of simplification, these have been specifically identified in the diagram as left front, left rear, left center, right front, right rear and right center. Such identification refers to the approximate position of the horn in a theatre. As shown in Fig. 14, the left and right center horns are handling the entire output of the audio input, the output being equally divided between the two front horns by reason of the setting of the mixer 64.

Attention is called to the fact that each of the devices 65 and 66 is provided with a movable "switch arm 61 and 61' which cooperates with a split ring, generally indicated at 68 and 68'. These two switch arms 61 and 61 can be mechanically coupled to the various switch arms of .the pads in devices 65 and 66 so that as the switch arm is moved on the top pad of device 65 and attenuation is increased from zero to v, infinity, the switch arm 61 maintains its contact with that portion of the ring 68 which is connected to the left front horn, but as the switch arm continues to move downwardly, attenuation in the circuit is gradually decreased and the switch arm 6'! now contacts the bottom half of the split ring 68 and thus connects the circuit with the left rear horn. The switch arm 61 therefore permits instantaneous switch over from one horn to another and when such switch arm is mechanically coupled with the differential attenuators, a smooth transition from front to back of the theatre can be attained with a single continuous movement of but a single control. It is to be noted that at an intermediate position of the devices 65 and 66 the center horns will be supplied with the amplified sound current while the front and rear horns are now quiet since infinite loss has been introduced in their correlated circuits.

Fig. 15 discloses a modification in which an attenuator 10 operates on the input terminals 7|, 12 whereas the attenuator H operates on the input terminals l3, 14. The outputs of the two attenuators are combined in parallel instead of in series, output terminals being indicated at 15, 16. The terminals l2, 13 are grounded. The two variable attenuators 10 and TI are mechanically coupled together inversely and such inverse coupling is diagrammatically indicated.

This parallel arrangement necessitates a bridging input on the amplifier connected to the output terminals 15, 16, as each side of the network provides a constant resistance termination for the other side and no further termination is necessary or even allowable. In cases where the networks are combined in series, as in Figs. 6 and 7, the benefits of an external termination can be realized. One of the main benefits is that higher gain is obtainable from the succeeding amplifier when the amplifier provides the termination. A bridging amplifier generally has a lower gain than a similar amplifier whose input circuit properly terminates its signal source.

Very spectacular sound effects may be attained by the use of these devices somewhat along the lines indicated in describing Fig. 4. The methods and devices of this invention open an entirely new field of entertainment and permit the creation of spectacular efiects for the emphasis of dramatic action, solo work, choral work, and the like.

In order to produce a smooth fade or transition from one source to another without apparent steps in intensity or level, it has been found that increments of loss of not more than about 1 db. should be used in the range between and 3 db. Those skilled in the art will perceive that by suitably spacing the contacts and by utilizing the bridging effect of the brush arm 6, the effect of attenuation increment can be made smaller than the attenuation increment between adjacent contacts 5. Generally, in order to accomplish a smooth change from one source to another, the sum of the attenuations in the circuits, expressed as power ratios, should be constant at all times. In operating in this manner, it has been found that the attenuation increments between contacts at the high loss end of a series should be greater than and different from the attenuation increments between contacts at the low loss end of the series of contacts in an attenuator. This is clearly brought out in the table of an exemplary form given in the first part of the specification hereof.

We claim:

1. A Junction network including two branch legs and a common leg, an attenuator in each branch leg, said two attenuators being connected to a common ground, each of said attenuators having a series of contacts, the attenuation increment between contacts at the high loss end of the series being greater than and different from the attenuation increment between contacts at the low loss end of the series, a movable element cooperating with a series of contacts on each attenuator, each of said movable elements being connected to a branch leg, said movable elements being operably associated to vary inversely, the attenuation increments of said attenuators and the association of said movable elements being correlated so as to produce a substantially constant total attenuation, expressed as sum of power ratios, along the series of contacts.

2. A four terminal junction network including two attenuators connected to a common ground, each of said attenuators having a series of contacts, the attenuation increment between contacts at the high loss end of the series being greater than and different from the attenuation increment between contacts at the low loss end of the series, said contacts defining a series of attenuation paths for each attenuator within an operative range of from zero to infinity, a movable element cooperating with said series of contacts on each attenuator, each of said movable "elements being connected to one of said four terminals, the remaining two terminals being connected to said attenuators, said movable elements being operably associated to vary inversely whereby substantially constant total attenuation, expressed as sum of power ratios, along the series of contacts, may be attained.

3. In a device of the character described, a pair of variable attenuators, each of said attenuators having a series of contacts defining terminals of a plurality of attenuation paths within an operative range of from zero loss to infinite loss, in decibels, the attenuation increment between contacts at the high loss end of the series being greater than and different from the attenuation increment between contacts at the low loss end of the series, a movable element cooperating with a series of contacts on each attenuator, said movable elements being operably associated for simultaneous movement, the attenuation increments of said attenuators and the association of said movable elements being correlated so as to produce a substantially constant total attenuation, expressed as sum of power ratios, along the series of contacts.

4. In a device of the character described, a four terminal network including an attenuator provided with two sets of contacts, a movable element cooperating with each set of contacts, a terminal connected to each of said movable elements, said movable elements being mechanically couple-d together to move inversely over their associated contacts, said contacts being arranged to produce a substantially constant total attenuation, expressed as sum of power ratios, at all times.

5. A method of manipulating electrical transmission characteristics of a plurality of circuits, comprising: introducing attenuation in some of said circuits and simultaneously decreasing attenuation in other circuits by a series of steps within an operable attenuation range of between zero and infinity, expressed in decibels; and maintaining the complement of attenuations, expressed as power ratios, substantially constant over the entire range of increase or decrease,

by increasing the attenuation in steps which bear an hyperbolic relationship to the simultaneous steps of decrease in attenuation.

6. A method of creating sound effects which comprises: positioning reproducers at different points in a theatre or other enclosure; connecting a sound current circuit to all of said reproducers through a junction circuit, and then gradually introducing attenuation in certain of said reproducer circuits and simultaneously decreasing attenuation from other of said reproducer circuits so as to cause sound to be reproduced from one and then another of said reproducers selectively without material change in the complement of attenuations in said reproducer circuits, expressed as power ratios.

7. A method of creating sound effects which comprises: positioning reproducers at different points in a theatre or other enclosure; connecting asound current circuit to all of said reproducers through a junction circuit; and then gradually introducing attenuation in relatively small loss increments in certain of said reproducer circuits and simultaneously decreasing attenuation in correlated larger loss increments in other of said reproducer circuits, whereby the total attenuation in the system is maintained virtually constant, expressed as a power ratio, and sound can be selectively reproduced from any one or more of said reproducers and transition from one to another reproducer is attained without material change in level over the level of the sound current circuit.

8. A method of regulata-bly controlling sound currents supplied to a plurality of circuits having reproducers located at different stations, which comprises: introducing attenuation in one or more of said circuits and simultaneously decreasing attenuation in the remaining circuits within an operative range of between zero loss and infinite loss, expressed in decibels; the sum of the attenuations in said individual circuits, expressed .as power ratios, being constant at all times.

9. A method of manipulating the transmission characteristics of a junction network during recording of sound, which comprises: positioning two or more microphones in operable relation to different sound sources, supplying sound currents from said microphones to a junction network, gradually introducing attenuation in relatively small loss increments in the sound current circuits from one of said microphones, and simultaneously decreasing attenuation in correlated larger loss increments in the sound current circuit from another of said microphones, the attenuation in one microphone circuit bearing an hyperbolic relation to the attenuation in the other microphone circuit so that the complement of attenuations, expressed as power ratios, is maintained constant, whereby the output of said network may be derived from any one or more of said microphones and smooth transitions are obtained.

10. A method of manipulating electrical transmission characteristics of a plurality of circuits which comprises: progressively introducing attenuation in at least one of said circuits, and simultaneously automatically producing complementary attenuation, expressed as power ratios, in the remaining circuits.

11. A method of manipulating the transmission characteristics in a sound reproducing system and of creating novel sound effects thereby, which comprises: positioning reproducers in the front, rear and in the center of a theatre or other enclosure; connecting a sound circuit including branch legs to all of said reproducers through a junction circuit whereby infinite loss may be introduced into any lr 3 leading to any two of said reproducers at the same time; gradually introducing attenuation in relatively small loss increments in a branch circuit leading to a front reproducer while simultaneously decreasing attenuation in correlated larger loss increments in a branch circuit leading to the center reproducer, and when infinite loss has been thus introduced in the front reproducer circuit, gradually introducing attenuation in the center branch circuit while decreasing attenuation in the rear reproducer branch circuit, the sum of the attenuations in all of said branch circuits being modified, expressed as power ratios, being constant at all times; whereby transition from front to rear reproducers may be obtained without material change in level.

12. A method of creating sound effects in theatres, which comprises: positioning reproducers in the front and in the center of a theatre or other enclosure; connecting a sound circuit to said reproducers through a junction circuit including front and center branches, each of said branches including variable attenuation means having an operative range of between zero loss and infinite loss, in decibels; gradually introducing attenuation in one of said branch circuits while simultaneously decreasing attenuation in correlated loss increments in the other branch circuit, and maintaining the complement of attenuations in said branches, expressed as power ratios, substantially constant throughout the range of variation, whereby the sound from said circuit may be selectively reproduced from front or center reproducers and smooth transitions obtain.

13. A junction network for sound current comprising: branch legs and a common leg; an attenuator in each branch leg, and means for varying the attenuation in each branch leg, said means being operably associated to produce a substantially constant complement of attenuations, when expressed as power ratios, throughout the operative range.

14. A junction network for sound current comprising: branch legs and a common leg; an attenuator in each branch leg, having an operative range of from zero loss to infinite loss, in decibels, and means for varying the attenuation in each branch leg, said means being operably associated to produce a'substantially constant complement of attenuations, when expressed as power ratios, throughout the operative range.

15. A network including two branch legs and acommon leg, a ladder type attenuation element in each branch leg, each of said attenuation elements including series impedance arms and shunt impedance arms, one end of each of said shunt impedance arms being connected to a common ground, each of said attenuation elements including a set of terminals associated with the series impedance arms, and a movable contact arm in each of said branch legs, each of said movable 16. A sound reproducing system for theatres and the like, including: two branch legs, each thereof provided with a modulated current source, an amplifier, and a variable attenuator having an operative range of from zero loss to infinite loss. in decibels; a common leg connected to said attenuators, said common leg including an amplifier and a loud speaker; said attenuators being operably coupled together to produce a substantially constant complement of attenuations, when expressed as power ratios, throughout the operative range.

1'7. A sound reproducing system for theatres and the like, comprising: a source of modulated currents, an amplifier therefor, a primary network connected to said amplifier, said network having two branches, an attenuator in each of said primary branches, means for varying the attenuation in each of said branches, a secondary network connected to each of said branches, a pair of output lines from each of said secondary networks, four loud speaker means, one of said loud speakers being connected to each of said output lines, a variable attenuator in each of said output lines, the attenuators in output lines of each of said secondary networks being coupled together to produce a substantially constant complement of attenuations in such secondary network, when expressed as power ratios, whereby sound may be reproduced from any one or more of said four reproducers selectively.

18. A sound reproducing system for theatres and the like, comprising: a source of modulated currents, an amplifier therefor, a primary network connected to said amplifier, said network having two branches, an attenuator in each of said primary branches, means for varying the attenuation in each of said branches within an operative range of from zero loss to infinite loss, in decibels, said means being operably associated to produce a substantially constant complement of attenuations, when expressed as power ratios; a secondary network connected to each of said branches, a pair of output lines from each of said secondary networks, four loud speaker means, one of said loud speakers being connected to each of said output lines, a variable attenuator in each of said output lines, the attenuators in output lines of each of said secondary networks being coupled together to produce a substantially constant complement of attenuations in such secondary network, when expressed as power ratios, whereby sound may be reproduced from any one or more of said four reproducers selectively.

19. A sound reproducing system for theatres and the like, comprising: a source of modulated currents, an amplifier therefor, a primary network connected to said amplifier, said network having two branches, an attenuator in each of said primary branches, means for varying the attenuation in each of said branches, a secondary network connected to each of said branches, a pair of output lines from each of said secondary networks, four loud speaker means, each being adapted for placement in a different position in a theatre, one of said loud speakers being connected to each of said output lines, a variable attenuator in each of said output lines, the attenuators in output lines of each of said secondary networks being coupled together to produce a substantially constant complement of attenuations in such secondary network, when expressed as power ratios, whereby sound may be reproduced from any one or more of said four reproducers selectively.

20. A sound reproducing system for theatres and the like, comprising: a source of modulated currents, an amplifier therefor, a primary network connected to said amplifier, said network having two branches, an attenuator in each of said primary branches, means for varying the attenuation in each of said branches within an operative range of from zero loss to infinite loss,

in decibels, said means being operably associated to produce a substantially constant complement of attenuations, when expressed as power ratios; a secondary network connected to each of said branches, 2, pair of output lines from each of said secondary networks, four loud speaker means, one of said loud speaker means being connected to each of said output lines, and a variable attenuator in each of said output lines.

21. A network circuit including two input circuits, one output circuit, and coupling means between the two input circuits and output circuit, each of said input circuits including an impedance matching device and a variable attenuation device between said impedance matching device and said coupling means; each of said variable attenuation devices including a plurality of operable circuits terminated by one contact in a series of contacts, each of said input circuits including a selector arm adapted to operatively connect each of said series of contacts in a fixed electrical sequence, said selector arms being mechanically coupled, one of said series of contacts being in reverse operable order to the other series so that complementary operable circuits are introduced when said coupled selector arms are moved together, such operably selected circuits oiTering complementary attenuations, expressed as power ratios.

22. An electric reproducer for sound accompaniment to motion picture films, including: a plurality of records of sounds, a plurality of electric current pick-up means, a loud speaker means, and a variable attenuator between each pick-up means and said loud speaker, each attenuator having an operative range of from zero loss to infinite loss, said attenuators being coupled together to produce complementary changes in attenuation between said plurality of pickup means and said loud speaker, the complement of attenuations, expressed as power ratios, being constant throughout said operating range.

23. A sound reproducing system including: a current division circuit including a source of sound current and two primary branches, a variable attenuation means in each primary branch, said attenuation means being coupled together to change attenuation in steps of equal magnitude but opposite algebraic sign, when expressed in power ratios; a current distribution circuit associated with each of said primary branches, the two current distribution circuits being of identical characteristics, each of said current distribution circuits including two variable attenuation means, and loud speakers connected to said attenuation means, one of said attenuation means having an effective range of from zero loss to infinite loss to zero loss, and the other attenuation means having an effective range of from infinite loss to zero loss to infinite loss, when expressed in decibels; two loud speakers connected to the attenuation means of the zero-infinity-zero range and one loud speaker connected to the other attenuation means; a switch connection between the first of said attenuation means and its associated loud speakers; means coupling all of the attenuation means in the distributing circuits for operating said attenuation means simultaneously in a predetermined relationship and for operating said switch whereby contact is automatically maintained between the attenuation means of the zero-infinity-zero range and one loud speaker when said attenuator is operative on the first half of said range, and whereby such contact is broken and the other loud speaker connected to said attenuation means in the second half of the operative range; said coupling means being 10 adapted to maintain a substantially constant complement of attenuations in the operative current distributing circuits, expressed as power ratios, whereby the reproduction of sound may be shifted from one loud speaker to any other loud speaker by manipulation of said coupling means.

WILLIAM E. GARITY.

JOHN N. A. HAWKINS.

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