US1947020A - Electrical music system - Google Patents

Description

Feb. 13, 1934. R H, R N ER 1,947,020

ELECTRICAL MUSIC SYSTEM Filed May 29, 1931 5 Sheets-Sheet I M IN VVENTOR Feb. 13, 1934. R. H. RANGER 1,947,020

ELECTRICAL MUSIC SYSTEM Filed May 29. 1951 s Sheets-Sheet 2 Feb. 13, 1934.

R. H. RANGER ELECTRICAL MUSIC S YSTEM Filed May 29, 1931 S'Sheets-Sheet 3 m WWW Feb. 13, R, H. RANGER ELECTRICAL MUSIC SYSTEM Filed May 29, 1951 5 Sheets-Sheet 4 e as a La 5/ vi INVENTOR 'Feb. 13, 1934. R. H. RANGER ELECTRICAL MUSIC SYSTEM s Sheets-Sheet 5 Filed May 29, 1931 QSW J Patented F eb. 13, 1934 UNITED STATES PATENT OFFICE 18 Claims.

My invention relates to a system for producing musical sounds. As embodiment of such a system, the invention concerns an instrument or apparatus capable of producing musical tones 6 of any desired volume or timbre throughout the audible range.

Many systems for the production of musical sounds by electrical generation, amplification, and reproduction according to the various techniques it of the telephonic arts have already been disclosed. There are, for example, systems which generate audio frequency oscillations by means of a1- ternators, using the physical principle known as Lenzs law. Typical examples of such systems are described in U. S. Letters Patent Nos. 580,035; 1,107,261; 1,213,803; 1,213,804; 1,295,691; and 1,749,685. Still other systems utilize a source of high frequency electrical oscillations in combination with a source of variable frequency waves,

causing the well-known heterodyne action and thus producing a beat note of the desired audible frequency, as disclosed in U. S. Letters Patent No. 1,661,058 by Mr. L. S. Theremin; and others, as specified in U. S. Letters Patent Nos. 1,376,288

and 1,543,990, use oscillating audion tubes as frequency generators.

All of these systems aim at the production of sustained electrical oscillations or alternating electrical currents of frequencies such that they may be apprehended by the human ear when properly translated into compression and rarefaction waves in a soundconducting medium such as air. The advantages of such electrical generation are manifold; starting with electrical waves of simple or sinusoidal characteristics, complex waves may be built up which when rendered audible will produce musical tones of novel and pleasing quality or timbre; the timbre is conveniently and infinitely variable, allowing one instrument to simulate many of the classical or fixed timbre type; the amplitude of separate tones or combinations of tones is smoothly variable between wide limits by simple electrical means; and the pitch and tuning of the musical tones may be made more constant and at the same time far easier to adjust or change than in a non-electrical instrument. These and other advantages of electrical musical systems I also have attained in this present invention.

My invention differs from all otherelectrical musical systems, however, in that it is not concerned with the generation of pure sinusoidal electrical waves as a starting point. On the contrary, generators are used which will produce tones of maximum complexity; that is,

tones which contain in addition to simple oscillations of fundamental frequency, the greatest possible number of oscillations of harmonlcally related frequencies. These harmonics are then separated from each other and from their funda- 9 mental tone by electrical or acoustic filtering means, their relative amplitudes are adjusted by the performer, and they are recombined and reproduced. While such a method adds another step-the separation of complex tones of fllter- 3 ing-to those already necessary for an electrical music system, its effect, as will appear below, is to reduce greatly the complexity and cost of the system and to improve its'performance.

' A pure wave, either of sound or of electricity 7 is one whose projection to cartesian coordinates with respect to time would appear as the mathematical figure known as a sine curve; one whose amplitude varies in simple harmonic fashion. Practically without exception the ordinary instruments known to the musical art set up complex sound waves in the air, and these complex waves have been shown to consist of a number of pure sound waves'in combination. The principle component pure wave is called the fundamental or first partial tone, and sets the pitch of the complex tone. The other components, called harmonics or upper partials, are generally of less amplitude than the fundamental and of higher frequency, than the frequency of the fundamental. The number of partials present in a musical tone, as well as their relative frequencies and amplitudes, determines the characteristic quality or timbre of the tone, whether string quality, brass quality, siren quality or the like.

No ordinary musical tone-producer may therefore he used for an instrumentswhich requires pure tones; it is necessary to resort to tuning forks or especially designed alternators, audion circuits, or photoelectric systems, and elaborate precautions are necessary to insure steadiness ofpitch and purity of tone in the generated oscillations, while in my invention a simple vibrating body such as a stringor a reed may be used.

Furthermore, as mentioned above, it is the aim of most electrical music systems to produce various synthetic timbre effects by combining pure tones in various proportions so as to make available for reproduction a variety of pleasing tone qualities. To accomplish this end they must either have available pure tones corresponding to the fundamental and the most important harmonics of each note of the tempered musical scale, or they must employ in place of the proper partials of each complex tone those tones of the musical scale which most nearly approach the partials in frequency. In the first case, assuming that a scale of 70 notes is desired and that six partials are used in each tone, 420 separate sources of pure tones are required, making the instrument; complicated, costly, and difllcult to maintain. In the second case the quality of the complex tones produced must of necessity suffer, since the simple tones used as the upper partials do not bear quite the proper frequency relation to each other for such use. In my invention each generator of tone produces both a fundamental tone and all its audible harmonics, so that only 70 generators are needed to achieve the same result as the 420 of the first case cited above.

It is, therefore, a primary object of my invention to develop an electrical musical system in which there is one tone generator for each note of the musical scale, this tone generator providing both the fundamental and all the audible harmonics of that note.

Another object of my invention is to provide an electrical musical system wherein complex tones are separated into their component simple tones so that these may be recombined to give any desired timbre to the system.

A further object of my invention is to provide an electrical music system wherein the keying makes or breaks direct current only, thus avoiding the objectionable noises which result when alternating current circuits are made or broken.

A fifth object of my invention is to provide an electrical music system in which some means is provided to prevent any note from being fed to the amplifying and reproducing system until the operation of keying its generator is over, thus preventing keying noises from becoming audible.

As a sixth object, I wish to provide an electrical music system in which the volume of each partial composing a tone is separately controllable in accordance with the timbre of the tone which is to be produced.

The seventh object of my invention is to provide separate amplifiers for particular groups of tones, both to prevent excessive cross modulation and overloading of the amplifiers, and to insure that tones within a certain frequency range will pass through an amplifier particularly suited to that range.

The eighth object of my invention is the provision of an electrical music system in which tremolo effects involving both frequency and amplitude fluctuations may be introduced into each amplifier to any desired degree. While either an amplitude variation or a frequency variation will give a satisfactory tremolo, a most pleasing effect results from a combination of the two.

The ninth object of my invention aims to provide a musical system capable of simulating the timbre of any one of a number of known instruments, the change from one timbre to another being easily and rapidly accomplished.

A tenth object of my invention is to provide means whereby an infinite range of timbre or tone color is at the command of the performer by means of multiple controls permitting the partials of all notes of the scale to be varied simultaneously.

As further objects, my invention aims to provide an electrical music system which may be entirely contained within an ordinary organ console, which is inexpensive to construct and easy to operate and maintain. Still other objects of my invention will become apparent from a consideration of the following portions of this specification and the appended claims.

To illustrate the principles involved in my invention and its manner of operation, I have included as part of my application certain drawings as follows:

Fig. l, a graphical representation of a typical complex musical tone, and its resolution into simple components; Fig. 2, depicting the construction of a single tone generating unit and the keying means associated therewith; Fig. 3, which shows a simple reed and an alternate method of picking up its vibrations; Fig. 4, a schematic wiring diagram of my musical system for one note of the scale; Fig. 5, a block diagram of my invention for several octaves of the musical scale; Fig. 6, a drawing of the timbre control mechanism for one harmonic; and Fig. 7, showing the application of my invention to a two-manual and pedal console.

As the actual generating device for my invention, I have used the reed, long familiar to the musical art as a specially shaped tongue of elastic material, which when fixed at one end in such a manner as to obstruct a passage through which air is being forced under pressure, will vibrate at a definite and constant period depending on the air pressure, producing a musical tone by virtue of the resultant periodic interruptions of the flow of air. The complex curve C of Fig. 1, represents the wave-form of a typical reed tone, and the sine curves 1 to 8 represent the most important pure tones which in combination in the phase and amplitude relations shown make up the complex tone C. in point of maximum complexity the reed meets most satisfactorily the requirements for tone sources outlined in the objects of my invention. It is also simple and inexpensive in construction,

It is at once apparent that 11'."

and as will appear below, the design technique of the common reed-organ or harmonium may easily be applied to a practical embodiment of my invention.

I do not wish, however, to limit my invention to the use of reeds as tone sources; it may well be that considerations of design might make it desirable to use some other source of complex musical tone such as the string, the organ pipe, or a sounding plate or membrane, for some specific embodiment of my invention. It might for instance be desired to add a musical system of the sort here disclosed to a piano or a pipe-organ, instead of to a reed-organ; such an application should be quite possible.

It is not even necessary in fact, that the primary generators for my system produce an audible tone, since vibrations of any sort may be picked up magnetically and fed through the electrical circuits in similar fashion to the output currents of the microphones in the form of my invention described below. Fig. 3, shows how a magnetic pickup may be applied to a reed. The reed 9, made of some magnetic material such as steel,

is mounted in the conventional manner over the air chamber 10, and is fixed at one end by the screws 11 and 12. As air is forced in either direction through 10, the reed 9 will vibrate in accordance with its characteristic tone, periodically varying the reluctance of the path of the mag- 1% netic field of the permanent magnet 13. and so inducing in the field windings 14 an electrical wave corresponding to the normal sound wave of the reed. This electrical wave may then be applied to the input winding of transformer 15 1 (shown in Fig. 4) in lieu of the microphone output.

My invention is shown in preferred form for a single note of the scale in Fig. 4. The reed 16 is used as tone generator, and is mechanically keyed as in the reed-organ; that is key 17, when depressed by the performer, causes the dowel pin 18 to open valve 19, admitting air under pressure to the chamber 20. The reed assembly is mounted in a sound-insulated box 21, which is connected by the tube 22 to'the sound insulated mounting 23 of a microphone 24.

The key 17 is so constructed that its first action when being depressed is to open valve 19 and start the reed 16 sounding. Further depression of the key causes contacts 25 and 26 to close.

- Contact 26 is connected to a source of direct current which fiows through wire 27, the primary winding 28 of transformer 15, and the microphone 24. The latter thus becomes responsive to the sound waves reaching it from reed 16 through tube-22, and superposes on the above-mentioned direct current an alternating electrical wave corresponding to the complex tone of the reed; i. e., similar to curve C of Fig. 1.

Up to this point the secondary winding 29 of transformer 15 has been short circuited through leads 30 and 31 and the contact points 32 and 33. However, mechanical connection has now been established from key 17 through the insulating buffer 34 and contacts 25 and 26 to a second insulating buffer 35, so that still further depression of the key separates contacts 32 and 33, removing the short-circuit from transformer winding 29, and allowing the electrical equivalent of the complex reed tone to be fed through leads 36 and 37.

At this point it seems pertient to clarify the definition of complex tone C. Hereafter, for purposes of simplicity, this term will be taken to represent the compound sound wave produced by the reed 16 both in its audible and its equivalent electrical forms, as depicted graphically at C in Fig. 1. Similarly, the sinusoidal or pure components of complex tone C, shown by curves 1 to 8 of Fig. 1, will be referred to as the fundamental and the first, second, third, fourth, fifth, sixth, and seventh harmonics respectively.

To return now to our consideration of Fig. 4, it has been shown that full depression of key 17 by a performer will cause three successive events; first, the sounding of reed 16; second, after an interval depending on the space between contacts 25 and 26, the energizing of microphone 24, and third, .the removal of the original shortcircuit from transformer winding 29. By this arrangement it is ensured that reed 16 will have reached a state of steady vibration before its tone is picked up by microphone 24, and that the amplifying and reproducing circuits will not become operative until the keying of the microphone is accomplished, thus preventing any transient phenomena, such as clicks or scratches which might be produced .during the keying operation, from becoming audible.

After keying is completed, complex tone C.

pedance to alternating currents of any other frequency. For example. assume that reed 18 is tuned to A (A=220 c. p. s. in the tempered scale. The notation of Helmholtz is used throughout this specification to locate notes of the scale). Filter circuit F1 would then be designed to pass all frequencies between 215 and 226 c. p. s., and the first harmonic of A (=ll-0.0 c. p. s.), the second harmonic of D (=73.42 c. p. s.), the third harmonic of A1 (55.0 c. p. s.), the fourth harmonic of F1 (=43.65 c. p. s.) and the fifth harmonic of D1 (=36.71 c. p. s.), as well as the fundamental tone of reed 16, would pass through the filter circuitand be impressed on the grid of the UY-227 type vacuum tube 43. On the other hand, the next adjacent fundamental tones of the tempered scale, gt =(207.6 c. p. s.) and at (=233.1 c. p. s.) would be excluded from tube 43 by filter circuit F1 as would the harmonics of those tones lower in the scale which are approximately equal to the aliquot parts of gt and at, and of course all other components of complex tone C outside of the fundamental.

Thus the fundamental tone of reed 16 passes to tube 43. After amplification by this tube it passes through band-pass filter circuit F2 consisting of condensers 44, 45, and 46, and inductance 47. Filter circuit F2, is used to supplement F1 in preventing undesired fundamental and harmonic tones from passing through the amplifying circuit. For reasons which will appear below, however, the range of frequencies which filter F2 will pass is considerably larger than that of filter F1: is equivalent, in fact, to the frequency range covered by the fundamentals of nine notes of the tempered scale and such harmonies as approximate these fundamentals in frequency. Thus, still assuming that the fundamental tone of reed 16 is a, filter F2 would be designed to pass all frequencies between 180 and 300 c. p. s., or all fundamental tones between it 115 and d (185.0 and 293.7 0. p. 5.).

Filter circuit F2 must eliminate all undesired components from the tone which leaves tube 43, and as we shall see, tube 43 may simultaneously be passing the amplified output of filter circuit 120 F1 and of five or six similar filter circuits. There is consequently the possibility that undesirable tones, produced by modulation, may be present in the output of tube 43, in addition to the harmonies which have not been completely elimi- 125 nated by the initial filtering. Thus in general it is necessary that F2 be a more elaborate and efilcient filter than F1. A two or three section filter may be required for best results, instead of the half-section'type shown.

The filtered output of F2 goes through transformer 48, is amplified by the power pentode 49, and reproduced by loud-speaker 50, to which it passes through transformer 51. The amplifying circuits shown in Fig. 4 were designed to suit the characteristics of the UY-227 tube 43, and the pentode 49; their operation is well known and requires no extended discussion. Resistors 52 and 53 are of high value and serve to prevent local oscillations; resistors 54 and 55 are used to hold 14,0 the grids of tubes 43 and 49 respectively to their 1 proper potentials; condensers 56, 57, 58, 59, and are all of two microfarad capacity, and act as by-pass condensers; the choke 61 prevents audio frequency currents from feeding back to the B voltage supply; and choke 62 (connected to form what is known as a parallel feed circuit) keeps direct current from reaching the windings of transformer 51. While any good amplifier may be used for my invention, the one shown in Fig. 160

its

4 is peculiarly suited for the purpose, due to its compactness, stability, and high gain.

As we have shown, of the complex tone C emitted by reed l6 and picked up by microphone 24 only the fundamental passes through filter circuit F1 to tube 43. Connected to lead 36, however, are a number of additional resistances exactly similar to 38. These resistances, shown at 63, and 64, and in Fig. 4, are each connected through a condenser to a separate filter circuit similar to F1. Each of these filter circuits is designed to pass a single harmonic of complex tone C; thus the filter connected to resistor 63 might pass the second harmonic, that connected to resistor 64-the third harmonic, and so on. Resistors are provided for as many harmonics of the fundamental note as are musically useful, that is, say those of 8000 c. p. 5. frequency or below.

A clearer idea of the operation of my invention may at this point be obtained by a study of Fig. 5, a block diagram of the interrelation of the apparatus involved in 27 notes of the tempered scale, from C to d. The tone corresponding to each of these notes is generated by a separate reed, picked up by a separate microphone, and controlled by a separate key. Thus key Kc controls the action of Rc, which generates the tone correspondng to C of the Helmholtz notation, the fundamental pitch being 65.41 c. p. s., and also operates microphone Mc, the action of the key being as explained for key 1'? of Fig. 4. In similar fashion key K03 controls reed Rc z and microphone Mat, and so on up to key Kc, controlling reed Rd and microphone Md. Twenty-seven filter circuits are shown in Fig. 6, lettered Fc, Fat, FD, etc., up to Fe. These filters correspond to filter F1, of Fig. 4, and each of them is designed to pass a narrow band of frequencies around the fundamental pitch of the note of the scale to which it corresponds. Six resistors, lettered I, II, III, IV, V, and VI, respectively, are connected in parallel to the output of each microphone, and we shall identify these resistors by the note with which they are associated, referring to those of note C as Is, He, IIIc, etc.; to those of note B as In, HE, 1118, etc., and so on. A1, A2, and A3, represent audio amplifiers, AF1, AFz, and AFa, filter amplifiers of nine-note band width (of filter F2 of Fig. 4), and L1, L2, and La, loud-speakers or other suitable sound reproducers. T1, T2, and T3 correspond to the coupling and amplifying tube 43 of Fig. 4.

We will take as example the operation of note C. When key Kc is depressed by the performer, air is admitted to reed Rc, microphone M0 is energized. and the short-circuit removed from the secondary of the output transformer (not shown) of N10. A complex tone similar to C of Fig. 1 and consisting of a fundamental of 65.41 c. p. s. and numerous harmonics is thus fed to resistors Io, IIc. IIIc. IVc, V0, and VIC. Now, resistor 10 is connected to filter Fc, tuned to pass frequencies between 63.50 and 67.40 c. p. s., resistor H0 is connected to filter Fc, which passes tones between 127.0 and 134.5 c. p. s., resistor IIIc ties to filter Fg, passing tones between 190.0 and 213.0 c. p. s., and resistor 1V0 is connected to filter Fe, passing a band of frequencies between 254.0 and 269.0 0. p. s. The limitations of Fig. 5, do not permit the connections of resistors V0 and We to be shown. but they are connected respectively to filter F0 (passing 320.0 to 330.0 c. p. s.) and F passing 380.0 to 403.0 c. p. 5.). Thus, the 65.41

cycle fundamental tone of reed He may pass only through resistor 10, filter Fc, amplifier A1, and filter-amplifier AF1, to be reproduced by loud-speaker Ll. Similarly the 130.8 0. p. s. first harmonic of the note C finds its only path through resistor IIc, filter Fe, amplifier A2, amplifier filter AF2, and loudspeaker L2, and the 196.23 c. p. 5. second harmonic of note C goes through IIIc, Fg, A3, AFa, and L3. Thus the complex output of reed Rc is separated into its simple components, and each of these components may be amplified and reproduced separately.

It is now also apparent that each of the simple filters Fc to Fe serves a manifold purposes, passing besides the fundamental tone of its associated note the upper harmonics of various other notes. Filter F for example, is used to separate out the fundamental (:196.0 c.p.s.) of reed R the first harmonic (:1960 c.p.s.) of reed Re, the second harmonic (=196.2 c.p.s.) of reed Re, the third harmonic (:1960 c.p.s.) of reed R01, and the fourth harmonic (=194.5 c.p.s.) of reed Rmt. All of these tones come within the passband of F; (:190.0 to 213.0 c.p.s.) and so are fed through it. With this method of construction but 72 primary filters are required in my invention for a scale of 60 notes, as against a total of 360 primary filters where a separate one is to be provided for each harmonic of each note.

An essential difference between my invention and other electrical music systems lies in the manner in which the ultimate compound tones are synthetized. Other systems, having produced the simple tones making up the compound note in the correct proportions for the timbre required, feed them into a single amplifier and reproduce them together. In my invention, on the other hand, the various components of a note may pass through different amplifiers and reproducers. We have seen, for instance that while the fundamental of a note C is reproduced by speaker. L1, the second harmonic will emanate from speaker L2, the third and fourth harmonics from L3, and so on. This action'is necessitated by the general design of my system and produces exactly the same musical result as the above-mentioned method of compounding an entire note in a single reproducer, since if the numerous reproducers of my system are close together and a listener some ten or fifteen feet away, the effect to such a listened will be that of a single compound tone made up of all the tones being simultaneously reproduced. It is of course necessary in my system that any difference in characteristics between various amplifier and reproducer groups be compensated for the timbre achustment.

To return for the moment to Fig. 4, the connection of the latter with Fig. 5 should now be quite clear. For example, let us say once again that reed 16 is tuned to a (:220 c.p.s.). Then key 17, reed 16, and microphone 24 of Fig. 4 would correspond to key Kg, reed Ru, and microphone Ma of Fig. 5. Similarly, resistors 38, 63, 64, and 65 of Fig. 4 correspond to resistors Is, 11:1, 111a, and IVs, of Fig. 5. and filter F1 of Fig. 4 is the same as filter Fa of Fig. 5. Coupling tube T3, amplifier A3, amplifier filter AFa, and loudspeaker L3 of Fig. 5 are of course equivalent to tube 43, Filter F2, and loud-speaker c0 of Fig. 4, together with their associated amplifier circuit. Fig. 5 shows that the tone outputs of filters Fit, Fg, F i, Fat, Fe, Fe, Ft' and Fe feed into coupling tube T3, as well as the output of Fri, and the corresponding points of connection of these tones are shown at points 230, 231, 232, 233, 234, 235, 236, and 237 in Fig. 4.

The timbre of each note is fixed by the relative values of its six associated resistors (see Fig. 5). since each of the latter controls the amplitude of one of the partials or harmonics of the note.

'I have therefore devised a simple, rapid, and

automatic means of setting these resistors so as to produce any one of a number of predetermined stop qualities. A special gang-control is provided to vary as a unit all the resistors controlling the same order of harmonic. In Fig. 5, for instance, one gang-control would regulate resistors Io, lot, In Id, another would control resistors Ho, to IId', etc. Assuming that the regulation of six principal harmonics were considered sufficient to simulate any tone quality, and that my instrument were built for a -note scale compass, six gang-controls would be necessary, each controlling 60 resistors.

In Fig. 6 I have shown one of these gangcontrols, and have assumed that it is used to control the amount of second harmonic present in any reproduced notes. Accordingly, resistors IIIc, IIIcr, IIIp, etc., are shown mounted on shaft 66. These resistors are of the common rotating-slider type extensively used in broadcast radio receiving sets. They are mounted so that the shaft 66, carrying the sliders 67, 68, 69, etc., rotates freely through their centers. The position of the various sliders of course determines the values of the various resistors, and the sliders are so fixed in relation to the shaft and each other that for any given position of shaft 66 a given percentage of second harmonic will be present in every note reproduced by the musical system.

Shaft 66 is driven by a small D. C. shunt motor 70. The shaft passes through a fixed pointswitch 101, carrying the ten control points numbered 71 to ,80. Switch blade 102 is mounted on shaft 66, but separated from it by an insulating bushing 91. Brush 92 makes contact with blade 102 through bushing 93, and connects it to one end of the motor field 94. Switch points 71 to 80 are connected to mains 81 to 90, and in parallel on these 10 mains are connected the contact fingers of 10 relays, only three of which (95, 96,

and 97) are shown in Fig. 6.

Contacts 111 to 120 of relay 95 are connected through leads 81 to to contact points 71 to w 80 of switch 101, contact 111 connecting through lead 81 to point 71, contact 112 connecting through lead 82 to point 72, and so on. Similarly, contacts 121 to 130 of relay 96, and contacts 131 to 140 of relay 97 are also connected to points 71 to 80.

Let us assume that, with blade 102 on point 74, switch 98 is closed, energizing relay and closing contacts 111 to 120. Through contact 110 and contact 231 of a secondary, single-contact relay 230, the coil of relay 95 receives just willcient voltage to hold all the relay contacts over, even when switch 98 is opened. Through contacts 111, 112, 113, 114, and 115, switch points 71, 72, 73, 74, and 75 receive positive potential of the proper value for energizing field-coil 94, and

through contacts 116, 117, 118, and 119, switch points 76, 77, 78, and 79, receive negative potential of the same value. Motor 70 is so connected that when positive potential is applied to the free end of its field coil it will rotate in a clock wise direction, and conversely, when negative potential is applied, it will rotate in a counterclockwise direction. Thus, with switch blade 102 on point 74 and the contacts of relay 95 closed, motor 70 will start clockwise rotation, carrying with it switch blade 102 as well as the slider arms 67, 68, 69, etc. Blade 102 now travels over points 74, 73, 72, and 71, conveying positive potential from each of them to shunt field 94, until it reaches point 80. At this point connection is established between the open end of the coil of relay 230 and ground, through field-coil 94. Relay 230 is supplied with positive potential of voltage high enough to energize the relay coil, but not high enough to operate motor 70, which consequently stops. Contact 231 of relay 230 of course opens as soon as the relay is energized, breaking the holding potential to relay 95 and causing all its associated contacts to open; Resistors IIIc, IIIcii, 1111) etc. have now been set and the system is again at rest and ready to be readjusted. The secondary relay 230 and its c0ntact2'3l are shown separated from other portions of the circuit by dotted lines, to avoid confusion with relay contacts 110 to 119.

Had switch blade 102 been on one of the nega-v tive points 76, 77, 78, or 79, rotation of the motor would have been counter-clockwise, again until neutral point 80 was reached.

If the action of relays 96 and 97 is followed through, it will be found exactly similar to that of relay 96, except that the neutral point upon which the blade 102 comes to rest is different in each case. Thus when switch 99 is closed, energizing relay 96, blade 102 is brought around from any position it may be in to point 79, and when switch 100 is closed relay 97 causes the motor to operate until blade 102 rests on point 78. In similar fashion, closing the switch of any one of the ten relays contained in the complete gangcontrol will rotate shaft 66 until blade 102 rests on the point corresponding to that relayin other words, ten different second-harmonic signal levels are at the command of the performer.

A complete quality-setting control for the entire system would of course involve a means of setting all harmonics contained in the notes reproduced by the sys'tem. This would be most simply achieved by providing six-pole singlethrow push button switches for each stop". Each pole of a stop switch will act as the starting switch (for example, switch 98 of Fig. 6) for that relay of the gang-control on each harmonic which gives the desired signal-level for that harmonic. 5

These buttons will be pushed momentarily and then released, just as are the combination-setting buttons on a modern-pipe-organ, and a signal light may be provided for each, to indicate the button last operated. Since in the embodiment we have described six harmonics are used, each having ten possible settings, it is apparent that 1,000,000 stops may be provided, each producing a different timbre. Of course, no practical instrument either requires or can make use of more than a few hundred stops, and for this reason it will generally be necessary to have no more than three or four settings of any of the gang-control resistors available.

For an inexpensive and yet most flexiblemusical instrument, the physical form of my invention may be made similar to that of the well-known reed-organ or harmonium. Fig. 2 shows how a key, reed, and microphone might be mounted in such an instrument. Pressure on key 141, transmitted through the dowel stick 142, opens valve 143, and admits air to reed 144, exactly as in the 145 leads the complex sound wave to microphone 146, which is flexibly suspended as shown from some point of support 147 so as to minimize vibratory and resonance effects. Tube 145 should be as short as is consistent with a practicable arrangement of the microphones, since otherwise there will be too great a decrement in the intensity of the sound waves over its length, and for the same reason it should be made of some fairly resilient material such as brass. By deepening by a few inches the space ordinarily used to mount the reeds in a harmonium, it may be used to contain the microphones and microphone transformers as well as the reeds. The timbre-regulating gang-control resistors may be mounted to'the rear of the console at the same level as the microphones; the primary filters may be installed on the next level below, and the amplifier filters, amplifiers, and loud speakers at the bottom. The rear cover of the console forms an ideal sounding board for the reproducers.

The actual finger-pressure required of the performer to operate the valve-mechanism of a reed is normally rather high, as compared to the action of a modern pianoforte or electrically keyed pipeorgan. Since the playing of a key in my invention must not only operate the reed but must in addition close numerous spring contacts, it is desirable, in order to facilitate rapid passage work, to provide a measure of mechanical assistance for the keying operation.

The construction of my approved means to this end is shown in Fig. 2, wherein 148 and 149 represent cross-sectional areas through a solenoid surrounding the lower end of dowel 142, the shaded section 150 of which is of magnetic material such as iron. The light spring 151 normally bears against pin 152, holding key 141 slightly away from dowel 142. It also forms part of a contact device of which point 153 is the other portion. This contact closes when key 141 is pressed, energizing solenoid 148149, which by attracting magnetic piece 150 assists in keying the reed 144. As soon as pressure is removed from key 141, spring contact 151 will disconnect the solenoid and permit the heavier spring 154 to restore the valve, dowel and key to their original positions.

Air under pressure may of course be supplied to the reeds in a number of different ways. Perhaps the most satisfactory method is to use a small silent electric blower unit of the type extensively employed for electric pianos. The insertion of a small electrically operated "shaker bellows in the air line, controlled by a switch or stop, will provide a most satisfactory tremolo. An intensity-varying tremolo such as described in my application, Serial No. 417,466, filed Dec. 30, 1929, now Patent No. 1,901,985, dated March 21, 1933, may be used to supplement the air tremolo if desired.

Two types of volume control may be applied to my invention. As an overall control, varying the volume of the entire range of the instrument as a unit, a suitable pedal-operated variable resistance may be inserted in series with the D. C. power supply to the microphone, as is resistance 155 in Fig. 4. As power is supplied to all the microphones from a single source, setting this single resistance will suffice to vary the output signal level of the instrument. In addition to in Fig. 4.)

by separate control levers or pedals, may be used at the discretion of the performer to vary the relative loudness of groups of tones of various pitches; accentuating, for example, the bass orthe solo part of a composition.

While the instrument described in the above three paragraphs would probably be the most suitable form of my invention for use in the home, it might be that for other purposes, such as concert-hall or theatre use, a more elaborate instrument would be needed. Accordingly, I have shown in Fig. 7 how with a quite inconsiderable increase in complexity my invention may be embodied in an instrument having a fiexibility and power rangeequal to the largest, pipeorgans.

We will assume for simplicity that our instrument is to be controlled by two manuals and a pedal keyboard. Keys 157, 158, and 159 each operate a reed tuned to produce note C (65.41 c. p. s.), 157 being one of the choir manual keys, 158 one of the swell manual keys and 159 one of the pedal keys. Under each of these keys are mounted eight contacts, operating on a set schedule according to their height as shown in Fig. 7; i. e., were key 157 to be depressed, it would first admit air to reed 168 and then close contact 160, energizing the circuit of microphone 169. Following this, contacts 161, to 166 would close simultaneously, and lastly, contact 167 would open, removing the short-circuit from the secondary winding of microphone transformer 170.

The tone outputs of microphones 169, 179, and 189, passing through transformer 170, 180, and 190 go to the resistor groups 201 to 206, 211 to 216, and 221 to 226. Up to this point the operation of the three keys has been identical and similar to that of key 17 of Fig. 4, but now the tones, instead of feeding directly from the timbre resistors to the primary filter circuits, feed back to the six simultaneously closing contacts under each key, and are thence distributed to the appropriate filters Fe, Fe, F Fe, Fe, and Fg'. Thus the fundamental of the complex tone produced by reed 168 passes through filter Fe, reaching it through resistor 201 and contact 161. Similarly, the first harmonic of the same complex tone passes through Fc, by way of resistor 202 and contact 162, the second harmonic reaches Fg, through resistor 203 and contact 163, etc. In exactly the same manner, filter F0 handles the fundamental of the complex tone produced by reed 188 when key 159' is operated; Fe separates out the first harmonic of the complex tone produced by reed 178 when the closing of key 158 passes tone to it through resistor 212, and contact 172, and the first harmonic of the complex tone produced by reed 188 when permitted to do so by the closure of contact 182; and filter F performs a like function for the second harmonies of the complex tones produced by reeds 178 and 188.

By the design shown in Fig. 7, then, I am able to use the same set of primary filters for a multi- Since the timbre resistors is prevented, and since the amplifiers are not operative before the short-circuits are re moved from the microphone transformers, there is no danger of keying noises becoming audible.

For each manual of the larger instrument I thus provide a separate set of reeds, microphones,

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microphone transformers, and gang-control resistors. Only one set of primary filters, filterampliflers, and loud-speakers is necessary for the entire'installation. If the instrument is to from the console: their exact location should be determined for maximum efficiency under the acoustic conditions prevailing in the hall. Two

or more consoles may of course be used if desirable.

I'do not wish to limit my invention to any of the above described patterns. since many different forms of instrument employing the same principles will readily suggest themselves to those skilled in the musical and electrical arts. I therefore believe myself entitled to make and use any and all of such modifications as fall fairly'within the spirit and scope of my invention as' defined by the appended claims. 7 I

What I claim and desire to secure by Letters 7 Patent is the following:

1. In an electrical music system, a plurality of generators of complex tones equal in number to the notes of the system. a plurality of tone-filtering devices each capable of segregating the fundamental tone of. a] single one or said generators, as

well as those upper partial tones of other generators which approachsald fundamental tone more closely in frequency than .they do any other fundamental tone, from all other tones of the system, and means for reproducing simultaneously the tones passed by said tonedlltering devices.

2. In an electrical music system. a plurality of generators of complex'tones equal in number to the notes of the system, a plurality of tone-filtering'devices associated therewith for the purpose of separating said complex tones into their simple component tones, amplifying systems of a number 'lessthan the number of notes in the system, a secondary tone-filtering device, and a sound reproducel' connected'with each of said amplifying systems.

3. In an electrical music system, a plurality of generators of complex tones equal in number to the notes of the system, a plurality of primary tone-filtering devices equal in number to the notes of the system plus those additional notes found by following the musical scale of the system above the highest pitched generated complex tone of the system to the audible limit, the frequency pass-band of each of said primary tone-filtering devices including the fundamental tone of a single one of said generators as well as those upper partial tones of others of said generators which approach said fundamental tone more closely in frequency than they do the fundamental tone of any other complex tone of the system, secondary toneflltering devices of a number less than the number of .notes in the system but greater than the number of musical octaves in the system, the frequency pass-band of each of said secondary tone-filtering devices including the fundamental tones of a group of adjacent notes covering a range of less than one octave, and means for amplifying and reproducing the outputs of said secondary tone-fil- 4 tering devices.

a said body to vibrate, means for translating the vibrations, of said body into electrical waves,"

' 4. A system for the production of musical tones comprising a resonant body, means for causing means for. amplifying said electricalwaves, means for translating said amplifiedv electrical waves into audible tones, and means for delaying the admission of said electrical waves to said amplifying means until such time as said vibrating body shall have reached a steady state of vibration.

5.,In an electrical music system, a plurality of sources of complex tones, means for separating said complex tones into their various simple component tones, means for amplifying said component tones, means for reproducing said complex tones simultaneously, and means for de-' laying the admission of the output of said sources of complex tones to the re'stof the system until suchtime as said sources shall have reached a steady operating state.

6. In an electrical music system, a generator of audible complex tone, means for translating said audible complex tone into a complex electrical wave, means for separating said complex electrical wave into its component pure electrical waves. means for separately varying the amplitude of each of. said pure electrical waves, andmeans for rendering said pure electrical waves simultaneously audible. I

7.. In an electrical music system, a plurality of generators of audible complex tones corresponding in number to'the notes of the-system- ,-a corresponding number of microphones, each picking up the tone of oneof said generators and trans lating it into a complex'electrical wave, a pinrality of electrical wave filters equalin number to the notes of the system plus those additional notes found by following the musical scale of the system above the highest pitched generated complex tone of the system to the audible limit, the frequency pass-band of each of said filters including the fundamental tone of a single one of said generators as well as those upper partial tones of others of said, generators which approach said fundamental tone more closely in frequency than they do the fundamental tone of any other complex tone of the system, keying means causing the said generators to become operative,

the microphones to become receptive tothe outputs of said generators, and the outputs of said microphones to pass to said electrical wave filters, these operations occurring in the order named and various generators being keyed according to the will of the performer, and means for controlling the relative amplitudes and simultaneously reproducing the outputs of said electrical wave filters. v

8. In combination in an electrical music system, a plurality of reeds, a corresponding plurality of microphones associated with said reeds, a plurality of primary electrical wave filters for the purpose of separating the complex tone outputs of said microphones into component pure waves, a r

plurality of resistors so arranged as to vary in similar fashion the relative amplitudes of the component pure waves making up each of said I complex tone microphone outputs, a plurality of secondary electrical wave filters each purifying a microphone associated with said reed, a source of operating potential for said microphone, means for amplifying and reproducing audibly the output of said microphone, a manually operated key, and means operable from said key for opening said air valve, for applying said operating potential to said microphone, and for connecting the said output of the said microphone to the said amplifier and reproducing means, in the order named.

10. An electrical music system comprising a reed, a source of air under pressure for the purpose of vibrating said reed, an air valve controlling the flow of air from said source to said reed, a microphone associated with said reed, a source of operating potential for said microphone, a plurality of primary electrical wave-filtersfor the purpose of separating the complex tone output of said microphone into its component pure waves, means for varying the relative amplitude of each of said pure waves, a secondary wave-filter for purifying the output of each of said primary wave-filters, means for amplifying and reproducing audibly the outputs of said secondary wavefilters, a manually operated key, and means operable from said key for opening said air valve, for applying said operating potential to said microphone, and for connecting the said output of the said microphone to the said primary electrical wave-filters, in the order named.

11. In an electrical music system as described in claim 9, a means of control for the overall volume of the system comprising a variable resistance in series with the operating potential supplied to the microphone oi the system.

12. A tremolo control for an electrical music system as described in claim 9 comprising a motor, means for controlling said motor, and means operable from said motor for causing a periodic variation in the pressure of the air applied to the reed in said electrical music system.

13. A tremolo control for an electrical music system as described in claim 9 comprising a motor, means for controlling said motor, and a shaker bellows in the air line between the source of air under pressure and the reed in said electrical music system, said bellows being operable from said motor.

14. A timbre-setting device for an electrical music system as described in claim 8 comprising a motor, means for controlling said motor, and

means operable from said motor for causing a change in the setting of those resistors controlling the amplitudes of the component tones of a given harmonic order of every complex note produced by the system.

15. A timbre-setting device for an electrical music system as described in claim 7 comprising a plurality of variable electrical resistors controlling the amplitude of a given order of partial of each of the complex tones produced by the system and mounted on a shaft in such fashion that rotation of the said shaft will cause a uniform change in setting in all the said resistors, a motor rotating said shaft, and means for controlling the said motor.

16. In an electrical music system comprising a plurality of sounding reeds, a plurality of microphones associated with said reeds, electrical wave filters separating the outputs of said microphones into simple tones, and means for amplifying and reproducing the outputs of said wave filters, a keying system including means for electrically dissociating said microphonesfrom said wave filters except when said reeds are sounded.

17. The method of operating an electrical music system which includes the production of compound sound waves, the translation of said sound waves into compound electrical waves, the separation of said complex electrical waves into their component pure electrical waves, the separate amplification or reduction of each of said simple waves, and the coordination of said simple waves with a suitable amplifying and reproducing system.

18. A system for the production of musical tones comprising a reed, means for causing said reed to sound, means for producing electrical waves in accordance with the sound waves produced by said reed, means for separating the harmonic components of said electrical waves, means for amplifying or reducing separately each of said harmonic components, and means for translating said harmonic components simultaneously into audible tones.

RICHARD nownmn RANGER.

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