Keying system for electrical musical instruments

United States Patent ££3,544,697

<td> [72]</td><td> Inventor</td><td> Walter Munch, Jr. Covington, Kentucky</td>

<td> [21]</td><td> Appl. No.</td><td> 004,444</td>

<td> [22]</td><td> Filed</td><td> Jan. 25,1960</td>

<td></td><td></td><td> Continuation-in-part of Ser. No. 657,085, May 6,1957, abandoned.</td>

<td> [45]</td><td> Patented</td><td> Dec. 1,1970</td>

<td> [73]</td><td> Assignee</td><td> D. H. Baldwin Company Cincinnati, Ohio</td>

<td></td><td></td><td> a corporation of Ohio</td>

[ 54 ] KEYING SYSTEM FOR ELECTRICAL MUSICAL

INSTRUMENTS

Claims, 15 Drawing Figs.

[52] U.S.C1........................................................ 84/1.26,

84/1.13:328/84,216

[51] Int. CI.........................................................GlOh 1/02,

H03k 17/52

[50] Field of Search............................................ 315/84 5

187, 190,201,205; 328/66,67,68^ 69, 125 84’ 210:84/1.19, 1.23(GDT), 1.26, 1.24,1.01, LIL

1.13, 1.17-1.19

[56] References Cited

UNITED STATES PATENTS

2,484,612 10/1949 Dehnetal....

2,535,303 12/1950 Lewis................

2,728,030 12/1955 Green............

2,811,069 10/1957 Faulkner.......................

2,811,887 11/1957 Andersonetal..............

2,819,640 1/1958 Anderson.....................

179/18 307/243 315/84.5

84/1.01 84/1.01

84/1.26

<td> 2,823,310</td><td> 2/1958</td><td> Anderson................</td><td> 84/1.01</td>

<td> 2,828,659</td><td> 4/1958</td><td> Hanert.........................</td><td> 84/1.26</td>

<td> 2,878,708</td><td> 3/1959</td><td> Hanert.........................</td><td> 84/1.08</td>

<td> 2,916,957</td><td> 12/1959</td><td> Hanert.......................</td><td> 84/1.26</td>

<td> 2,951,412</td><td> 9/1960</td><td> Hanert.........................</td><td> 84/1.26</td>

<td></td><td colspan="2"> FOREIGN PATENTS</td><td></td>

<td> 66,516</td><td> 1/1927</td><td> Sweden........................</td><td> 328/27</td>

Primary Examiner—W. E. Ray Attorney—Hurvitz &amp; Rose

ABSTRACT: A gating circuit for transmitting electric oscillations corresponding to musical tones comprising a continuously operating source thereof, a load circuit, a common return to which said source and said load circuit are both connected, said gating circuit comprising a first gaseous discharge tube and a second gaseous discharge tube connected in series between said source and said load circuit, said tubes having ignition and extinction potentials, said source being coupled to said first tube, said oscillations having a peak voltage insufficient to ignite said tubes, said load circuit being coupled to the second of said tubes, and means for applying to said gating circuit at a point between said tubes a direct current potential of a value which will provide a potential above the ignition voltage of said tubes, said source, said load circuit, and said means for applying said direct current potential being connected to said common return, whereby said tubes are caused to fire alternately depending upon the direction ofthe oscillations, and whereby a signal is produced in said load circuit in the form of direct current impulses of the same frequency as said oscillations.

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PATENTED DECI 1970

3,544,697

SHEET 1 OF 3

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ATTORNEYS.

PATENTED OEC1 1970

3,544,697

SHEET 2 OF 3

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ATTORNEYS.

PATENTED DECI 1970

SHEET 3 OF 3

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<img file="US3544697A_D0005.tif" />

attorneys.

3,544,697

KEYING SYSTEM FOR ELECTRICAL MUSICAL INSTRUMENTS

This application is a contin’uation-in-part of my copending application Ser. No. 657,085, bearing the same title, filed May 6,1957, which is abandoned.

The invention relates to keying or switching systems, particularly those including means for obtaining percussive effects in electrical musical instruments, by which is meant a circuit arrangement resulting in a decay of the tone produced by a generator in an output system upon release of a playing key, the decay being in accordance with a predetermined curve. Without such provision, the release of the key would result in an abrupt cessation of the tone.

The percussive system is applicable to key or switch operated instruments of monophonic and polyphonic character, and will be described herein in connection with an electric organ. It is one of the objects of this invention to provide a keying or gating circuit which will be devoid of key clicks even though a simple make-and-break switch is used. Other objects have primarily to do with the attainment of percussive effects.

In an electric organ, even when equipped with a percussive system, in sostenuto playing, the predetermined tone decay characteristics are not ordinarily apparent as such to the ear, although an effect of reverberation may be achieved. When, however, the instrument is played in a staccato fashion, the decay characteristics become immediately apparent. With proper control of timbre and of the duration and characteristics of decay, tones may be produced which simulate the tones of bells, bars, plucked strings (as in a harp), chimes, struck strings (as in a piano), and the like. With vibrato, the effects of instruments such as the vibraharp may be closely simulated. The percussive system is arranged to be made effective or ineffective as desired by means of suitable stop tabs, so that it can be used alone or as an adjunct to other organ voices.

Hitherto in the obtaining of percussive systems, it has been necessary to provide for each generator output to be given the percussive effects, a relatively elaborate gating circuit comprising an expensive thermionic tube and other components.

It is an object of this invention to provide a gating circuit having few components, and making use of simple and inexpensive neon bulbs as hereinafter set forth.

It is an object of the invention to provide percussive means which are simple in nature, readily adaptable to printed circuitry, and capable of being combined with the generating system of an electrical musical instrument so as to simplify construction and save space within the organ console.

It is an object of the invention to provide a percussive system which coacts with a high impedance switching means for the normal organ tones, whereby substantial savings are made in the construction of the organ.

The invention will be described in connection with an electronic instrument such as that set forth in U.S. Pat. No. 2,233,948, issued Mar. 4, 1941 in the name of Winston E. Kock as inventor. Reference is made to this patent for the details of exemplary generator systems (although others may be used as, for example, the generator system of U.S. Pat. No. 2,555,038 issued May 29, 1951 in the name of Edward M. Jones), means for simultaneously deriving octavely related oscillations in different headers and producing voices therefrom by utilizing the outputs of the several headers alone and in combination, means for obtaining voices rich in odd order harmonics by outphasing, means normally consisting of filter networks for controlling timbre, and for the general organization of an exemplary polyphonic instrument. It will be understood, however, that the utility of this invention is not confined to the specific instrument of the said Kock patent. The objects of the invention set forth above, and others which will be set forth hereinafter or will be apparent to one skilled in the art upon reading this specification, are accomplished in that construction and arrangement of parts of which certain exemplary embodiments will now be described.

Reference is made to the accompanying drawings wherein:

FIG. 1 is a diagrammatic circuit representation illustrative merely of the principles of operation of a novel gating circuit of this invention.

FIGS. 2α, 2b, 2c and 2d are respective representations of the wave forms of oscillations existing at various points in the circuit of FIG. I.

FIG. 3 is a circuit diagram of a gating circuit containing means whereby the transmissivity of the circuit can be controlled at ill, and containing means for producing a controlled decay in the transmitted oscillations.

FIG. 4 is a circuit diagram of similar nature including means whereby the rate or time of decay can be varied.

FIG. 5 is a similar circuit diagram including means for controlling the shape of the decay curve.

FIG. 6 is a circuit diagram including means for minimizing high frequency feed-through.

FIG. 7 is a circuit diagram including all of the above features and showing how gating circuits for various oscillators may be combined in an output circuit.

FIG. 8 is a circuit diagram showing a modified circuit for achieving greater output.

FIG. 9 is a diagrammatic representation of a complete percussive system, including a partial showing of means for obtaining normal organ voices.

FIG. 10 is a circuit diagram of a type of gating circuit which is of especial value in applying percussion to the pedal clavier of an electrical musical instrument.

FIG. 11 is a circuit diagram of a modification of the circuit of FIG. 10.

FIG. 12 is a diagrammatic representation of a pedal clavier switching system including the circuit arrangement of this invention.

The gating circuit of this invention makes use of inexpensive neon bulbs, by which is meant gaseous discharge devices preferably of a type in which a pair of simple electrodes are mounted in parallelism in a neon atmosphere in a glass envelope. More expensive gaseous discharge devices may be employed; but the additional cost is not normally warranted. The preferred type of neon tube is the type known as NE-2. The bulbs are quite small and are very low in cost. While this does not constitute a limitation on the invention, for the sake of clearness the invention will be described in connection with the use of neon bulbs having a firing potential of 70 volt and an extinction potential of 50 volts.

In FIG. 1 an oscillator or generator 1 is shown as connected to two neon bulbs 2 and 3 in series to an output point 4. The oscillator is indicated as grounded at 5. Between the two neon bulbs is shown a supply circuit containing a resistor 6 and a source of potential 7, there being at 8 a connection to a common return, conventionally illustrated as ground. Beyond the two neon bulbs there is another circuit containing a load resistor 9, and connected to the common return at 10.

The generator 1 may be thought of as producing oscillations having a peak-to-peak voltage of between 20 and 100 volts with about equal positive and negative peaks. If the source of voltage 7 were not present, the illustrated circuit would not transmit oscillations from the generator 1 to the output point 4 because the peak signal amplitude of the generator is not great enough to fire the neon bulbs. If, however, the source of potential produces a potential of 70 volts or more, one of the neon bulbs will fire depending upon the direction of the generator voltage at the moment. As the generator voltage swings from positive to negative and back again, the neon bulbs will fire alternately. When the neon bulb 2 fires, the current flowing through the resistor 6 will flow through the generator. In this operation, the generator must supply a direct current path; but this is characteristic of the generators of the Kock patent referred to above in that the generator output is taken across a resistance to the common return, and similar provision may be made in the case of other generators. When the neon bulb 3 fires, the current flowing through resistor 6 will return to ground through resistor 9, developing at the output point 4 a rectangular half wave, having, however,

3,544,697 lowed by a period of relatively much slower decay. The system of this invention lends itself readily to the obtaining of effects of this character. FIG. 5 is illustrative of one mode of accomplishment. In this FIG., where again like parts are given the 5 same index numerals, the neon bulb 18 is shown as having applied to it a positive potential of 75 volts. In the particular organization, this means that while the bulb 18 will fire when the switch 16 is closed, and will remain conductive for a brief interval after the switch 16 is opened again, thus increasing the 10 rate of decay, it will continue to conduct for only a portion of the decay period. Thus, the tube 18 will reach its extinction potential prior to tubes 2 and 3, giving what may be termed a “double-rate decay” characteristic.

It will be understood by those skilled in the art that there is a small stray capacity across the neon bulbs. In some organizations, this may present no problem; but if difficulty is had with feed-through (which feed-through increases with frequency), the circuit may be provided, as illustrated in FIG. 6, with a bypass to ground containing a small capacitor 21 from the point between the neon bulbs 2 and 3. Resistors 22 and 23, respectively ahead of and after the neon bulbs 2 and 3 in the output line of the oscillator, are added to prevent the circuit from going into relaxation oscillations when the bypass includes ing the capacitor 21 is used. It is readily possible to select a suitable small value for the capacitor 21, which will reduce the feed-through to an acceptable level without impairing the operation of the circuit. The component values shown in FIG. 7 indicate that the bypass impedance provided by the capaci30 tor 21 (20 /quf.) is relatively low (about 8M at 1,000 Hz.) compared to the nonconductive state of the gas tubes 2 and 3, but of the same order of magnitude when the gas tubes 2 and 3 are conductive. In other words, the bypass impedance of approximately 8M is comparable in magnitude to the 2.2M value 35 of the gating sections which, in this FIG., comprise resistor 22 and tube 2 on the one hand and resistor 23 and tube 3 on the other.

FIG. 7 is illustrative of a useful gating circuit incorporating various of the features discussed above, and is also indicative 40 of the way in which a plurality of the gating circuits may be coupled together. Like parts have been given like index numerals. The output point 4 of the illustrated gating circuit is shown as located on an output header 24 to which other gating circuits may be connected as the points 25, 26 and 27. The ⁴³ output to tone color filters may be taken at the point 28, maintained above ground by a resistor 29. A dotted line box has been used in this FIG., to indicate that the switch 19, together with its connections to ground or the common return and to a source of positive potential of selected value, may be common to the several gating circuits, as at a collector 19α. The switch 16 for each gating stage will, of course, be a playing key operated switch, but it may be a simple make-and-break contact device. The switch 19 will normally be located on a panel of the instrument where the player will have access to it. Thus, ⁵⁵ it may be arranged to be operated by a stop tab, whereby the player can select the rate of decay desired; The percussive system will ordinarily have a plurality of tone color devices as hereinafter described, also actuated by stop tabs. It is within 60 the scope of the invention to cause the stop tab selectors to actuate a switch or switches which select a rate of decay appropriate to particular tone colors, and/or to vary the shape of the decay curve as set forth above.

In FIG. 8, the circuit is essentially similar to those 65 hereinabove described, excepting that the generator is isolated from the rest of the circuit by a capacitor 30, and a d.c. path to the common return is provided through resistor 30α. Thus current is prevented from flowing back through the generator, which reduces the tendency of the percussive cir70 cuit to pull the generator out of synchronism.

It will be seen from FIGS. 7 and 8 that exclusive of the switches, the preferred gating circuits of the invention comprise each three neon bulbs, not more than five resistors, and two capacitors. These elements are small in size and are readi75 ly adapted to interconnection by printed circuitry, as will be the same frequency as that of the generator signal. This is shown in FIGS. 2α to 2d inclusive. In FIG. 2α the generator output has been shown as a sinusoidal wave 11 for illustrative purposes only. Normally the generator output will have a complex wave form rich in harmonics, especially where tone colors are to be produced by filter networks.

FIG. 2b, as related to the illustrative sine wave of FIG. 2α, shows at 12 the wave form at the junction of the neon bulbs 2 and 3 and the resistor 6. When the voltage at this junction reaches the firing potential of the neon bulbs, the bulb 3 fires, lowering the potential at the junction to the operating potential of the bulb 3 plus the small voltage drop across the resistor 9. The neon bulb 2 is extinguished at this time since the voltage across it has become smaller than its operating potential. The bulb 3 will, however, continue to conduct until the generator voltage reaches —20 volts. At this time the firing potential of bulb 2 is reached. Bulb 2 fires and bulb 3 is extinguished. The voltage at output point 4 will be zero since the current in resistor 6 will be flowing through the generator. The bulb 2 remains conductive until the generator voltage reaches +20 volts, whereupon the bulb 3 fires, and the cycle is repeated. .

FIG. 2c will be seen to be illustrative at 13 of the voltage across the bulb 2; and FIG. 2d shows at 14 the voltage effective at the output point 4.

The current flowing in the resistors 6 and 9 depends upon the difference between the voltage applied by the potential source 7 and the operating potential of the bulb 3. It follows that the output voltage at the point 4 may be controlled by varying the voltage applied at 7. Turning now to FIG. 3, where like parts have been given like index numerals, it will be noted that a capacitor 15 has been inserted between the resistor 6 and the common return at 8, and that the source of potential 7 has been eliminated as such. However, a source of potential, not shown but indicated by the legend +150V, has been connected to the point in the supply circuit between resistor 6 and capacitor 15 through a single-pole, single-throw switch 16. Closing the switch 16 places! 50 volts across the capacitor 15 and renders the system transmissive as hereinabove explained. When the switch 16 is again opened, the capacitor 15 (previously charged while the switch was closed) will discharge through the resistor 6, maintaining the system in a transmissive condition until that voltage is reached at which the neon bulbs no longer fire. As the capacitor 15 which the neon bulbs no longer fire. As the capacitor 15 discharges, the output voltage at the point 4 will not remain uniform, but will decay, and the time of the decay will be determined by the time constant of resistor 6 and capacitor 15 acting together. Thus a percussive effect as hereinabove defined is produced. Exemplary but nonlimiting values for elements 6, 9 and 15 have been indicated in FIG. 3.

In attaining various percussive effects, it is desirable to be able to change or vary the rate of time of the tone decay. In FIG. 4 where again like parts have been given like index numerals, there is shown a means whereby this may be accomplished. Another circuit is shown as connected to the supply circuit between resistor 6 and capacitor 15. This circuit contains in series a resistor 17, a neon bulb 18, and a single-pole, double-throw switch 19. One of the contacts of this switch is connected to the common return as at 20; the other is connected to a source of positive potential, not shown, but marked +100V as an exemplary value.

If the switch 19 is in the common return position, the neon bulb 18 will fire when the switch 16 is closed. When the switch 16 is again opened, the current flowing in the neon bulb 18 will discharge the capacitor 15 more rapidly, thus shortening the decay time. When switch 19 is in the other position, the tube 18 will not fire, irrespective of the position of switch 16, and the decay rate will be unaffected, i.e. it will be the same as that obtained with the organization of FIG. 3.

In the simulation of certain percussive effects, a control of the shape of the decay curve is highly desirable. For example, in nianniikp tones, the initial decav is very rapid, but this is fol3,544,697 understood by the skilled worker in the art. The gating circuits take up little room and are preferably incorporated in the generator assembly of the instrument, especially since the generators may be connected directly to them, the switches such as switch 16 being located elsewhere, i.e. in connection with the playing keys.

Furthermore, the gating circuits disclosed are high impedance circuits and work very well in an electrical musical instrument with high impedance switching means for the usual organ tones such, for example, as capacitative switching means. Thus, in a complex polyphonic instrument, where the playing keys each operate a plurality of electrostatic switching means (so as to derive oscillations of different footages in different headers), it becomes possible to connect the several generators directly with the appropriate electrostatic elements of the appropriate switches, and to the gating circuits of this invention without the use of the isolating resistors heretofore found necessary with low impedance output paths. The cost of these resistors is thus saved. Because electrostatic switches produce a gradual onset of the tones, there is no need to employ gradual contact switches of the resistive type.

In the percussive voices themselves, a gradual onset of the tones is not necessary, but is produced to a considerable degree by the fact that the capacitor 15 must charge through resistor 31 when the switch 16 is closed, and the attack may be controlled by varying the value of resistor 31. The structures of this invention are thus adapted to be used as keying or switching means for the tones of electrical musical instruments, with or without percussion, to avoid key clicks, in lieu of other keying devices such as resistive switches or the capacitative keying switches just mentioned.

While other forms of tone color circuits such as ordinary filters may be employed, it is preferred to use vacuum tube filter or voicing circuits with percussive circuits, particularly in view of the output wave form illustrated in FIG. 2d hereof. The percussive gating circuits of this invention are capable of use in the manner set forth in the copending application of Alfred J. Bissonette and Frank J. Kramer, Jr., Ser. No. 621,769, filed Nov. 13, 1956 and entitled ELECTRONIC MUSICAL INSTRUMENT, now U.S. Pat. No. 2,986,964. A simplified arrangement of this type is illustrated in FIG. 9. The so-called vacuum tube filters are preferably vacuum tube amplification stages employing negative feed back; and the voicing obtained is a function of the frequency selectivity of the passive elements in the feed back loop. Each stage is characterized by a “parallel T” network. In a three-voice system, three types of networks may be employed, viz. (a) a network tuned to exhibit a null in the fundamental frequency of operation; (b) a network tuned to exhibit a null at twice the fundamental frequency; and (c) a network tuned to exhibit a null at four times the fundamental frequency. Since the networks are used in a negative feed back loop, the overall stage frequency will peak at the null frequency. Thus, if the null is at the fundamental frequency, the output will be nearly sinusoidal. If the null is at twice or four times the fundamental frequency, entirely different and rich wave forms will result. It will be understood that many more than three voices may be provided if desired. Bissonette and Kramer found that the vacuum tube filters would each handle the output of four generators related as adjacent semitones. This, coupled with the fact that a filter with a negative feed back loop tuned to null at twice the fundamental frequency of a given oscillator constitutes a filter with a negative feedback loop tuned to null at the fundamental frequency of ari oscillator an octave above the first, and so on, enabled Bissonette and Kramer greatly to diminish the number of vacuum tube filter circuits required for any given organ range. This system is equally applicable to the gating circuits of the present invention.

The gaseous tube percussion circuits of this invention are particularly adaptable, without the need for additional impedance-matching circuitry, to systems employing high-impedance key switches such, for example, as disclosed by Hugh LeCaine in an article entitled “Touch-Sensitive Organ Based on an Electrostatic Coupling Device,” in Journal of the Acoustical Society of America Vol. 27, No. 4, 781-786, July 1955. To keep signal-to-noise ratios at acceptable values, such switching systems necessitate relatively high generator voltages, of the order of that required to operate percussion circuits of the type disclosed in my application herein. In FIG. 9 the generator 1 is shown as coupled directly to the percussive or gating circuit 32, which may be the circuit illustrated in FIGS. 7 or 8 hereof. Three other adjacent generators marked la, lb, and 1c are shown as directly coupled respectively to their percussive circuits 33,34, and 35. The generators 1 to 1c will encompass a range of four semitones, e.g. if generator 1 is C, generator la will be C#, generator 1ft, D, and generator 1c, D#. The gating circuits respectively for these several generators will be coupled together as at 24 so that their outputs can be transmitted selectively to various vacuum tube filters as hereinafter explained.

Each gating circuit will have its switch 16, 16α, etc. connected as shown to a bus fed by d.c. source 16d. In FIG. 9 the generator 1 is shown as having a branch connection 36 to a header 37, preferably through a high impedance switch diagrammatically indicated at 38 as a variable capacitor. Any form of switch may be employed. Such a switch may be but is not limited to that described in the LeCaine article referred to above. It will be key actuated, as will the switch 16. A key has been diagrammatically shown at 39, and dotted lines indicate that this key simultaneously actuates capacitive switch 38 and the make-break switch 16 of the gating circuit 32. Similarly the generator la will have a branch lead 40 to the header 37, the lead containing a capacitive switch 41, and so on for the other generators.

It will be understood, particularly in the light of the Kock patent above referred to, that each of the generators may also have branch connections to capacitative switches operated by octavely related keys, the switches being connected to various headers in which the tones may be correlated in terms of footage. This has not been illustrated. Yet again, in a plural keyboard instrument, the generators may have branch connections to switches operated by the keys of the other keyboards. This also has not been shown.

The rectangles 42,42α, and so forth in FIG. 9 indicate other groups of four adjacent oscillators together with their respective gating stages. These oscillators will also be connected to the header 37 through groups of capacitative key switches such as are diagrammatically illustrated at 43, 43α, etc. At intervals along the header 37 capacitors 44,44α, etc. may be inserted for the purpose of attenuating groups of notes in lower registers with respect to higher registers, thus producing a more uniform loudness in view of the opposite effect of lowpass filters which will be employed for tone color.

The header 37 is connected to an amplifier indicated at 45. This amplifier may, if desired, be a cathode-follower amplifier circuit such as is shown in FIGS. 6—13 on page 106 of Electron-Tube Circuits, by Seely (McGraw-Hill, 1950).

The output of the amplifier 45 is provided with a plurality of paths to a reproduction system through various tone color filters as taught in the Kock patent above set forth. The rectangles 46, 47, 48 and 49 are representative of tone color filters. The filters are provided with switches 50, 51, 52 and 53 normally operated by stop tabs on the console of the instrument. There may be as many tone color filters as desired for tonal flexibility in the instrument and various ones of the tone color filters may derive oscillations from other headers than the header 37 or from combinations of headers containing octavely related oscillations, or from combinations of headers in which respectively the oscillations are out of phase, all as taught in the Kock patent.

The output from the tone color system may be delivered by a lead 54 to a preamplifier 55, and thence to a main amplifier with volume control and to one or more loud speakers (not illustrated).

The output from the gating stages 32 to 35, collected in the header 24, may be delivered through a switch 56 and lead 57

3,544,697 to the common return; and a source of d.c. potential 79 is conto a vacuum tube filter of the type described above and diagrammatically illustrated by the rectangle 58. Or the output may be delivered through a switch 59 and a lead 60 to a vacuum tube filter 61. Yet again, the output may be delivered through a switch 62 and lead 63 to a vacuum tube filter 64. It may be assumed for purposes of this disclosure that the filter 58 peaks at the average fundamental frequency of the oscillations coming through the gating stages 32 to 35, that filter 61 peaks at twice that frequency, and filter 64 at four times that frequency.

Switches 56, 59 and 62 are parts of relay gang switches, as illustrated. The gang switches are provided with electromagnetic operating devices actuated by stop tab switches controlling the percussive waves. These have not been illustrated but will be readily understood by the skilled worker in the art, or can be ascertained from the copending Bissonette and Kramer application referred to above.

In a similar fashion, and by means of the same tone color relays, the group of gating stages represented by the rectangle 42 can be connected selectively to vacuum tube filters 65, 66 and 67. The group of gating stages represented by the rectangle 42α is similarly connectable to vacuum tube filters 68, 69 and 70. The average frequency of the oscillations in the gating stages forming the group 42fe is octavely related to the average frequency of the oscillations in gating stages 32 to 35. As a consequence, switch 71 will connect the output of 42h to vacuum tube filter 61, now acting as a filter peaking at the fundamental frequency. Similarly, switch 72 will connect the output of 42i to vacuum tube filter 64 now acting as a filter peaking at twice the fundamental frequency. Switch 73 will connect the output of 42b to vacuum tube filter 74. This arrangement is repeated throughout the assembly.

While three vacuum tube filters have been shown for each group of gating stages, their number may be multiplied as desired for different tonal effects. It is also within the scope of the invention to employ band pass filters of linear character for the obtaining of some or all of the percussive voices.

The output leads ofthe various filters in the percussive assembly are connected to a bus 75 which carries the oscillations to the preamplifier 55.

In the arrangement illustrated, the instrument may be played with organ voices alone, or with percussive voices alone, or with a combination of the two types of voices. Where organ voices are combined with percussive voices, the effect of percussion will still be apparent in staccato playing, but the tonality will be modified, thus providing great richness and variability of tone. It will also be apparent that percussive effects may be used as accents in the playing of organ music.

The gating circuits of this invention have the advantage of being comparatively inexpensive so that without unduly increasing the cost of the instrument percussive effects may be made available on more of the claviers of the instrument or in a greater range on any one clavier, or both. Especially valuable results are obtained by making percussive effects available on the pedal clavier.

A basic circuit comprising a resistor, a first gaseous discharge tube, a second gaseous discharge tube and a second resistor in cascade, as shown in FIG. 7, for example, requires a generator source which is substantially devoid of a d.c. component. Where the oscillation source delivers such a component, an rc network between the generator and the gating stage may be employed as shown in FIG. 8. It was found that the blocking capacitor could be placed between the first and second gaseous discharge tubes if the generator signal contained a d.c. component having a value no greater than about 20 to 30 volts, and providing the gaseous discharge tube was ofthe NE-2 type. Such a circuit is illustrated in FIG. 10 where following the oscillation generator 1 there is a resistor 22, a neon tube 2, a capacitor 76, a neon tube 3, a resistor 23 and a load resistor 9 in cascade. Resistors 77 and 78 arc connected respectively to either side of the capacitor 76 and to the key switch 16 and one side of a second capacitor 15. The other side ofthe last-mentioned capacitor is grounded or connected nected between the switch 16 and the common return.

This circuit has the additional advantage that the firing potentials ofthe neon tubes do not have to be as well matched as in other circuits hereinabove described.

A further simplification of this circuit is indicated in FIG. 11 where like parts have been given like index numerals. Here a single resistor 80 located between the neon tubes takes the place of the two resistors 22 and 23 and serves the same purposes. It suppresses the high frequency oscillations which occur when no series resistance is used.

FIG. 12 illustrates a pedal percussive system using the gating circuits of FIG. 11. Sources of oscillations are indicated respectively at C, C#, D,C. For the derivation of oscillations of nonpercussive character from these generators, seriesconnected switches are employed, each connected with a key ofthe pedal clavier. The first of these switches is designated at 81 and is a single-pole, single-throw switch. Others of these switches, designated 81α, 81b, 81n are double-throw, singlepole switches. The connection of these switches in series insures that only one note in the pedal clavier can sound at any one time; and it is only necessary to connect the lead from the last of these switches through appropriate tone color circuits (not shown) to a pedal output system 82.

The gating circuit of FIG. 11 will be recognized in the dotted box 83. Other boxes 83α, 83ft, 83u will be understood as representing similar gating circuits. Each gating circuit has a single-pole, single-throw switch 84, 84α, 84b, 84n. These switches are connected together and through the source 79 of d.c. potential to the common return.

The several gating circuits are connected to a common bus 85 which will normally contain a percussion stop switch 86. The bus may be connected to a separate pedal percussion output system 87, or if desired, the output system 87 may be omitted and output of switch 86 may be connected to the pedal output system 82. The switches 84 etc. of the gating stages are mechanically coupled with the generator switches 81 etc. ofthe pedal keyboard as indicated by dotted lines. The system is a simple one especially desirable for pedal percussive use where the low frequencies involved minimize feedthrough.