US2986964A - Electronic musical instrument - Google Patents

Description

June 5, 1961 A. J. BlssoNl-:TTE ET AL 2,986,964

ELECTRONIC MUSICAL INSTRUMENT Filed NOV. 13, 1956 2 Sheets-Sheet 1 Bylluw/ wa...

ATTORNEYS.

June 6, 1961 A. J. BISSONETTE ET AL 2,986,954

ELECTRoNc MUSICAL INSTRUMENT Filed NOV. 13, 1956 2 Sheets-Sheet 2 62 .90K

74 250V. 90V. 35V.

United States Patent C 2,986,964 ELECTRONIC MUSICAL INSTRUMENT Alfred J. Bissonette, Milford, and Frank J. Kramer, Jr.,

Cincinnati, Ohio, assignors to The :Baldwin Piano Company, Cincinnati, Ohio, a corporation of Ohio Filed Nov. 13, 1956, Ser. No. 621,769 8 Claims. (Cl. 84-1.26)

The invention relates to electronic musical instruments of the organ type wherein, selectively, effects may be obtained such that upon release of the playing keys the tones attenuate in accordance with a predetermined exponential curve. Such effects will be referred to hereinafter, for convenience, as percussive eifects; and they are useful in producing tones simulating those of bells, bars, plucked strings and the like.

One of the objects of the invention is the production of an electronic organ capable of being played in the ordinary way with the production of organ tones, but with which the musician can obtain percussive effects as desired, with or without the immediate actuation of stop means. This is not merely a matter of the provision of selectable percussive voices. It involves the provision of a system in which, when the instrument is played either sostenuto or with normal tone duration, percussion will not be evident as such (although it may contribute to an eifect of reverberation) whereas when the instrument is played staccato, percussion will be immediately perceptible. Thus percussive effects become possible as accents in ordinary playing.

It is an object of the invention to provide an instrument in which not only is a Wide variety of definitive percussive voices available, but in which definitive percussive voices may be modified by the usual or available organ voices to give great flexibility of tone color.

It is an object of the invention to provide a means whereby the number of tone-envelope circuits may be diminished for a given range.

It is an object of the invention, in the use of filters with percussive circuit means, to provide an arrangement whereby individual lters may be used in a plurality of stages and for dilferent purposes, thus diminishing the number of filters required.

These and other objects of the invention which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications are accomplished by that structure and arrangement of parts of which exemplary embodiments will next be described. Reference is -made to the accompanying drawings, wherein:

FIGURE l is a circuit diagram showing the essentials of a simplified circuit for imparting a percussive effect to oscillations elsewhere generated.

FIGURE 2 is a partial circuit diagram showing means whereby the number of percussive circuits employed can be made less than the full number of tones within the gamut (or portion thereof) of the instrument to which percussive eects are to be imparted.

FIGURE 3 is a partial circuit diagram illustrating the percussive assembly of an electric organ.

FIGURE 4 is an adjunctive diagram showing voicing and decay-duration selection means for attachment to the organization of FIGURE 3.

FIGURE 5 is a circuit diagram for alternate voicing means.

A simplified percussive circuit is shown in FIGURE l as comprising a vacuum tube having an envelope 1, a cathode 2, a grid 3` and a plate 4. The cathode is connected through a capacitor 5 to a point 6 from which a lead containing a resistor 7 goes to the grid 3l and another lead containing a resistor 8 goes to ground. 'Ihe grid has an input lead containing a capacitor 9 and con- ICC nected to a source of electrical oscillations of audio frequency (not shown). A switch 10 is connected in shunt with the capacitor 5l. A source of positive voltage is connected as at 11 between the cathode and a ground connection (not sho-wn).

When the switch 10 is in the open position, the voltage across the capacitor 5 is equal to the voltage applied to the cathode of the tube. The signal (oscillations from a suitable generator) is applied to the grid circuit through the capacitor 9; but the signal will not be transmitted by the tube because the tube is biased to cut-oi. Closing the switch 10 discharges the capacitor 5, resulting in a zero grid-to-cathode voltage. The cut-olf bias is thus destroyed, and the tube becomes conductive, transmitting the signal to an output circuit through the capacitor 12. It will be understood that the plate of the tube will be connected to a source of B+ voltage through a resistor 13.

So long as the switch 10 remains closed, the zero grid bias is maintained; and the generator signal will be transmitted through the tube at maximum level. Opening switch 10 causes the capacitor 5 to become charged again. The capacitor 5 and the resistor 8 form a time-delay combination which causes the capacitor to charge gradually at a predetermined rate. As the capacitor gradually charges the tube is driven to cut-off; and the transmitted signal decays exponentially.

If the switch 10 (normally open) is operated by the playing key of `an electric organ it will serve as a means for deriving the signal in the output circuit at the times desired in accordance with the requirements of a musical composition. As explained above, the signal will be maintained so long as the key is depressed and the switch 10 remains closed, giving a continuous organ tone. If the time duration of the organ tone is relatively long with respect to the period of the exponential decay, the percussive effect will not be noticeable as such. If, however, the key is struck and immediately released, as in staccato playing, the exponential decay will impart to the tone percussive characteristics similar to those of the tones of bells, bars and plucked or struck strings.

Although we have herein described a vacuum tube percussive circuit, it is within the scope of our invention to use circuits employing transistors or other suitable devices.

Percussion thus becomes a useful adjunct in the playing of organ music. It is intended that the percussive organizations herein described will be combined with the features of an electric organ adapted for the production of non-percussive tones. These features are not herein illustrated because they are well known in the art. Without limitations, an electric organ which is suitable for use in this connection is that shown in U.S. Letters Patent No. 2,233,948 in the name of Kock. By way of a brief description, the electronic instrument of this patent comprises a series of electronic oscillation generators adapted to produce electrical oscillations rich in harmonics so that various voices may be obtained through the use of formant filter means. Preferably the various generators are organized into octavely related series, each with a master oscillator and a number of controlled oscillators. Normally there will be an oscillator for each tone within the gamut of the instrument, although it is possible to derive some tones otherwise, as by methods of frequency multiplication or division.

Oscillations are derived from the various generators into suitable headers by means of switches operated by playing keys in the manual or manuals of the instrument or in a pedal keyboard. Preferably a plurality of switches is operated by each key, the switches so operated are connected to octavely related generators through appropriate isolating resistors, and are also connected to different headers so that upon depression of a key,

eight-foot oscillations will be derived in one header, four-foot oscillations will be derived in another header, and so on. 'Ihe outputs of the various headers, either singly or in combination, are sent selectively through various formant or other filter means to an output system comprising an amplifier and one or more loud speakers. In this way a wide variety of voices may be obtained, the Voices being selected at will through the operation of stop tabs controlling filter circuit switches by the musician. Additional woodwind tones (which are rich in the odd-order harmonics) may be produced by combining octavely-related oscillations which are out of phase with each other. In such combined oscillations the even-order harmonics tend to cancel each other. The output may be filtered as desired. Y

Preferably the key switches aforesaid are of the resistive type to minimize key clicks. Exemplary resistive switches are shown in the Kock and Jordan U.S Letters Patent No. 2,215,124. Although these switches have some effect on the tone-envelope at the onset and conclusion of the tones, their primary effect lies in preventing surges at the instant a generator is connected to a header. They do not normally produce percussive effects, although mechanical means for this purpose have been devised.

To provide an instrument with the ability to produce percussive effects, within the purview of this invention, additional switches, corresponding to the switch of FIGURE l, will be arranged to be operated by the playing keys; and tones will Kbe derived by means of additional connections to the oscillation generators through percussive circuits such as that hereinabove described. The outputs of these percussive circuits, with suitable provision for voicing, may be fed to the same or a different output system.

There is no need that the switch 10l be resistive in character. Simple make-and-break switches are employed. The operation of the switches, however, should be synchronized with the operation of the other organ key switches. Preferably the switches 10 should close either simultaneously with or immediately following the closure of the resistive switches; and the switches 10 should be arranged to open either simultaneously with or after the effective opening of the resistive switches so that the percussive effect of the exponential decay will not be masked by a persistence of non-percussive tones derived from the same keys in the instrument.

Percussive circuits such as have been described above result in a reversal of the phase of a signal. Since the instrument of this invention is intended to have a normal organ output produced by conventional means and also a percussive output where desired, on many occasions during playing oscillations from the headers and filter system would be mixed with oscillations derived through the percussive assembly, it is desired that these oscillations be not combined in out-of-phase relationship, since otherwise serious disturbance of the over-all voicing may occur. This can be accomplished by employing in connection with the oscillations derived through the percussive system voicing means in the nature of electronic voicing circuits as hereinafter described. These result in a re-reversal of t-he phase of the oscillations and eliminates the difficulty aforesaid. Alternately, as will be described hereinafter, inductance-capacitance voicing circuits can be employed, and phase-reversal can then be accomplished by separate means, such as transformers or appropriate electronic circuits. Either type voicing means are of especial value in producing voices particularly appropriate to the tones of bells, bars, plucked strings, etc.

The means herein described thus far involve separate means for deriving oscillations from the normal generators of the instrument, separate percussive circuit means and separate voicing means which may be and preferably are connected to the output system already forming part of the conventional instrument. Thus, the organization of this invention is not only adapted to form a part of the original construction of an instrument, but is also well adapted for manufacture and sale as an organization which may be installed in instruments already in use.

The instrument of this invention may be played as a conventional organ using the conventional stops provided in such an instrument. It has also certain percussive stops appropriately marked. When these alone are used, percussive effects are obtained in staccato playing which by reason of the Voicing as well as the exponential decay characteristics are particularly appropriate to the production of tones simulating those of tone producing instrumentalities which have percussive characteristics, such as bells, bars and plucked or struck strings already mentioned. Since in the exemplary instrument the effect of vibrato is applied to the oscillations at their sources, it follows that vibrato may be imparted to the percussive tones by the same means and through the same controls (stop tabs or the like) as are conventional in the instrument. Or the stop tabs controlling certain percussive voices may be arranged automatically to actuate vibrato control means. Thus, in the practice of the invention it is possible Very closely to simulate the tones of instruments such as the Xylophone-like instrument employing metallic bars and airvibrato means, sometimes known as the vibra-harp.

It will be understood that irrespective of the sole use of the percussive stops the percussive eect will be very greatly diminished or will become unnoticeable if the instrument is played sostenuto as in ordinary organ playing; and for this the voices controlled by the percussive stops will be found quite pleasing.

The conventional organ voices may be employed along with the percussive voices, where desired. Again, as explained above, sostenuto playing will diminish the percussive effect or render it unnoticeable as such; and the result is a combination of voices. When both types of stops are being used, staccato playing will give definite percussion; and the result of the addition of normal organ voices to the opposite percussive voices is to modify the percussive tonality in ways which are useful and highly pleasing.

In view of these factors as outlined, it becomes possible in the playing of a composition by ordinary organ techniques, to employ percussive effects as accents, without taking time to shift sop tabs, since any note, chord or run can be given a pronounced percussive effect merely by playing it in a sufficiently staccato fashion, with such control of volume through the expression pedal, as may be desired.

Arrangements may be made for the obtaining of percussive effects respecting all of the keys of all of the keyboards of a multi-keyboard instrument. `In most instances, however, it will be found sufiicient to provide for percussion only on the swell manual of a two-manual instrument or only in the upper register, say, of a single manual instrument with'a divided keyboard.

As thus far described, it will be evident that a separate percussive circuit will be required for each note in the instrument with respect to which percussion is desired. A means whereby a single percussive circuit may be used for -two yadjacent notes is illustrated in FIGURE 2. This system employs relays which are differentially actuated upon the depression of either of adjacent playing keys to switch the input of a percussive circuit from `one generator to another. This will preclude the simultaneously derivation of adjacent semi-tones if they happen to be switched by the same signal relay; but this will not normally be important. Provision is made whereby if Ithe -keys representing two such semi-tones are simultaneously actuated only one of the semi-tones will result in a signal.

Assume for purposes of explanation that the instrument or section thereof to which percussion is toy be applied has a generating system with a range of four octaves, fortyeight semi-tones. The semi-tones within this range may be grouped C Cil, D Dit, E F, Fit G, Gil A, A# B and so on. If a single switching relay is provided tot handle all of the C C# tones, another tall of the D Dit tones and so on, it will be evident that only six signal switching relays will be required. The circuits appropriate to one such switching relay are diagramed in FIGURE 2.

In the figure, four percussive circuits are shown in tandem, the tubes of which are respectively indicated at 14, 15, 16 and 17. The circuits in connection with these tubes are those described above in connection with FIG- URE l. There is a common lead 18 for the B+ voltage, and a common lead 19 for the cathode biasing voltage designated +V. The input circuit leads of the several percussive circuits are connected as shown to the movable contact elements 20, 21, 22 and 23 of a relay 24 having a biasing means diagramed at 25 and a magnetic operating means 26. Leads from the C and Cil generators of the instrument are brought out to cooperating contacts marked respectively 136C, 138C etc. In the relaxed or normal position of the relay the movable contacts 20 to 23 will make connection with the C# leads. lf, however, the solenoid 26 be energized, the movable contacts will make connection with the C leads. There is a holding circuit for the relay comprising a movable contact 27 and a stationary contact 28, so arranged that when the relay is actuated it will remain in the actuated position until the holding circuit is broken.

C and C4 playing keys are indicated respectively at 29, 30, 31, 32, 33, 34, 35 and 36. In the arrangement herein disclosed each playing key actuates two switches. Thus depression of the C key 29 closes a normally open switch 37 in the relay holding circuit while another normally open switch 38, being simultaneously closed, shorts and discharges the capacitor 39 of the first percussion circuit to destroy the cut-off bias on the tube 14. This is because the switch is connected by lead 40 to one side of the capacitor and also connected to the other side of the capacitor at the point 41 also marked +V in the diagram. Similarly the C key 31 is provided With a normally open switch 42 in parallel with the switch 37 and a normally open switch 43 which is connected between the +V point and the other side of the percussive capacitor in the stage represented by tube 15. The C key 33 has a normally open switch 44 in parallel with the switch 37 and a normally open biasing switch 45 connected to discharge the blocking capacitor in the percussive stage represented by tube 16. The C key 35 has a normally open switch 46 connected in parallel with the switch 37 and a normally open switch 47 arranged to discharge the capacitor in the percussive stage represented by tube 17. Thus upon the actuation of any C key in the group, an appropriate C oscillation will be derived in an output system through an appropriate one of the percussive circuits. The output points of these circuits are designated respectively 48, 49, 50 and 51. Once any of the C keys has been depressed, the relay will remain in the actuated position because of the holding circuit aforesaid until the actuation of a Cit key as hereinafter explained.

The Clt key 30 is provided with a normally closed switch 52 located in a lead 53 which is connected to a source of power for the solenoid and holding circuit. The source of power is not shown. It will be understood as being grounded or as having some other suitable return to the solenoid circuit. The C# key 30 also actuates a normally open switch 54 which is connected (as above explained) to short the capacitor 39 in the first percussive stage. It will be evident that actuation of the Cil key 30 will not only result in the derivation of C# oscillations through the first percussive stage, but will also effect the return of the relay to the normal or relaxed position (illustrated) if the relay was being held in the actuated position because of previous depression of a C key.

The C# keys 3-2, 34 and 36 are provided respectively with normally closed switches 55, 56 and 57 in series in the lead 53. The opening of any one of these switches will break the power connection to the solenoid and holding circuits. These C# keys are also provided respectively with normally open switches 58, 59 and 60 connected (as hereinabove explained) to discharge the capacitors and destroy the blocking bias in appropriate ones of the other percussive stages.

Circuit arrangements for the other tive relays in the system, i.e. the D Dit relay etc., will be similar and do not need to be separately described.

Should a C key and a C# key be actuated simultaneously only a C# signal will sound, because the power will have been cut oif from the solenoid, and the relay will either return to or remain in the illustrated relaxed position.

Figures 3 and 4 taken together show an assembly of apparatus forming the percussive section of an instrument such as herein discussed. Percussive circuits of the type hereinabove Set forth produce a satisfactory tone envelope, but the wave form of the signal is not itself appropriate for the purpose. Also, it is desirable to have a plurality of Wave forms available for different percussive voices.

In view of this, frequency-selective ci-rcuits are employed, referred to for convenience hereinafter as voicing circuits. These circuits may be vacuum tube amplification stages employing negative feed-back; and the voicing 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 are employed, viz: (a) a network tuned to exhibit a null at the fundamental frequency of operation; (b) a network tuned to exhibit a null at twice the yfundamental frequency, and (c) a network tuned to exhibit a null at four times the fundamental Ifrequency. Since the networks are used in a negative feed-back loop, the over-all stage frequency response 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 yfundamental, entirely different and richer wave forms will result. The use of vibrato with `any or all of these wave forms provides yet another means of varying the tonal quality of the system. It will be understood that many more than three voices may be provided if desired. yIt will also be understood that L-C circuits of the type illustrated in FIGURE 5, described hereinafter, may be used in place of electronic type frequency-selective circuits.

It would ordinarily be supposed that a separate series of voicing circuits would have to be provided for each percussive circuit in the instrument. This, however, is not the case. It has been found, first, that each voicing circuit is capable of handling the output of four percussive circuits representing four adjacent semi-tones. This immediately cuts down the required number of voicing circuits. Second, a voicing circuit having a network tuned to null at twice the operating frequency of a group of adjacent semi-tones in a lower register can serve as the voicing circuit having a network tuned to null at the operating frequency of the corresponding group an octave above, and so on. Cross-sections for this purpose are provided, and the required number of voicing circuits is still further cut down. In the particular embodiment, the selection of voicing circuits is accomplished by means of solenoid-operated gang or relay switches or the like, the cross-connections being located on the output sides of these switches.

In the embodiment of FIGURE 3, provision is indicated for ten groups of percussive circuits providing a range of forty semi-tones or something over three octaves, with which sixteen voicing circuits are employed giving a range of three voices. These factors, however, may be varied as desired by multiplication of parts.

In the assembly shown in FIGURES 3 and 4, use is made of certain improvements in percussive circuits and assemblies thereof set forth and claimed in the copending application Serial No. 621,807 of Walter Munch, Jr., entitled Percussive Circuit and Assembly, now Patent No. 2,918,576. Referring to FIGURE 3, the letter A designates a group of four percussive circuits each having a thermionic element comprising a plate, a grid and a cathode. This element may be half of a double triode tube. Such half tube is indicated at 61 in FIGURE 3. The grid has an input circuit 62 containing a capacitor. There is a grid resistor 63 as hereinabove described. The cathode of the tube is connected to a source of positive potential indicated by the indicia 35 v.

At the bottom of -FIGURE 3 there will be seen a multiple power transformer 64. One of the secondaries of which 65 is connected to a full-wave rectifier tube 66, the output of which feeds a smoothing filter network indicated at 67. This network has taps delivering respectively thirty-live volts, ninety volts and two-hundredifty volts, so marked. The cathodes of the several tubes in the several percussive stages will be connected to the 35 v. tap. The ninety volt tap of the system forms the plate supply for the several percussive stages and is connected as at 90 v. through a resistor to a lead 68 which is common to the tubes in the group A. The time-delay capacitor 69 is connected to a tap G at the bottom of FIGURE 3 which results in its being returned to the cathode through a large capacitor 70 and to ground through a resistor 71. The time-delay resistors (resistor 72 of the first stage) are connected to a lead 73 which through terminal `5 of a plug-in connector 74 goes by means of a lead 75 to the blade 76 of a threeway switch (FIGURE 4). One of the contacts of this switch is connected as at 77 to ground. Another contact is connected through lead 78 and terminal 8 of the plug-in connector in a resistor 79. The third contact is connected through a lead 80 and terminal 9 of the plug-in connector 74 to a network in which it is separated from ground by resistors 81, 82, 83 and 79, pairs of these resistors being in parallel. The switch having the blade 76 is a selector switch determining the rate of tone decay of the several percussive circuits, and it does this by determining the level to which the capacitor 69 discharges.

The wiring for the four percussive stages in the group A is the same. The plates of the several stages are connected together by means of the lead 68; and a signal take-olf circuit comprising a capacitor 84 and a resistance 85 connects the plate lead 68 with a signal lead 86 which is returned to ground potential by a resistor 87. The input leads of the several stages may be brought out to a plug-in connector 88 as shown. Leads from the grid side of the time-delay resistors of the several percussive stages (such as the lead 89 from resistor 72) may be brought out to a plug-in connector 90 by means of which they are connected to playing key switches. One of these switches is indicated at 91 in FIGURE 3. The switches are returned to the 35 v. tap.

The specific arrangement of percussive circuits, which as aforesaid is the development of Walter Munch, Jr., has certain specilic advantages. Since the rate of decay is determined by the level to which the delay capacitor discharges, the gain does not vary with the extent position of switch 76. By returning the time-delay capacitor to ground through a resistor, ciphers are avoided if the capacitor becomes leaky. By returning the capacitor to the cathode through a large capacitor 70, key clicks are avoided when a number of notes are played simultaneously or in rapid succession. Moreover, the manner in which the stages are coupled involves a simplification of parts.

The blocks designated A1 to A9 represent in FIGURE 3 additional groups of percussive circuits which are similar to group A. Thus if group A provides percussive circuits for C, Cil, D and Dit, group A1 will provide circuits for E, F, Fll and G, and so on, in ascending register. Each group is shown as having a pair of leads. Thus the lead 92 of the group A1 may be considered as a cable made up of the input leads of the four percussive stages in the group while the lead 93 may be considered as a cable made up of the leads to the several key switches for the group.

The output lead 86 for the group A is connected to switches 94, 95 and 96 forming parts respectively of gang or relay switches designated respectively as 97, 98 and 99. If the gang switch 97 tbe actuated so as to close the switch 94, the output of percussive `group A will be sent through lead 100 to a vacuum tube lter marked B in FIGURE 3. This lter does not require detailed description but comprises a vacuum tube 101 with appropriate circuits involving a negative feed-back loop of parallel T form 102 designed to null at a frequency substantially that of the operating frequency of the circuits in group A. What this means is that if group A comprises C (130.81), C# (138.59), D (146.83) and Dit (155.56), the network 102 will be designed to null at 142.5 cycles. As explained above, the result of the negative feed-back is to cause the gain of the amplilier stage B to peak at the null frequency. Consequently signals from group A sent through the vacuum tube iilter B will have sinusoidal characteristics.

If, instead, the relay switch 98 be actuated, switch 9S will be closed, and the output in lead 86 will be sent through lead 103 to a vacuum tube lilter designated B1. This is a similar circuit; but it has a negative feed-back loop `104 designed to null at a frequency twice that of loop 102.

Similarly if the relay switch 99 be actuated the result of closing switch 96 will be to send the output of lead 86 through lead 105 to a vacuum tube lter B2. This again is similar excepting that its negative feed-back loop 106 is designed to null at a frequency four times that of loop 102.

There are a plurality of other vacuum tube iilters in the system designated B3 to B15 inclusive.

If group A of percussive circuits handles the notes C to Dl?, it will be evident that group A3 will handle the same notes an octave above. It will further be noted that when relay 97 is actuated the output lead 107 of group A3 will -be connected by means of the switch I4108 to lead 103 and that the vacuum tube filter` B1 now acts as the fundamental frequency lter for group A3. Similarly, when relay 98 is closed the result of closing switch 109 will be to connect output lead 107 to lead lfor the vacuum tube filter B2 which now acts as the twice-fundamental filter for group A3. The result of actuating relay 99 will be to close switch 110 thereby connecting the lead 107 from group A3 to vacuum tube filter B9 which is the four times fundamental filter for group A3. This type of arrangement is carried throughout the assembly so that substantial saving in the number of vacuum tube filters is effected. Note from the diagram that the lter B2 also acts as the fundamental frequency lter for group A6.

The relay switches have magnetic actuators diagrammatically indicated in FIGURE 3 at 112, 113 and 114. To power these a secondary of the transformer 64 is connected to a full wave rectifier 116 which in turn has one of its leads connected in parallel to the several magnetic actuators. The other lead 117 from the rectifier is brought out to terminal 4 of the plug-in connector 74, while leads from the individual magnetic devices 112 to 114 are brought out respectively to terminals 1, 2 and 3. Referring to FIGURE 4, it will be seen that the plugin connector serves to connect these various leads to selector switches 118, 119 and 120 which are actuated by stop tabs of the instrument. In the particular embodiment these switches are so interconnected that if one is closed 9 it breaks a necessary connection to the others. This has the effect of permitting only one percussive voice to be used at any one time, which has certain advantages. However, other arrangements can be made permitting more than one percussive voice to be sounded.

The outputs of all of the vacuum tube lters are combined in a lead 121 which is connected to terminal 7 of the plug-in connector 74. This is an output terminal connected (FIGURE 4) by a shielded cable 122 to a reproducing system for the instrument comprising an amplifier and one or more loud speakers (not shown). If desired, a special loudness control or volume selector may be provided for the percussive assembly by including a single-pole single-throw switch 123 having a connection to ground through a resistor 124. It will be evident that when the switch 123 is closed the signals from the percussive assembly will be attenuated.

As mentioned above, L-C type filters or voicing circuits may be employed in place of electronic filters for obtaining desired selectivity as to frequency. FIGURE 5 illustrates an example wherein filter B may be substituted for B (of FIGURE 3). Similar filters B1', etc. may replace B1 etc. T-he network B comprises resistors 126 and 127 connected as shown to the parallel com-bination of condenser 128 and inductor 129, both of which are connected to ground. Outputs of similar filters B1 etc. are connected to a common output lead 121', corresponding to lead 121 of FIGURE 3. However, for phase-reversal purposes, as mentioned hereinbefore, the common output lead 121 is passed through -a phase-reversal device, such as transformer 130, before being connected to the output terminal, such as 7 of the connector 74 of FIGURE 3. A worker skilled in the art would, of course, design the filter B', B1', etc., to peak at the desired frequency, as taught above, and with a sharpness of resonance equivalent to that of the tube filter previously described.

A secondary 125 may be provided on the power transformer 64 for use in energizing the filaments of the several tubes in the assembly through leads x and y. The plate circuits of the several tubes in the filter circuits B to B are connected to the 250 V. tap on the power network 67. The arrangement shown including the use of plug-in connectors makes the system suitable not only for incorporation into new instruments, but also suitable for addition to instruments already in use. The switches of which 91 is an example, will be simple make and break switches arranged to be actuated by the playing keys. The portion of the assembly shown in FIGURE 4 is designed to be located in the voice box of the instrument, i.e. that portion which contains the switches and filters controlled by the stop tabs. Hence the plug-in connector 74. It will be realized that the percussive assembly herein taught, while connected with the generators of the instrument, and while it may be connected to the same reproducing system, is essentially separate so that either the percussive assembly of the normal instrumentalities of the organ 'may be used alone, or both may be used together as desired. If none of the switches 118 to 120 is closed, the percussive assembly will be inactive so far as the performance of the organ is concerned. lf the normal stop tabs of the organ are left open and a percussive stop tab is closed, then percussive effects will be obtained in a percussive voice when the instrument is played in a staccato. fashion. However, normal organ voice stops may be used along with percussive stops. In this event a very wide tonality is obtainable. If the instrument Lbe played sostenuto the effect of percussion will not be noticeable, but staccato playing will bring out the exponential decay of the tones as has been explained. Thus percussive effects may be used as accents in ordinary playing without changing the stops. While a loudness selector 123 has been indicated for the percussive assembly, it will be understood that the lead 122 may be so connected to the pre-amplifier or amplifier that the output of the percussive assembly will be controlled by the expressioin pedal of the instrument.

Modifications may be made in the invention without departing 4from the spirit of it. The invention having been described in certain exemplary embodiments, what is claimed as new and desired to be secured by Letters Patent is:

1. In combination in an electrical musical instrument, a plurality of continuously operating sources of complex oscillations related as the notes of a musical scale, a plurality of key operated switches for deriving oscillations therefrom in accordance with the requirements of a musical composition, the said derived oscillations ceasing abruptly upon release of the keys, header means connected to said switches for combining said oscillations as derived, tone color means connected to said header means for modifying the harmonic content of said oscillations, output means connected to said tone color means for converting said modified oscillations to sound, a plurality of percussive circuit means connected respectively to said oscillation sources for providing derived oscillations characterized by abrupt attack and gradual decay, a second plurality of key switches respectively connected to said percussive circuit means and operable substantially simultaneously with said first mentioned key operated switches, collector means connected to said percussive circuit means, and circuit means including frequency-selective filter means connecting said collector means to an output means, whereby the simultaneous derivation of oscillations from said first rnentioned tone color means and from said percussive circuit means will result in the production of percussive effects in staccato playing, in which percussive effects the tone color changes during tone decay.

2. The structure claimed in claim l in which said percussive circuit means comprise each an amplifier normally biased to cut-off, wherein said second plurality of key switches operate respectively to remove the cut-off bias, and in which time delay circuit means are included acting to restore said cut-off bias in accordance with an exponential curve upon release of the key switches.

3. The structure claimed in claim l wherein said frequency-selective filter means constitute amplifier stages peaking at selected frequencies related to the frequencies of oscillations delivered thereto by said percussive circuit means.

4. The structure claimed in claim l wherein the outputs of said percussive circuit means are formed into groups consisting of a small number of percussive circuit means connected to sources of oscillations related as adjacent semi-tones, and wherein said frequency-selective filter means are connected respectively to said groups and are tuned respectively to the mid-fundamental frequencies of said groups.

5. The structure claimed in claim 4 including cross connections between said groups respectively and other frequency-selective filter means tuned to partials of the fundamentals of the said groups.

6. The structure claimed in claim 4 wherein said percussive circuit means and said frequency-selective filter means each constitute amplifiers tending to reverse and re-reverse the phase of the applied oscillations whereby oscillations are derived from said frequency-selector filter means which are in phase with the oscillations derived from said tone-color means.

7. The structure claimed in claim 4 wherein said first mentioned plurality of key operated switches are gradual contact switches, and wherein said second plurality of key switches are make-and-break switches.

8. The structure claimed in claim 5 wherein said connections and cross connections between said percussive circuit means and said frequency-selective filter means are controlled by a plurality of multi-contact switches actuated by stop tabs so that a plurality of percussive voices may be obtained in an output system characterized by `different amplitudes of partial content.

References Cited in the file of this patent UNITED STATES PATENTS Smiley Sept. 26, 1939 Kock Mar. 4, 1941 Riddle June 10, 1941 Ford et al. Mar. 27, 1945 10 Munch Dec. 22, 1959

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