US3288904A - Tone frequency control system for electronic musical instruments - Google Patents

Description

Nov. 29, 1966 T. J. GEORGE 3,288,904

TONE FREQUENCY CONTROL SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS Filed Sept. 25, 1962 4 Sheets-Sheet 1 Ali. MIC.

Amn $2 EU PDmPDO MOFUQ J UWO INVENTOR. moms J. GEORGE 5 WM NRW Nov. 29, 1966 T. J. GEORGE 3,288,904

TONE FREQUENCY CONTROL SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS Filed Sept. 25, 1962 4 Sheets-Sheet 2 Q (Q ("I P V :s 92 O Q) SWKTCH 41 INVENTOR. 9 THOMAS J. GEORGE 9' BY Nov. 29, 1966 -r. J. GEORGE 3,288,904

TONE FREQUENCY CONTROL SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS Filed Sept. 25, 1962 4 Sheets-Sheet 5 u) E m P M A P m E {if g .3 (\1 1 i W Z w v LL. U

2 m uJ Q a u MALE:

INVENTOR. THOMAS J. GEOEG E AMM (N Nov. 29, 1966 T. J. GEORGE 3,283,904

TONE FREQUENCY CONTROL SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS MALE. VOICE FEMALE VOICE INVENTOR. THOMAS J. GEORGE United States Patent 3,288,904 TONE FREQUENCY CONTROL SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS Thomas J. George, North Hollywood, Calif., assignor to Hammond Organ Company, Chicago, 111., a corporation of Delaware Filed Sept. 25, 1962, Ser. No. 226,085 39 Claims. (Cl. 841.01)

This invention pertains in general to electronic musical instruments and more particularly to electronic circuits and arrangements for producing new and unusual musical effects using conventional keyboard instruments.

It is generally considered by serious musicians that the human voice is the most beautiful of all musical instruments. For years, most pipe organs and electronic organs have included a stop known as the vox humana which is intended to simulate the human voice. However, it is well-known that the effect, though usually pleasing, bears but little resemblance to the human voice.

I have found that five major characteristics determine the sound of the human voice. These characteristics are tone quality, portamento, pitch range, attack and release of the tones, and vibrato. When these five characteristics are accurately simulated the artificial male voice is easily distinguishable from the artificial female voice, and the realism is so striking that even experienced listeners may believe they are listening to actual human voices.

Of the five characteristics, but little attention has heretofore been given to the importance of portamento and tone quality. It should be mentioned here that although the term glissando has been commonly used, portamento is the correct musical term for describing the effect here referred to, i.e., a glide in which all intervening frequencies are played. A glissando, in contrast, is a glide from note to note in which discrete notes are successively played. Portamento is considered peculiar to the human voice, the violin, and the trombone and heretofore could not be accomplished on any known conventional musical instrument utilizing a keyboard.

To accurately imitate the human voice or a like instrument having .a portamento characteristic, with an electronic keyboard instrument, some means is needed for conveniently and accurately creating the portamento effect in response tothe conventional keying techniques which produce the discrete pitches. Prior efforts to provide instruments which produce portamento effects have not been very successful because the instruments require special equipment and playing techniques which are abnormal to conventional keyboards. Instruments utilizing such techniques include, for example, the Theremin and the instrument shown in the Trautwein Patent No. 2,141,231.

Furthermore, as pointed out, no known instrument is capable of simulating the tone quality or timbre of the human voice accurately. Acoustic analyses of the human voice indicate that there are three identifying attributes of the tone quality which are peculiar to the human voice when singing or speaking vowel sounds. These attributes are: (l) the first harmonic is nearly always lower in amplitude than the second harmonic or other low order harmonic; (2) a low frequency peak occurs in the harmonic analysis of the voice tones approximately between 500 and 900 cycles per second; and (3) a high frequency peak occur in the harmonic analysis approximately between 2100 and 2900 cycles per second. The three attributes have never been accomplished in combination in any known conventional keyboard instrument. Of these three attributes, the first is the most difficult to obtain electronically, because nearly all electronic oscillators which generate a complex wavetorm also generate a first harmonic of greater amplitude than all other har' monies.

In addition to the five above-mentioned characteristics, when the human voice is used as a solo musical instrument accompanied by one or more other musical instruments, by design or otherwise, it usually assumes the highest note (an accented melody note) for emphasis. Various devices of the prior art are capable of accenting the highest note of any chord played, and known instruments have used'this feature. One such device (as used on pipe organs) is called the melody octave coupler. However, such devices require the player to always depress first the highest key of any chord played and, likewise, to release it last when the chord is released. If the highest key is inadvertently released too soon, then the accented note drops down to the next lower note in the chord, producing an effect which is very unmusical and disturbing. Since a skillful player will at times fail in this keying technique, arrangements based thereon have proved unsuitable for accenting the melody note. Various attempt-s to correct the difficulty inherent in known devices have been made, but no real solution has been found.

Accordingly, it is an object of the invention to provide means for accurately imitating the human voice on a conventional keyboard instrument.

Another object of this invention is to provide means for accurately imitating the tone quality of a human voice by a conventional keyboard instrument.

It is another object of the invention to provide means for playing notes with a portamento effect on an electronic musical instrument which employs a conventional keyboard.

A further object of the present invention is to provide unique arrangements for controlling tone quality and portamento effects of an electronic musical instrument by means of a conventional keyboard.

Another object of the present invention is to provide a unique oscillator arrangement for furnishing variable two-frequency output signals, the oscillator having a memory circuit input for accomplishing portamento effects.

It is an additional object of the invention to provide an improved arrangement for accenting the highest or lowest note of any chord played on a conventional keyboard.

It is yet another object of the invention to provide simplified means for accomplishing various musical effects including means for actuating a switch by the operation of any one or more of a plurality of playing keys.

These and other objects are accomplished in accordance with the present invention by a unique circuit arrangement which includes an oscillator capable of producing signals which have a second harmonic content that is greater in magnitude than the first harmonic content, and may therefore be used to simulate the human voice. A novel memory circuit is provided to supply an exponentiallyvarying control signal to the oscillator in response to keying changes for causing a portamento effect. The memory circuit is operated from a conventional keyboard by a mechanical-electrical arrangement which provides a high-note effect without regard to fingering release.

The device of the present invention also includes a unique human-voice output filter which allows it to imitate the singing human voice with striking realism; The filter is such as to provide the twin peaks of frequency which are peculiar to the human voice. Other filtering means are provided for furnishing alternative output signals for simulating other portamento instruments.

A better understanding of the invention may be derived from the following detailed description and the accompanying drawings in which like elements have like designations and in which:

FIG. 1 is a circuit diagram of one arrangement of a musical instrument in accordance with the present invention;

FIG. 2 is an illustration of a waveform generated by the circuit of FIG. 1;

FIG. 3 is an illustration of another waveform generated by the circuit of FIG. 1;

FIG. 4 is an illustration of still another waveform generated by the circuit of FIG. 1;

FIG. 5 is a perspective drawing of a temperature compensated resistor for use in the arrangement of FIG. 1;

FIG. 6 is a diagram illustrating the portamento elfect accomplished by the arrangement of FIG. 1;

FIG. 7 is a perspective view of a key-actuated switch for use in providing an accented melody note in accordance with the invention;

FIG. 8 is a side view of another key-actuated switch for use in providing an accented melody note in accordance with the invention;

FIG. 9 is an end view of the key-actuated switch of FIG. 8;

FIG. 10 is a graphical illustration of the frequency response of a filter employed in accordance with the invention;

FIG. 11 is an illustration of the harmonic content of a particular signal generated by the circuit of FIG. 1;

FIG. 12 is an illustration of the harmonic content of another particular signal generated by the circuit of FIG. 1;

FIG. 13 is a diagram of a dual-voice simulating arrangement in accordance with the invention;

FIG. 14 is a block diagram of a polyphonic musical instrument utilizing balanced oscillators;

FIG. 15 is a circuit diagram of a stabilized oscillator which may be used in the invention; and

FIG. 16 is a circuit diagram of an alternative form of musical instrument in accordance with the invention utilizing a reactance-controlled oscillator.

A preferred embodiment of the invention arranged in an electronic organ circuit is shown in FIG. 1 of the drawings. The functional components or blocks of the embodiment of FIG. 1 have been enclosed within dotted lines and labeled in order to facilitate an undertaking of the overall concept of the invention. A keying arrange- -ment including a conventional keyboard provides input signals for operating the system. The conventional keyboard is mechanically coupled to operate a series of selecting switches to make the appropriate connections for providing input signals to a memory circuit. The selecting switches are connected in a unique electrical-mechanical arrangement for accenting the highest note of any chord played without the prior art problems of keying and release. The memory circuit provides a control bias which varies exponentially in response to the discrete signals provided by keying changes for achieving the glide between notes peculiar to the human voice and other portamento instruments.

The output of the memory circuit is furnished to an oscillator which is advantageously adapted to provide two .output signals one octave apart, as required to simulate the tone quality of the human voice. The oscillator is tunable, maintaining the octave frequency difference between signals, over a wide range depending on the variable input control signal supplied thereto from the memory circuit. The oscillator has an arrangement for adjusting the relative amplitudes of the chosen frequencies thereby to better simulate the human male and female voices or other selected musical instruments. The output signals from the oscillator are furnished to a gating circuit which selectively passes the signals to a filtering circuit, adapted to selectively provide signals having the frequency peaks characteristic of the human voice or other portamento instruments. The signals from the filtering circuit are furnished to an output circuit which includes an amplifier and a speaker in a well-known arrangement for producing sounds representing the input signals.

As the efiects accomplished by the arrangement are dependent on the production of two frequencies, the oscillator provides a convenient starting point for a description of the invention. The oscillator is a modified form of multivibrator circuit which employs two triode electron tubes 10 and 11. The tubes 10 and 11 have their plates connected by resistors 12 and 13, respectively, to a source of positive potential which is applied at a terminal 14. The plate of the tube 10 is coupled to the grid of the tube 11 by a capacitor 15, and the plate of the tube 11 is coupled to the grid of the tube 10 by a coupling capacitor 16 and an adjustable capacitor 28 connected in parallel therewith. Grid resistors 17 and 18 connect the grids of the tubes 10 and 11, respectively, via a bias control lead 34 to the memory circuit. Resistors 22 and 23 connect the cathodes of the tubes 11) and 11, respectively, via a common cathode resistor 24 to ground potential. The common cathode resistor 24 may advantageously be temperature compensated, for reasons to be explained hereinafter, by means of a heater winding 25 which may be energized by a low voltage source connected across the terminals 26 and 27.

In operation, the oscillator functions to produce signals, the frequencies of which are determined principally by the values of the grid resistors 17 and 18, the values of the capacitors 15 and 16, and the magnitude of the grid bias as controlled by the memory circuit via the conductor 34. As will be explained, the grid bias furnished by the memory circuit varies with the input signal. As the bias decreases, the frequency of oscillation is lowered, and as it increases, the frequency of oscillation is raised. Using circuit values which will be given later, the frequency range of the oscillator of FIG. 1 may be made to extend .over three octaves while the output signal amplitude and waveform remain substantially unchanged.

A significant feature of the oscillator of FIG. 1 is that, when it is correctly adjusted, it will generate, simultaneously, signals of two discrete frequencies which are one octave apart. To achieve this performance, the oscillator utilizes pairs of components which are balanced within a tolerance of approximately ten percent. For example, the cathode resistors 22 and 23, the grid resistors 17 and 18, the coupling capacitors 15 and 16, and the plate resistors 12 and 13 are balanced. To further achieve the necessary balance, two adjustments are provided for affecting 00th the resistance and the reactance of the circuit. The variable capacitor 28 is connected in parallel with the capacitor 16, and a high resistance potentiometer 29 is connected in parallel with the plate resistor 13 to furnish the adjustments.

With an oscilloscope (not shown) connected to the upper terminal 30 of the resistor 24, this balance can readily be observed. The waveforms of FIGS. 2 and 3 illustrate conditions of unbalance and balance, respectively. As balance is approached, the diiference in height of alternate peaks A and B diminishes; and at balance (as shown in FIG. 3), peaks A and B are exactly the same height. FIG. 2 is representative also of the waveform appearing at the cathode of the tube 11 which remains substantially unchanged, regardless of the balance adjustment. The waveform appearing at the plate of the tube 11 is represented in FIG. 4. This wave is approximately rectangular and is characteristic of a multivibrator circuit. The waveform appearing at a potentiometer contact 32 is adjustable and, depending upon the position of the contact 32, this waveform may be varied between the limits indicated by the waveforms of FIGS. 2 and 3.

The difference between the waveforms of FIG, 2 and FIG. 3 (those of the signals at the terminals 30 and 31) monics of the oscillation frequency in the signal at terminal 30 becomes more effective, and no difficulty is encountered in reducing the first harmonic, for example, to an amplitude more than 40 decibels below that of the second harmonic. The same action reduces all odd order harmonics simultaneously, so that at balance the signal at the terminal 30 contains only even harmonics of the oscillation frequency. This, in effect, is a signal of twice the oscillation frequency having a harmonic family containing both odd and even harmonics of twice the oscillation frequency. This is illustrated by the fact that there are twice as many cycles in the diagram of FIG. 3 as in that of FIG. 2 or FIG. 4.

Such complete cancellation of the odd harmonics of the oscillation frequency is not necessary for the simulation of the human voice. The signal obtainable at the contact 32, the harmonic content of which can be varied, is therefore desirable for this purpose, for the second harmonic of the signal may be adjusted to be higher in amplitude than the first harmonic to effectively simulate the human voice.

The balanced oscillator of FIG. 1 is frequency sensitive to changes in voltages at the grids, the plates, and to some extent at the heaters of the tubes and 11. During the warm up period after the oscillator is first turned on, the frequency of oscillation will drift slightly higher, so that the instrument might be out of tune with any other instrument with which it is played. To compensate for this drift, the resistance of the cathode resistor 24 may be caused to increase slightly. For example, the resistor 24 may comprise a temperature sensitive resistor which is heated to slowly increase its resistance during the Warm up period. The heating may be accomplished by the heater winding 25 which may be constructed of resistance wire Wound around the resistor 24 and connected to a low voltage supply at a pair of terminals 26 and 27, as shown in FIG. 5. The amount of heating required is determined from the physical size of the resistor 24, its positive temperature coefficient and the rate of drift of the oscillator. Temperature compensation may also be employed with voltage divider resistor 48 if desired, and in this case resistor 48 should have a negative temperature coefficient. Alternatively a temperature compensated resistor 48a may be connected in series with resistor 48 as shown in FIG. 13. These resistors may be constructed as shown in FIG. 5. It is desirable for the B+ voltage supplies at terminals 50 and 14 in the figures to be regulated.

In operation, input signals are applied to the tubes 10 and 11 by the bias control coductor 34 which is connected to the plate of an electron tube 35 in the memory circuit. The plate of the tube 35 is also connected by a plate resistor 36 to the source of potential at the terminal 14. The tube 35 has a cathode resistor 37 connected to ground and a cathode biasing resistor 38 connected to the source at the terminal 14. The grid of the tube 35 is connected to ground potential by a capacitor C39 and to a switch 41 by a parallel arrangement including a resistor 40 and a diode 53. The switch 41 is connected to a voltage divider including serially connected resistors 47A-47K. A series of key switches 42-46 are arranged to connect the terminals between the resistors 47A-47K to terminals between variable resistors 49A-49L of a second voltage divider, connected between ground potential and a source of positive potential at a terminal 59. As indicated by dashed lines, a conventional keyboard 52 has its playing keys arranged to operate the key switches 42 to 46 by means of suitable mechanical linkages. The operation of any playing key and the corresponding one of the key switches 42-46 simultaneously closes the switch 41, the mechanical details of which are given below.

As noted, the bias control lead 34 is connected to the plate of the memory circuit tube 35. Accordingly, if different direct current voltages are applied to the grid of the memory circuit tube 35, the plate voltage and the voltage on the conductor 34 will vary, controlling the frequency of the oscillator in accordance with the magni- 6 tude of the voltages applied to the grids of the tubes 10 and 11.

When any key of keyboard 52 is operated to close a switch, for example the switch 42, the switch 41 is closed to provide a first potential .at the grid of the tube 35 which charges the capacitor C39. Assuming that there are no substantial leakage currents fnorn grid to ground, any voltage charge upon capacitor C39 will remain, so long as the voltage does not exceed the positive cathode bias of tube 35. If good insulation is used on the wiring of the grid circuit, and if the capacitor C39 has low leakage, as for example a good ceramic dielectric capacitor, then the charge will remain unchanged for an appreciable period of time; and for that period of time the grid voltage which determines the frequency of the oscillator will remain unchanged. Thus, it will be seen that every charge placed upon the capacitor C39, and the corresponding oscillation frequency, will be remembered by the circuit until a different charge is placed upon the capacitor C39.

When a different key is operated and a lower voltage is applied to the tube 35 through the resistor 40, an appreciable time will be required for the voltage on capacitor C39 to reach the new value as determined by the time contant of the resistor 40 and the capacitor C39. During this time interval, the input signal provided to the oscillator will glide smoothly from the old to the new value to produce a portamento effect, the final frequency of which is determined by the magnitude of the new charging voltage.

Suppose that the playing key of the keyboard 52 linked to the switch 42 is depressed, closing simultaneously the switches 41 and 42. The voltage appearing at the switch 42 from the voltage divider is applied through all of the resistors 47A-47K in series and through the switch 41 to charge the capacitor C39. The oscillator will generate the corresponding frequency, which in this case is the lowest frequency of the keyboard. Now if the first key is released, and another key depressed, for example the key associated with the switch 46, then the switches 41 and 46 will simultaneously be closed, and a lower voltage will be applied through the switch 41 to discharge the capacitor C39 gradually through the resistor 40 until its voltage reaches the lower level. The frequency will glide up to the new note, and will remain there, even after the playing key is released. If thereafter a lower key, for example the key linked to the switch 45 is depressed, then a higher positive voltage will be applied to the capacitor C39, and at this point the diode 53 which is connected in parallel with the resistor 40, will be rendered conducting. The diode, as indicated, is poled so that it will conduct current toward the capacitor C39 but not away from it. Therefore, when a positive potential appears across the diode 53, the capacitor C39 is charged through the diode 53 instead of the resistor 40, provided that the value of the resistor 40 is appreciably higher than the forward resistance of the diode 53. This charges the capacitor C39 very rapidly, and little or no glide or portamento occurs.

Thus, when the new note played is lower in frequency than the last note, the capacitor C39 is charged through the diode 53 almost instantaneously. When the new note is higher than the last note, the capacitor C39 is gradually discharged through resistor 40, and there is a pleasing portamento. This action can easily be reversed by reversing the polarity of the diode 53, but it has been found for most musical applications, that a portamento with rising frequency is much more pleasing than with falling frequency. If the; diode 53 is omitted there will be portamento with either rising or falling frequency. Also if the value of the resistor 40 is made very low, there will be no portamento in either direction, but always an instantaneous change in pitch.

According to another feature of the invention, the degree of the portamento effect may be varied by .arranging a variable capacitor C150 in parallel with the resistor 40-. The connection may be made by a switch 151. Depending on the value chosen for the capacitor C150, the tuning voltage may be caused to move instantaneously to a chosen point between the old .and new values before the portamento effect begins. For example, as shown in FIG. 6, if the value of the capacitor C150 is set to equal that of the capacitor C39, the tuning voltage moves to the midpoint between the old and new values; and then the glide to the new value begins. The effect produced is more natural in the simulation of certain instruments. Examples of the effect of the capacitor C150 are shown in FIG. 6 where the voltage changes on the capacitor C39 for various values of the capacitor C150 are illustrated.

The variable resistors 49A-49L function as the tuning controls, and each may be of a relatively low value, such as 500 ohms. While only five tuning resistors 49 are shown, any number of separate tuning resistors and key switches may be used, depending upon the keyboard range desired, with a range of from two to three octaves being adequate. The resistor 48 has a unique current limiting function which greatly simplifies the tuning of the instrument. If the resistor 48 has a resistance value not less than three or four times the total resistance value of all of the tuning resistors 49A-49L, the small tuning adjustments of the resistors 49A-49L will not appreciably affect the current through the voltage divider because the resistor 48 limits the current flow. It is thus possible to tune individual notes without appreciably changing the tuning of other higher notes of the instrument. However, if a number of notes are to be tuned, the notes should .be tuned in sequence starting with the highest notes to be tuned, because all lower notes will be affected. One advantage of this arrangement is that the resistor 49L which interconnects switch 46 and ground serves as a master tuning control. By tuning the resistor 49L, all notes may be moved up or down simultaneously to bring the device into tune with some other instrument which is not so easily tuned.

The resistors 47A-47K should each have a resistance value which is approximately ten to fifteen times the resistance of each resistor 49A-49L. If this switching arrangement is used as a part of a polyphonic musical instrument, then several of the playing keys may be depressed at one time, When this is done, it is important that the tuning of the individual solo notes should not be disturbed. If for example, the key switches 42 and 46 are closed simultaneously, then all the resistors 47A-47K between the two key switches will be connected in parallel with all of the resistors 49A49K. If resistors 49A- 49L are each approximately 500 ohms, then resistors 47A-47K should be not less than 5000 ohms. The resistor 40 may be one megohm or larger, depending upon the rate of portamento desired.

Another point of importance in relation to use of the invention with a polyphonic instrument is the arrangement which selects the highest or lowest note when several keys are played simultaneously. A conductor 54 connects the switch 41 to the switch 46 as shown, or, alternatively, to the lowest frequency switch 42. When the conductor 54 is connected to the switch 46, if several keys are depressed, the highest note will have precedence. If lead 54 is connected to switch 42, then the lowest note in any chord will have precedence. In this way either the highest or lowest note of any chord may be the solo voice. This is a very useful feature, because prominence can be given the melody, which is usually the highest note of any chord. However, the feature is also useful for accenting the lowest note of any chord played in providing bass accompaniment. In a small electronic organ, the bass part can be provided in this way very economically. An alternative circuit for this purpose is described hereinafter.

In accordance with one aspect of the present invention, the difficulty of prior art arrangements relating to the inadvertent release of the highest key of a chord is solved by the operation of the control mechanism for the switch 41. This mechanism is such that if several notes of a chord are depressed, the solo device will sound the highest note, as previously described. If the highest key is inadvertently released, while one or more lower keys remain operated, the switch 41 opens immediately, even before the tuning switch 42-46 is opened, so that the voltage on the capacitor C39 remains unchanged and the oscillator continues at the same frequency. The only way to close the switch 41 again is to play either the same or a different key.

To accomplish the foregoing, the switch 41 is of special design. The details of two suitable forms for its construction are shown in the perspective drawing of FIG. 7 and the views of FIGS. 8 and 9. In FIG. 7 the rear ends of four playing keys 89a89d of the keyboard 52 are shown. The key 8% is indicated as depressed while the keys 89a, 89c and 89d are in normal position. A flexible cord 91, such as braided wire or dial cord, is mounted above the top surfaces of all keys 89 and is stretched between a mounting post 92 and a slide rod 93. Rigid stop members 94 are mounted between the keys 89 immediately above the flexible cord 91 so that the cord 91 touches the upper surfaces of the keys and the lower surfaces of the stop members 94. The slide rod 93 of friction switch 41 is loosely mounted in a pair of bearing blocks 95a and b so that it is free to move either to the left or the right. A retractile spring 96, anchored to a post 97, pulls the slide rod 93 to the right, thus maintaining a tension upon the flexible cord 91. A spring contact member 98, which may be made of spring silver wire, is mounted upon a metal support post 99. The contact member 98 passes through a friction block which is loosely mounted upon the slide rod 93. The friction block 100 and the bearing blocks 95 may be constructed from a suitable smooth bearing material such as nylon. Two electrical contact posts 101 and 102, are vertically mounted close to, but not normally touching, the spring contact member 98. A pair of connecting leads 54 serve to connect the switch 41 with the keying and memory circuits shown in FIG. 1. The spring contact member 98 may be tensioned downwardly so that it urges the friction block 100 against the slide rod 93, causing friction therebetween. The spring contact member 98 is not however, tensioned either to left or right, and has little or no tendency to touch either of the contact posts 101 or 102.

Upon the operation of any playing key, such as 8%, the inner end of the key rises, pulling the cord 91 upwardly as indicated. The restraining action of the two stop members 94 on each side of the key, causes the cord 91 to be drawn tight, thus pulling the slide rod 93 to the left. The movement of the slide rod 93 moves the friction block 100 to the left, causing the contact member 98 to move to the left and make electrical connection with the contact post 101. This connection will be maintained until the key is released, at which time the spring 96 will draw the slide rod 93, the friction block 100, and the contact member 98 to the right, thus breaking the connection with the contact post 101. If while key 89b is operated, one or more additional keys are operated, the flexible cord 91 will be pulled still more, causing the slide rod 93 to move still farther to the left. But since the contact member 98 is already pressing against the post 101, the slide rod 93 moves within the friction block 100. Due to the friction between the slide rod 93 and the friction block 100, the contact 98 is held in firm engagement with the post 101 during this movement.

If one or all of the keys are released, the spring 96 draws the slide rod 93 to the right. The contact member 98 is disengaged from the contact post 101 and moves against the post 102 which acts as a stop to prevent the friction block 100 from following the slide rod 93 for more than a very short distance in its movement to the right. The actual spacing between the contact posts 101 and 102 is very small, only slightly more than the thickness of the contact member 98, so that although the movement of the slide rod may be substantial if a number of keys is played, yet the movement of the friction block 100 and the contact member 98 is always very small. Thus, when a key 89 is next operated, the contact member 98 moves immediately to the left, upon the first slight motion of the flexible cord 91. On the other hand, when any key 89 is released, the first slight motion of the cord 91 causes the contact member 98 to break electrical contact with the post 101, even though other keys may simultaneously remain operated. Thus, it will be seen that the switch 41 makes contact if one or more keys are operated, but what is more important, it breaks contact instantly upon the release of any key, even though other keys are still held depressed.

The friction switch mechanism of FIG. 7 thus makes it possible to obtain melody note accent with a polyphonic instrument, without the necessity of learning new and difiicult playing techniques. The friction switch 41 could of course be controlled by some other mechanical device or electrical device common to all the playing keys, instead of the flexible cord shown in the figure. A sliding or rotating rod for example, could be substituted for the cord. It should be noted that where the invention is to be used only as a solo instrument, and not in conjunction with a polyphonic instrument, the switch 41 is not required, since in this case only one key at a time will normally be played.

In FIGS. 8 and 9 is shown another arrangement for operating the switch 41 of FIG. 7, FIG. 8 being a side view and FIG. 9 a rear view of the keys. The key 89 has a pair of intermeshed nylon pulleys 160 and 161 mounted to its rear surface which establish a slot 162 for carrying the flexible cord 91.

The arrangement operates substantially like that shown in FIG. 7 to operate the switch 41 except that the friction of operation attributable to the movement of the cord 91 is substantially reduced. As a key is depressed, the pulleys 160 and 161 mounted thereto raise the cord 91 and cause the switch 41 to close. As any key is released, the cord 91 is lowered and the switch 41 opens.

It will be understood in the appended claims that where the invention is used in conjunction with a polyphonic musical instrument having a greater keyboard range than that normally employed by the invention, that the invention may be adapted to be operated by only a selected portion of the entire keyboard. It will be further understood that the term friction switch refers to the switch 41 shown in FIG. 7.

Referring now to the gating section of FIG. 1, an electron tube 55 is arranged to gate the output signals from the oscillator. Since the oscillator, although generating different frequencies, is in continuous oscillation, it is necessary that means, controlled by the playing keys, be provided to selectively transmit the signal to the output system only when keys are depressed to play selected notes. The gating tube 55 has a plate resistor 56 connected to the voltage source at the terminal 14. A voltage divider including the resistors 57 and 58, connected in series between the terminal 14 and ground is arranged to bias the cathode of the tube 55 at cutoff. The grid of the tube 55 is connected to the switch 59 by serially arranged resistors 60 and 61. The switch 59 is in turn connected between the resistors 62 and 63, of a voltage divider arranged between the source of positive potential at a terminal 51 and ground. When the switch 59 is open, the tube 55 is cut OE; and when closed, the tube 55 is conducting. A timing capacitor 64 is connected from the junction of the resistors 60 and 61 to ground for controlling the attack (the time required for tube 55 to conduct) and release (the time required for tube 55 to cease conducting) of the tones. The resistor 60 affects the attack, and the resistor 65, connected between the grid of the tube 55 and ground, afiects the release of the tones. The resistor 61 is a grid coupling resistor.

A switch 66 is arranged to selectively connect the grid of the gating tube 55 to either a switch point 67 or a switch point 69. When connected to the point 67, a signal from the potentiometer 23 is passed to the grid of tube 55 by a capacitor 68. When the switch 66 is connected to the point 69, a signal from the plate of the oscillator tube 11 is passed by a direct current blocking capacitor 70 to the grid of the gating tube 55. The operation of the switch 66 and the adjustment of the potentiometer 23 allow the selection of any of the waveforms shown in FIGS. 2, 3 and 4.

The signal output of the gating tube 55 is passed by a capacitor 71 to a voicing selector switch 72. When the switch 72 is connected to a point 73, the signal is passed by a resistor 76 to an output amplifier 78 and thence to a speaker 79. When the switch 72 is connected to a point 74, the signal is passed to the output amplifier through a capacitor 80, which functions as a high pass filter to attenuate the lower harmonics in the tone for the simulation of violin tones.

When the switch 72 is connected to a point 75, the signal path to the speaker 79 is through a filter which produces the two response peaks necessary to the accurate simulation of the tone quality of the human voice. As previously mentioned the two frequency peaks in the human voice are an important identifying characteristic. The frequency response curve of this filter is shown in FIG. 10, and it will be seen that it meets this requirement. The filter comprises a first section including an inductor 81 connected in series between the point and the speaker 79, and a pair of shunt capacitors 85 and 86 which determines the gently rising curve up to about 900 cycles per second and the fairly rapid cut otf above approximately 1000 cycles per second. The filter also comprises a second section including an inductor 82 and capacitor 83 in series which provides a band pass filter with a response peak at approximately 2300 cycles per second. As indicated, this latter peak should be approximately 6 or 8 decibels lower than the peak at 900 cycles per second.

As indicated by the dashed lines, the operation of any one of the switches 42 to 46 in response to the depression of a key is accompanied by the simultaneous operation of the gate switch 59. Upon operation of any key, the gate circuit is operated by the closure of the gate switch 59; and the oscillator signal is passed to the output system.

FIG. 11 is a harmonic analysis of an artificial male voice produced by the arrangement of this invention, corresponding to the signal appearing at the input to the amplifier 78. The frequency of the tone is approximately cycles per second; and it will be observed that the first harmonic, at 100 cycles per second is considerably lower in amplitude than the second harmonic. In fact, the second harmonic is the strongest of the entire series. This harmonic relationship is necessary to imitate accurately the male voice, and it is obtained as previously described from the balanced oscillator, by selective adjustment of the contact 32 of the potentiometer 23. It will be seen that above the second harmonic, the amplitudes of succeeding higher harmonics drop 01f rapidly, and then rise to a peak at approximately 2300 cycles per second following the general shape of the curve of FIG. 10.

FIG. 12 is an analysis of an artifical female voice of a frequency of approximately 200 cycles per second which may be produced in accordance with the invention. Here the amplitude of the first harmonic is almost as great as that of the second harmonic. This difference between the relative strengths of the first and second harmonics is an important distinguishing feature of the human male and female voices and is controlled in the arrangement of FIG. 1 by the potentiometer 23. The drop off of harmonic amplitudes above 1000 cycles per second is approximately the same as in FIG. 11, with a peakalso in the region of 2300 cycles per second.

Examples of harmonic analyses of human voices, il lustrated on page 230 of Musical Acoustics by Culver, published by McGraw-Hill Publishing Co. in 1956, show their similarity to the analyses of FIGS. 11 and 12. It should be noted that the actual numbers of the harmonies which fall within the secondary peak at 2300 cycles per second is of little importance, so long as the peak itself is in the neighborhood of 2300 cycles per second, and the analyses indicate the general distribution rather than the actual numbers of harmonics. It may be found that this peak, for the female voice, should be slightly higher in frequency than for the male voice.

It should be noted that two voice simulating arrangements, one tuned to simulate a male voice and the other to simulate a female voice, may be operated in tandem to provide a duet elfect. Such an arrangement is shown in FIG. 13, for example. The two memory circuits connect the tubes 35F and 35M of the female and male voice channels, respectively, to the opposite ends of the resistor 47 so that the tubes 35F and 35M receive the appropriate input signals for accenting the highest and lowest notes played to produce the duet effect. Excepting the common switching system, the two channels are entirely separated, and for best spatial separation of the two voices, each channel has its own output system. The details of each channel of the arrangement are as shown in FIG. 1 so no further description thereof is believed to be required.

In normal operation of the arrangement of FIG. 1, the oscillator is in continuous operation. With no key depressed, the gating tube 55 is in the cut off condition; and no signal reaches the amplifier. Now, suppose that the lowest note of the keyboard 52 is depressed; the switch 42 closes, and simultaneously the switches 41 and 59 close. The oscillator is tuned to the lowest frequency, and at the same time the positive keying voltage through the switch 59 begins to charge the capacitor 64 and to render the gating tube 55 conducting. A signal appears at the output of the gate tube 55 and speaker 79. The attack will be gradual because of the delaying action of the attack resistor 60 and the capacitor 64. Now, suppose that the highest note is played. The gating tube 55 remains conducting; and in the memory circuit, the lower positive voltage from the switch 46 slowly discharges the capacitor 39 through the resistor 40 to the lower positive tuning voltage corresponding to that note. The frequency glides smoothly from the lower note to the higher note. Now, if the key is released opening the switches 41 and 59, the voltage on the capacitor 39 and the frequency of oscillation remain the same. The release control capacitor 64 slowly discharges through the resistors 61 and 65, in series; and the gating tube 55 gradually becomes nonconducting, producing smooth and gradual release of the tone. If the capacitor 64 is made quite large, the release of the tone will be quite slow; and the effect of a sustain will result. Also, if resistor 60 of the gate circuit is quite small while the capacitor 64 is large, the opening of the gate circuit will be practically instantaneous, and the release of the tones quite slow; resulting in a percussion effect. If vibrato is desired, it may very easily be obtained by applying a low frequency signal to the cathode of the tube 35. This signal can usually be obtained from the vibrato oscillator of the organ with which the device is to be used.

The switch 88 in the human voice filter is arranged to connect an additional capacitor 87 across the shunt capacitor 86. The switch 88 is normally closed. The dashed lines indicate that this switch is also controlled by the keyboard 52; and mechanical means, not shown, operate to open the switch 88 whenever a playing key in the upper octave of the keyboard is depressed. The reason for this action is as follows. When a singer has been singing a low note, and then glides up to a high note, there is a seeming slight change in the frequency response of the acoustic filters formed by the mouth and throat, perhaps caused by opening the mouth slightly more for the higher notes. To simulate this effect, opening of the switch 88 raises the cut off point of the filter curve of FIG. 10 slightly, say from 900 cycles per second to about 1000 cycles per second, when playing notes in the high octave of the instrument, so that the realism of the human voice effect is still further enhanced. The effect is equally useful with both male and female voice effects.

It has been mentioned that the solo device of this disclosure may be employed to advantage in conjunction with a polyphonic musical instrument, and such an instrument is briefly described as follows. Because the balanced oscillator of FIG. 1 generates simultaneously two discrete frequencies one octave apart, it is possible in accordance with another aspect of the invention to provide a polyphonic musical instrument which employs half the number of oscillators usually necessary, by sharing each balanced oscillator between two keys, one octave apart. A substantial economy can thereby be realized. FIG. 14 is a block diagram of such an instrument, which employs a four octave keyboard 104. The block contains twelve balanced oscillators as in FIG. 1, and the block 106 contains another twelve balanced oscillators. The oscillator of FIG. 15 may also be used here and is described later. The twelve oscillators of the block 105 are tuned to the twelve chromatic notes of the lowest octave of the instrument, and the oscillators of the block 106 are tuned to the twelve notes of the octave which is two octaves above the lowest octave. Signal leads 107 join the output terminals 31 (FIG. 15) of the oscillators to the key switches (not shown) of the lowest octave of playing keys. A common output bus 108 carries the combined signals from the keys to an output amplifier 109 and a speaker 110. Details of the switching circuit are not shown, as they are well known in the art. Twelve signal leads 111 join the output terminals 30 (FIG. 15) to the switches of the second octave of the instrument. Thus signal frequencies for two octaves are obtained from only twelve balanced oscillators.

In like manner, the oscillators in block 106 are wired to the key switches of the third and fourth octaves of the keyboard, the leads 112 connecting to oscillator terminals 31, and the leads 113 connecting to the oscillator terminals 30. By this means, considerable economy is possible in the design of an electronic organ. Although this arrangement is a form of shared oscillator organ, yet the system does not have the limitations so common in shared oscillator organs of the prior art, because in the present invention any combination of keys can be played simultaneously.

To improve the frequency stability of the balanced oscillator of FIG. 1 when used at one frequency only, a center tapped inductor may be substituted for the two plate resistors 12 and 13. FIG. 15 shows a circuit which employs such an inductor 114. A center tap 116 of the inductor 114 is connected to the terminal 14, and the two terminals 117 and 118 of the inductor 114 are connected to the plates of the tubes 10 and 11. The inductor 114 is in parallel with a tuning capacitor which controls the frequency of oscillation. As in FIG. 1 the fundamental frequency signal will appear at the terminal 31, and the frequency an octave above will appear at terminal 30. Since there are no plate resistors in the circuit of FIG. 15, a balance control potentiometer 29 is connected in parallel with the cathode resistor 23 and serves the same balancing function as in FIG. 1. Balancing capacitor 28 is connected in parallel with the capacitor 16 as in FIG. 1. The waveforms of the signals at terminals 30 and 31 are an octave apart in fundamental frequency and are of complex waveform as in FIG. 1. The waveform of the signal at terminal 33 is a sine wave of the frequency of the signal at the ter- 13 'rninal 31. The grid voltage adjustment 20 of potentiometer 19 is no longer a major factor in controlling the frequency of oscillation but is useful as a fine tuning control. The common cathode resistor 24 serves the same function as before but may be used without the frequency compensating heater 25. This balanced oscillator' is very stable in frequency and can be used to advantage in the instrument of FIG. 14, when substituted directly for the oscillator of FIG. 1.

Another useful form of the invention is shown in FIG. 16. An L-C oscillator 119 using the conventional Hartley circuit is arranged to be tuned over a range of frequencies in a manner similar to the oscillator of FIG. 1. The oscillator 119 comprises a triode tube 120, a tapped inductor 121, a parallel tuning capacitor 122, a grid capacitor 123, a grid resistor 124, a plate resistor 125 and a plate shunt resistor 126. A resistor 132 interconnects the cathode of the tube 120 and the tap on the inductor 12L Output signals may selectively be taken from the oscillator'plate, the cathode, or from the inductor. The oscillator 119 is tuned by means of a reactance tube 128 and a capacitor 129, as is well known in the art. The reactance tube 128 has a plate resistor 130 connected to the terminal 14, and the tuning capacitor 129 interconnects the plate of the reactance tube 128- and the grid end of the oscillator tuning inductor 121. The grid of the'tube connects directly to the same point on the inductor 121.

A memory tube 35 and associated switching circuit are used as in the circuit of FIG. 1, the keyboard having been omitted from the drawing of FIG. 16. The plate of the tube 35 connects directly to the terminal 14. The tube functions as a cathode follower, having a cathode resistor 131 common with the reactance tube 128. The tube 35.0perates to vary the cathode bias of the reactance tube 128 which in turn controls the frequency of the Hartley oscillator by causing an apparent variation of the tuning capacitor 129. The key switches 42 to 46, in conjunction with the voltage divider resistors 49A-49L and resistor 48, selectively control the grid bias on the tube 35, in the manner previously described, to tune the oscillator 119 to the desired musical pitches. The relative values of capacitors 122 and 129 control the frequency range of the oscillator. When they are about equal the frequency range is one octave. When capacitor 129 ismade larger and capacitor 122 smaller the frequency range increases. Capacitor 122 may be omitted entirely for maximum range.

The Hartley oscillator has one advantage, for certain applications, over the balanced oscillator circuit of FIG. 1 because it will deliver simultaneously a sine wave and choice of two complex waves. The sine wave, which is not obtainable directly from the balanced oscillator, is very useful in simulating certain kinds of musical effects such as flutes, and percussive effects such as chimes, vibra-harp, bells, etc.

The circuit of FIG. 16 also includes a gating tube 55 which is employed for the same purpose'as in the circuit of FIG. 1. Additional components, designated by the same characters as used in FIG. 1, have similar functions. A blocking capacitor 127 interconnects the grid of the gate tube 55 and a selector switch 140. When the selector switch 140 is connected to a switch point 137, the signal from the oscillator inductor 121 is transmitted to the gate tube 55. This signal is substantially a sine wave. When the switch is on a point 138, a complex wave from the cathode is transmitted to the gate tube 55. When the switch is connected to a point 139, a

complex wave from the plate is transmitted to the gate tube 55. The tube 55, as previously mentioned, is normally at cathode bias cut off. A switch 133 (which, as indicated by the dashed line, is operated simultaneously with any of the keying switches) is normally connected to back contact 134. A normally open front contact 135 is connected to the attack resistor 60. With the switch 133 in the normal position, a storage capacitor 136 is charged to a positive keying potential. The potential is determined by the relative values of resistors 62 and 63, arranged in series between the terminal 14 and ground. When the switch 133 is operate dto connect with the front contact 135, the positive charge on the capacitor 136 is transmitted through the attack resistor 60 to a normally discharged timing capacitor 64 and to the grid of the gate tube 55. The gate tube 55 opens and transmits the oscillator signal through tone color filters 137 to the output amplifier 78 and the speaker 79. As the charges on the capacitors 136 and 64 are dissipated through the serial resistors 60, 61 and 65, the gain of the gate tube 55 gradually decreases; and the tone from the speaker dies away, producing a percussive musical effect. When the switch 133 is restored to normal, the capacitor 136 is charged again for the next note to be played.

In the memory circuit of FIG. 16, the charging resistor 40 for capacitor 39 may be made relatively small, approximately 33,000 ohms. Frequency changes of the oscillator 119 with keying will therefore be practically instantaneous.

The circuit of FIG. 16 is very useful as a generator of bass pedal notes for an organ and can be manufactured inexpensively. Since two pedal notes are almost never played together, a solo pedal circuit is quite practical. Percussive pedal effects are very useful for rhythm playing in popular music. Also pedal sustain is very useful as it provides a pseudo reverberation effect, which makes it easier to play the organ, especially for inexpert players. The gate keying circuit of FIG. 1 is a sustain circuit which maintains any note played as long as the key is held, which then dies away gradually when the key is released. The gate keying circuit of FIG. 16 is a percussion circuit. The note dies away after the note is struck, whether or not the key is held depressed, and the memory circuit holds the oscillator on the last frequency played during the die away period. The capacitor 64 should be large enough to provide an appreciable period even though switch 133 is released. Usufollows:

Resistor 12 ohms 33, 000 Resistor 13 do 33, 000 Source of potential at terminal 14 volts Resistor 15 rnicrofarad- .002 Resistor 16 microfarad .0017 Resistor 17 ohms 560, 000 Resistor 18 do 560, 000 Resistor 19 do 250, 000 Resistor 21 do 100, 000 Resistor 22 do 3, 300 Resistor 23 do 3, 300 Resistor 24 do 100, 000 Capacitor 28 microfarad .0005 Resistor 29 ohms 250, 000 Resistor 36 d0 100,000 Resistor 37 do 22, 000 Resistor 38 do 330, 000 Capacitor 39 microfarad .01 Resistor 40 megohms 1 to 5 Resistor 47 ohms 5, 000 Resistor 48 do 42, 000 Thermister 48a do 75 to 750 Resistor 49 do 500 Source of potential at terminal 50 volts 150 15 Diode 53 Type 1T1 rectifier Resistor 56 ohms 560, 000 Resistor 57 do 220, 000 Resistor 58 do 33, 000 Resistor 60 do 100, 000 Resistor 61 do 330, 000 Resistor 62 do 120, 000 Resistor 63 do 710, 000 Capacitor 64 microfarad .25 Resistor 65 megohms 2.4 Capacitor 68 microfarad .01 Capacitor 70 do .01 Capacitor 71 do .01 Resistor 76 ohms 560, 000 Capacitor 80 microfarads .001 Inductor 81 lhenrys 14 Inductor 82 do 17 Capacitor 83 microfarad (female) .0002 Capacitor 83 microfarad (male) .0005 Resistor 84 hms 330, 000 Capacitor 85 rnicrofarad .002 Capacitor 86 do .002 Capacitor 87 microfarad 0005 Inductor 114- henrys Capacitor 115 microfarad .013 Inductor 121 henrys 100 Capacitor 122 microfarad .017 Capacitor 123 microfarad .022 Resistor 124 ohms 330, 000 Resistor 125 ohms 56,000 Resistor 126 do 27, 000 Capacitor 127 microfarad .05 Capacitor 129 do .019 Resistor 130 ohms 330, 000 Resistor 131 do 33, 000 Resistor 132 do 6, 800 Capacitor 136 microfarad .25 Capacitor 150 do Zero to .1

All tubes shown are 12AU7 tubes, excepting 10 and 11 which are 12AX7 tubes. It should be stressed that the vacuum tubes in the circuits shown in the drawings might in some cases be replaced by transistors, Without departing from the spirit of the invention.

Although there have been described above specific arrangements of organ circuits for the purpose of illustrating the manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations or equivalent arrangements falling within the scope of the annexed claims should be con sidered to be a part of the invention.

What is claimed is:

1. An electronic musical instrument comprising a variable frequency tone generator having a control terminal, a keyboard, and means for applying signals to the control terminal to change the frequency of operation of the generator in response to the manipulation of the keyboard, said signal applying means including unilaterally conductive means for decreasing the frequency in discrete intervals and means for imparting a portamentoeffect to increases in the frequency of operation of the generator.

2. An electronic musical instrument comprising a voltage controlled variable frequency oscillator, means for providing discrete voltage input signals for controlling the frequency of the oscillator and means for selectively coupling said discrete input signals to control the frequency of operation of the oscillator, said coupling means including afirst conductive path for gradually changing the control voltage applied to said oscillator to vary the frequency of the oscillator with a portamento effect in response to changes in discrete input signals in a first sense and a second conductive path for changing the control voltage applied to said oscillator by discrete intervals to 16. vary the frequency of ope-ration of the oscillator by discrete intervals in response to changes in discrete input signals in a second sense.

3. An organ circuit comprising a variable oscillator having input and output terminals; selection means for furnishing a plurality of discrete input signals; and means for operating the oscillator at frequencies dependent upon the input signals furnished, said oscillator operating means comprising means for providing an-exponentially varying signal to the input terminal of the oscillator in response to changes in one direction in the discrete input signals provided and for providing a discrete change in the signal to the input terminal in response to changes in the other direction in the discrete input signals provided. I

4. A variable tone frequency generator comprising a multifrequ'ency oscillator having input means, output means, and means for generating a complex output signal including a first frequency and a second harmonic of said first 'frequency of greater amplitude than said first frequency; a plurality of mechanically operated means for furnishing a plurality of discrete input signals; means connected to said input means and operative responsive to individual ones of the discrete input signals for varying the frequencies of operation of the oscillator, said last-mentioned means comprising a memory circuit connected to said plurality of mechanically operated means; a frequency filtering means for selectively attenuating certain frequencies in accordance with a desired tone quality and means for selectively connecting the frequency filtering means to the output means of the oscillator.

5. A tone generator comprising an oscillator having input and output terminals; utilization means connected to the output terminal of the oscillator; means for providing a plurality of discrete input signals, each of said plurality being operable to provide a particular discrete input signal representative of a given tone and being operable with others of said plurality for providing a combination of discrete input signals representative of a different tone; a memory circuit coupled to the input terminal of the oscillator, said memory circuit comprising an amplifier having an input terminal and an output terminal connected to the input terminal of the oscillator, a current limiting resistor for providing said input signals therethrough to the input terminal of said amplifier, and a timing capactor connected to shunt the input terminal of the amplifier for providing exponentially varying signals thereto in response to changes in the input signals; and a switch means responsive to the operation of any of said plurality of means for selectively coupling said input signals to' said memory circuit and for selectively uncoupling all of said plurality of means from said memory circuit whenever the operation of any one of a number of simultaneously operated ones of said plurality of means is terminated so that the signal provided by said timing capacitor is maintained substantially unchanged until a subsequent operation of one of said plurality of means.

6. A tone generator ras defined in claim 5 further comprising a diode connected in parallel with the resistor.

7. A tone generator as defined in claim 6 further comprising a capacitor connected in parallel with the resistor.

8. A multi'frequency tone generator comprising a multivibrator including first and second vacuum tubes each having a cathode, a plate and at least one grid, a pair of balanced capacitors each of which is connected between the plate of one of said tubes and the grid of the other of siad tubes, a pair of balanced grid resistors, a pair of balanced cathode resistors, a thermally-sensitive resistor connected in common to the cathode resistors, means for increasing the ambient temperature of the thermally-sensitive resistor, and means for biasing the multivibrator circuit; and input circuit for varying the potentials fiu-rnished the grid resistors of the multivibrator comprising an input vacuum tube having a plate coupled to said grid resistors, means for biasing the input vacuum tube, and means for applying input signals between the grid and cathode of the input vacuum tube including a capacitor connected therebetween and an input resistor connected to the grid of the input tube; an arrangement for furnishing signals to the input circuit comprising a D.C. potential source, a plurality of variable resistors coupled in series across the DC, potential source, a voltage divider circuit having a plurality of electrical input connections distributed at approximately equal intervlals therealong, means for selectively connecting terminals between said variable resistors to the input connections of the voltage divider, and switching 'rneans operative in response to the connection of the input connections of the voltage divider to one of said terminals for connecting the voltage divider to the input resistor of the input vacuum tube and operative in response to the release of any connection between the voltage divider and one of said terminals for disconnecting the voltage divider from the input resistor; a gating circuit comprising a vacuum tube biased at cut off, means responsive to the connection of the voltage divider to one of said terminals for biasing the vacuum tube of the gating circuit in the operating condition, means for selectively applying a signal from the multivibrator to the input of the vacuum tube of the gating circuit; and an output arrangement comprising a high-pass filter, a resistive output channel, and a combination filter having first and second frequency peaks at predetermined frequency points, said combination filter including means for selectively retuning the combination filter so that the frequency point of one of said peaks is varied in response to the connection of predetermined ones of said terminals to said voltage divider, and means :for selectively connecting the output of the gating circuit to one of said filters or to said output channel.

9. A multirrequency tone generator circuit as defined in claim 8 wherein the gating circuit includes means for causing changes in the bias applied to the vacuum tube of the gating circuit to take place exponentially.

10. A multitone generating circuit comprising a multivibrator circuit having first and second active elements and a resistor connected in common with said first and second elements; an arrangement for applying variable input signals to the multivibrator circuit comprising a Voltage sensitive amplifier circuit having input means comprising a voltage storage arrangement, a source of direct current potential, a first voltage divider connected across said source and having a plurality of substantially evenly spaced points for connection thereto, a second voltage divider having a plurality of substantially evenly spaced points for connection thereto, means for selectively con necting a point on the first voltage divider to 3. corresponding point on the second voltage divider and means for selectively connecting the second voltage divider to the voltage storage arrangement; a frequency filtering circuit; means for selectively sampling signals appearing at various discrete points of the multivibrator circuit and furnishing indications representative thereof to the filtering circuit; and output means connected to the filtering circuit.

11. A multitone generating circuit as in claim 10 wherein the means for connecting the second potentiometer to the voltage storage arrangement comprises a switch operated in response to the connection of any point of the first voltage divider to any point of the second voltage divider, said switch comprising means for connecting the second voltage divider in the input storage arrangement immediately upon an initial connection and for opening said switch immediately upon the opening of any connection.

12. A multitone generating circuit as in claim 11 wherein the switch comprises a flexible cord connected to a first stationary point, a rod connected to the flexible cord, a

spring connected between a second stationary point and the rod, a pluraltiy of mechanical means for moving the flexible cord perpendicular to its length in response to the movement of individual keys of a keyboard, a first switch contact fixedly mounted adjacent the rod, a second switch contact of a flexible material mounted to engage the first switch contact, and a block arranged in sliding friction contact with the rod and engaging the second switch contact for movement with the rod.

13. In a polyphonic musical instrument, a, solo device for accenting the highest note of any plurality of notes simultaneously played including a voltage sensitive variable frequency electronic generator having a control terminal, a voltage divider having a plurality of taps, a source of voltage connected across said voltage divider, circuit means interconnecting said generator control terminal and said voltage divider taps, said circuit means including a plurality of switches, each of said switches having a first terminal and a second terminal, each of said first terminals being connected to a respective tap of said voltage divider, a plurality of serially connected resistors, all said second terminals being sequentially connected to junction points between said plurality of resistors so that a single resistor interconnects said second terminals of every adjacent pair of switches, and a connection from the first resistor in the series to said generator control terminal.

14. In a musical instrument, a duet device for accenting the highest note and the lowest note of any plurality of notes simultaneously played including a pair of voltage sensitive variable frequency electronic generators, a first control terminal connected to one of said generators, a second control terminal connected to the other of said generators, a voltage divider having a plurality of adjustable taps, a source of voltage connected across said voltage divider, circuit means interconnecting said generator control terminals and said voltage divider taps, said circuit means including a plurality of switches, each of said switches having a first terminal and a second terminal, each of said first terminals being connected to a respective tap of said voltage divider, a plurality of serially connected resistors, all said second terminals being sequentially connected to the junction points between said plurality of resistors so that a single resistor interconnects said second terminals of every adjacent pair of switches, a connection from the first resistor in the series to said first generator control terminal, and a connection from the last resistor in the series to said second generator control terminal.

15. In a polyphonic musical instrument a solo device for accenting the highest note of any plurality of simultaneously played notes including a voltage sensitive variable frequency electronic generator having a control terminal and an output terminal, a plurality of selected volt age points for controlling the frequency of said generator in accordance with the notes played, selective circuit means interconnecting said voltage points and said control terminal, said circuit means including a friction switch and a memory circuit, said memory circuit including a time delay means to control the rate of change of voltage to said control terminal, said friction switch including means responsive to the termination of the playing of any note being played alone or as one of a plurality of simultaneously played notes for disconnecting said control terminal from all of said voltage points and thereby preventing a change of voltage at said control terminal, said memory circuit being operative to maintain said voltage at said control terminal substantially unchanged until another note or plurality of notes is played, and an output system cou pled to said output terminal.

16. A musical device as defined in claim 15 in which said time delay means includes a unilaterally conductive device for rendering the time delay means effective when control voltage of one sense is transmitted to said source, and ineifective when control voltage of opposite sense is transmitted to said source.

17. In a polyphonic musical instrument a solo device for accenting the lowest note of any plurality of notes simultaneously played including a voltage sensitive variable frequency electronic generator having a control terminal, a voltage divider having a plurality of taps, a source of voltage connected across a voltage divider, circuit means interconnecting said generator control terminal and said voltage divider taps, said circuit means including a plurality of switches, each of said switches having a first terminal and a second terminal, each of said first terminals being connected to a respective tap of said voltage divider, a plurality of serially connected resistors, all said second terminals being sequentially connected to junction points between said plurality of said resistors so that a single resistor interconnects said terminal of every adjacent pair of switches, and a connection from the last resistor in the series to said generator control terminal.

18. In a polyphonic musical instrument having a plurality of playing keys operated to produce electrical signals to be applied to means for producing solo tones, a friction switch having normally open contacts coupling said electrical signals to said solo means, an elongated member mounted in engageable relationship with at least some of said keys and frictionally coupled to one of said contacts to close the contacts of said friction switch upon the operation of any number of said keys and to open the contacts of said friction switch upon the release of any one of said keys.

19. The combination set forth in claim 18 in which said elongated member is a flexible cord with one end fixed and the other end frictionally coupled to one of the contacts of said friction switch, and is maintained in said engageable relationship by means of a pair of intermeshed pulleys mounted upon each key.

20. The combination in claim 18 in which said friction switch comprises a slide rod coupled to said elongated member, a pair of fixed contacts, a flexible electrical contact mounted between the pair of fixed contacts, a friction member mounted in engageable relationship with said slide rod and adapted to move said flexible contact relative to said pair of fixed contacts from one of said fixed contacts to the other fixed contact upon movement of said slide rod.

21. In an electronic musical instrument for simulating the effect of the singing human voice, variable frequency tone generating means and a frequency control circuit coupled thereto, a keyboard, said keyboard coupled to said control circuit to change the frequency of said tone generating means in accordance with the notes of a musical scale, and an output system coupled to said tone generating means, said output system including an audio filter for establishing two peaks in the frequency response curve of said output system, said peaks occurring at approximately 900 cycles and 2300 cycles, said tone generating means further including means for producing complex wave signals in which the second harmonic is of greater amplitude than the first harmonic.

22. In a polyphonic electronic musical instrument for producing solo percussive effects, an output system, a voltage sensitive variable frequency tone generator having a frequency control terminal and an output terminal, a plurality of selected voltage points corresponding to the notes of a musical scale, circuit means interconnecting said voltage points and said frequency control terminal, said circuit means including a plurality of switches and a memory device, selective mechanical means for actuating said switches, said memory device including a friction switch, a capacitor having first and second access terminals, said first access terminal being connected to one of said voltage points, said second access terminal being connected through said friction switch to said switches to charge said capacitor to a voltage selected by the operation of a corresponding one of said plurality of switches, and said friction switch being mechanically coupled to said mechanical means to be closed upon actuation of any one of said plurality of switches and to be opened upon deactuation of any of said plurality of switches, a normally inoperative gate circuit interconnecting said output terminal and said output system, percussive control circuit means for rendering said gate circuit operative, said percussive control circuit including a source of control voltage, a percussion switch, a storage capacitor normally connected to said source of control voltage by means of said percussion switch, a normally discharged timing capacitor coupled to said gate circuit, and means for operating said percussion switch to transfer the charge on said storage capacitor to said normally discharged timing capacitor to render said gate circuit operative to transmit a percussive signal to said output system.

23. In an electronic musical instrument, a plurality of playing keys, a voltage divider connected across a source of regulated voltage, said divider having a plurality of preselected voltage points corresponding to notes in a musical scale; a plurality of switches sequentially connected to said voltage points and adapted to be selectively operated by said keys; a voltage sensitive utilization circuit having an input terminal; a memory circuit coupled to said utilization circuit to control'the voltage transmitted thereto, said memory circuit including an electron conductive device having a control terminal, a capacitor connected to apply a bias voltage to said control terminal, and circuit means between said plurality of switches and the capacitor for applying a voltage thereto and including means for terminating the application of such voltage when the operation of any playing key is terminated.

24. The device as defined in claim 23 in which said circuit means comprises a friction switch.

25. The device as defined in claim 24 in which said circuit means further comprises a diode and resistor in parallel, serially connected between said friction switch and said control terminal.

26. In a polyphonic electric musical instrument, a plurality of playing keys; a plurality of balanced oscillators, the number of oscillators being half the number of playing keys, each of said oscillators including two electronic amplifying devices, a first output terminal, and a second output terminal, the signal frequency appearing at the second output terminal of each oscillator being twice the frequency of the signal appearing at the first output terminal of the oscillator; an output amplifier; and circuit means interconnecting the first and second output terminals of said oscillators and said amplifier, said circuit means including key switches operable by said playing keys.

27. A multifrequency tone generator comprising: a multivibrator for generating variable frequency tone signals including first and second triodes each having cathode, plate and control grid elements, a pair of balanced capacitors connecting the plate element of each triode to the grid element of the other triode, a pair of balanced grid resistors each forming a timing circuit with a respective one of the pair of balanced capacitors, a pair of bal- .anced cathode resistors connected in series between the cathode elements of the first and second triodes, a common cathode resistor connecting the junction between the pair of balanced cathode resistors to a reference potential, and a source of operating potential coupled to the plate element of said first and second triodes; a frequency control circuit for providing a variable bias potential to the grid resistors to control the frequency of the multivibrator including a voltage memory circuit; a circuit arrangement for furnishing D.C. voltages to the voltage memory circuit comprising a DC. potential source, a plurality of variable resistors coupled in series across the DC. potential source, a voltage divider circuit having a plurality of electrical input connections distributed at approximately equal resistance intervals there along, a tone selector means for selectively coupling junctions between the series coupled variable resistors to corresponding ones of the input connections of the voltage divider, and switching means operative in response to the coupling of an input connection to the corresponding junction for providing an output from the voltage divider to the voltage memory circuit and operative in response to the release of any coupling between the input connection and the corresponding junction for uncoupling the output of the voltage divider from the voltage memory circuit; a normally closed gating circuit coupled to receive the tone signals from said multivibrator circuit; means responsive to the coupling of any one of said input connections of the voltage divider to its corresponding junction for providing a control signal to said gating circuit, said gating circuit being responsive to said control signal for passing the tone signals from the multivibrator; and an output arrangement for receiving the tone signals passed by the gating circuit comprising a filter means for selectively attenuating lower frequency tone signals, a resistor output channel, and a combination filter means having first and second frequency peaks in predetermined frequency ranges corresponding to a desired tone quality, and means for selectively connecting the tone signals passed by the gating circuit to one of said filter means or to said resistor output channel.

28. A multitone generating circuit comprising: a voltage controlled audio oscillator circuit having an output frequency responsive to the amplitude of an applied control voltage; a circuit for generating a variable control voltage including a DC. amplifier having an output terminal coupled to provide a control voltage to said voltage variable oscillator, 21 fixed potential source, a first voltage divider connected across said fixed potential source and having a plurality of substantially evenly spaced connection points, a second voltage divider having a corresponding plurality of substantially evenly spaced connection points, a tone selection means for selectively interconnecting corresponding connection points of the first and second voltage dividers, and switch means responsive to the operation of said tone selection means for selectively coupling the output of the second voltage divider to the input terminal of the DC. amplifier; a storage capacitor coupled to said input terminal of the D0. amplifier for producing a voltage at the input terminal corresponding to the output voltage from the second voltage divider whenever said switch means connects the output from the second voltage divider to the input terminal of the DC. amplifier and for maintaining a voltage at the input terminal when said switching means disconnects the output from said second voltage divider from the input terminal.

29. In a multitone generating circuit having a voltage controlled oscillator circuit for generating tones having a frequency proportional to an applied control voltage, a circuit for generating a tone control voltage comprising: a fixed potential source; a first voltage divider circuit connected across said fixed potential source and having a plurality of connection points distributed in accordance with tones in a musical scale; a second voltage divider circuit having a corresponding plurality of connection points substantially equally distributed and having an output terminal at one end; a voltage storage capacitor coupled to provide the frequency control voltage to the voltage controlled oscillator; switch means operated in response to the coupling of any connection point of the first voltage divider with a corresponding connection point of the second voltage divider to conple the output terminal of the second voltage divider to the storage capacitor to develop the control voltage for providing the selected tone, said switch means also being responsive to the disconnection of any corresponding points of the first and second voltage dividers for uncoupling the output terminal of said second voltage divider from said storage capacitor to maintain the previously established control voltage.

30. The control voltage generating circuit of claim 29 in which said switch means comprises a flexible cord connected to a first stationary point, a rodconnected to the flexible cord, a spring connected between a second stationary point and the rod, a plurality of mechanical means for moving the flexible cord perpendicular to its length in response to the coupling of any corresponding connection points of the first and second voltage dividers, a first switch contact fixedly mounted adjacent the rod, a second switch contact of a flexible material mounted to engage the first switch contact, and a block arranged in sliding frictional engagement with the rod mounting the second switch contact for movement with the block.

31. A friction switch for completing an electrical circuit whenever one of a plurality of rnechanical selection means is operated and for open circuiting the electrical circuit whenever one of the plurality of mechanical selection means is released comprising: an elongated flexible member coupled between two stationary points, said flexible member including expandable spring means at one end coupled to one of said stationary points, said flexible member being disposed for engagement by each of said mechanical selection means to move the flexible member perpendicular to its length in response to the movement of individual ones of the mechanical selection means, a first switch contact, movable means for mounting said first switch contact in sliding frictional engagement with a portion of said flexible member adjacent the spring means, and a second switch contact fixedly mounted relative to said pair of stationary points and disposed to be contacted by said first switch contact when said flexible member is moved longitudinally by actuation of the mechanical selection means, whereby the second switch contact contacts the first switch contact to restrain further longitudinal movement of the movable means.

32. The friction switch of claim 31 further comprising a stop member fixedly mounted adjacent said second switch contact on the opposite side of said first switch contact to be engaged by said first switch contact when the flexible member is moved longitudinally in the other direction by the release of any of said mechanical selection means for preventing further longitudinal movement of the movable means in the other direction.

33. In a polyphonic musical instrument having a plurality of playing keys for producing solo tones from a voltage controlled tone generator, means providing a variable control voltage from a source, and circuit means for coupling the control voltage to control the frequency of said tone generator, said circuit means including switch means coupled to be operated by at least some of said playing keys to provide said control voltage to said tone generator upon the playing of at least one of said some of said playing keys and for disconnecting said control voltage means from said tone generator upon ceasing to play any one of a plurality of said some of said playing keys being simultaneously played.

34. An electronic polyphonic musical instrument for producing solo tones comprising: a plurality of playing keys for selecting certain musical tones; a voltage variable oscillator for producing oscillatory signals at the frequency of these selected tones; voltage divider means dividing a control voltage for said voltage variable oscillator to produce said selected tones; first switching means operated by said playing keys to select the proper control voltage from said voltage divider means; second switch means serially connected with said first switch means for providing the selected control voltage to said voltage controlled oscillator, said second switch means including switch control means operated by said playing keys for closing said second switch means upon operation of any one or more of said playing keys and for opening said second switch means upon release of any one of a plurality of said playing keys formerly operated simultaneously.

35. In a polyphonic musical instrument having a keyboard upon which chords may be played, the combination comprising: a voltage controlled variable frequency oscillator for generating the highest note of any chord played; a memory circuit for providing a control voltage to said variable frequency oscillator; a source providing a plurality of voltage amplitudes corresponding to the notes provided by keys of the keyboard; first switching means controlled by individual ones of said keys for contacting selected ones of said plurality of discrete voltage amplitudes; second switching means serially connected with said first switching means for providing a selected discrete voltage amplitude representative of the highest note of the chord played from said first switching means to said memory circuit upon operation of any key on said keyboard and for uncoupling said first switching means from said memory circuit upon releasing any of said keys played prior to releasing all of said notes in a chord to disconnect said first switching means from said source.

36. In an electronic musical instrument, a device for simulating the effect of the singing human voice comprising: the combination of a voltage responsive variablefrequency balanced oscillator, 21 memory circuit comprising a vacuum tube having anode, cathode and control grid elements, said cathode element being connected to control the frequency of said oscillator, a plurality of switching means, a voltage divider having a plurality of selectable voltage points, a timing capacitor interconnecting the grid and cathode of said tube, a charging resistor interconnecting the grid of said tube and said switching means for limiting the flow of charging current to said timing capacitor, and a uni-directional circuit path having a relatively small resistance compared to said charging resistor shunting said charging resistor for conducting a flow of discharging current from said timing capacitor, said switching means being adapted to connect said resister to diiTerent selected voltage points of said voltage divider to change the voltage on said timing capacitor, whereby the frequency of said oscillator is varied gradually in one direction by the flow of charging current through said charging resistor and is varied in discrete intervals in the other direction by the flow of discharging current through said uni-directional device in response to selection of diiferent switching means.

37. In an electronic solo musical instrument having playing keys for selectively sounding various notes in a musical scale, the combination comprising: a variable frequency oscillator having a control terminal; a memory circuit connected to the control terminal for selectively controlling the frequency of said oscillator; a control voltage source for providing a selectable control signal to the memory circuit and to the control terminal for controlling the frequency of said oscillator; switch means interconnecting said memory circuit to said source; and means responsive to the operation of at least one of said playing keys for closing said switch means to connect said source to said memory circuit and responsive to terminating the operation of any one of a plurality of simultaneously operated playing keys for opening said switch means to disconnect said source from said memory circuit to maintain the voltage signal applied to said control terminal by said memory circuit constant until a subsequent operation of at least one of said playing keys.

38. In a polyphonic electronic musical instrument, the combination comprising: a plurality of playing keys; a plurality of variable frequency balanced oscillators at least some of said oscillators including a multivibrator circuit having two electronic amplifying devices, a selectively variable source of supply voltage responsive to the operation of said keys for selectively varying the oscillation frequency, circuit means interconnecting said devices with said source of supply voltage for causing said devices to conduct in alternating fashion at selected audio oscillation frequencies corresponding to different notes in a musical scale, a first biasing resistor connected between one of said devices and a common terminal, a second biasing resistor connected between the other of said devices and the common terminal, said first and said second biasing resistors being connected in series combination between said devices, a third biasing resistor connecting said common terminal to said source, a first signal output terminal connected to the series combination of said first and second biasing resistors at a balance point on one of said resistors where a first signal voltage is developed at a frequency of twice the selected oscillation frequency, and a second output terminal connected to one of said devices where a second signal voltage is developed at the selected oscillation frequency, the number of oscillators being less than the number of playing keys; utilization means including an audio amplifier and speaker means for sounding the different musical notes having the frequency of the signal voltage applied thereto; and switch means for selectively connecting said first and second signal output terminals to said utilization means and operable in conjunction with said playing keys.

39. In a polyphonic electronic musical instrument, the combination comprising: a plurality of playing keys; a plurality of variable frequency oscillators having two electronic amplifying devices, a source of supply voltage selectively variable by operation of said keys for controlling the frequency of said oscillator, a separate biasing resistor for each of said devices, a first output terminal, each of said separate biasing resistors interconnecting one of the devices to said output terminal, a third biasing resistor interconnecting said output terminal to said source, at least one of said first and second biasing resistors being adjustable for balancing said oscillator so that a first output signal appearing at said first output terminal across said third resistor contains principally even harmonics of the oscillator frequency, the amplitude of the second harmonic being at least forty decibels greater than the amplitude of the first harmonic, and a second output terminal connecting to one of said devices for providing a second output signal at said oscillator frequency, the number of oscillators being less than the number of playing keys; utilization means including an audio amplifier means for sounding notes at the frequency of the output signal applied thereto; and switch means for selectively applying said first or second output signal to said utilization means and operable in conjunction with said playing keys.

References Cited by the Examiner UNITED STATES PATENTS 2,274,199 2/1942 Hammond 84-1.01 2,355,287 8/1944 Firestone 84-124 2,499,576 3/1950 Farr 331-167 2,540,478 2/1951 Frost 331-144 2,544,017 3/1951 Golicke 331-179 2,563,477 8/1951 Martin 84-125 2,720,133 10/1955 Morgan 841.24 2,918,576 12/1959 Munch 84-126 3,048,719 7/1962 Grigsby 307-885 3,049,959 8/1962 Meyer 84-1.17

DAVID J. GALVIN, Primary Examiner.

Claims (1)

1. AN ELECTRONIC MUSICAL INSTRUMENT COMPRISING A VARIABLE FREQUENCY TONE GENERATOR HAVING A CONTROL TERMINAL, A KEYBOARD, AND MEANS FOR APPLYING SIGNALS TO THE CONTROL TERMINAL TO CHANGE THE FREQUENCY OF OPERATION OF THE GENERATOR IN RESPONSE TO THE MANIPULATION OF THE KEYBOARD, SAID SIGNAL APPLYING MEANS INCLUDING UNILATERALLY CONDUCTIVE MEANS FOR DECREASING THE FREQUENCY IN DISCRETE INTERVALS AND MEANS FOR IMPARTING A PORTAMENTO EFFECT TO INCREASES IN THE FREQUENCY OF OPERATION OF THE GENERATOR.

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