Keagle, Charles (New York, NY)
Waggoner, Alan (Seattle, WA)
Phillips, Peter (New York, NY)

05/119714

01/02/1973

03/01/1971

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84/695

84/703, 984/309, 84/697, 84/699, 84/707

G10H1/02; G10H3/00

84/1.01,1.09,1.17,1.24,1.27,1.26,DIG.7,DIG.8,1.11

Myers, Lewis H.

Weldon U.

What is claimed is

1. An electronic sound generator comprising: means for generating a train of oscillating waves; a plurality of circuit means for generating d.c. signals of different amplitudes; a plurality of means for selectively actuating said plurality of circuit means for generating corresponding d.c. signals; means for summing the output of the d.c. signals generated by said actuated circuit means; means responsive to the sum of said generated d.c. signals for generating a control voltage, the amplitude of which varies in accordance with the variation in the amplitude of the sum of said generated d.c. signals; means for modulating said train of oscillating waves with said control voltage; and means for converting said modulated train of oscillating waves into audible sounds.

2. The generator according to claim 1, including a d.c. voltage supply wherein said plurality of circuit means include a plurality of electronic switches and means for biasing said switches so that they are normally turned off; said plurality of actuating means include a plurality of touch plates, each plate having a dielectric means, first and second conductors spaced from each other by said dielectric means, said first conductor connected to said d.c. voltage supply and said second conductor connected to a corresponding one of said switches wherein said dielectric means is dimensioned so that it can be bridged by a fingertip to provide a conducting path for said d.c. voltage supply to actuate the corresponding switch.

3. The generator according to claim 2, wherein each of said switches includes a field effect transistor connected to the corresponding one of said touch plates so that said field effect transistor is actuatable by said d.c. voltage supply when the corresponding one of said dielectric gaps between the first and second conductors is bridged over conductively, a transistor responsive to the actuation of said field effect transistor for generating the d.c. signal, and a variable impedance means connected to the output of said transistor for setting the amplitude of said d.c. signal.

4. The generator according to claim 1, wherein said responsive means includes first and second metal oxide silicon field effect transistors and an operational amplifier connected in series, the source electrode of said first field effect transistor being connected to the said summing means, and the drain electrode of said first field effect transistor being connected to the gate electrode of said second field effect transistor, the source electrode of said field effect second transistor being connected to said operational amplifier.

5. The generator according to claim 4, wherein said responsive means further includes a potentiometer interposed between said d.c. supply voltage and the source electrode of said first metal oxide silicon field effect transistor for controlling the amplitude of said control voltage.

6. The generator according to claim 4, wherein said responsive means includes a capacitor shunted between the input terminal of said second field effect transistor and the output terminal of said operational amplifier for maintaining the control voltage output at the previous level between successive actuations of said switches.

7. The generator according to claim 2, including a common emitter transistor stage interposed between the drain electrodes of said field effect transistors in said plurality of electronic switches and unipolar conducting means connected to the collector electrode of said common emitter transistor stage to respond to the actuation of any said plurality of circuit means for generating a positive gating voltage, wherein said converting means is adapted to respond to said gating voltage for synchronizing the operation thereof to the actuation of said circuit means.

8. The generator according to claim 7, wherein said means for generating oscillating waves includes a first wave generator for generating trains of first sawtooth waves, a second wave generator for generating first square waves, in response to said first sawtooth waves, and means for sending out said sawtooth waves and square waves selectively, and a third wave generator responsive to the output of said first and second wave generators and said control voltage, for generating trains of second square waves, triangular waves and second sawtooth waves, and means for combining said trains of waves into a single train of composite waves.

9. The generator according to claim 8, wherein said converting means include filtering means responsive to said gating voltage for filtering said train of composite waves.

10. The generator according to claim 9, wherein said filtering means includes a variable RC impedance network and first operational amplifier connected in a series, connected to the output of said third wave generator to respond to said train of composite waves, and a control circuitry responsive to said gating voltage for generating a control signal for modifying the filtering characteristics of said variable RC impedance network.

11. The generator according to claim 10, wherein said control circuitry includes a filter input control circuitry having a field effect transistor, first and second passive impedance networks interposed between the gate electrode of said field effect transistor and the gating voltage output terminal, and a grounded capacitor connected to the gate electrode, said networks being adjustable to control the rise and fall time of said control signal, respectively.

12. The generator according to claim 11, wherein said first and second passive impedance networks are connected in parallel and respectively include a variable resistor for controlling the amplitude range of said control signal and a diode connected in series, and wherein the diode of said first network is poled opposite to that of said second network.

13. The generator according to claim 12, wherein said control circuitry includes means for setting the control signal to zero amplitude when the gating voltage is set at zero.

14. The generator according to claim 13, including second and third operational amplifiers connected in series and responsive to the output of said filter input control circuitry, said variable RC impedance network including the first half of a dual field effect transistor and a capacitor, the other half of said dual field effect transistor being shunted by the inverting input of said third operational amplifier to ground.

15. The generator according to claim 14, wherein the source electrode of said first half of the dual field effect transistor is connected to the output of said second wave generator, the drain electrode thereof is connected to the input of said first operational amplifier, the gate electrode thereof is connected to the output of said third operational amplifier, and a capacitor is shunted between the input to said first operational amplifier and ground, for providing a low pass filtering action.

16. The generator according to claim 14, wherein the capacitor of said variable impedance is interposed between the input terminal and said first operational amplifier, said first half of said dual field effect transistor is connected between the input of said first operational amplifier and ground, for providing a high pass filtering action.

17. The generator according to claim 10 wherein said converting means includes an envelope control circuitry responsive to said gating voltage for providing a high and a low pass filtering action, selectively, and a voltage controlled amplifier responsive to the output of said envelope control circuitry for shaping the attack and decay characteristics of the modulated and filtered signal from the output of said filtering means.

18. The generator according to claim 17, wherein said envelope control circuitry includes a field effect transistor, a first and second impedance network connected in parallel and interposed between said field effect transistor for controlling the output of said field effect transistor proportional to the amplitude of the gating voltage, and means for setting the output of said field effect transistor to zero voltage when said gating voltage is set at zero.

19. The generator according to claim 17, wherein said voltage controlled amplifier circuitry includes first and second amplifying stages connected in series, and said envelope control circuitry controlling the attack and decay characteristics of the amplification provided by said first amplifying stages.

20. The generator according to claim 1, wherein said converting means includes a mixer for combining the outputs of said modulating means, and a series network of reverberator, tone control circuit, power amplifier and speaker responsive to the output of said mixer.

21. An electronic sound system comprising means for supplying d.c. voltage; a plurality of generators for producing a plurality of decaying a.c. signals, said generators including a plurality of networks having twin - T tuned oscillators connected to inverting amplifiers, a keyboard means having a plurality of conductive paths connected between said generators and said d.c. voltage supply means respectively, dielectric means interposed in said plurality of conductive paths, wherein shorting of selected ones of said conductive paths, energizes corresponding ones of said generators, means for converting said a.c. signals into audible sounds, and a disturbance generator connected between said T tuned oscillators and said conductive paths, wherein aid disturbance generator includes a field effect transistor connected to a conductor pair of said keyboard means for setting said field effect transistor in a normally non-conducting state, and a transistor coupled to said field effect transistor for supplying an enabling trigger signal to one of said T tuned oscillators upon actuation of said field effect transistor when said pair of conductors is touched thereby supplying enabling power to said field effect transistor.

22. The system according to claim 21, wherein each of said plurality of conductive paths includes, first, relatively flat, elongated conductive strips having bifurcated projections and, second, a relatively flat, elongated conductive strip positioned between said bifurcated projections, and a dielectric material interposed between said first and second strips, wherein the plurality of corresponding pairs of conductive strips are provided with exposed conductive surfaces which can be shorted by touching.

23. The system according to claim 22, wherein each of said plurality of generators includes a ringing circuit continuously tunable over a range of frequencies and one of said disturbance generator for applying a trigger signal to said ringing circuit when a pair of corresponding strips is shorted by the touch and capacitive means shunted across ringing circuit for slowing the return of said disturbance generator to its off state after the touch across the conductor pair is removed.

24. The system according to claim 21, further including means for enabling said transistor to turn off gradually when the touch is removed and the field effect transistor is thereby de-energized.

25. The system according to claim 26, wherein said preventing means includes a capacitor connected across said transistor.

26. The system according to claim 21, further including an inverting amplifier network coupled to said ringing network, said amplifier network having means for introducing high and low distortion to the output of said collector selectively.

27. The system according to claim 26, wherein said high and low distortion introducing means includes a series network of a diode and a switch shunted across said amplifier network.

28. The generator according to claim 27, further including an output amplifier stage coupled to the outputs of a plurality of inverting amplifiers.

29. The system according to claim 21, wherein said plurality of generators include a plurality of ringing networks adapted to generate damped ringing signals of different frequencies respectively for simulating multi-frequency drum signals, a plurality of local mixers for combining the outputs of a predetermined number of said ringing networks, and a final mixer for combining all of the outputs of said plurality of local mixers, and a converting means for producing sounds responsive to the output of the final mixer.

30. The system according to claim 29, wherein each of said plurality of generators includes a ringing network and a disturbance generator for enabling said ringing network to generate a damped ringing oscillatory signal in response to the voltage applied thereto through said keyboard means upon touching and shorting of corresponding pairs of said conductor paths.

31. The system according to claim 30, wherein said ringing circuitry includes means for tuning it to a different frequency, and said disturbance generator includes a field effect transistor circuit connected in series, and capacitive means shunted across said transistor for slowing the return of said transistor to the off state after the touch across the conductor pair is removed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electronic instruments for generating audible sounds generally and,more particularly, to an electronic sound synthesizer for generating orchestrated and other sounds of different characteristics.

2. Brief Description of the Prior Art

Electronic instrumentation to generate sounds which are similar to those produced by more generally known means such as the human voice and conventional musical instruments is a relatively recent innovation. Generally speaking, available electronic sound generators are complex and expensive.

BRIEF DESCRIPTION OF THE INVENTION

It is therefore an object of the present invention to provide a simplified and relatively inexpensive electronic system for generating sounds of certain characteristics in general and, more particularly, orchestral sounds of different natures.

It is another object of the present invention to provide an electronic system which can produce and synthesize sounds having different characteristics.

It is a further object of the present invention to provide the combination of an electronic sound synthesizer and novel electronic distribution means for providing plurality of audible outputs.

It is still another object of the present invention to provide means for modifying the tonal character of the electronically generated sounds.

These and other objects of the present invention are achieved by providing an electronic sound synthesizer which includes one or more generators, each designed to generate voltages of predetermined amplitudes, and means for converting the voltages into audible sounds. The generator is provided with a d.c. voltage source, a plurality of electronic switches, and a plurality of conductive paths for selectively connecting the switches to the d.c. voltage source. Each path includes a relatively flat conductor pair, spaced by a dielectric means of such a dimension that the space can be readily bridged over by a fingertip to short the path and thereby energize the corresponding switch. The switch provides a selective current path through a variable resistor to a summing point at the input of a current summing amplifier. The output of this amplifier provides variable potentials which are used to control voltage sensitive wave generators. The plurality of conductive paths may be conveniently mounted on a dielectric board and aligned in the manner of a conventional musical keyboard.

The wave generators are designed to provide wave forms of desired characteristics. The wave forms are modulated and filtered to produce outputs of certain desired characteristics. The converting means includes a mixer, reverberator, tone control circuit, power amplifier and speaker interconnected for converting the electrical signals produced by one or more of the sound generators into audible sounds.

It is a feature of the present invention to provide one or more auxiliary wave generators for generating a train of waves which are used to modulate the output of other wave generators as described above and a filter and voltage controlled amplifier for modifying the attack and decay characteristics of the modulated electrical signals before they are applied to the converting means. In this manner, the various parameters of pitch, overtones, amplitude envelope, and duration of tones, etc., of the sounds produced by the synthesizer are shaped to produce output sounds having the desired characteristics.

It is still another feature of the present invention to provide a synthesizer having a plurality of oscillators for generating a plurality of percussive sounds such as those of drums.

It is another feature of the present invention to provide a plurality of ringing circuits in a touch controlled generator of a design that can operate as a multi-voice rhythm band.

It is a further feature of the present invention to provide wave generators, ringing oscillators, filters and voltage controlled amplifiers uniquely designed to enhance the overall function of the electronic sound synthesizer.

It is still another feature of the present invention to provide a light controlled multi-channel distributor for distributing the outputs of the synthesizer to different channels in a predetermined sequence or sequential set.

The aforementioned and other objects and features of the present invention will become more apparent from the following detailed description of the present invention and the accompanying drawings showing several embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic block diagram of an embodiment of the electronic sound synthesizer in accordance with the present invention;

FIGS. 2 through 6 show in detail various components of the block diagram of the synthesizer shown in FIG. 1 in which the figures detailing the blocks are parenthetically identified, wherein;

FIG. 2 shows in detail a novel touch controlled voltage generator in accordance with the present invention;

FIG. 3 shows a wave generator designed to generate any combination of trains of square waves and sawtooth waves either of a fixed frequency or in response to the touch controlled generator shown in FIG. 2;

FIG. 4 shows a second wave generator designed to generate any combination of trains of square waves, sawtooth waves and triangular waves in response to the outputs of the first wave generator shown in FIG. 3 and the touch controlled generator shown in FIG. 2;

FIG. 5 shows filter responsive to the output of the touch controlled generator and the output of the second wave generator shown in FIG. 4;

FIG. 6 shows a voltage controlled amplifier responsive to the outputs of the touch controlled generator, and the filter for modifying the transient amplitude characteristics of the generator output;

FIGS. 7 and 8 shows wave forms at various locations in the synthesizer shown in FIGS. 2 through 6;

FIG. 9 shows another embodiment of the present invention including a touch controlled generator for producing percussive sounds similar to those of drums;

FIG. 10 shows wave forms at certain locations of the circuit of FIG. 9;

FIG. 11 shows still another embodiment of the present invention including a touch controlled generator designed to produce a multi-voice rhythm band;

FIG. 12 shows in detail a twin-T oscillator, a plurality of which may be used in the multi-voice rhythm band shown in FIG. 11;

FIGS. 13 through 15 show a multi-channel sound distribution system wherein FIG. 13 shows a system having photosensitive elements interposed between a plurality of input and output terminals, respectively;

FIG. 14 shows a housing for enclosing the system shown in FIG. 13; and

FIG. 15 shows means for selectively exposing the photo-resistive elements to a beam of light.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring generally to FIGS. 1 through 8 of the drawings, the electronic sound synthesizer of the present invention includes a touch controlled generator having a plurality of electronic switches which are selectively actuable when a d.c. voltage source is applied thereto by shorting normally open conductive paths or touch plates interposed between the switches and the d.c. voltage source.

With apparatus in accordance with the invention, rather complex sounds having a wide range of frequency, amplitude, attack and decay, and overtone characteristics can be produced by modulating trains of predetermined wave shapes such as square, triangular, and/or sawtooth waves with the aforedescribed touch controlled generator and then putting the modulated outputs through a filter, reverberator, voltage controlled amplifier, and thereafter through a tone control circuit, power amplifier and speaker, as generally illustrated in FIG. 1, and more particularly shown in FIGS. 2 through 8.

The touch controlled generator also may be designed to generate certain sounds such as those of drums and multi-voice rhythm bands without the use of the variable d.c. voltage generators, filter and voltage controlled amplifier. Thus, as shown in FIG. 9, the synthesizer may be modified to generate drum sounds or, as shown in FIG. 11, it may be modified to generate sounds of a multi-voice rhythm band.

In the case of the drum sounds or multi-voice rhythm band generator, the outputs thereof may be fed directly into their own mixer and speaker to produce the desired audible sounds. As an alternative, the outputs thereof may be mixed with a plurality of other inputs, reverberated and amplified, and then converted into audible sounds.

Referring to FIG. 2, the touch controlled generator is designed to generate two output signals, namely a gating pulse and a control voltage, when any one or more of the touchplates in the generator are shorted selectively. More particularly, the generator includes a plurality of electronic switches 15a, 15b - - 15n, respectively, connected to a +12 volt source through normally open conductor paths or plates 16a, 16b - - 16n, and a current limiting resistor 17. Each of the switches includes a field effect transistor FET 18, and NPN transistor 19, and a variable potentiometer 21.

Each of the conductive paths 16a, 16b - - 16n, has a bifurcated, flat conductor strip 23 connected to the current limiting resistor 17 and another flat strip 25 positioned between the bifurcation 23 and connected to the gate electrode 27 of the FET 18. The conductor paths 16a, 16b - - 16n may be formed on a flat, dielectric substrate board 29 in a conventional manner so that the surfaces of the paths are in the surface plane of the dielectric board. Preferably, the dielectric gap between the conductors of each strip pair 23 and 25 is dimensioned so that the gap and the strip pair form a touch plate which can be shorted by a finger tip. The normal moisture on the surface of the fingers provides an excellent conducting path for short circuiting the dielectric gap.

Each of the gate electrodes 27a - - 27n of the FET is negatively biased with a -12 volt source through its current limiting resistor 33a, 33b - - 33n. A transistor network 35, connected to all of the switches in the manner shown, includes a PNP transistor 37 connected in a common emitter configuration with its emitter electrode connected to the +12 d.c. voltage source and its collector electrode connected to a bias resistor 39.

The drain electrodes 41a, 41b - - 41n of the FETs 18a, 18b - - 18n are respectively connected to the +12 volt d.c. voltage source through a resistor 43 shunted across the base and emitter electrodes of the transistor 37. The source electrodes 45a, 45b - - 45n of the FETs 18a, 18b - - 18n are respectively connected to ground through the base and emitter electrodes of the corresponding NPN transistors 19a, 19b - - 19n as shown. The collector electrodes of the transistors 19a, 19b - - 19n are connected to the respective variable potentiometers 21a, 21b - - 21n through corresponding range limiting resistors 22a, 22b - - 22n. Currents through the switches 15a, 15b - - 15n pass through a summing bus 51 which forms a common junction at the outputs of all of the variable potentiometers 21a - - 21n along with the range limiting resistors 22a - - 22n.

The touch controlled generator further includes one or more sets of cascade connected metal oxide semiconductor field effect transistors MOSFET 55 and 57 and a suitable operational amplifier 59 such as the integrated circuit type 741 operational amplifier/manufactured by Fairchild Semiconductor (Model μA741) which responds to the current produced in the common bus 51 whenever any one of the touchplates is activated or touched. In this manner, a voltage is generated at the output terminal 60 the magnitude of which can be selected by touching one or more of the touchplates and adjusting the respective potentiometers. The generator includes another output terminal 61, connected to the collector electrode of the transistor 37 through a current limiting resistor 62 and a diode 63 connected as shown to provide a positive gating pulse when any touchplate is activated or touched.

More specifically, the aforementioned MOSFETs 55 and 57 and amplifier 59 are connected in the following manner: the common bus 51 is connected to the source electrode 65 of the MOSFET 55. The collector electrode 64 of the transistor 37 is connected via a resistor 68 to the gate electrode 67 of the MOSFET 55. The drain electrode 69 of the MOSFET 55 is connected to the gate electrode 71 of the MOSFET 57. The source electrode 73 of the MOSFET 57 is connected to a ground through a resistor 75. The voltage across the resistor 75 forms an input to the negative (-) input terminal of the amplifier 59. The drain electrode 74 of the MOSFET 57 is connected to a +12 volt d.c. voltage source. The positive (+) input terminal of the amplifier 59 is provided with a positive d.c. bias by means of the voltage dividing resistors 81 and 82 connected between the +12 volt source and ground. The amplifier 59 includes the capacitors 83, 84 and 85 connected in the manner shown to bypass a.c. ripples or noise signals. The amplifier 59 itself is furnished with +12 volt and -12 volt d.c. supplies in a conventional manner as shown. A storage capacitor 86 is connected from the output terminal 87 of the amplifier 59 to the gate electrode 71 of the MOSFET 57. This holds the output voltage at 87 at the previous level, even if the touching finger is removed, and until another switch is energized.

The bias voltage at the output terminal 87 of the amplifier 59 is set by a biasing network comprising resistors 91, 92, and 93. The amplitude range at the output of the amplifier 59 is controlled, that is, compressed or expanded, by varying the magnitude of the resistor 92. Similarly, the source electrode 65 of the MOSFET 55 is biased at a suitable level by a network comprising resistors 91, 96 and 97 connected in the manner shown and the bias level at the source electrode 65 is controlled by varying the resistor 96.

The touch controlled generator operates as follows: Each of the conductor paths or touch plates 16a, 16b - - 16n controls its associated FET 18a, 18b - - 18n and in turn the base drive of the corresponding NPN transistor 19a, 19b - - 19n. The FETs are normally turned off by applying the -12 volt source to the gate electrodes 27a, 27b - - 27n through the resistors 33a, 33b - - 33n. When a touchplate or path,for example 16a, is touched and activated, the bias on the gate electrode 27a changes from -12 volts to a value near zero. This causes a few micro amperes of current from the +12 volt source to flow through the touchplate 16a and the performer's touching finger. This turns on the FET 18a. When the FET 18a is turned on, its drain electrode 41a draws current from the +12 volt source through the resistor 43 and the source electrode 45a. This current flows through the base electrode of the transistor 19a, and then to ground. When the current so drawn reaches approximately one milliampere, the transistor 37 turns on, and the voltage on its collector goes from -12 volts to approximately +12 volts. This is used as the gating pulse signal source. The gating signal is applied to the output terminal 61 through the resistor 62 and the diode 63. The diode 63 allows only the positive portion of the gating pulse to reach the output terminal 61. A resistor 99 is connected in the manner shown to provide a ground reference at the output terminal 61.

The gating signal at the collector of the transistor 37 is also used to turn on the MOSFET 55 through the resistor 68. The MOSFET 55 is designed to function as a switch so that it is either on or off. When one of the conductor paths 16a - - 16n is shorted, the voltage on the gate 67 of the MOSFET 55 changes from approximately -12 volts to +10 volts. When a particular touch plate or path,for example 16a, is touched, the particular FET 18a and transistor 19a associated therewith are turned on and draw current through the corresponding range limiting resistor 22a and range controlling potentiometer 21a. This current is applied to the source electrode 65 of MOSFET 55 through the summing bus 51. At this point, the MOSFET 55 is turned on by the action of the voltage change at the collector electrode of the transistor 37 and thereby effectively connects the summing bus 51 to the gate 71 of the MOSFET 57 via the drain electrode 69 of the MOSFET 55. The MOSFET 57 functions as a source follower for applying signals to the inverting, or the negative (-), input of the amplifier 59. Amplifier 59 acts as a current summing amplifier. MOSFET 57 acts as a high impedance negative input terminal to the amplifier 59 and allows the capacitor 86 to function as a storage memory, or holding device. The output voltage of the MOSFET 57, acting as the source follower, is developed across the resistor 75. The voltage at the output 87 of the amplifier 59 is controlled by the amount of current drawn in the current summing bus 51 which is in turn controlled by the potentiometer 21a through the particular switch connected to the touch plate 16a that has been activated by a touch of a finger. When the activating touch is removed, the voltage at the gate 67 of the MOSFET 55 goes negative and thereby turns it off. This breaks the connection from the gate 71 of the MOSFET 57 to the summing bus 51. The voltage output of the amplifier 59, however, remains at the value at which it was set when the MOSFET 55 was conductive, even after the performer has released his touch and the MOSFET 55 is turned off. This is made possible by the charge stored in the memory capacitor 86.

The output, at 87, of the amplifier 59 is attenuated by the potentiometers 94 and 95. A switch 98 makes it possible to apply the output at terminal 87 directly to the potentiometer 95 or through potentiometer 94 and then to the potentiometer 95 in order to attenuate it. The switch 98 functions to switch the output at the terminal 60 from one voltage range to another, while the potentiometers 21a, 21b - - 21n are used to vary the voltage range selectively, as the various conducting paths are touched. The control voltage and gating pulse generated in the aforedescribed manner are applied, respectively, to the wave generator B, the filter, and the voltage controlled amplifier through a suitable plug type connector, shown in the form of a block 64.

FIGS. 3 and 4 show wave generators A and B, respectively, which are voltage sensitive types. They are essentially identical except for certain differences in the processing of the incoming signals.

Referring to FIG. 3, wave generator A includes a type 741 operational amplifier 101, which may embody integrated circuitry, used as a voltage integrator. It integrates a d.c. voltage at its positive terminal and stores the integrated voltage in a capacitor 105. When the voltage of the capacitor 105 reaches the firing potential of the unijunction transistor UJT 103, it breaks down and conducts. This causes the capacitor 105 to discharge through a diode 135. This cycle is repeated to produce, at the output 107 of the amplifier 101, a sawtooth wave-form having a constant magnitude and a repetition rate depending on the input voltage level at the positive (+) input terminal 109 of the amplifier 101. Generally, known integrators have the positive (+) input terminal 109 grounded and a current applied to the negative (-) input terminal 111. Thus such integrators are current integrators in that the output voltage is proportional to the negative integral of the current applied to the negative terminal. In contrast, according to the present invention, the input voltage is applied to the positive (+) input 109 through a network consisting of the resistors 119, 121 and 122. In the case of wave generator A, a voltage may be applied through the jack 115 or, alternatively, the output plug 64 of the touch controlled generator may be coupled to the jack 100 so that the control voltage of the touch controlled voltage generator controls the output frequency of the wave generator A. The input voltages are attenuated through the resistors 119 and 121, and through the potentiometer 122. There is also a constant d.c. potential of +6 volts applied to the jack 115 at the point 120 from the +12 volts supply 123 as divided by the resistors 125 and 126. This potential of +6 volts produces a reasonably high audio frequency oscillation that remains constant if nothing is plugged into the jack 115. If a plug is inserted in the jack 115, the +6 volts bias is disconnected.

An attenuated signal from the jack 115 or the terminal plug 100 is applied to the positive terminal 109 of the amplifier 101 and causes the amplifier 101 to operate. A current will flow to the negative terminal 111 from the amplifier output 107 through a diode 127 and a capacitor 105 so that an equivalent positive voltage appears at the negative terminal 111 across a resistor 129. When the voltage across the capacitor 105 reaches the firing potential of the UJT 103, the resistance between the emitter 131 and the base 132 of the UJT 103 becomes very small. When the UJT 103 fires, the capacitor 105 discharges through the UJT 103 and the diode 135. A resistor 136 provides a means for holding the base 132 of the UJT 103 at the ground potential. Thus the diode 135 serves the dual function of isolating the negative input 111 of the amplifier 101 from the resistor 136 to ground and of providing a path for the discharging capacitor 105. The diode 139 prevents the output 107 of the amplifier 101 from producing a large negative voltage if a negative voltage is applied to the positive input 109. The output 107 of the IC 101 is a positive going sawtooth wave whose repetition rate depends on the magnitude of the positive control input voltage at the positive input terminal 109. The amplitude of the sawtooth wave depends on the characteristics of the particular unijunction transistor UJT 103 used. The output at 107 is coupled to a potentiometer 142 via a d.c. isolating capacitor 143. The potentiometer 142 is an attenuator which allows adjustment of the amplitude of sawtooth wave signals applied to the input of a two-input, common emitter, inverting, transistor amplifier 154 of a conventional design, as shown. Various parameters of the inverting amplifier are adjusted to invert the inputs and provide unity gain.

Another input of a square waveform also may be applied to the inverting amplifier, the square waveform being derived from the sawtooth wave by a conventional transistorized squaring network 170 of an appropriate design, as shown. The squaring network includes the attenuating potentiometers 173 and 174 so that the duty cycle and the amplitude respectively of the output can be adjusted. Either or both of the outputs of the squaring network 170 and the amplifier 101 may be applied to the inverting amplifier 154 by means of the switches 178 and 177, respectively, as shown. The output of the inverting amplifier 154 at its collector 157 is RC coupled to an output jack 181. The output so obtained is internally applied via a conductor 201 to the input jack 203 (FIG. 4) of the wave generator B, so long as neither of the jacks are plugged.

While its normal function is to provide a suitable output for use in modulating the wave generator B, the wave generator A may also be used to produce pitches by connecting the plug 64 to the jack 100, then externally connecting its output directly to one of the mixer input jacks. In this way, the wave generator A can be modulated by the control voltage output of the touch controlled generator through the conductor 60 via the jack 100.

FIG. 4 shows the wave generator B, which is essentially the same as the wave generator A except in the way the input and output means are arranged. The wave generator B is the primary frequency (pitch) generator of the embodiment of the invention. It is designed with the potential of being frequency modulated by the output of either the wave generator A or that of the touch controlled generator or both.

The input at point 201 is attenuated by a potentiometer 205 to control the magnitude of the effect that the wave generator A has on the wave generator B. Thus the inputs to wave generator B are either from the output of wave generator A, through the conductor 201 or from the jack 203. Another input may be obtained from the jack 207, or through the conductor 60 from the jack 102 connected to the plug 64 which, in turn, is connected to the touch controlled generator shown in FIG. 2. These inputs are summed through the resistors 119' and 121' and fed to the positive input terminal 109' of a type 741 operational amplifier 101'. (Reference numerals are primed where they are identical with those of FIG. 3).

As shown in FIG. 7A and 7B, the output of the wave generator A is a train of inverted sawtooth and square waves, respectively, depending on which of the switches 177 and 178 is closed and which is open. Given a d.c. voltage of a fixed amplitude at terminal 109', the wave generator B will produce a square wave train as shown in FIG. 7C, a triangular wave train, FIG. 7D, and a sawtooth wave train, FIG. 7E, at potentiometers 174', 217 and 142', respectively.

The output of the wave generator B at 107' is a train of waves whose frequency varies according to the voltage present at the input 109', which is obtained from the wave generator A through the conductor 201, or from a source of voltage external to the system through either jack 203 or 207, or from a control voltage from the touch controlled generator through the jack 102 and the conductor 60, or from any combination of these sources. Thus, if the output of the wave generator A is adjusted to a square wave (shown in FIG. 7G) and this is applied through the internal conductor 201 to the input of the wave generator B, the output of wave generator B at point 107' will appear as shown in FIG. 7F, assuming that all other voltages at input points to generator B are constant. The sawtooth wave train is coupled through a d.c. blocking capacitor 143' and is attenuated by a potentiometer 142'. After passing through the inverting amplifier 154', the wave appears at the jacks 221 and 223 as an inverted sawtooth wave train.

As in the oscillator A, a squaring network 170' is connected to the output of the operational amplifier 101'. This produces a train of square waves (FIG. 7C) at its output 171 of the same frequency as the train of sawtooth waves at the output 107', and the duty cycle T of the waves can be varied by a potentiometer 173' in the squaring network. The output of the squaring network is RC coupled to the summing point 158' of the inverting amplifier 154' through an attenuating potentiometer 174' and the resistor 210. Two RC networks formed by a resistor 211 and a capacitor 212 and a resistor 214 and a capacitor 215, respectively, function as an integrator to convert the square wave train, such as FIG. 7C, into a triangular wave train, FIG. 7D. The triangular wave train is relatively low in harmonic content and is attenuated by a potentiometer 217 and applied to the summing point 158' through a resistor 219. Accordingly, the inverting amplifier 154' functions as the summing amplifier of the three aforementioned input waves.

The output voltage of the inverting amplifier 154' is proportional to the sum of the square wave input as attenuated by the potentiometer 174', the triangular wave input as attenuated by the potentiometer 217, and the sawtooth wave input as attenuated by the potentiometer 142'. If, for example, the train of rectangular waves, as shown in FIG. 7G, from the wave generator A through the conductor 201 is applied to the input of the wave generator B, and if the attenuators 174' and 217 are set to full attenuation, the output wave form at the conductor 225 would appear in the form shown in FIG. 7F, but inverted. Thus, the output of the wave generator B at the jacks 221 and 223 may be an inverted sawtooth, a square or triangular wave individually, or any additive combination of the three, each having the same frequency. The output of the inverting amplifier 154' is RC coupled to the jacks 221 and 223. If the jack 223 is not plugged, then the output of the oscillator B is directly connected through the conductor 225 to the input of the voltage controlled filter, shown in FIG. 5. With a control voltage wave train of the shape shown in FIG. 7I from the output conductor 60 of the touch controlled generator applied to input conductor 60' of the wave generator B through the plug 64 and the jack 102 and with the attenuators 142' and 217 adjusted so as to null the sawtooth and triangle waves generated by the wave generator B, the output at terminal 225 is in the form shown in FIG. 7H. For the sake of clarity, FIGS. 7H and I assume the output 60 of the touch controlled generator and are the only voltage appearing at the input to the wave generator B.

However, it is evident from the above description that the output of the wave generator B, at the jacks 221 and 223, is a composite of the trains of sawtooth waves, triangular waves, and rectangular waves of varying amplitudes, and the frequency of the output is largely dictated by the amplitude of the control voltage from the touch controlled generator.

FIG. 5 illustrates the voltage controlled filter of an RC type wherein a capacitor 231 is used as the capacitive element, and one half of a dual field effect transistor FET 233a is used as the variable resistor. The capacitor 231 and the FET 233a may be connected as shown in FIG. 5 to act as a low pass filter, or in the manner shown in the inset 135 as a high pass filter. The various parameters of the filter are adjusted to provide a 6 dB per octave rolloff.

As shown, the output signal from the jack 223 of the wave generator B, FIG. 4, is applied as the input signal at the jack 237. The input signal is attenuated by a voltage divider network formed of resistors 239 and 241 to a level of approximately 0.1 volts. It is then applied to the FET 233a, which acts as a variable resistor having a value which is determined by the voltage at its gate 243. The high frequency components are filtered out through the capacitor 231 connected in the manner shown. A 741 type integrated circuit operational amplifier 242 is provided to amplify the resulting signal across the capacitor 231. Another input, unfiltered, is applied to the negative terminal (-) of the amplifier 242 via the jack 248 and the resistor 249. The resistors 251 and 253 set the feedback characteristics around the amplifier 242 to compensate for the losses through the voltage divider network resistors 239 and 241, the FET 233a and the capacitor 231.

The drive voltage for the gate 243 of the FET 233a is derived from the gating voltage output at the conductor 61 of the touch controlled generator applied through a filter control network 241, a pair of 741 type integrated circuit operational amplifiers 243 and 245, and the other half of the FET 233, namely FET 233b, as explained in detail below.

The resistors 251 and 253 form a voltage divider to bias the positive input of the amplifier 245 to approximately -0.1 volts. A small current flows through the FET 233b, and the voltage at its gate 255 is varied by the input 257 of the amplifier 245, so that approximately -0.1 volts appears across the FET 233b at point 257. Thus the FET 233b acts as a variable resistor whose value is set by the current flowing therethrough. A larger current will cause the amplifier 245 to change the voltage at the gate 255 of the FET 233b so that the resistance from the point 257 to ground through the FET 233b decreases. The current through the FET 233b is set at some minimum value, for example approximately 1.0 microamperes, by the resistor 261. Additional current can flow through the FET 233b, resistor 263 and diode 265 from the output of the amplifier 243.

The amplifier 243, used in conjunction with the resistors 267 and 269, functions as a unity gain, inverting voltage amplifier under the control of the filter input control circuitry 241. The resistance across the source and drain terminals 275 and 277 of the FET 233a is inversely proportional to the output voltage amplitude of the amplifier 245 applied to the gate electrode 243. This makes the cutoff frequency of the filter output at 307 directly proportional to the voltage at the input 271 of the amplifier 243. This is illustrated in FIG. 8A.

The filter input control circuitry is designed to provide somewhat less than unity gain and is a source follower type amplifier which changes the rise and fall speeds of a square wave input at the filter control jack 279 and applies the changed square wave at its output terminal 281. A square wave of approximately 10 volts is applied to the filter at the jack 279 or, alternatively, the pulse train output at the conductor 61 of the touch controlled generator, FIG. 2, is applied to the jack 279 as shown. A series network of resistors 283, 285, and the diode 287, in conjunction with the capacitor 295 connected in the manner shown, determines the fall time of the output of the control circuitry. Another similar series network of resistors 289 and 291 and the diode 293 in conjunction with the capacitor 295 determines the rise time. When the potentiometers 283 and 289 are set at their minimum values, the rise and fall of the waveform at the output terminal 281 are sharp as shown in FIG. 8B, whereas when they are set at their maximum values, the rise and fall are slow as shown in FIG. 8C. An FET 297 is used as a follower to allow a relatively low impedance output without loading the capacitor 295. The resistor 299 functions as a trimmer and allows the output voltage at the terminal 281 to be set to zero when the input voltage at the jack 279 is zero. A resistor 301 is used to connect a -12 volt negative power supply to the trimmer 299.

The aforedescribed voltage controlled RC filter alters the frequency content of the input signal at the input terminal 237 in response to a changing low frequency voltage which may be applied at the jack 279 or to the gating pulse of the touch controlled generator at the conductor 61 shown in FIG. 2. The rise and fall times of the low frequency voltage are individually adjustable by varying the potentiometers 283 and 289. FIG. 8D shows the effect on the wave shape of the output of the filter at the terminal 307, with a square wave input at the conductor 237, as affected by the voltage at the output 281 (FIG. 8E) of the input control circuitry 241 of the filter.

The filter may be either a high-pass or low-pass device as previously described. Inset 135 illustrates the reversal of the positions of the FET 233a and the capacitor 231 necessary for implementing the high-pass filter version. In either embodiment, the filter will track the voltage vs. frequency relationship in a predictable manner as illustrated in FIG. 8A. Briefly restated, the gating pulse from the output conductor 61 of the touch controlled generator is applied to the filter input control circuitry 241 through the jack 279 to control the nature of the filtering action of the voltage controlled filter. The range of change in the frequency response is made adjustable by a potentiometer 303 connected to the output of the filter control circuitry 241 which, in turn, controls the output at the conductor 307 of the filter in FIG. 5. This output is then applied to a voltage controlled amplifier shown in FIG. 6.

The voltage controlled amplifier is designed so that its gain can be varied from zero, i.e., zero signal output, to approximately unity. Briefly, it includes first and second amplifying stages 313 and 315 and envelope control circuitry 317. The output from the filter is applied to the first stage whose gain is modulated by the gating pulses from the touch controlled generator, or any train of low frequency pulses, via the envelope control circuitry 317. The first stage is essentially a low level and differential type amplifier. The output of the first stage is amplified by the second stage for subsequent application to a mixer.

More specifically, the envelope control circuitry 317 may be of the type which is similar to the filter input control circuitry 241 of the voltage controlled filter in FIG. 5. It includes a capacitor 321 and a pair of series networks of resistors 323, 325, 327 and 331, and the diodes 329 and 333, respectively, connected in the manner shown to control, respectively, the rise and fall time of the voltage across the capacitor 321. A field effect transistor FET 335 is connected to perform the function of a follower amplifier and to provide a relatively low impedance output from the signal that appears across the capacitor 321. The trimming resistor 337 and a resistor 339 connected to the -12 volts terminal of a power supply in the manner shown provide means for adjusting the potential at output point 341 of the FET 335 to 0 volts when the input 343 of the envelope control circuitry is 0 volts. A varying voltage, appearing at the base of the transistor 345 in response to the envelope control signal, varies the amount of current drawn by the transistor 345. Thus the transistor 345 acts as a current source the magnitude of which depends ultimately on the voltage at the input 343 of the envelope control circuitry 317. This current flows through a resistor 347 and the transistor 345, and is applied to the first amplifier stage 313.

The first amplifier stage includes a pair of transistors 351 and 353 connected as a differential circuit to which the output of the filter in FIG. 5 is coupled through a capacitor 359 after an attenuation by the resistors 355 and 357. The base electrodes of the transistors 351 and 353 are connected, respectively, through the base resistors 361 and 363 to a common junction 365. An AC voltage at the common junction 365 is bypassed to ground via the capacitor 367. The DC voltage at this junction is determined by two voltage divider networks, the first of which includes the resistors 371 and 373 that divide the +12 volts supply to provide approximately +6 volts at the point 375, and the second of which includes the resistors 376 and 377 which reduce the 6 volt potential to +4.5 volts for application to the base electrodes of the transistors 351 and 353. The collectors of the two transistors 351 and 353 are connected to +6 volts through the collector resistors 379 and 381, respectively. The emitters of the two transistors are tied together and connected to the collector of the transistor 345.

The amplifier operates as follows: The differentially connected transistors 351 and 353 divide the control current flowing through the common emitter junction 370 from the collector of the transistor 345 to the two collectors 383 and 385 in proportion to the difference in voltage between the two base electrodes 387 and 389. Therefore, the magnitude of the differential currents that flow in the two collector leads 383 and 385 is proportional to the product of the input voltage between the two base connections 387 and 389 and the current flowing in the common junction 370 via their emitters. The current at the common junction 370 is modified by the gating pulse voltage applied at the input 343 of the envelope control circuitry 317. The signal at the collector electrodes 383 and 385 of the transistors 351 and 353 could be used directly as the output of the amplifier and applied to the mixer. However, the signal amplitudes at the collector electrodes 383 and 385 are at a very low level. Accordingly, a second amplifying stage 315 having a pair of transistors 391 and 393 is used to amplify the low level signals. The two transistors are provided with resistors 395 and 397 connected to the emitter electrodes thereof to improve the linearity and to reduce the noise and distortion of the signal being amplified. The two resistors are connected to a ground through a common junction 399 and a resistor 401. The voltage present at the common junction 399 is set at slightly less than +5 volts, and the resistor 401 is selected to limit the current flowing therethrough to approximately 2 milliamperes.

A capacitor 415 is connected between the +12 volt terminal of the power supply and ground in the manner shown to prevent oscillation and to stabilize the amplifier. The gating pulse(which functions as the control signal) is applied to the input lead 343 of the envelope control circuitry 317 through the jack 102 and the conductor 61 if a plug is not inserted in jack 417. The same gating pulse which controls the filter (FIG. 5) is also applied to the voltage controlled amplifiers (FIG. 6) to assure synchronous operation. The effect of the voltage appearing at point 341 on the amplitude of a square wave applied to the voltage controlled amplifier input 307 is shown in FIGS. 8G and 8F. The output signal is taken from the junction of the collector electrode 314 of the transistor 391 and collector resistor 403 and is applied to the jacks 409 and 411 through a d.c. blocking capacitor 405 and across a resistor 407. If a plug is not inserted in jack 411, the output is fed to the mixer through the conductor 413.

Referring again to FIG. 1, the output of the voltage controlled amplifier (FIG. 6) is applied to a conventional mixer. The output of the mixer is a sum of inputs including the aforedescribed output from the voltage controlled amplifier. The outputs of the mixer may be RC coupled to an attenuator in a conventional manner before they are fed to a reverberator and tone control circuit, the power amplifier and then to a speaker. The inputs to the mixer may include a microphone pre-amplifier 421 (FIG. 1) consisting of a transistor used as an inverting amplifier which amplifies an input to a suitable level. The jack 423 may be used to connect the microphone input to the mixer when necessary. Such a pre-amplifier may be used very advantageously in connection with any low impedance input, such as a magnetic guitar pickup or low impedance microphone. The output of the pre-amplifier also may be coupled externally to an auxiliary mixer if necessary (not shown).

The reverberator may be of a conventional type having a spring unit driven by a drive coil activated by the output from the mixer. The tone control circuitry may be of a conventional design having means for producing a loss of up to 20 dB, or a factor of 10 in voltage at mid-frequencies and having means for providing bass and treble control. The output of the tone control circuit is then fed to the power amplifier to drive the loud speaker.

OPERATION OF THE ELECTRIC SOUND SYNTHESIZER

The overall operation of the electronic sound synthesizer of the present invention shown in FIGS. 1 through 8 will be more clearly understood from the following description. In describing the operation, it is assumed that plugs are not inserted in the jacks, so that the synthesizer operates as a system, as shown in FIG. 1. The system may be energized by 110 volts 60 hertz AC converted to provide appropriate positive and negative DC potentials of desired stability and magnitude using a generally available AC to DC converted, or alternatively by a battery that supplies appropriate DC voltages.

At this point, the switches 15a, 15b - - 15n of the touch controlled generator are open and the associated circuits are inactive. When a conductor path or touch plate, for example 16a, is touched, the switch 15a is activated and passes a current of a particular amplitude as determined by the corresponding potentiometer 21a. With the switch 15a activated, the MOSFET 55 is switched on and the operational amplifier 59 is activated to produce a control voltage signal of a particular amplitude at the output conductor 60. The amplitude of the control voltage is directly proportional to the amplitude of the current flowing through the summing bus 51. The current in the summing bus is the combination of the currents flowing through the variable potentiometers 21a, 21b - - 21n of one or more of the switches 15a, 15b - - 15n that have been activated. The memory capacitor 86 holds the control voltage at the same level until another plate is touched, even after the shorting touch is removed from the paths or plates and the switches 15a, 15b - - 15n and MOSFET 55 are opened. The overall range of the voltage of the output can be changed using one or the other of the potentiometers 94 and 95. The control voltage obtained in this manner is then applied to the input of wave generator B through the conductor 60.

The generator also produces a positive DC pulse of a given magnitude through its output conductor 61. Here the duration of each of the DC pulses is limited to correspond to the time duration during which any one or more of the touch plates are shorted. This output is used preferably, as a gating pulse for the voltage controlled filter in FIG. 5 and the amplifier in FIG. 6.

When the switch 177 of wave generator A (FIG. 3) is open and the switch 178 is closed, it generates a square wave train as shown in FIG. 7A. If desired, the output of the wave generator A can be modified to produce an inverted sawtooth wave train by closing switch 177 and opening switch 178. By closing both switches, the output of the wave generator A is a mixture of the aforementioned sawtooth and square wave trains, summed in proportion to the settings of the attenuators 142 and 174 respectively. This wave train is then applied to one of the two inputs of the wave generator B, shown in FIG. 4. In this manner, the wave train from the output of wave generator A frequency modulates wave generator B. The control voltage from the touch controlled generator is applied to the other input through the conductor 60. As shown in FIG. 7H, this control voltage also frequency modulates the wave train from wave generator B. The frequency of the modulated output is proportional to the summed amplitude of the two voltages -- one from the output of wave generator A, the other from the touch controlled generator.

The modulated wave output, which may be any mixture of three different types of wave trains(square, sawtooth and triangular waves) appearing at the output conductor 225, is then applied to the voltage controlled filter shown in FIG. 5. The filter performs a low pass filter action on the input in response to the gating pulse from the touch controlled generator. The cut-off frequency of the filter is proportional to the amplitude of the voltage at the inverting input 271 of amplifier 243, and the peak value is set by attenuator 303 whereas the transient characteristics are controlled by the filter input control circuitry 241. In this manner, the filter normally controls the transient harmonic content of the output signal from the wave generator B.

The output of the filter, at its output terminal 307, is then fed into the voltage controlled amplifier, whereas the gating pulses from the touch controlled generator are applied to the envelope control circuitry 317. The envelope control circuitry 317 shapes the transient characteristics (attack and decay) of the input signal from the filter under the control of the gating pulses, as illustrated in FIGS. 8F and 8G. In this manner, the tonal qualities of the sounds produced by the synthesizer are effectively controlled. The output of the voltage controlled amplifier is then reverberated, tone controlled, amplified and applied to the loud speaker.

DRUM GENERATOR

FIG. 9 shows a touch controlled generator in accordance with the present invention designed to generate drum-like sounds. The generator includes three twin-T oscillators (only one of which is shown) each of which is connected to a d.c. voltage source through a conductor path or touch plate 451 having a dielectric gap 453 which, when shorted by a touch of a finger, energizes the corresponding twin-T oscillator.

Each of the twin-T oscillators includes a disturbance generator 500 coupled to the touch plates, an inverting amplifier 455 designed to provide a high gain, and a twin-T network 463 interposed between the disturbance generator and the inverting amplifier. More particularly, the inverting amplifier 455 has a transistor 459 connected in a common emitter amplifier configuration, and a second transistor 461 connected to the first transistor in an emitter follower fashion as shown. The output of the second transistor 461 is coupled to the twin-T RC network 463 through a capacitor 462. The network 463 includes the resistors 465, 467, 468, 469, 471, and 473 and capacitors 475, 477 and 479 connected in the manner shown. The junction 481 of the twin-T network 463 is connected to the input of the inverting amplifier 455, namely, the base electrode 483 of the transistor 459. The characteristics of twin-T network 463 are such that it will pass all frequencies except the frequency to which it is tuned. In this manner, the network will provide a low gain at all frequencies, except at the resonant frequency where it will provide a high gain.

More specifically, the inverting amplifier 455 includes a resistor 485 for biasing the transistor 459. Another resistor 487 is used as a trimmer to set the gain of the twin-T oscillator to something slightly less than that required for free oscillation so that the oscillator produces an output which is in the form of a damped, decaying sine wave. Accordingly, the decay time of the output signal depends on the setting of the trimmer 487. The resistor 489 is connected from the collector electrode of the transistor 459 to the +12 volt supply. A resistor 491 connects the emitter electrode of the transistor 461 to the +12 volt supply. The resistors 467, 468 and 473 form a three-section potentiometer for tuning the twin-T oscillator without the necessity of making adjustments on the trimmer 487.

The disturbance generator 500 includes a transistor 495 and an FET 497 which triggers the twin-T oscillator into operation. The disturbance circuitry is similar to the electronic switch circuitry of the touch controlled generator in FIG. 2. The gate 499 of the FET 497 is biased so that it is normally turned off by a resistor 501 connected to a -12 volt supply. The gate terminal 499 is connected to the touch plate 451 through the plugs 503 and 505. When the touch plate 451 is shorted, the FET 497 and the transistor 495 are turned on and produce a negative going pulse of approximately 6 volts on the collector electrode 507 of the transistor 495, in the form shown in FIG. 10C. This produces a pulse of current through a resistor 509 and at the juncture of the capacitors 475 and 477 and triggers the twin-T oscillator to produce a decaying sinusoidal wave as shown in FIG. 10A. A capacitor 511 is connected in the manner shown to keep the transistor 495 from turning off too quickly, thus preventing the disturbance generator from turning off immediately and triggering when the operator's finger is removed from the touch plate.

The output of the twin-T oscillator is coupled through a capacitor 513 and a resistor 515 to a single transistor inverting amplifier 517 consisting of the transistor 519 and its associated resistors 521 and 523 and coupling capacitor 525 as shown. The inverting amplifier 517 further includes a series network including a switch 527 and the diode 529 shunting the inverting amplifier 517 in the manner shown. This amplifier may be operated in two modes: (a) a low distortion mode by having the switch 527 open so that the amplifier functions as a standard inverting amplifier and (b) a high distortion mode producing higher overtones by having the switch 527 closed. FIGS. 10A and 10B shown the wave forms of the output of the touch controlled generator at the low and high distortion modes, respectively. The output of the inverting amplifier 517 is coupled through a capacitor 525 to a potentiometer 528 and this permits adjustment of the amplitude of the output of the twin-T oscillator.

The three twin-T oscillators are mixed, respectively, by resistors 535, 537 and 539 and fed to the summing point 541 of an inverting summing amplifier comprising a transistor 543, the collector resistor 545 and the biasing resistors 547 and 549 connected as shown. The output of the amplifier is therefore an inverted sum of the outputs of the three twin-T oscillators, each having its own level controlling potentiometer 528. The output at the collector electrode of the transistor 543 is applied to the output jack 555 through a d.c. blocking capacitor 551 and a resistor 553 as shown. If a plug is not inserted in the jack 555, the output signal from the twin-T oscillators will be fed to the mixer through a conductor 557.

When the touch plate 451 is touched, a connection is made between the gate 499 of the FET 497 and the positive +12 volt supply through the resistor 559, the jack 503, and the plug 505. This causes the disturbance generator 500 to trigger the twin-T oscillator to generate the ringing oscillation illustrated in FIG. 10A. The other two oscillators (not shown) are triggered into action in a similar manner through their corresponding touch plates 570 and 572 and conductors 571 and 573, 575 and 577. The +12 volt potential applied through the resistor 559 serves all three touch plates.

The output of the drum generator may be applied to the mixer, the reverberator and tone control circuit, the power amplifier and then to a speaker, as shown in FIG. 1, to generate the drum sounds.

Multi-Voice Rhythm Band

Another embodiment of the present invention involves the provision of a multi-voice rhythm band percussion generator. This unit, expanding on the principle of the drum generator, is designed for use with the aforedescribed synthesizer shown in FIG. 1.

FIG. 11 shows, in schematic form, the multi-voice rhythm band generator which includes five groups 601, 602, 603, 604 and 605 of six twin-T oscillators 610a, 610b - - 610f with associated touch control paths or plates 611a, 611b - - 611f. The twin-T oscillators of the generator are designed to produce outputs in the form of damped sine waves.

The outputs of oscillators, in groups of six, are summed at a local mixer 621 and form a UNIT. There are five such UNITS, all identical except for the tuning of the oscillators. The outputs of each UNIT are attenuated through a potentiometer 623 and then summed by a final mixer 625.

Circuitry for the mixers 621 of each of the six twin-T oscillators may be in the form of a conventional, common emitter, transistor amplifier -- each having suitable biasing resistors. The outputs of the amplifiers are RC coupled via a capacitor 627 and an attenuating potentiometer 623 to the final mixer 625 of a similar design. The output of the final mixer 625 is RC coupled through a capacitor 629 to an attenuator potentiometer 631 which acts as the master volume control of the multi-voice rhythm band. The jacks 635 and 636 are connected to the attenuator potentiometer 631 of the mixer 625 to provide an output normally connected externally to one of the inputs of the mixer illustrated in FIG. 1.

Each of the paths or touch plates 611a, 611b - - is connected to its corresponding twin-T oscillator 610a, 610b - - through a connector of a plug-in type having a plurality of pins and jacks 628a, 628b - - . The touch plates,mounted in groups of six on a dielectric mounting board, are so designed that they are connected to the generator through a current limiting resistor 630 when the connector is plugged in. When a performer touches the touch plates, he shorts them and energizes corresponding oscillators which generate the output sounds.

The oscillators of the present generator are designed to produce 30 different percussive sounds, each independently triggered when a corresponding touch plate is touched These sounds are grouped in sets of six. The output of each of the sets can be controlled independently by its own attenuating potentiometer 623.

FIG. 12 shows in detail a single twin-T oscillator that may be used in the twin-T oscillator network of the multivoice rhythm band shown in FIG. 11. The oscillator includes a disturbance generator 637, the inverting amplifier 638 and a standard twin-T network 640. The inverting amplifier 638 includes a transistor 641 whose output 642 is coupled to its base electrode 645 through the standard twin-T RC network 640 having the resistors 643, 644 and 645, the trimming potentiometer 646, and the capacitors 647, 648 and 649 connected in the manner shown. The parameters of the twin-T network are adjustable so that the amplifier 638 exhibits a high gain at the resonant frequency of the twin-T network and produces damped, ringing oscillations when a disturbance is injected into it. A capacitor 651 provides d.c. blocking at the output of the transistor 638. A resistor 653 is shunted across the collector and base electrodes to provide bias for the base electrode. A variable resistor 655 is connected to the emitter electrode of the transistor 638 to set the gain of the oscillator to a point slightly less than that required for free oscillation, as the decay time of the oscillating signal depends on the setting of the variable resistor 655. The resistor 657 is connected from the collector electrode of the transistor 638 to a positive power supply source 659 of a suitable magnitude. There are 30 of these oscillators in the generator, each tuned to a different frequency by setting the values of the resistors 643, 644 and 645 and adjusting the trimming potentiometer 646 for final tuning.

The disturbance generator 637 includes a transistor 661 and the FET 663 which trigger the twin-T oscillator in response to a d.c. voltage supplied thereto when the corresponding touch plate is shorted. The FET 663 is normally biased by a -18 volt source applied through the terminal 665 to the resistor 667 so that it is turned off. The gate electrode 669 of the FET 663 is connected to a touch plate through an input conductor 670 coupled to a corresponding one of the connector assembly contacts 628a in such a way that the gate electrode 669 is switched to a positive potential when the corresponding touch plate 611a is touched and a path is established through the performer's finger to the +12 volt supply. In this manner, both the FET 663 and the transistor 661 are turned on and produce a negative-going pulse of approximately 6 volts at the collector electrode 671 of the transistor 661. This produces a pulse of current through the resistor 673 connected between the common junction 675 of the capacitors 648 and 649 and the collector electrode of the transistor 661. The voltage at the collector electrode 671 triggers the twin-T oscillator which generates a decaying ring at its output terminal 677. A capacitor 679, connected in the manner shown, keeps the transistor 661 from returning to its off state too quickly when the touch plate is released. A resistor 681 connects the collector 671 of the transistor 661 to the positive voltage supply at the terminal 659. A resistor 683 is connected between the positive supply and the drain electrode of the FET 669 to limit the current drain in the circuit to a minimum value.

The output terminal 677 of the twin-T oscillator is coupled through a capacitor 685 and a resistor 687 to a single transistor, an inverting amplifier comprising a transistor 689, the biasing resistor 691 and the collector resistor 693 connected in the manner shown. The amplifier provides undistorted amplification of the low-level output from the twin-T oscillator. As an optional feature, an inverting diode 695 may be connected in the manner shown to clip the output signal and thus provide an output having a higher harmonic content. The output of this amplifier is RC coupled through a capacitor 697 and appears across resistor 699. It is then applied to the UNIT mixer 621 through the resistor 701 via the conductor 702.

Multi-Channel Distributor

FIGS. 13 through 15 show a multi-channel sound distributor designed to be used with the aforedescribed synthesizer.

Referring now to FIG. 13, the sound distributor may include two input terminals in the form of the jacks 751 and 753 and four output terminals in the form of the jacks 755, 756, 757 and 758 and the photosensitive elements 761 - 768 interposed between the inputs and outputs in the manner shown. Various parameters of the distributor may be adjusted so that any reasonably high level audio signal of one or more volts of amplitude may be applied to either or both inputs and have the output signal appear at the output jack when a photosensitive element interposed between the output jack and the source is illuminated.

By way of an example, for each input channel, there may be provided four voltage divider networks consisting of the photosensitive elements 761 - 764 and 765 - 768 and the fixed resistors 771 - 774 and 775 - 778 respectively, as shown. The photosensitive elements may be photoresistors such as those shown in FIG. 13, or any other suitable light sensitive elements, such as photodiodes. When light does not fall on the photoresistors 761 - 768, each of the photoresistors exhibits a high resistance compared to its associated fixed resistors 771 - 778 and attenuates the input signal so that transmission of the signal is interrupted. However, when a light beam strikes a photoresistor, for example 761, its resistance decreases to a lower value compared to the corresponding fixed resistor 771 and a signal path is provided to the output jack 755. The amount of decrease in the resistance of the photoresistor is directly proportional to the intensity of the light so that the amount of signal transmitted can be controlled by controlling the light intensity. In this manner, a signal entering the jack 751 may be routed to any one or more of the output jacks 755, 756, 757 and 758 by selectively illuminating the corresponding photoresistors 761, 762, 763, and 764. Signals entering the jack 753 likewise may be routed to any one or more of the same output jacks 755, 756, 757, and 758 by selectively illuminating the photoresistors 765, 766, 767, and 768.

FIG. 14 shows a top view of a housing containing the channel distribution circuitry shown in FIG. 13. It has a plurality of apertures 781 - 788 which may be positioned superjacently to the photoresistors 761 - 768. The photoresistors may be either recessed slightly in the aperture or shielded by rings at the apertures to minimize the unwanted interaction from stray or reflected light. Jacks for the inputs 751 and 753 may be mounted at one side of the housing (at 751' and 753') and jacks for the outputs at the opposite side (at 755', 756', 757', and 758') as shown. In this manner, the housing normally shields the photoresistors, but makes it possible to subject selected photoresistors to light beams of controlled intensity.

FIG. 15 shows another variation of the housing. It shows a side view of a housing 791 designed to fit on top of a board 793 having the photoresistors 761 - 768 mounted thereon. The housing 791 may be a light-tight box containing diffuse light sources 795 and 796 and two rotatable discs 798 and 799 made of sections having various degrees of transparency, or it may be made of a completely opaque material with a number of apertures at the positions corresponding to those of the photoresistors 761 - 768. The discs 798 and 799 may be rotated about their respective shafts 801 and 803 by the cranks 805 and 807, which may be driven manually or by a motor (not shown). As the discs are rotated, light beams from the light sources 795 and 796 are projected through the discs 798 and 799 to the photoresistors 761 - 768. In this manner, conductive channels are formed from the signal input sources to the output terminals which are determined by the sequences in which the photoresistors are subjected to the light beams, and the amount of signal transmitted is determined by the amount of light applied to the photoresistors.