US2873637A - Touch control for polyphonic musical instruments - Google Patents

Touch control for polyphonic musical instruments Download PDF

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US2873637A
US2873637A US419004A US41900454A US2873637A US 2873637 A US2873637 A US 2873637A US 419004 A US419004 A US 419004A US 41900454 A US41900454 A US 41900454A US 2873637 A US2873637 A US 2873637A
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circuit
grid
audio
control
oscillator
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US419004A
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Edward W Herold
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RCA Corp
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RCA Corp
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    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10HELECTROPHONIC MUSICAL INSTRUMENTS; INSTRUMENTS IN WHICH THE TONES ARE GENERATED BY ELECTROMECHANICAL MEANS OR ELECTRONIC GENERATORS, OR IN WHICH THE TONES ARE SYNTHESISED FROM A DATA STORE
    • G10H1/00Details of electrophonic musical instruments
    • G10H1/02Means for controlling the tone frequencies, e.g. attack or decay; Means for producing special musical effects, e.g. vibratos or glissandos
    • G10H1/04Means for controlling the tone frequencies, e.g. attack or decay; Means for producing special musical effects, e.g. vibratos or glissandos by additional modulation
    • G10H1/053Means for controlling the tone frequencies, e.g. attack or decay; Means for producing special musical effects, e.g. vibratos or glissandos by additional modulation during execution only
    • G10H1/055Means for controlling the tone frequencies, e.g. attack or decay; Means for producing special musical effects, e.g. vibratos or glissandos by additional modulation during execution only by switches with variable impedance elements
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S84/00Music
    • Y10S84/07Electric key switch structure

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  • This invention relates to electronic musical instruments, and more particularly to a new system for controlling the output of such instruments.
  • An ideal electronic musical instrument should be one which is capable of producing several notes at a time, i. e. a-polyphonic type. Such an ideal musical instrument should minimize the physical effort required for playing and include means for easily controlling the attack, overtone content, or loudness of the tone produced.
  • circuits and playing key arrangements whereby touch alone, without mechanical motion of the key, is suicient to produce a note.
  • a single multigrid tube or a double triode tube is used as a combination tone generator and radio frequency oscillator.
  • the tone generator is normally inoperative when the radio frequency oscillator is operating. Touching the key stops the radio frequency oscillator due to body capacitance and losses, so that the tone generator operates.
  • motion of the key or the location of the finger on the key is used to control one of the other important factors such as attack, decay, loudness or timbre.
  • Use of conductive rubber and light beam control are embodied in other forms of the invention.
  • 1t is an object of this invention to provide an improved polyphonic device.
  • Figure 1 is a schematic block diagram ofV a touchoperated musical system embodying the present invennon;
  • Figure 2 is a detailed schematic showing of a form of capacitance-operated control circuit applicable for use in the system of Figure l;
  • FIG. 3 is schematic showing of a touch control system embodying the present invention in which a single tube serves yboth as a control circuit and a tone generator;
  • Figure 4 shows, by way of example, an arrangement for controlling the volume or other characteristic of a tone in accordance with the invention
  • Figure 5 is schematic showing of an arrangement in accordance with the invention in which the illustrated touch control makes use of body resistance
  • Figure 6 is a schematic showing of an arrangement in accordance with the invention illustrating touch control combined with tone control
  • Figure 7 is a schematic showing of an arrangement in 'accordance with the invention wherein touch control is combined with control of attack;
  • Figure 8 is a schematic showing of an arrangement in accordance with the invention wherein a photo-electric device is associated with a control circuit;
  • Figure 9 is a set of characteristic curves representing various conditions of operation of the circuit shown in Figure 7.
  • FIG. 2 there is shown in detail a diagram of one form of capacitance-operated control circuit, such as might be used for one of the blocks of Figure 1.
  • the circuit involves only a single note of an electronic musical instrument, it being obvious that a plurality of circuits of the same type may be employed to produce more than one note without departing from the scope of this invention.
  • a triode oscillator tube 1S uses a Hartley type oscillator circuit comprising an inductance 20 and a capacitance 22.
  • a resistor 24 provides a grid leak bias for the tube.
  • a connection 26, to the grid 28 provides means to permit an operator to affect the operation of the oscillator.
  • the bias which is generated across the resistor 24 when tube 28 is in an oscillating state, is applied to the control grid 36 of an amplifier pentode electron tube 38, by means of the resistance-'capacitance filter shown as 32 and 34 in Figure 2, together with the grid resistor 40.
  • This pentode amplifier 38 is used in the path between the electrical tone generator 42 and a common audio amplifier which is coupled to the pentode amplifier through a capacitor 44 and a loudspeaker for all the notes of the instrument (not shown).
  • the operating voltages for the pentode 38 are chosen so that the bias supplied by the triode tube cuts ofi the anode current of the pentode, and no tone signal is transmitted to the common audio amplifier.
  • the circuitry associated with the tube 36 and the common amplifier and loudspeakers provides for the utilization of the generated tones.
  • connection 26 When the connection 26 is touched with the hand, or when the hand is brought sufficiently close to it ⁇ (the choice as to how close the hand should be brought to stop the oscillator is governed by the constants of the oscillating circuit and, in particular, the size of the grid capacitor the oscillator stops oscillating and the bias across the grid-leak, resistor 24 is thereby removed'.
  • the pentode 38 is then no longer cut off and operates as a normal amplifier with its bias supplied by cathode resistor 46.
  • the tone generator signal is transmitted to the common audio amplifier and can be heard in a loudspeaker.
  • a pentode amplifier is shown in Figure 2 because it is essential that, when full cut-off bias is appliedV to its grid, no tone must get into the plate circuit by the way of inter-electrode capacitance.
  • a capacitor may be inserted in the lead to the key, and the key grounded by means of an R. F. choke, provided such a capacitor is substantially larger than the capacitor 30. This will not affect operation in any way.
  • a touch control system embodying the present invention using a single tube is shown in the form of a double triode.
  • This single tube serves as both control circuit and tone generator.
  • Two triode sections 46 and 48 are connected in an audio-frequency, multi-vibrator type of circuit.
  • a radio-frequency Hartley type oscillator circuit comprising an inductancef and a capacitor 52.
  • a grid leak resistor 54 and a capacitor 56 are placed onthe ground end of the coil.
  • a capacitor 53 between the cathode 6ft and a tap 62 on the radio frequency coil is a radio-frequency by-pass capacitor which does not appreciably passaudio frequency.
  • a capacitor 6,4f between the plate 65 and ground is a radio-frequency by-pass capacitor which affects slightly the 'audio frequency generated by the multivibrator but not its oscillating capability.
  • a resistor 68 and a capacitor 70 form a radio-frequency filter circuit to conduct the oscillator grid-leakyoltage, produced across the resistor 54, onto the grid 72 of the second triode through a resistor 73.
  • VThe multi-vibrator circuit consists of a common cathode resistor 74 to ground, the plateresistors ⁇ 76 and 7S.
  • this type of multivibrator circuit is known as Potter circuit (because it was described by Potter in the EProceeding by the I. R. E. in I une 1938).
  • the radio-frequency oscillator of the rst triode 46 stops oscillating. The bias is thereby removed from the second triode 48 so as to actuate the audio multi-vibrator circuit, thereby producing an audio tone rich in harmonics, as desired by a musical instrument.
  • the radio frequency oscillator therefore acts as a control circuit associated with manual means for varying its operation.
  • a tone generator liti having an electrical audio signal output is coupled to the grid 114 of an amplifier tube 112 through a capacitor liS.
  • a source of negative potential designated as E- is applied to the grid through resistors 116' and 118.
  • An output voltage is developed across the plate 12) and cathode 121.
  • the associated output circuit is not shown for purposes of simplification.
  • the finite resistance of the human finger to electrical current is utilized.
  • a touch'control electrode 22, which may, for example, be equivalent to a key on a piano or organ, comprises two closely spaced parallel bars H4 and 126. When the finger is touched to these bars, the finger resistance cornpletes the circuit to ground.
  • the bias on the audio amplifier i12 willv be reduced substantially.
  • the amplifier then becomes conducting and the audio tone from the tone generator is amplified.
  • a capacitor 125 or disturbance is detectable'to the performer.
  • FIG. 4 A simple circuit in which touch control may be use to control volume or other sound characteristics is shown in Figure 4. It is intended that any one of the previous circuits can be used to initiate control, i. e. by touch only, whereas by additional control of finger position, a second auxiliary sound characteristic can be altered.
  • a series of contact bars 88 is provided for each note, so
  • Y that, when the finger is placed on the proper pair of contacts, the circuit is completed through the nger resistance and appropriate auxiliary control thereby attained.
  • the finger may also be slid forward and backwards, that is, from left to right as viewed in Figure 4, in order to obtain a continuously variable control, while theperformer is playing the particular note to which the contact is connected.
  • Figure 4a illustrates an equivalent circuit.
  • Various resistors and 92 may be included in an electrical circuit by movement of the finger. Appro ⁇ priate circuits to which such means may be applied are not shown.
  • FIG. 6 another method of using a single tube is shown and combines touch control with a tone controlV circuit'ln this embodiment, a radio frequency oscillator and an audio oscillator are combined within a single tube envelope.
  • a pentagrid tube V12S such as is commonly used in broadcast receivers for the converter stage, is employed in this embodiment.
  • a radio frequency oscillator provides a capacitance or touch-operated control cirfcuitand the audio oscillator Yprovides a musical tone.- Only one of these oscillators is operative at any*giventime.
  • the cathode and the grid 132 are connected as a Hartley type radio-frequency oscillator, for which the grid 134 acts as an anode.
  • the tuned circuit comprises an inductor 133 and a capacitor 135.
  • the grid 154 is by-passed to ground through a radio-frequency by-pass capacitor 136.
  • the suppressor grid 151 is directly connected to the cathode.
  • a key 138 comprises a metal spring 140 and a bottom metal plate 142 separated by a dielectric material 144.
  • Grid leak capacitance is provided by a capacitor 137.
  • the bias across the grid leak 146 is applied to the second control grid 134 through resistor-capacitor filter 150 and 157 and through resistor 152. When radio-frequency oscillations are present, this bias is enough to cut off the second control grid 134.
  • the radio-frequency oscillator stops oscillating and the bias across the grid leak resistor 146 is removed. This, in turn, removes the bias from the second control grid 134 and permits this grid to operate on the electron current available to it through resistors 150 and 152.
  • the screen grids 154 and 148 which are internally connected in the tube and the-second control grid 134 form a negative-transconductance audio oscillator, which oscillates at an audio frequency determined by the time constant of the combination comprising the resistors 155 and 152 and the capacitors 136 and 156.
  • Such an oscillator in its simple uncombined form is well-known and Was described in an article by the applicant on negative resistance devices in the Proceedings of the I. R. E. in October 1935.
  • the negativetransconductance oscillator cannot oscillate however, if the bias on the grid 148 is in excess of the cut-off bias of that grid so that the audio tone is generated only when the key 138 is touched.
  • the grid 134 is a remote cut-ofi ⁇ grid, as is often the case in commercially available tubes, one must only provide sufficient bias to cut-off the grid to prevent oscillation, since the small negative transconductance at high control -bias voltages is not sufficient for oscillation. It is therefore seen that when the radio-frequency section of the tube is oscillating, the negative-transconductance audio oscillator cannot oscillate. No audio tone is then produced in the plate circuit of the pentagrid tube, which may be connected to an audio amplifier or other utilization circuit through a coupling capacitor 158.
  • the radio-frequency oscillator becomes inoperative.
  • the bias is therefore removed from the grid 154, and the negative-transconductance oscillator starts oscillating at an audiofrequency rate.
  • the audio frequency in the plate circuit may then be transmitted to an audio amplifier. It will be appreciated that if the grid leak 146 has large impedances at audio frequencies, touching the finger to the metal spring may produce some pickup or hum voltage which may be transduced into the audio amplifier in addition to the desired note. However, this may be overcome by expedients wellknown in the art.
  • a variable capacitance may be used in any type of circuit which will operate with a variable capacitance, whether as a tone control, as a loudness control, or as an attack control.
  • the spring member may be made of two insulated pieces, one above the other. The upper piece could be used in the radio frequency circuit and would be touched by the finger, whereas the lower piece would be separately connected to the capacitance circuit. Such an arrangement would minimize the effect of hum in the audio output circuit.
  • the oscillator type of capacitive touch control does not require the finger actually to touch a piece of metal.
  • the piece of metal may have a plastic coating, since it is only the finger capacitance and body loss at radio frequencies which cause the radio frequency oscillator to stop and allow the audio oscillator to start.
  • a circuit wherein the attack may be controlled by the performer. Control of attack of an audio tone is considered by many to be more important than a control of volume or tone quality. However, it is realized that the circuit shown may, with slight modification, be also used to control the volume, tone content or other sound characteristic.
  • a pair of triodes 162 and 164 which may be incorporated into a single envelope if desired, include a radio frequency oscillator in the first triode 162 and an audio oscillator in association with the second triode 164.
  • the radio frequency oscillator comprises a conventional Hartley type having a tapped inductor coil 166 and a capacitor 168 providing the tuned circuit. Resistor 170 and a capacitor 172 provide grid-leak bias for the oscillator.
  • the radio-frequency oscillations are stopped by a performer placing a finger on the key 174, as previously described.
  • the audio oscillator comprises a triode 164 used in conjunction with a resistance-tuned type audio oscillator comprising capacitors 176, 178 and 180 together with resistors 182, 184 and 186.
  • This oscillating circuit operates only when the finger of the operator touches the key since the cut-off bias is otherwise impressed on the grid 188 through the resistors 190 and 186.
  • the radio-frequency oscillator stops. The bias is therefore removed from'the audio oscillator, which then becomes operative.
  • the audio frequency voltage is taken off and applied to a grid 192 of an amplifier tube 194. It will be noted in this case that the grid-leak resistor of the tube 194 is resistor 182.
  • the lower end of the resistor 182 is connected so that, if the key is not depressed, a bias designated by a battery 196 is placed on the grid 192 of the amplifier tube 194.
  • This bias may be adjusted so that a very weak audio tone appears and, when the instrument is played very softly, the key need not be depressed but is merely touched. If, however, the key is depressed at the end 198 of the key so as to touch the resistor 200 at its lefthand end, it will be noted that this connects the end of the capacitor 202 which is connected to terminal 19S, to ground through the key and radio frequency coil, which is very low in impedance at D. C. or audio frequencies. As a result, the bias voltage is instantly removed until the capacitor 202 charges up. The audio tone reaches full volume suddenly and then gradually decays as in the tone of a piano or banjo type.
  • the curves indicate the type of attack which may be expected from touching the finger to the key at different places.
  • Each curve shows the amplitude of the audio output as a function of time.
  • Curve 204 represents the output 7 whenthe key is touched, but not pressed into contact with resistor 200.
  • Curve 206 represents the output when the key is pressed at the end i923.
  • Curve 268 represents the output when the key is pressed between the points 198 and the middle of the key represented by a tap 199.
  • Curve 21@ represents the output when the key is pressed at the tap 199, as illustrated in the drawing.
  • Curve 212 represents the output when the key is pressed between the middle and the end 2l4 of the key.
  • Figure 216 represents the output when the key is played near the end 214.
  • the various combinations, such as described, may be obtainedV by judicious choice of the tapped resistor 20) and the capacitors 2tl2 and 139', together vwith the resistor 182 and the capacitors 176 and T178 associated with it.
  • the Operation of the circuit can be readily determined by examining the curves of Fig. 9 showing the transient characteristics of the key circuit.
  • the key is made of rubber having an electrically conductive material added.
  • This conductive rubber has advantages over other types of pressure controlled resistance's, since it is low in cost and practical to apply.
  • FIG. 8 of the drawing there is shown a photo-electric cell 22).
  • a light source 222 striking the cathode of the device causes current to flow, thereby developing voltage across a resistor 224. Variations in light will produce a voltage variation across the resistor 224. This variation may be used to vary the gain of an amplier tube 225.
  • a tone generator 228 is applied tothe grid 232 of the ampliiier through a coupling capacitor 230.
  • a resist'or'234 is used to provide means for biasing the amplifier.
  • a resistor 236 provides a' load for the amplifier.
  • the phototube current is a function of the finger position and may 'be used to control the amplitude of other characteristic of an audio tone.
  • Other' arrangements may include theV light source within the instrument. The light beam may then be projected upward and' diffusedV byithe nger. Again, the ingers position would determine the amount of light reaching aereas? the phototube, thus providing means to vary the amount of current and the volume or othercharacteristic of a tone.
  • theV combination comprising a tone generator having an electrical audio-frequency signal output, a utilization circuit, means for applying said audio signal output to said utilization circuit, a radio-frequency oscillator circuit to develop a bias, means for applying said Vbias to maintairi's'aid tone generator normally inoperative, a control circuit for varying the operation of said radio frequency oscil-V l ⁇ atcr, ⁇ rneans connecting said control circuit to said oscillator, means associated with said control circuit having a'yariable electrical characteristic, said la'st named means being accessible to the linger of an operator, whereby a touch of the linger of an operator is effective to vary said electrical characteristic to render said radio frequency osciilator inoperative thereby reducing said bias to permit operation of said tone generator, and means for varying said audio signal output from said tone generatorY to said utilization circuit.

Description

Feb. 17, 1959 E. w. HEROLD 2,873,637
. TOUCH CONTROL FOR POLYPHONIC MUSICAL INSTRUMENTS Filed March 26. 1954 2 Sheets-Sheet 1 E'yj. ff f6 y Eff/JTAA/CE BY LA L QAM :l TTOR NE Y E. W. HEROLD Feb. 17, 1959 2 Sheets-Sheet 2 Filed March 26, 1954 la m a w. m z m ma M W Il NAM GIS- 1 MW E z z im ,m .l a F m z rw f d f I .n we f a mm lW- w rm z IE.. 4 z z l www...
United States Patent O TOUCH CNTROL FUR POLYPHONIC MUSICAL INSTRUMENTS Edward W. Herold, Princeton, N. J., assignor to Radio 'Corporation of America, a corporation of Delaware Application March 26, 1954, Serial No. 419,004
The terminal fteen years of the term of the patent to be granted has been disclaimed 2 Claims. (Cl. S11- 1.04)
This invention relates to electronic musical instruments, and more particularly to a new system for controlling the output of such instruments.
The use of electronic means for the creation of music is well-known and has been embodied in numerous commercial instruments, of which the most successful have been those which improve upon or imitate the sounds of their acoustical counterparts.
An ideal electronic musical instrument should be one which is capable of producing several notes at a time, i. e. a-polyphonic type. Such an ideal musical instrument should minimize the physical effort required for playing and include means for easily controlling the attack, overtone content, or loudness of the tone produced.
In accordance with the present invention, circuits and playing key arrangements are provided whereby touch alone, without mechanical motion of the key, is suicient to produce a note. In one form, a single multigrid tube or a double triode tube is used as a combination tone generator and radio frequency oscillator. The tone generator is normally inoperative when the radio frequency oscillator is operating. Touching the key stops the radio frequency oscillator due to body capacitance and losses, so that the tone generator operates. In other forms of the invention, motion of the key or the location of the finger on the key is used to control one of the other important factors such as attack, decay, loudness or timbre. Use of conductive rubber and light beam control are embodied in other forms of the invention.
1t is an object of this invention to provide an improved polyphonic device.
It is a further object of this invention to provide an improved polyphonic device which may 'be operated with a minimum amount of physical effort.
It is still a further object of the invention to provide r an improved polyphonic device in which the attack, overtone, loudness or other sound characteristic may be easily controlled.
Other objects and` advantages of the present invention will become apparent and immediately suggest themselves to those skilled in the art to which the invention is directed from a reading of the following specication in connection with the accompanying drawing in which:
Figure 1 is a schematic block diagram ofV a touchoperated musical system embodying the present invennon;
Figure 2 is a detailed schematic showing of a form of capacitance-operated control circuit applicable for use in the system of Figure l;
Figure 3 is schematic showing of a touch control system embodying the present invention in which a single tube serves yboth as a control circuit and a tone generator;
Figure 4 shows, by way of example, an arrangement for controlling the volume or other characteristic of a tone in accordance with the invention; i
2,873,637 Patented Feb. 17, 1959 ICC Figure 4a is a schematic showing of a circuit which is substantially equivalent to the circuit of Figure 4; y
Figure 5 is schematic showing of an arrangement in accordance with the invention in which the illustrated touch control makes use of body resistance;
Figure 6 is a schematic showing of an arrangement in accordance with the invention illustrating touch control combined with tone control;
Figure 7 is a schematic showing of an arrangement in 'accordance with the invention wherein touch control is combined with control of attack;
Figure 8 is a schematic showing of an arrangement in accordance with the invention wherein a photo-electric device is associated with a control circuit; and
Figure 9 is a set of characteristic curves representing various conditions of operation of the circuit shown in Figure 7.
In the conventional piano or organ, it is necessary not only to place the iingers on the proper key, Ibut to actually press these keys and do an appreciable amount of Work. With an electronic instrument, such as one embodying one form of the present invention, it is not necessary to press a key because the mere touch of a finger sulhces to sound the note. 'Referring particularly to Figure l, an arrangement of keys 12 is shown, connected to a set of capacitance-operated control circuits 14. The control circuits, in turn, actuate tone generators 16. When the nger of an operator is placed in contact with, or very close to, a particular key, the capacitance-operated control circuit operates a tone generator producing a desired note in a utilization device, such as will include a loudspeaker 17.
One form of capacitance-operated control circuit has been described heretofore in an article by F. H. Shepard, proceeding of the I. R. E., December, 1936. When the control grid connection of a vacuum tube oscillator, using a grid-leak Vbias circuit, is touched with the hand, the oscillations stop. There are two reasons for this. First, the additional grid-to-ground capacitance, combined with the grid condenser capacitance, form a voltage divider which reduces the grid excitation; second, the radiation and ohmic loss of the body load the oscillator circuit severely. If, instead of touching the grid connection, the hot end of the grid inductance is touched, only the second cause is operative and the phenomenon is somewhat less sensitive, although it still works. Since, in the usual grid-leak biased oscillator, the plate current increases when the oscillation is stopped, one is able to use this principle for a simple control circuit.
Of course, although this invention is described in connection with vacuum tubes, it is evident that various other types of devices may Ibe used. Transistors, for example, are coming into extensive use. Such transistors are small, compact and require no filament power. The same general principle, embodying the present invention and described in connection with vacuum tubes, may be employed with transistors. The circuits, however, would be altered to conform to the difference in behavior between the transistor and the electron tube.
Referring particularly to Figure 2, there is shown in detail a diagram of one form of capacitance-operated control circuit, such as might be used for one of the blocks of Figure 1. As shown in Figure 2, the circuit involves only a single note of an electronic musical instrument, it being obvious that a plurality of circuits of the same type may be employed to produce more than one note without departing from the scope of this invention. A triode oscillator tube 1S uses a Hartley type oscillator circuit comprising an inductance 20 and a capacitance 22. A resistor 24 provides a grid leak bias for the tube. A connection 26, to the grid 28, provides means to permit an operator to affect the operation of the oscillator.
The bias, which is generated across the resistor 24 when tube 28 is in an oscillating state, is applied to the control grid 36 of an amplifier pentode electron tube 38, by means of the resistance-'capacitance filter shown as 32 and 34 in Figure 2, together with the grid resistor 40. This pentode amplifier 38 is used in the path between the electrical tone generator 42 and a common audio amplifier which is coupled to the pentode amplifier through a capacitor 44 and a loudspeaker for all the notes of the instrument (not shown). The operating voltages for the pentode 38 are chosen so that the bias supplied by the triode tube cuts ofi the anode current of the pentode, and no tone signal is transmitted to the common audio amplifier. The circuitry associated with the tube 36 and the common amplifier and loudspeakers provides for the utilization of the generated tones.
When the connection 26 is touched with the hand, or when the hand is brought sufficiently close to it `(the choice as to how close the hand should be brought to stop the oscillator is governed by the constants of the oscillating circuit and, in particular, the size of the grid capacitor the oscillator stops oscillating and the bias across the grid-leak, resistor 24 is thereby removed'. The pentode 38 is then no longer cut off and operates as a normal amplifier with its bias supplied by cathode resistor 46. Thus, as soon as the control element or connection 26 is touched, the tone generator signal is transmitted to the common audio amplifier and can be heard in a loudspeaker.
A pentode amplifier is shown in Figure 2 because it is essential that, when full cut-off bias is appliedV to its grid, no tone must get into the plate circuit by the way of inter-electrode capacitance. To eliminate shock hazard in case of a shorted tube, a capacitor may be inserted in the lead to the key, and the key grounded by means of an R. F. choke, provided such a capacitor is substantially larger than the capacitor 30. This will not affect operation in any way.
The use of two tubes for each capacitance-operated control circuit, in addition to the tube used for the tone generator, all duplicated for each note, represent a large number of tubes. For this reason, there is provided in this invention, improved systems involving the useof fewer tubes.V However, it is still recognized that the principles involved in this invention are notV necessarily limited to vacuum tubes.
Referring particularly to Figure 3` of the drawing, a touch control system embodying the present invention using a single tube is shown in the form of a double triode. This single tube serves as both control circuit and tone generator. Two triode sections 46 and 48 are connected in an audio-frequency, multi-vibrator type of circuit. In addition, in the grid-cathode circuit of the sect-ion 46 there is connected a radio-frequency Hartley type oscillator circuit comprising an inductancef and a capacitor 52. A grid leak resistor 54 and a capacitor 56 are placed onthe ground end of the coil. A capacitor 53 between the cathode 6ft and a tap 62 on the radio frequency coil is a radio-frequency by-pass capacitor which does not appreciably passaudio frequency. Similarly, a capacitor 6,4f between the plate 65 and ground is a radio-frequency by-pass capacitor which affects slightly the 'audio frequency generated by the multivibrator but not its oscillating capability. A resistor 68 and a capacitor 70 form a radio-frequency filter circuit to conduct the oscillator grid-leakyoltage, produced across the resistor 54, onto the grid 72 of the second triode through a resistor 73. VThe multi-vibrator circuit consists of a common cathode resistor 74 to ground, the plateresistors` 76 and 7S. in the two triode plate circuits, the plate-tofgrid coupling capacitor 80 between the first andAV se'condtriodesilam a V ':apacitor S2 from the plate 84 Vto ground. `Wl1n usedby itself, this type of multivibrator circuit is known as Potter circuit (because it was described by Potter in the EProceeding by the I. R. E. in I une 1938). When the control electrode 86 is touched by an operator, the radio-frequency oscillator of the rst triode 46 stops oscillating. The bias is thereby removed from the second triode 48 so as to actuate the audio multi-vibrator circuit, thereby producing an audio tone rich in harmonics, as desired by a musical instrument. The radio frequency oscillator therefore acts as a control circuit associated with manual means for varying its operation.
Referring now to Figure 5, a different touch control circuit is shown, which makes use of body resistance. A tone generator liti having an electrical audio signal output is coupled to the grid 114 of an amplifier tube 112 through a capacitor liS. A source of negative potential designated as E- is applied to the grid through resistors 116' and 118. An output voltage is developed across the plate 12) and cathode 121. The associated output circuit is not shown for purposes of simplification. In this embodiment of the invention, the finite resistance of the human finger to electrical current is utilized. A touch'control electrode 22, which may, for example, be equivalent to a key on a piano or organ, comprises two closely spaced parallel bars H4 and 126. When the finger is touched to these bars, the finger resistance cornpletes the circuit to ground. If the resistance of the resistor ld'in series with the cut-off voltage is very high compared to the finger resistance, the bias on the audio amplifier i12 willv be reduced substantially. The amplifier then becomes conducting and the audio tone from the tone generator is amplified. A capacitor 125 or disturbance is detectable'to the performer.
In the embodiments of the invention described up to this point, reduction in physical effort in playing polyphonic instrument by use of a touch-control system has been indicated. However, in many cases, it is important that the performer be also able to control either the loudness, the attack or the harmonic content (timbre) of the note, as he wishes. Y
A simple circuit in which touch control may be use to control volume or other sound characteristics is shown in Figure 4. It is intended that any one of the previous circuits can be used to initiate control, i. e. by touch only, whereas by additional control of finger position, a second auxiliary sound characteristic can be altered. A series of contact bars 88 is provided for each note, so
Y that, when the finger is placed on the proper pair of contacts, the circuit is completed through the nger resistance and appropriate auxiliary control thereby attained. The finger may also be slid forward and backwards, that is, from left to right as viewed in Figure 4, in order to obtain a continuously variable control, while theperformer is playing the particular note to which the contact is connected. Figure 4a illustrates an equivalent circuit. Various resistors and 92 may be included in an electrical circuit by movement of the finger. Appro` priate circuits to which such means may be applied are not shown. Y
Referring particularly to Figure 6, another method of using a single tube is shown and combines touch control with a tone controlV circuit'ln this embodiment, a radio frequency oscillator and an audio oscillator are combined within a single tube envelope.
A pentagrid tube V12S, such as is commonly used in broadcast receivers for the converter stage, is employed in this embodiment. A radio frequency oscillator provides a capacitance or touch-operated control cirfcuitand the audio oscillator Yprovides a musical tone.- Only one of these oscillators is operative at any*giventime. Y The cathode and the grid 132 are connected as a Hartley type radio-frequency oscillator, for which the grid 134 acts as an anode. The tuned circuit comprises an inductor 133 and a capacitor 135. The grid 154 is by-passed to ground through a radio-frequency by-pass capacitor 136. The suppressor grid 151 is directly connected to the cathode. A key 138 comprises a metal spring 140 and a bottom metal plate 142 separated by a dielectric material 144. Grid leak capacitance is provided by a capacitor 137. The bias across the grid leak 146 is applied to the second control grid 134 through resistor-capacitor filter 150 and 157 and through resistor 152. When radio-frequency oscillations are present, this bias is enough to cut off the second control grid 134.
When the key 138 is touched the radio-frequency oscillator stops oscillating and the bias across the grid leak resistor 146 is removed. This, in turn, removes the bias from the second control grid 134 and permits this grid to operate on the electron current available to it through resistors 150 and 152. The screen grids 154 and 148, which are internally connected in the tube and the-second control grid 134 form a negative-transconductance audio oscillator, which oscillates at an audio frequency determined by the time constant of the combination comprising the resistors 155 and 152 and the capacitors 136 and 156. Such an oscillator, in its simple uncombined form is well-known and Was described in an article by the applicant on negative resistance devices in the Proceedings of the I. R. E. in October 1935. The negativetransconductance oscillator cannot oscillate however, if the bias on the grid 148 is in excess of the cut-off bias of that grid so that the audio tone is generated only when the key 138 is touched. In the event that the grid 134 is a remote cut-ofi` grid, as is often the case in commercially available tubes, one must only provide sufficient bias to cut-off the grid to prevent oscillation, since the small negative transconductance at high control -bias voltages is not sufficient for oscillation. It is therefore seen that when the radio-frequency section of the tube is oscillating, the negative-transconductance audio oscillator cannot oscillate. No audio tone is then produced in the plate circuit of the pentagrid tube, which may be connected to an audio amplifier or other utilization circuit through a coupling capacitor 158.
If the finger of an operator touches the spring material member 140 of the key 138, the radio-frequency oscillator becomes inoperative. The bias is therefore removed from the grid 154, and the negative-transconductance oscillator starts oscillating at an audiofrequency rate. The audio frequency in the plate circuit may then be transmitted to an audio amplifier. It will be appreciated that if the grid leak 146 has large impedances at audio frequencies, touching the finger to the metal spring may produce some pickup or hum voltage which may be transduced into the audio amplifier in addition to the desired note. However, this may be overcome by expedients wellknown in the art.
It is seen that, when the finger of the operator is depressed, so as to curve the metal piece 140 down over the bottom metal plate 142, additional capacitance is introduced between the touched piece 140, which is at audio-frequency ground potential, and the other piece 142 of the metal spring, which is connected to the audio output anode 160. The amount of this capacitance is controlled by the finger pressing the metal spring and acts as a tone control for the audio frequency which is passed on to the audio amplifier. Thus, when the finger first touches the metal spring, the audio tone starts and may be rich in harmony and overtone. lf, however, the finger is depressed harder, the capacitance between the metal spring 138 and the bottom plate 142 is increased so as to bypass more and more of the higher frequency from the anode circuit, thereby making the tone more mellow. The performer, therefore, is able to control the characteristic of the tone produced by pressing the key harder or less hard. It should be realized that many other ways may be employed to accomplish this tone control without departing from the scope of this invention. Essentially a variable capacitance may be used in any type of circuit which will operate with a variable capacitance, whether as a tone control, as a loudness control, or as an attack control. If desired, the spring member may be made of two insulated pieces, one above the other. The upper piece could be used in the radio frequency circuit and would be touched by the finger, whereas the lower piece would be separately connected to the capacitance circuit. Such an arrangement would minimize the effect of hum in the audio output circuit.
It should be appreciated that the oscillator type of capacitive touch control does not require the finger actually to touch a piece of metal. The piece of metal may have a plastic coating, since it is only the finger capacitance and body loss at radio frequencies which cause the radio frequency oscillator to stop and allow the audio oscillator to start.
Referring particularly to Figures 7 and 9 of the drawing, a circuit is shown wherein the attack may be controlled by the performer. Control of attack of an audio tone is considered by many to be more important than a control of volume or tone quality. However, it is realized that the circuit shown may, with slight modification, be also used to control the volume, tone content or other sound characteristic.
A pair of triodes 162 and 164, which may be incorporated into a single envelope if desired, include a radio frequency oscillator in the first triode 162 and an audio oscillator in association with the second triode 164. The radio frequency oscillator comprises a conventional Hartley type having a tapped inductor coil 166 and a capacitor 168 providing the tuned circuit. Resistor 170 and a capacitor 172 provide grid-leak bias for the oscillator. The radio-frequency oscillations are stopped by a performer placing a finger on the key 174, as previously described.
The audio oscillator comprises a triode 164 used in conjunction with a resistance-tuned type audio oscillator comprising capacitors 176, 178 and 180 together with resistors 182, 184 and 186. This oscillating circuit operates only when the finger of the operator touches the key since the cut-off bias is otherwise impressed on the grid 188 through the resistors 190 and 186. When the finger touches the key, the radio-frequency oscillator stops. The bias is therefore removed from'the audio oscillator, which then becomes operative. At the junc- .tion of capacitors 176 and 178, the audio frequency voltage is taken off and applied to a grid 192 of an amplifier tube 194. It will be noted in this case that the grid-leak resistor of the tube 194 is resistor 182. The lower end of the resistor 182 is connected so that, if the key is not depressed, a bias designated by a battery 196 is placed on the grid 192 of the amplifier tube 194. This bias may be adjusted so that a very weak audio tone appears and, when the instrument is played very softly, the key need not be depressed but is merely touched. If, however, the key is depressed at the end 198 of the key so as to touch the resistor 200 at its lefthand end, it will be noted that this connects the end of the capacitor 202 which is connected to terminal 19S, to ground through the key and radio frequency coil, which is very low in impedance at D. C. or audio frequencies. As a result, the bias voltage is instantly removed until the capacitor 202 charges up. The audio tone reaches full volume suddenly and then gradually decays as in the tone of a piano or banjo type.
Referring particularly to Figure 9 of the drawing, the curves indicate the type of attack which may be expected from touching the finger to the key at different places. Each curve shows the amplitude of the audio output as a function of time. Curve 204 represents the output 7 whenthe key is touched, but not pressed into contact with resistor 200. Curve 206 represents the output when the key is pressed at the end i923. Curve 268 represents the output when the key is pressed between the points 198 and the middle of the key represented by a tap 199. Curve 21@ represents the output when the key is pressed at the tap 199, as illustrated in the drawing. Curve 212 represents the output when the key is pressed between the middle and the end 2l4 of the key. Figure 216 represents the output when the key is played near the end 214. ,A
. The various combinations, such as described, may be obtainedV by judicious choice of the tapped resistor 20) and the capacitors 2tl2 and 139', together vwith the resistor 182 and the capacitors 176 and T178 associated with it. The Operation of the circuit can be readily determined by examining the curves of Fig. 9 showing the transient characteristics of the key circuit.
In connection with this circuit, the key is made of rubber having an electrically conductive material added. Experiments have shown that the resistance between two points varies with pressureA or tension. This conductive rubber has advantages over other types of pressure controlled resistance's, since it is low in cost and practical to apply. Y
Referring particularly to Figure 8 of the drawing, there is shown a photo-electric cell 22). A light source 222 striking the cathode of the device causes current to flow, thereby developing voltage across a resistor 224. Variations in light will produce a voltage variation across the resistor 224. This variation may be used to vary the gain of an amplier tube 225. A tone generator 228 is applied tothe grid 232 of the ampliiier through a coupling capacitor 230. A resist'or'234 is used to provide means for biasing the amplifier. A resistor 236 provides a' load for the amplifier.
,When the finger of a performer is placed near one end ofthe slit, almost the full amount of light is put on the phototube. As the ringer is pushed inward, and touches more and more closely the inner portions of the slit towards the other end, less'and less light strikes the phototube. Thus, the phototube current is a function of the finger position and may 'be used to control the amplitude of other characteristic of an audio tone. Other' arrangements may include theV light source within the instrument. The light beam may then be projected upward and' diffusedV byithe nger. Again, the ingers position would determine the amount of light reaching aereas? the phototube, thus providing means to vary the amount of current and the volume or othercharacteristic of a tone. Y Y
rIt is apparent that principles described Yin connection with the embodiments shown are not limited to any particular musical instrument or tone.
The use of transistors in touch control generally, of the type described, can be achievedpby making use of the same general principles described in connection with electron tubes. i Y
What is claimed is:
l. In a polyphonic musical instrument, theV combination comprising a tone generator having an electrical audio-frequency signal output, a utilization circuit, means for applying said audio signal output to said utilization circuit, a radio-frequency oscillator circuit to develop a bias, means for applying said Vbias to maintairi's'aid tone generator normally inoperative, a control circuit for varying the operation of said radio frequency oscil-V l`atcr,`rneans connecting said control circuit to said oscillator, means associated with said control circuit having a'yariable electrical characteristic, said la'st named means being accessible to the linger of an operator, whereby a touch of the linger of an operator is effective to vary said electrical characteristic to render said radio frequency osciilator inoperative thereby reducing said bias to permit operation of said tone generator, and means for varying said audio signal output from said tone generatorY to said utilization circuit.
2. The invention as defined in claim 1 wherein saidy means for varying said audio signal output voltage com# prise electrically conductive rubber member and a resistance associated with said tone generator disposed in close proximity lto said rubber'xnember whereby a pressure applied by the finger of'an operator `to said rubber is etectiveto electrically connect said rubber to a certain portion of lsaid resistance,
References Cited in the ile of this patent UNlTED STATES PA'ENTS r1,661,058 Theremin Feb. 28', 1928 1,847,1l9 Lertes ot al. Mar. l, 1932 2,l4l,231 Trautwein Dec. 27, 1938 2,142,580 Williams Jan. 3, 1939 2,20l,232 l-lelberger May 21, 1.940 2,270,789 SmithV Ian.. 20, 1942 2,732,545 Passow et al Jan. 24, 1956
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Cited By (27)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3077136A (en) * 1959-02-26 1963-02-12 Hammond Organ Co Capacity tuned oscillator
US3247311A (en) * 1960-08-31 1966-04-19 Jenny Georges Electronic musical instrument
US3681507A (en) * 1971-01-06 1972-08-01 Kimball Piano & Organ Co Electronic organ voicing control mounted on voice tab
US3694559A (en) * 1970-11-04 1972-09-26 Nippon Musical Instruments Mfg Electronic musical instrument employing variable resistor fingerboards
US3708603A (en) * 1971-03-01 1973-01-02 C Keagle Electronic sound synthesizer
US3749810A (en) * 1972-02-23 1973-07-31 A Dow Choreographic musical and/or luminescent appliance
US3754495A (en) * 1970-10-27 1973-08-28 M Honegger Sounding note board for music instruction
US3769869A (en) * 1972-04-24 1973-11-06 Opsonar Organ Corp Electronic musical instrument keying assembly providing a minimum of electrical noise
US3784935A (en) * 1972-06-15 1974-01-08 Arp Instr Touch sensitive polyphonic musical instrument
US3828108A (en) * 1972-03-22 1974-08-06 F Thompson Binary organ and coding system for operating same
US3836909A (en) * 1972-04-06 1974-09-17 Electronic Music Studios Ltd Data input devices
US3938419A (en) * 1974-05-20 1976-02-17 David De Rosa Electronic musical instrument
US3943812A (en) * 1973-11-02 1976-03-16 Nippon Gakki Seizo Kabushiki Kaisha Touch responsive sensor in electronic keyboard musical instrument
US3968717A (en) * 1971-06-01 1976-07-13 Melville Clark, Jr. Musical instrument with means for scanning keys
US3968716A (en) * 1971-06-01 1976-07-13 Melville Clark, Jr. Musical instrument with means for scanning keys
US3969968A (en) * 1971-06-01 1976-07-20 Melville Clark, Jr. Musical instrument with means for scanning keys
US3999457A (en) * 1972-03-17 1976-12-28 Adolf Michel Key system for controlling the rate of attack in electronic musical instruments
US4027569A (en) * 1975-06-19 1977-06-07 Norlin Music, Inc. Keyboard for an electronic musical instrument employing variable capacitors
US4091610A (en) * 1974-05-08 1978-05-30 Sharp Kabushiki Kaisha Switching mechanism for electronic wristwatch
US4241636A (en) * 1978-12-28 1980-12-30 Christopher Long Electronic musical instrument
US4247929A (en) * 1974-05-08 1981-01-27 Sharp Kabushiki Kaisha Switching mechanism for electronic wristwatch
US4430917A (en) * 1979-08-22 1984-02-14 Peptek, Incorporated Hand-held musical instrument and systems including a man-machine interface apparatus
US4438674A (en) * 1980-04-11 1984-03-27 Lawson Richard J A Musical expression pedal
US4665788A (en) * 1983-10-14 1987-05-19 Jeff Tripp Keyboard apparatus
US5270711A (en) * 1989-05-08 1993-12-14 U.S. Philips Corporation Touch sensor array systems and display systems incorporating such
US5465091A (en) * 1991-06-28 1995-11-07 Showa Shell Sekiyu K.K. Touch sensor
US20030167907A1 (en) * 2002-03-07 2003-09-11 Vestax Corporation Electronic musical instrument and method of performing the same

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US2270789A (en) * 1940-04-13 1942-01-20 Wurlitzer Co Method and apparatus for volume control of electronic amplifiers
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US2732545A (en) * 1956-01-24 Pilot light switch
US1661058A (en) * 1924-12-08 1928-02-28 Firm Of M J Goldberg Und Sohne Method of and apparatus for the generation of sounds
US1847119A (en) * 1928-12-19 1932-03-01 Lertes Peter Electrical musical instrument
US2141231A (en) * 1930-03-24 1938-12-27 Trautwein Friedrich Electrical musical instrument
US2142580A (en) * 1933-03-06 1939-01-03 Hammond Instr Co Electrical musical instrument
US2201232A (en) * 1938-04-21 1940-05-21 Helberger Bruno Electrical musical instrument
US2270789A (en) * 1940-04-13 1942-01-20 Wurlitzer Co Method and apparatus for volume control of electronic amplifiers

Cited By (29)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3077136A (en) * 1959-02-26 1963-02-12 Hammond Organ Co Capacity tuned oscillator
US3247311A (en) * 1960-08-31 1966-04-19 Jenny Georges Electronic musical instrument
US3754495A (en) * 1970-10-27 1973-08-28 M Honegger Sounding note board for music instruction
US3694559A (en) * 1970-11-04 1972-09-26 Nippon Musical Instruments Mfg Electronic musical instrument employing variable resistor fingerboards
US3681507A (en) * 1971-01-06 1972-08-01 Kimball Piano & Organ Co Electronic organ voicing control mounted on voice tab
US3708603A (en) * 1971-03-01 1973-01-02 C Keagle Electronic sound synthesizer
US3968717A (en) * 1971-06-01 1976-07-13 Melville Clark, Jr. Musical instrument with means for scanning keys
US3969968A (en) * 1971-06-01 1976-07-20 Melville Clark, Jr. Musical instrument with means for scanning keys
US3968716A (en) * 1971-06-01 1976-07-13 Melville Clark, Jr. Musical instrument with means for scanning keys
US3749810A (en) * 1972-02-23 1973-07-31 A Dow Choreographic musical and/or luminescent appliance
US3999457A (en) * 1972-03-17 1976-12-28 Adolf Michel Key system for controlling the rate of attack in electronic musical instruments
US3828108A (en) * 1972-03-22 1974-08-06 F Thompson Binary organ and coding system for operating same
US3836909A (en) * 1972-04-06 1974-09-17 Electronic Music Studios Ltd Data input devices
US3769869A (en) * 1972-04-24 1973-11-06 Opsonar Organ Corp Electronic musical instrument keying assembly providing a minimum of electrical noise
US3784935A (en) * 1972-06-15 1974-01-08 Arp Instr Touch sensitive polyphonic musical instrument
US3943812A (en) * 1973-11-02 1976-03-16 Nippon Gakki Seizo Kabushiki Kaisha Touch responsive sensor in electronic keyboard musical instrument
US4247929A (en) * 1974-05-08 1981-01-27 Sharp Kabushiki Kaisha Switching mechanism for electronic wristwatch
US4091610A (en) * 1974-05-08 1978-05-30 Sharp Kabushiki Kaisha Switching mechanism for electronic wristwatch
US4270199A (en) * 1974-05-08 1981-05-26 Sharp Kabushiki Kaisha Switching mechanism for electronic wristwatch
US3938419A (en) * 1974-05-20 1976-02-17 David De Rosa Electronic musical instrument
US4027569A (en) * 1975-06-19 1977-06-07 Norlin Music, Inc. Keyboard for an electronic musical instrument employing variable capacitors
US4241636A (en) * 1978-12-28 1980-12-30 Christopher Long Electronic musical instrument
US4430917A (en) * 1979-08-22 1984-02-14 Peptek, Incorporated Hand-held musical instrument and systems including a man-machine interface apparatus
US4438674A (en) * 1980-04-11 1984-03-27 Lawson Richard J A Musical expression pedal
US4665788A (en) * 1983-10-14 1987-05-19 Jeff Tripp Keyboard apparatus
US5270711A (en) * 1989-05-08 1993-12-14 U.S. Philips Corporation Touch sensor array systems and display systems incorporating such
US5465091A (en) * 1991-06-28 1995-11-07 Showa Shell Sekiyu K.K. Touch sensor
US20030167907A1 (en) * 2002-03-07 2003-09-11 Vestax Corporation Electronic musical instrument and method of performing the same
US7247785B2 (en) * 2002-03-07 2007-07-24 Vestax Corporation Electronic musical instrument and method of performing the same

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