US 3562400 A
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United States Patent [72 Inventor Royce L. Cutler  References Cited 2] A I N 2 6 2 1 2 UNITED STATES PATENTS f 20 1968 3,247,306 4/1966 Milho 84/1.13 Patented Feb. 9 1971 2,918,576 12/1959 Munch 84/1.26X  Assignee G4: Elecmnics, Inc. 3,003,383 10/ 1961 wllIIamS 84/ 1 .26 a cor ration of Texas 3,109,878 11/1963 Hanert 84/1.12 p0 3,180,919 4/1965 Stiefel 84/1.26 3,383,453 5/1968 Sharp 84/1.26 3,465,088 9/ 1969 Kohls 84/1 .26 Primary ExaminerW. E. Ray 541 PERCUSSION KEYER WI'I'I-I PEDAL SUSTAIN FOR WW-Donald ELECTRONIC MUSICAL INSTRUMENT 4 chums 2 nratvmg ABSTRACT: A percussive musical note is simulated. A switch  US. Cl 84/l.26 passes a pulse to an RC circuit which differentiates the leading  Int. Cl G10h 1/02 edge. The formed signal simulates a percussive instrument. A  Field of Search 84/1.01, second switch adds a sustained voltage to the pulse. A diode 1.04, 1.06--1.08, 1.1, 1.13, 1.17, l.241.27, blocks part of the discharge path of the RC circuit and extends (E,F ,0) its decay time. Hence the note may be short or sustained.
2 6 +v 7 Z \3 z PERCUSSION KEYER WITI-I PEDAL SUSTAIN FOR ELECTRONIC MUSICAL INSTRUMENT SUMMARY OF PROBLEM AND SOLUTION Percussive keyboard instruments normally include the piano, harpsichord, clavichord, and the like. The musical tones from such instruments can be simulated in electronic signal generating apparatus. However, certain striking characteristics are inherently involved in the construction of such keyboard musical instruments. For instance, most percussive keyboard instruments use a striking mallet or hammer which taps a plurality of strings to obtain the tone. The manner of striking the strings materially alters the quality of the tone and its duration. The modern piano sustains a note for a long period if the piano key remains depressed. On release, the note is damped or muted rather quickly. An alternative mode of operation is presently provided wherein the keys of the entire keyboard are provided with the sustain feature so that all notes struck are sustained through operation of a foot pedal.
It is with the foregoing percussive keyboard tones and qualities that the present invention is described as an apparatus for simulating percussive keyboard striking characteristics. More particularly, the circuit of the present invention is adapted to provide an electronic keying apparatus which simulates the sustain or muted characteristics of a conventional percussive instrument keyboard and wherein a sustain pedal feature is also incorporated with the present invention. With the above summary in view, those skilled in the art will perceive many objects of the present invention, which will be more readily understood from a consideration of the following specification and included drawings, wherein:
FIG. 1 is a block diagram schematic of the device of the present invention cooperating with an electronic tone generating apparatus; and,
FIG. 2 is a schematic wiring tion.
Attention is first directed to FIG. 1 of the drawings which illustrates a musical tone generator signal source indicated by the numeral 10. Suchv a signal source is an electronic tone generator as typically found innumerous electronic organs or other devices wherein the musical tone is an electrical signal conducted by appropriate wiring to the present invention for use as will be explained. The signal source is nonnally communicated with the keying simulator 12 of the present invention. Since the present invention is designed for use with an entire keyboard, additional keying simulators are indicated at 14 in FIG. 1, it being appreciated that the number is increased without limit and that allsi'mulators are preferably identical save for their connwtion to signals of different frequencies or voicing from the musical tone generator 10. The outputs of the various simulators l2 and 14 are input to a suitable amplifier 16 which then communicates with a suitable output device, a speaker 18, or the like. The means l0, l6 and I8 are shown as supporting structures for an understanding of the present invention 12, and may vary in many details in a variety of instruments presently made or available in the future.
The device of the present invention incorporates the keying simulator I2 which is actuated by a switch means 20. While the switch means 20 is represented as a single-pole, singlethrow switch in FIG. 1, it will be appreciated that it is preferably a key of the keyboardwhich is adapted to control the output signal from the tone generator l2 to shape the musical note supplied to the amplifier 10. Moreover, the additional keying simulators indicated generally at 14 are likewise provided with suitable keyboard means 22 which are represented schematically as identical switches and which are suitably connected for operation of the keying simulators 14 for the entirety of the keyboard. Preferably, all of the keys 20 and 22 are connected in parallel to a voltage source 24 at a suitable level of perhaps 10 to 20 volts cooperative with the solid state circuitry to be described. I
The present invention includes a sustain pedal 26 connected to a suitable voltage source 28. The'pedal 26 is represented diagram of the present invenschematically in FIG. I as a single-pole, single-throw switch when the input to all the keying simulators I2 and I4 are sustained as a group. Again, referring to the example of the modern piano, the sustain pedal 26 operates the entirety of the keyboard whereby striking any note forms a sustained tone without regard to the duration of the key depression.
Referring now to FIG. 2, it will be noted that the switches 20 and 26, having the preferred 'forms of a keyboard striking means and a foot-operated sustain pedal, respectively, are connected to the indicated voltage sources for operation of the present invention. Two series resistors 32 and 34 each having a resistance approximating l00,000 ohms communicate the switches 20 and 26. The switch means 20 is preferably grounded by a smaller resistor 36. A series capacitor 38 and appropriately grounded resistor 40 cooperate as a differentiator for the pulse formed by the switch means 20. On operation of the switch means 20', it will be appreciated that an essentially square pulse is formed by the means 20. The pulse has apositive-going leading edge in the circuitry presently illustrated. The trailing edge, generated on opening the switch 20, is a negative-going voltage change. The derivative of the leading and trailing edges of the pulse is a positivegoing spike and then a negative-going spike output by the differentiating means to the diode 42. The diode 42 passes the positive-going spike which occurs onclosure of the switch means 20. However, on opening the switch means 20fwhich generates the negative-going spike, fonns a signal which the diode means 42 blocks, its anode falling below the voltage of the cathode.
The positive-going spike passed by the diode 42 charges a capacitor 44 with a positive charge on its ungrounded plate. A
very large resistor 46, preferably in the megohm range, forms a path to ground through the base of a transistor 48. The emitter of the transistor 48 is grounded to complete the ground path for discharging the positive charge placed on the plates of the capacitor 44. Significantly, bleeding the charge from the capacitor 44 through resistor 46 and the base of the transistor 48 serves as the bias voltage for the transistor 48 which amplifies in response to its bias voltage.
The musical tone from the generator means 10 is input to the simulator 12 by a conductor50 which has a suitable blocking capacitor 52 interposed between theconductor and the base. In the quiescent condition, the absence of a suitable bias voltage for the base of the transistor 48 prevents amplification. However, provision of the bias for the base of the transistor then enables the transistor to substantially amplify the tone signal from the conductor 50 for an output conductor The complete transistor circuit incorporates a load resistor 56 in the collector circuit and a suitable DC blocking condenser 58 to prevent passage of the DC level to the output conductor 54. Thus, it will be understood and appreciated that bleeding the charge on the ungrounded plate of the capacitor 44 through the transistor forms a suitable bias for the transistor to turn it on, somewhat rapidly, upon closing the switch 20 just as a key of a percussive keyboard instrument strikes a note.
Considering now operation of the circuitry when the switch 20 is maintainedclosed, the following will be noted. Closure and subsequent opening of the switch '20 forms first a positive going and then a negative-going spike presented to the anode of the diode 42. The positive-going spike, which occurs first, is passed to charge the capacitor 44. The bias of the transistor rises rapidly and then decays somewhat in an exponential manner through a resistive network to ground including the resistor 46 and the base-emitter junction of the transistor 48. This decay continues exponentially and is unaltered by the negative-going spike from the differentiator which is blocked by the diode 42. Therefore, it should be concluded that closure of the key 20 for an indefinitely long interval simulates a On the other hand, should the key be closed and rapidly opened, the following occurs. First, the positive-going spike is passed by the diode 42 and quickly charges'the'capacitor 44 which begins the exponential decay. However, when the key (the switch means 20) is opened a short interval after closure, a second conductingpath to ground for the capacitor 44 is enabled. As previously noted, the resistor 46 is preferably in the megohm range This providesa first path to ground, in-
eluding portions of the 'transistor'48. However, when the key 20 is opened, it isessentially grounded by the relatively small resistor 36. This provides a secondor parallel path to ground from the capacitor 44 through the diode, 60 in the forward direction, and the resistors 34 and 36.,This path to ground has a resistance of perhaps about l25,000 ohms, which is perhaps one-tenth to one-fiftieth of the resistance of the other path to ground. This causes a substantially rapid discharge of the capacitor 44 and consequently drops the bias voltage for the transistor48.
Describing the bias voltage of the transistor 48, rapid closure and opening of the switch means 20 in simulation of a rapidly struck percussion instrument keyboard, the bias voltage rises quite rapidly, begins its exponential decay, and then falls rapidly toward zero, beginning at the interval of opening the switch means 20 whereby the note is terminated or muted and is not sustained. Through occurrence of the foregoing variations of the bias for the transistor 48, a keyboard percus-.
sive instrument is simulated in the same manner as the key is struck or held down by the player.
in operation of the sustain pedal which is represented schematically by the switch means 26, the quiescent condition is at the grounded terminal'indicated in FIG. 2. This occurs in the resistor 46 and the transistor 48 to continue the exponential decay associated with a sustained note. This results from the blocking conduction through the diode 60 which thereby dcnies a second and substantially smaller path to ground which rapidly bleeds the condenser 44 when the sustained function is not desired. 1
From the foregoing, itwill be appreciated and understood that the device of the present invention simulates percussive absence of the sustain pedal operation. However, when it is desired to'sustain a note without holding a key closed, the switch means 26 is closed to communicate'a suitable bias potential through the switch 26 to the resistor 32. in the preferred embodiment, economy of power supply construction is provided by making the potentials 24 and 28 equal.
in the preferred embodiment, the sustain pedal function operates in the following manner. On closure of the switch 26 to the bias potential 28, the resistors 32 and 34 (a voltage divider) fonn a fairly high blocking voltage at the cathode of the diode 60. The blocking voltage, operates in the following manner when the sustain pedal is used. Assume, for purposes of discussion, that the switch 20'is rapidly closed and then opened after the sustain pedal is operated. As before, rapid closure and opening forms a positive square wave way whichis differentiated by the circuitry, The differentiation provides first a positive-going spike and then a negativegoing spike to the diode 42. The positive-goingspike is passed bythe diode 42 and is stored on the capacitor 44 and exponentially decayed by the resistor 46 through the base of the transistor to control its amplification. When the switch means 20 is opened, the potential at the midpoint between divider resistors 32 and 34 remain high because the sustain pedal is closed. This blocks operation of the diode 60 to prevent discharge through the second path to ground from the capacitor 44. Thusly, the capacitor 44 is discharged only through the blocked condition to reduce the rate of discharge and therefore extend the discharge time of RC circuit means.
keyboard instruments as described for the preferred embodiment. While those skilled in the art may provide substantial modifications in the device of the present invention, the scope of the present invention is determined by the claims appended hereto.
l. A transistorized circuit for use in an electronic musical instrument to simulate a percussive keyboard effect when supplied with a signal representative of a musical note comprisll'l i. A transistor having base. collector and emitter;
b. A switch suitably adapted to be used as a key of a keyboard; t
c. A voltage source connected to said switch;
d. Diode means connected to the other'side of said switch and having an anode and cathode arranged to pass a voltage surge of one polarity;
e. RC differentiating circuit means connected to receive a voltage level on closure of said switch for forming an output signal which builds toward a peak and decays toward a lesser value in an exponential fashion;
f. Said base of said transistor means being connected to receive the output signal from said RC circuit means in a manner to control operation of 'said'transistor;
g. .Said transistor being connected to amplify a signal representative of a musical note with the gain of said transistor being imposed on the signal representative of the musical note; 1
h. An additional switch connected with a voltage source to provide a voltage level when closed;'and
i. Said additional switch being connected to said base to manner such that gain of said transistor is varied.
3. The invention of claim 1 wherein said additional switch is connected by a series resistor to said series capacitor and provides a voltage level tending to sustain its voltage level after I closing and opening of said switch.
4. The invention of claim 1 wherein the time rate of operation of said RC circuit means is determined at least partially'by a first resistive discharge path and a second resistive discharge path and wherein said additional switch means is connected to a diode to bias one of said resistive discharge paths to a