Electronic Musical Instrument With Plural Rc Circuits For Decay

Abstract

An electronic circuit is disclosed to produce an output voltage which controls the volume of a note produced by a struck key as determined by the velocity with which the key is struck. The electronic circuit includes a changeover switch, changing between two predetermined voltages, coupled to each key of the musical instrument keyboard. The wiper of the switch is connected to ground by a series circuit including a parallel RC network and the cathode-to-anode path of a first diode. A second diode is connected in parallel with the RC network with its cathode being connected to the cathode of the first diode and the output voltage is taken off the cathode of the first diode by the anode-to-cathode path of a third diode. The cathode of this third diode is connected by a second capacitor to ground and is also subjected to an adjustable control voltage.

Description

BACKGROUND OF THE INVENTION

This invention relates to electronic organs and more particularly to circuit arrangements for influencing the volume of a struck tone of an electronic keyboard instrument depending on the key-striking velocity.

The circuit arrangement shown in FIG. 1 of the accompanying drawing is disclosed in the German Published Application 2,044,462. This circuit causes the volume of the struck tone to be dependent on the velocity at which the key is struck, so that an electronic keyboard instrument containing this circuit arrangement enables piano-like play.

As shown in FIG. 1 of the drawing, this circuit arrangement includes a changeover switch S, which must be provided for each key of the keyboard, a parallel-RC (resistor capacitor) network R1 and C1, and a diode D1. The parallel-RC network is connected, at one end, to wiper K of changeover switch S and, at the other end, via the cathode-to-anode path of diode D1 to ground. The break contact of the changeover switch S is connected to the first d.c. (direct current) voltage potential U.sub.1, while the make contact is connected to a second d.c. volate potential U.sub.2, which in the case of the above cited German Published Application, is ground. The voltage u.sub.a, which determines the volume of the struck tone, is taken off the cathode of diode D1.

FIG. 2 of the drawing shows the variation of the volume-determining voltage u.sub.a with respect to time of the arrangement of FIG. 1, it being assumed that the first d.c. voltage potential U.sub.1 is negative and that the second d.c. voltage potential U.sub.2 is identical to ground potential. If the changeover switch S is operated by depression of a key, the switching time t1, which starts when the wiper lifts from the break contact and ends when it rests against the make contact, depends -- as is well-known -- on the velocity at which the key is struck. The values of the switching time t1 of a typical changeover switch were measured to be between 2 and 20 ms (milliseconds) were measured.

As long as wiper K contacts the break contact, capacitor C1 is charged to voltage U.sub.1 through diode D1. If the changeover switch is operated by depression of the key, capacitor C1 will, during the switching time t1, discharge through resistor R1 by a value depending on the switching time t1. Thus, when contact is made with the make contact, the a positive pulse is provided at the cathode of diode D1 whose amplitude A is dependent on the switching time t1 and which decays according to an exponential-function.

In FIG. 2, this behavior is illustrated by the triangular curve, with the leading and trailing edges, corresponding to exponential-functions, drawn as straight lines for simplicity. The slope of the leading edge during the rise time t2 depends on the capacitance of capacitor C1 and the latter's loss angle and is therefore practically infinite.

The slope of the trailing edge of the pulse shown in FIG. 2 depends on the time constant of parallel-RC network R1 and C1. The trailing edge of the pulse has a "decay time" t3.

The just described known circuit arrangement can be used in electronic keyboard instruments only for the register "percussion", where, in general, the behavior of a struck or plucked string is imitated. In this case the dependence of the volume on the striking speed and the decay of the output signal u.sub.a after the wiper has contacted the make contact are both governed by the same time constant, namely, by the time constant of the parallel-RC network R1 and C1. Therefore, if the key-striking velocity is to provide a volume variation by the factor 10, a parallel-RC network with a small time constant will be necessary, while a parallel-RC network with a longer time constant will be desirable to provide the tailing edge of the output voltage u.sub.a. It is obvious that this cannot be realized with the known circuit.

SUMMARY OF THE INVENTION

It is the object of the present invention to eliminate the above-described disadvantage of the known circuit arrangement, so that the time constant determining the volume dependent on the key-striking velocity and the time constant determining the dying-out of the struck tone are selectable largely independent of one another.

Another object of the present invention is to provide a circuit arrangement which not only is suitable for the register "percussion" which also permits during normal organ-playing, i.e. when producing a continuous tone while the changeover switch is depressed, and during play with the register "sustain" the volume to be determined dependent on the key-striking velocity. In addition, normal organ-playing is possible with a volume independent of the key-striking velocity but having an adjustable onset time and an adjustable dying-out time.

A feature of the present invention is the provision of a circuit arrangement for influencing the volume of a struck tone of an electronic keyboard instrument depending on the key-striking velocity comprising: a different changeover switch associated with each key of the keyboard instrument, each of the changeover switch having a wiper, a break contact connected to a first direct current voltage, and a make contact connected to a second direct current voltage; a parallel resistor-capacitor network connected to the wiper; ground potential; a first diode having its cathode-to-anode path connected between the parallel network and the ground potential; a second diode connected in parallel to the parallel network having its cathode connected to the cathode of the first diode; a third diode having its anode connected to the cathodes of the first and second diodes to provide at its cathode a voltage determining the volume of the struck tone; a capacitor connected between the ground potential and the cathode of the third diode; an adjustable control voltage source; and a first resistor connected between the source and the cathode of the third diode.

BRIEF DESCRIPTION OF THE DRAWING

Above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a schematic diagram of one known prior art arrangement upon which the present invention is based;

FIG. 2 illustrates the waveform of the voltage determining the volume of the struck tone;

FIG. 3 illustrates a schematic diagram of one embodiment of the inventive circuit in accordance with the principles of the present invention;

FIG. 4 illustrates the waveform of the voltage determining the volume of the struck tone employing the embodiment of FIG. 3;

FIG. 5 illustrates a schematic diagram of another embodiment of the inventive circuit in accordance with the principles of the present invention;

FIG. 6 illustrates a schematic diagram of still another embodiment of the inventive circuit in accordance with the principles of the present invention;

FIG. 7 illustrates the waveforms of the circuits of FIGS. 5 and 6, which determines the volume of the struck tone; and

FIG. 8 illustrates a schematic diagram of the inventive circuit in accordance with the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 3, the inventive circuit arrangement includes the circuit arrangement of FIG. 1 and a second diode D2 connected in parallel to the parallel-RC network R1 and C1, with the cathode of this diode connected to the cathode of the first diode D1. In addition, the cathode of diode D1 is connected to the anode-to-cathode path of a third diode D3, from whose cathode is taken the voltage u.sub.a, which determines the volume. The cathode of the third diode D3 is also connected via a second capacitor C2 to ground, while being subjected to the adjustable control voltage U.sub.3 via the second resistor R2.

In FIG. 3, the adjustability of the control voltage U.sub.3 is insured by the voltage U.sub.3 ' being applied to one end of the potentiometer P1, whose other end is connected to ground, while its tap is connected to the second resistor R2. The voltage U.sub.3 ' may be a d.c. voltage. Also, a square-wave voltage adjustable in its mark-to-space ratio may be provided as control voltage U.sub.3 directly, i.e. without the potentiometer P1, as already proposed in the copending U.S. application of H. Mielke, Ser. No. 285,683, filed Sept. 1, 1972, commonly assigned and now abandoned. In this latter case, a buffer diode must be connected in series with second resistor R2 and the input of control voltage U.sub.3 by switches S1' and S2' being placed in the position other than shown. By choosing the control voltage U.sub.3 to be a d.c. voltage or a square-wave voltage adjustable in its mark-to-space ratio, the decay time t3 of FIG. 2 is made adjustable, so that the behavior shown as a broken line in FIGS. 2 and 4 is obtained during the decay time t3'.

In the circuit arrangement of FIG. 3, part of the charge still stored in capacitor C1 following the changeover of the wiper K is transferred via the third diode D3 to the second capacitor C2, with the charge splitting up according to the ratio of the capacitance values of these two capacitors. The discharge of the second capacitor C2 is not, however, determined by resistor R1 of the RC-network because discharge through this resistor is prevented by the third diode D3. Instead, the second capacitor C2 discharges through the second resistor R2, which is also being influenced by the applied control voltage U.sub.3.

If, for example, the second resistor R2 is connected via potentiometer P1 to ground, the discharge time of the second capacitor C2 is extended and corresponds to an expotential-function, as is indicated by the broken curve in FIGS. 2 and 4. If, however, the second resistor R2 is connected via the potentiometer P1 to a negative control voltage U.sub.3, the discharge curve approximates a straight line because the discharge of the second capacitor C2 takes place toward this negative voltage but is stopped abruptly by the diodes D1 and D3 when the discharge curve passes through zero.

If the circuit of FIG. 3 is operated like the known circuit arrangement with respect to the two d.c. voltage potentials U.sub.1 and U.sub.2, i.e. if the d.c. voltage potential U.sub.1 is negative, and the second d.c. voltage potential U.sub.2 is identical to the ground potential, piano-like playing with the register "percussion" is possible in which the volume of the struck tone is dependent on the velocity at which the key is struck, and in which the dying-out time of the struck tone, which is identical to the decay t.sub.3 or t.sub.3 ' of FIGS. 2 and 4, is adjustable.

If, however, the polarity of the two d.c. voltage potentials U.sub.1 and U.sub.2 is chosen conversely, i.e. if the d.c. voltage potential U.sub.1 = zero, and the d.c. voltage potential U.sub.2 > zero, organ-playing with the characteristics of the register "sustain" is possible whose dying-out time is again adjustable with the potentiometer P1, but in which there is no dependence of the volume on the velocity at which the keys are struck. FIG. 4 shows the waveform of the voltage u.sub.a for this case. It can be seen that, during the key-depression time T, a continuous tone is produced whose volume falls off during the decay time t3 or t3', which is dependent on the potentiometer setting.

The circuit arrangement of FIG. 3, like the circuit arrangements of FIGS. 5, 6 and 8, to be explained hereinafter, may contain the resistor R5, which is inserted between the wiper of the changeover switch S and the anode of the second diode D2 by switches S1 and S2 being placed in their position opposite to that shown. With this resistor R5, the rise time of the voltage u.sub.a, which time is given by the losses of capacitor C1, can be further influenced. To provide the shortest possible rise time t2, given by the value of resistor R5 for all keys (changeover switches) or for one or more groups of keys, as is desired e.g. for sacral play (church organ), a square-wave voltage variable in its mark-to-space ratio may be used instead of the d.c. voltage potential U.sub.2. This circuit variation would be similar to control voltage U.sub.3 as stated hereinabove and as disclosed in the above-cited co-pending application. As mentioned hereinabove, a buffer diode would also have to be provided in this case, too.

FIG. 5 illustrates a modification of the circuit arrangement of FIG. 3. In this circuit arrangement, one end of the second resistor R2 is no longer connected directly to the cathode of the third diode D3. Rather it is connected, on the one hand, via the cathode-to-anode path of a fourth diode D4 to the cathode of the third diode D3 and, on the other hand, via the cathode-to-anode path of a fifth diode to the tap of a voltage divider including the resistors R3 and R4, one of whose terminals is connected to the wiper K of the changeover switch S, while its other terminal is connected to an auxiliary potential U.sub.4. The terminal of the second resistor R2 remote from diode D5 is again connected to the control voltage U.sub.3, which may be a d.c. voltage adjustable at the potentiometer P1 and derived from the voltage U.sub.3 ' or a square-wave voltage variable in its mark-to-space ratio, in which case the above-mentioned buffer diode may be omitted because the buffer diode's function is performed by the fourth and fifth diodes.

Advantageously, the voltage divider including resistors R3 and R4 is designed so that its total resistance is high compared with the resistance of resistor R1 and of any resistor R5 but low compared with the resistance of R3. To be as free as possible from any dependency upon the individual resistance values, it is also advantageous if, as shown in FIG. 6, the tap of the voltage divider including resistor R3 and R4 is connected via an impedance-converter stage to the fifth diode D5. Likewise, the voltage u.sub.a, determining the volume, may be provided via an impedance converter. In FIG. 6, the two transistors T1 and T2 are provided for this purpose. Each of transistors T1 and T2 is operated in an emitter-follower configuration and is of the npn-type.

In the arrangement of FIG. 6, the variability of the auxiliary voltage U.sub.4 is insured by the fixed auxiliary voltage U.sub.4 ' being applied to a voltage divider including resistor R6 and potentiometer P2 connected to ground. The variable auxiliary voltage U.sub.4 can be taken from the tap of potentiometer P2. Thus, the resistor R3 in the embodiment of FIG. 6 is connected to the tap of potentiometer P2. The fixed auxiliary voltage U.sub.4 ' simultaneously serves as supply voltage for the interconnected collectors of transistors T1 and T2.

The emitter of transistor T1 is connected to the anode of the fifth diode D5, while its base is connected to the tap of the voltage divider including resistors R3 and R4. The base of transistor T2 is connected to the common junction point of the cathode of the third diode D3, the anode of the fourth diode D4, and capacitor C2, while its emitter, from which the voltage u.sub.a, determining the volume, is taken, is connected via resistor R7 to ground.

To illustrate the operation of the circuits of FIGS. 5 and 6, it is again assumed that the d.c. voltage potential U.sub.1 is negative, while the d.c. voltage potential U.sub.2 is identical to the ground potential. When the changeover switch S is operated, the voltage across the second capacitor C2 first jumps to the amplitude A of FIG. 7 and then, during the time at3, drops to the value A', which is determined by the value of the variable auxiliary voltage U.sub.4 in such a manner that the discharge of capacitor C2 through resistor R2 toward the control voltage U.sub.3 is over when the fourth diode D4 is cut off. Thus the level A' is adjustable at will by means of the variable auxiliary voltage U.sub.4. When the changeover switch S is released, i.e., when its wiper rests against the break contact again, capacitor C2 again discharges, as in the case of FIG. 3, during the time (1-a)t3. The discharge interrupted by diode D4 is thus continued after the changeover switch S has returned to its initial position. The slope of the falling portion of the curve is again selectable by means of the control voltage U.sub.3, as is indicated in FIG. 7 by the broken lines and by the associated times at3' and (1-a)t3'.

With the circuit arrangements of FIGS. 5 and 6, the following four modes of operation are possible:

1. U.sub.1 < 0, U.sub.2 = 0, U.sub.4 or U.sub.4 ' > 0 and variable:

In this case, normal organ-playing with a volume depending on the key-striking velocity is possible, the dying-out time being selectable via the potentiometer P1.

2. u.sub.1 < 0, u.sub.2 = 0, u.sub.4 or U.sub.4 ' = 0:

In this case, play as stated hereinabove in connection with FIG. 3 for U.sub.1 < 0 and U.sub.2 = 0 is possible, i.e. piano-like playing or organ playing with the register "percussion", with the volume depending on the key-striking velocity and with the dying-out time controlled by the potentiometer P1.

3. u.sub.1 = 0, u.sub.2 > 0, u.sub.4 or U.sub.4 ' = 0:

This case corresponds to the case described hereinbefore with reference to FIG. 3 for U.sub.1 = 0 and U.sub.2 > 0, i.e. organ register "sustain" with dying-out time controlled by the potentiometer P1 but without dependence of the volume on the key-striking velocity.

4. U.sub.1 slightly negative, U.sub.2 slightly positive, U.sub.4 or U.sub.4 ' > 0 and variable:

This case corresponds to the curve shown in FIG. 7 and permits guitar-like play, with the volume of the value A depending on the key-striking velocity.

Regarding the effect to be achieved, the circuit arrangements according to this invention are thus usable in a multiple manner, which can be achieved by simply reversing the polarity of the two d.c. voltage potentials U.sub.1, U.sub.2 and of the auxiliary potential U.sub.4 or U.sub.4 '. Hence, the same components can be used for the registers "percussion" and "sustain", so that considerable component savings can be achieved.

FIG. 8 shows a preferred modification of the circuit arrangement of FIG. 3. Connected in parallel to the anode-to-cathode path of the third diode D3 is the emitter-to-collector path of the npn transistor T3. The base of the npn transistor T3 is either open-circuited or connected to ground. In the former case, the anode of the first diode D1 is simultaneously connected to ground, while in the latter case the anode of the first diode D1 is simultaneously open-circuited. This is illustrated in FIG. 8 by the changeover switch S', whose wiper K' is connected to ground and contacts either the anode of diode D1 or the base of the npn transistor T3. If necessary, a collector resistor R8 may be inserted between transistor T3 and the second capacitor C2 by switches S3 and S4 being moved to their position other than that shown. Regarding the choice and application of the control voltage U.sub.3, the remarks made in connection with FIG. 3 apply analogously.

With the circuit arrangement of FIG. 8, the following modes of operation are possible:

1. U.sub.1 = 0, U.sub.2 > 0, U.sub.3 .ltoreq. 0 or square-wave voltage, the base of transistor T3 open-circuited; and the anode of diode D3 connected to ground:

The amplitude response corresponds to that of FIG. 4, i.e. normal organ-playing is possible whose volume is not dependent on the key-striking velocity. The amplitude A is determined by the value of the d.c. voltage potential U.sub.2, while the rise time t2 is determined by the value of resistor R5, which may be provided, or by the loss resistance of the capacitor C2 and by the latter's value, while the decay time t3 depends on the values of the capacitor C2 and of resistor R2.

If the control voltage U.sub.3 is made negative, the decay time is shortened. By the use of the square-wave voltage variable in its mark-to-space ratio, the decay time can be extended with the exponential decay characteristic being maintained, so that play with the register is possible "sustain".

If the d.c. voltage potential U.sub.2 is replaced by such a square-wave signal, the rise time can be extended ("sacral play", see above).

2. U.sub.1 < 0, U.sub.2 = 0, U.sub.3 .ltoreq. 0 or square-wave voltage; base of transistor T3 open-circuited; and the anode of diode D1 connected to ground:

In this case, piano-like play with operated pedal or organ-playing with the register "percussion" is possible, with the volume depending on the key-striking velocity. The amplitude response corresponds to that of FIG. 2. The decay time t3 behaves as described in 1. above. The decay process is not influenced by the release of the key S, so that the tone fades away slowly even if the strike is very short.

3. U.sub.1 < 0, U.sub.2 = 0, U.sub.3 .ltoreq. 0 or square-wave voltage base of transistor T3 connected to ground; and the anode of diode D1 open-circuited:

In this case, piano-like playing without operation of the pedal is possible, with the volume depending on the key-striking velocity, as shown by the curve of FIG. 2, but with an abrupt break-off of the decaying portion of the curve. The reason for this abrupt break off is that the transistor T3 is rendered conductive as soon as the wiper K comes into contact with the d.c. voltage potential U.sub.1 after the release of the changeover switch (key) S, so that capacitor C2 discharges rapidly. The duration of this rapid discharge is determined to a first degree of approximation by resistors R5 and R8 and capacitor C2. If the resistors R5 and R8 are not provided, i.e. if R5 = R8 = 0, it is possible that the collector-to-emitter saturation resistance of transistor T3 must be taken into account, too.

4. U.sub.1 < 0, U.sub.2 = 0, U.sub.3 > 0 + buffer diode the base of transistor T3 connected to ground; and the anode of diode D1 open-circuited:

In this case, organ-playing with the volume depending on the key-striking velocity is possible. This corresponds to case no. 3 with a very long dying-out time ("percussion"). After the operation of the changeover switch (key) S, the output voltage u.sub.a jumps to the value determined by the key-striking velocity and decreases slowly because capacitor C2 can discharge only through its leakage current and through the base current of transistor T2, so that virtually no decrease in volume can be noticed for several seconds. When the key is released, capacitor C2 discharges very rapidly as stated in 3 above.

5. U.sub.1 slightly negative, U.sub.2 slightly positive, U.sub.3 .ltoreq. 0 or square-wave voltage the base of transistor T3 open-circuited; and the anode of diode D2 connected to ground:

This permits a combination of the registers "percussion" and "sustain" to be realized, with the duration of the dying-out ("sustain") determined by the value of U.sub.3. The amplitude response thus corresponds to that of FIG. 7, with the value A determined by U.sub.1, the value A' by U.sub.2, and the value of t3 or t3' by U.sub.3. However, if the base of transistor T3 is connected to ground and the anode of diode D1 is open-circuited the output voltage u.sub.a becomes zero as soon as the key S is released.

The circuit arrangements of FIGS. 5 and 8 are thus adjustable to the respective manner of play simply by switching, or reversing the polarity of, potentials, i.e. this switching of the potentials is effected only once for the entire electronic musical instrument, so that the number of components necessary for switching is small.

If the control voltage U.sub.3 is replaced by the above-mentioned square-wave voltage of variable mark-to-space ratio or becomes positive as stated in 4., a buffer diode must be connected in series with resistor R2 by switches S1' and S2', as mentioned hereinbefore with reference to FIG. 3.

The given polarities of the d.c. voltage potentials U.sub.1, U.sub.2, of the control voltage U.sub.3, and of the auxiliary potential U.sub.4 or U.sub.4 ' as well as the direction of the diodes D1 to D5 as shown in the figures and defined in the claims and the conducitvity type of the transistors T1 and T2 npn type (in FIGS. 6 and 8) may, of course, be replaced by the opposite polarities by the other direction and the opposite conductivity type without departing from the scope of the present invention.

In the literature, the curves shown in FIGS. 2, 4, and 7 are referred to as "envelopes" because this shape corresponds to the amplitude response of the struck tone. As was shown, the envelope of FIG. 7 represents the addition of the envelopes of FIGS. 2 and 4, the position of the value A' being determined by the auxiliary potential U.sub.4 or U.sub.4 ' (FIGS. 5 and 6) or by the d.c. voltage potential U.sub.2 (FIG. 8). If, in FIGS. 5 and 6, this potential is equal to the potential U.sub.2, the value A' is zero ("percussion").

While I have described above the principles of my invention in connection with specific apparatus it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

Claims

I claim:

1. A circuit arrangement for influencing the volume of a struck tone of an electronic keyboard instrument depending on the key-striking velocity comprising:

a changeover switch for each key of said keyboard instrument, each of said changeover switches being directly connected to its associated one of said keys and each of said changeover switches having

a wiper,

a break contact connected to a first direct current voltage, and

a make contact connected to a second direct current voltage;

a parallel resistor-capacitor network connected to said wiper;

ground potential;

a first diode having its cathode-to-anode path connected between said parallel network and said ground potential;

a second diode connected in parallel to said parallel network having its cathode connected to the cathode of said first diode;

a third diode having its anode connected to the cathode of said first and second diodes, said third diode providing at its cathode a voltage determining the volume of the struck tone;

a capacitor connected between said ground potential and the cathode of said third diode;

an adjustable control voltage source; and

a first resistor connected between said source and the cathode of said third diode.

2. A circuit arrangement according to claim 1, further including

a fourth diode having its anode-to-cathode path connected between the cathode of said third diode and said first resistor;

an auxiliary potential;

a voltage divider connected between said auxiliary potential and said wiper; and

a fifth diode having its cathode-to-anode path connected between the cathode of said fourth diode and a tap of said voltage divider.

3. A circuit arrangement according to claim 2, further including

an impedance converter connected between the anode of said fifth diode and said tap of said voltage divider.

4. A circuit arrangement according to claim 3, wherein

said impedance converter is an emitter follower transistor.

5. A circuit arrangement according to claim 1, further including

an npn transistor having its emitter-to-collector path connected in parallel with the anode-to-cathode path of said third diode; and

a switch having a first position to open-circuit the base of said npn transistor and to simultaneously connect the anode of said first diode to said ground potential and a second position to connect the base of said npn transistor to said ground potential and to simultaneously open circuit the anode of said first diode.

6. A circuit arrangement according to claim 5, further including

a collector resistor connected between the collector of said npn transistor and the cathode of said third diode.

7. A circuit arrangement according to claim 1, further including

a series resistor connected between said wiper and said parallel network.

8. A circuit arrangement according to claim 1, wherein

said adjustable voltage source is an adjustable direct current voltage source, said first resistor being directly connected to said adjustable direct current voltage source.

9. A circuit arrangement according to claim 1, wherein

said adjustable voltage source is a source of square wave voltage having an adjustable mark-to-space ratio, said first resistor being connected to said source of square wave voltage by a buffer diode.