Description:
The present invention relates to a touch-responsive tone envelope control circuit for electronic musical instruments, and more particularly, to a specific tone envelope control circuit which can improve the tone envelope effects in a key-operated electronic musical instrument such as an electronic organ to provide excellent effects of music being played.
It, therefore, is the principal object of the present invention to provide a tone envelope control circuit which is simple in construction, and easy and inexpensive to manufacture and which permits the electronic musical instrument incorporating the circuit to provide a variety of excellent tonal effects by making use of the effect that the tone envelope is subjected to the intensity of a playing key depression, called a "touch-responsive control effect."
According to the present invention, there is provided a combination of a plurality of keyer circuits and a circuit connected through a manual changeover switch and allowing the keyer circuits to provide a loud tone signal having a predetermined large amplitude regardless of the intensity of key depression while providing a soft tone signal having a predetermined small amplitude when the intensity of the key depression is very low, so that the player can easily provide various kinds of keying effects at will.
Other objects, features and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which,
FIG. 1 is a circuit diagram showing an embodiment of the present invention,
FIGS. 2 and 3 are partial circuit diagrams showing modifications of the essential portion of the embodiment of FIG. 1.
The same characters or references are hereafter used to indicate the same parts.
Reference is made in detail to a preferred embodiment of the present invention with reference to the accompanying drawings.
L designates a coil grounded at one end thereof and adapted to vary the interlinking fluxes in association with depression of an operating key arranged on a keyboard of an electronic musical instrument (e.g. the key carries a magnet thereunder), the other end of which is grounded through a series circuit of a rectifying element D and a capacitor C. A junction d between the element D and the capacitor C is connected to a movable contact SAo of a changeover switch SA of one-pole two-position type, which is actuated in association with the operation of the key K. The connection point d is also connected respectively through resistors R1 and R2 to the gates of field effect transistors Q1 and Q2 (hereunder referred to as FET's) between whose sources series connected resistors R3 and R4 are connected. The connection point ra of the resistors connects with the juncture ra1 of bleeder resistance elements R5 and R6 connected in series between a DC voltage +Vcc of a power source and ground. The juncture ra1 is also grounded via a capacitor Co.
The sources of the FET's Q1 and Q2 are adapted to receive through terminals t1 and t2 individual tone signals each having a predetermined frequency of different footage, produced by conventional tone generators of the electronic musical instrument (not shown), respectively. At the drains of the FET's Q1 and Q2, load resistors R7 and R8 connected to the power voltage +Vcc at their one ends are connected at the other ends, respectively. At the connection points of the drains of the FET's Q1 and Q2 and the load resistors are provided respectively output terminals T1 and T2 which are adapted to develop the tone signals each having a required envelope (amplitude) and a different footage number applied to the input terminals t1 and t2 from the respective drains thereof by varying the gate potentials at the FET's Q1 and Q2 in association with the operation of the key. As a whole, the above-mentioned arrangements are shown as a key depressing speed detecting circuit S1 and a keyer circuit S by two two-dot chain blocks in FIG. 1.
In the detecting circuit S1, one stationary contact SA1 (normally closed) of the circuit changeover switch SA is grounded via a resistor Ro, and the other stationary contact SA2 (normally open) is connected through a unidirectional conducting element Do such as a diode to a movable contact SBo of one-pole three-position type changeover switch SB, which may be manually operated and is used in common to the whole keying circuit in the electronic musical instruments. One stationary contact SB1 of the switch SB is grounded, while other stationary contacts SB2 and SB3 respectively are connected to rb and rc which are connection points between series-connected bleeder resistors R9, R10 and R11 connected between the power voltage +Vcc and ground. The movable contact SBo is connected to a common line lo, to which the indicated Do and all the other Do 's in other detecting circuits (not shown) are connected.
The keyer circuit S is so constructed that the gate-to-source potential of each FET's Q1 and Q2 is set through the resistors R5 and R6 at such a required value that when each of the gate potentials is at an earth potential, i.e., 0 volts, each of the FET's is caused to be nonconducting so that the drain-source impedance is rendered extremely high. The movable contact SAo of the changeover switch SA provided in the detecting circuit S1 is arranged to contact the stationary contact SA2 only when the key is depressed. The number of the detecting circuits S1 and the keyer circuits S which are installed in the console of the electronic musical instrument corresponds in number to the playing keys, for example, 61. Now, it is to be noted that the changeover switch SB may be of one-pole two-position type in case either of SB2 contact and SB3 contact is not required in design.
Now, description will be made on the operation of the above-mentioned circuit arrangement.
At first, under a condition that the movable contact SBo of the circuit changeover switch SB is contacted by the contact SB1, when any one key K provided in the electronic musical instrument is depressed, a magnetic member attached to the key moves close to or away from a fixed coil L, thereby resulting in a damped pulse voltage approximately proportional to the intensity or speed of depression of a playing key due to a variation in interlinking fluxes established round the coil. The induced alternative voltage is rectified through the element D and as a result, a positive DC voltage developed at the element D is stored in the capacitor C. As soon as the charge stored on the capacitor C is applied respectively through the resistors R1 and R2 to the gates of the FET's Q1 and Q2, the respective drain-source impedances are caused to be reduced in response to the gate input levels of the FET's, so that the individual tone signals applied to the sources of the FET's may be derived at the output terminals T1 and T2 provided at the drain side thereof. At this time, since the movable contact SAo is actuated in interlocked relation with the operation of the key K, namely, since the contact SAo is made in contact with the stationary contact SA2 only during depression of the key as shown by a dotted line in FIG. 1, the positive charge stored on the capacitor C is blocked by a reversely connected diode Do to flow in the common line lo, thus, no discharge is caused, and hence, the charge is applied through resistors R1 and R2 to the gates of the FET's Q1 and Q2, resulting in reduction of the source-drain impedance of each of the FET's in response to the intensity of key depression as mentioned above. As a result, the tone input signals separately applied to the respective sources of the FET's may be derived at the output terminals T1 and T2 which are on the drain side of the FET's separately. The envelope (amplitude) of the output tone signal varies in response to the intensity or speed of the key depression. That is, upon quick depression of key, the charge stored on the capacitor C provides a high potential, causing an output tone signal of a high level, while with slow depression of key, the output tone signal may be obtained at a low level. Thus, the present arrangement permits a tone envelope control which provides a so-called touch-responsive effect in an electronic musical instrument and which provides said effect resembling that of a piano.
In the case described above, if the playing key K is kept depressed, no further alternating voltage is induced in the coil L. However, since the input gate impedance of each of the FET's Q1 and Q2 is very high (for example, 109 ohms) the charge stored on the capacitor C immediately after depression of the key has no discharging path, and accordingly, it does not discharge for a long period of time, so that the FET's Q1 and Q2 are held in their conducting states during the depression of the key, at each of terminals T1 and T2, continuously providing the output tone signal having a level responsive to the intensity of the key depression.
Upon release of the key being depressed, the key is made restored by its self-return action and simultaneously, the movable contact SAo of the changeover switch SA is also returned to be in contact with the contact SA1 at the position as shown by a solid line in FIG. 1, so that the charge stored on the capacitor C discharges in a short period of time through the resistor Ro having a relatively low resistance. Accordingly, the gate potential of each of the FET's Q1 and Q2 becomes the earth potential, i.e., 0 volts to render the FET's Q1 and Q2 to be in their nonconducting states, so that no output signal is developed at both terminals T1 and T2.
Now, considering the case where the playing key K is quite slowly depressed, voltage induced in the coil L is too small, and as a result, there will occur the case where the gate of each of the FET's Q1 and Q 2 cannot be at a positive voltage sufficient to be conductive between the source and the drain. Further, there is a possibility of producing no output even though the key is depressed depending upon the intensity of key depression, and hence, the player is required to be skillful in playing the instrument in order to produce desired soft tones without fail, resulting in nervous strain.
On the contrary, when the electronic musical instrument is played at a loud tone level the key K is always required to be quickly and strongly depressed, and a long play under such a condition results in the fatigue of the player. In the present invention, various attempts have been made to obviate these conventional defects. The bleeder resistors R9, R10 and R11 are arranged to divide the power voltage +Vcc at a predetermined ratio, and a positive voltage V1 appearing at the connection point rb is set at substantially the same as the charged voltage across the capacitor C when the intensity of key depression is weak. That is, in case any one key is too slowly depressed under the state in which the movable contact SBo is in contact with the stationary contact SB2, the induced voltage in the coil L will be too small and the voltage V1 will prevail to be applied to the capacitor C for charging it via the unidirectional conducting element Do and the movable contact SAo being in contact with the contact SA2 by key depression. The voltage V1 is also applied respectively through the resistors R1 and R2 to the respective gates of the FET's Q1 and Q2. As a result, the source-drain impedance of each FET is lowered to some limited extent, so that input tone signals of different footage number which are separately applied to the respective sources thereof can surely be derived separately at the terminals T1 and T2 on the drain side thereof as output tone signals with low levels. That is, since the voltage V1 at the connection point rb is set substantially the same as the storage voltage of the capacitor C upon weak key depression, even an extremely slow key depression permits soft tone to be produced with the help of the voltage V1. Therefore, the above arrangement facilitates the soft tone producing play as well as a long playing, and the nerve strain of the player is greatly reduced. In this case, release of the depressed key allows both the key and the changeover switch SA to return to their initial state, and allows the charge stored on the charged capacitor C to be discharged in a short period of time via the resistor Ro, so that each FET is turned to its nonconducting state to shut off any output signals.
The bleeder resistors R9, R10 and R11 serve to divide the power voltage +Vcc at a predetermined ratio to provide a positive voltage V2 at the connection point rc. The voltage V2 is determined to be substantially the same as the charged voltage across the capacitor C upon key depression with a high intensity. Therefore, in case key depression is effected under the condition in which the movable contact SBo of the changeover switch SB is in contact with the stationary contact SB3, the voltage V2 is always greater than the induced voltage in the coil L and is applied-- via the unidirectional conducting element Do and the movable contact SAo which, by key depression, is brought into contact with the contact SA2 --to the capacitor C for charging it, and is also applied respectively via resistors R1 and R2 to the gates of the FET's Q1 and Q2, so that the source-drain impedances thereof are extremely reduced to allow the output terminals T1 and T2 separately to derive desired output tone signals irrespective of the intensity of key depression.
This can be explained as follows. That is, since the voltage V2 at the point rc is substantially the same as the charged voltage across the capacitor C when the intensity of key depression is high, loud tone-producing play on the electronic musical instruments can be performed independently of the intensity of key depression. For example, even if the player slowly depresses the key K, such loud tone-producing play becomes possible. The operational manner in the circuit upon release of the depressed key is the same as described above. This will be convenient, when the player wants to play the entire music loudly.
Further, as the manual changeover switch SB, a one-pole two-position type switch may be employed. Another embodiment using a switch of this type is shown in FIG. 2, in which a series circuit of a bleeder resistor R9, a potentiometer R12 and a resistor R11 is connected between the power voltage +Vcc and ground, the stationary contact SB2 is connected to a movable contact r12 of the potentiometer R12 whereby the whole tone envelopes in soft or loud tone generating play by key depressing operation can be varied by changing the dividing voltage ratio by adjustment of the slidable contact r12. Further, if there is provided an arrangement that the common line lo is connected directly to a slidable contact r13 of a potentiometer R13 as shown in FIG. 3, the above-mentioned actions such as variations in tone levels or envelopes, etc. can be performed without using the changeover switch SB.
As the key depression speed detecting circuit S1, magneto-sensitive elements or pressure-sensitive elements may be used in place of the induction coil used here. Furthermore, the FET's used in the keyer circuit may be substituted by other switching elements such as transistors, diodes or vacuum tubes etc.