Sound Level Control Device In Electronic Musical Instrument Employing Touch Responsive Keying Means

Abstract

In an electronic musical instrument of keyboard type, a sound level control device comprises a required number of coils and magnets respectively associated with the keys in the keyboard to induce a voltage in response to the key depression speed in one of the coils when a key in the keyboard is depressed, a capacitor connected across each of the coils to be charged by said induced voltage through a diode, a semiconductor switch element having a signal input electrode, a signal output electrode and a control electrode which is connected with one terminal of the capacitor, and a series-connected circuit which includes a first resistor and a normally closed switch interlinked with each key in the keyboard and is connected between said one terminal of the capacitor and the cutting-off potential point. An improvement resides in that the other terminal of the capacitor is connected through a second resistor to a variable voltage source for variably biasing the gate potential by superposing a variable voltage over the charged voltage in said capacitor, and the resistance value of said second resistor is selected to be substantially greater than the resistance value of the first resistor.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to sound level control devices employed in electronic musical instruments, and more particularly to a type thereof wherein the sound level (maximum amplitude) obtainable in response to the force or speed with which the key is depressed can be regulated as desired, and the attenuation of the sound also can be controlled as desired.

In a "natural" (ordinary mechanical) musical instrument such as a piano, harp, guitar, or cembalo, the output sound level versus depression strength characteristics are somewhat different depending on the kind of the instruments. For instance a piano, because of the provision of an escapement or releasing mechanism, no sound is created when the key is depressed with a weaker force than a certain value, whereas in a harp or guitar, a sound is created whenever the string is touched, for instance, by finger, and therefore the lightest touch (key depression) causes the weakest sounding of tones. Different from these instruments, a cembalo produces, owing to the plucking mechanism, a considerable sound volume even when the key is touched very lightly, while the stronger depression force causes the louder sounding.

Although in playing music on conventional electronic musical instruments the "touch responsiveness" has not been considered in many cases, the electronic musical instrument is fundamentally so organized as to simulate natural musical instruments, and for this reason it is desirable to match its sound level versus touch characteristic to that of the natural musical instrument. More specifically, it is desirable to provide a sound level control device of variable nature so that a considerable sound level is maintained even in the case where the music speed increases to a higher tempo, and the touching force on each key is decreased as a natural result.

In the conventional sound level control device employing a tough-responsive keyboard including a plurality of magnets interlinked respectively with keys in the keyboard and a plurality of coils cooperative with these magnets, it has been so arranged that an induced voltage in any one of these coils as a result of a relative movement from the corresponding magnet charges a capacitor disposed in parallel with the coil through a diode, and the potential variation of the capacitor is thereafter introduced into the gate electrode of a field effect transistor for controlling a tone signal passing through the draw and source electrodes of the field effect transistor.

However, because of the fact that the induced voltage in each of the coils is a characteristic increasing substantially in proportion to the depressing speed of the key of the keyboard, the charged potential of the capacitor in such a conventional control device has been varied along a curve (line) shifted from the above mentioned characteristic by a constant voltage corresponding to a forward voltage drop across the diode, whereby the output sound level versus key touch force or speed characteristic similar to that of the above described charged voltage of the capacitor can be obtained. Furthermore, the adjustable range of the conventional control device has been far narrowed, and faithfully variable sound level characteristics not be obtained.

SUMMARY OF THE INVENTION

Therefore, the primary object of the present invention is to eliminate the above described drawbacks of the conventional sound control device employed in an electronic musical instrument.

Another object of the present invention is to provide an improved sound level control device in an electronic musical instrument, whereby a considerable level of sound can be maintained even in the case of an extremely light touch on the key in the keyboard.

Still another object of the invention is to provide an improved sound level control device wherein the above mentioned voltage drop across the diode can be compensated for.

A further object of the invention is to provide an improved sound level control device wherein the sound level versus key touch characteristic is made variable.

A still further object of the present invention is to provide an improved sound level control device wherein the decaying characteristic is also made adjustable.

These and other objects of the present invention can be achieved by an improved sound control device in an electronic musical instrument which comprises for each key an inductive coil producing an induced voltage in accordance with the depression speed of the associated key in the keyboard, a capacitor charged through a diode from the voltage thus induced in the inductive coil, a field effect transistor the drain electrode of which is supplied with the tone signal, the source electrode delivers the switched output and the gate electrode of which is connected to one terminal of the capacitor, and a series connected circuit connected between said one terminal of the capacitor and a point of a cutting-off potential and consisting of a first resistor and a normally closed switch interlinked with the corresponding key on the keyboard, and is characterized in that it further comprises a variable voltage source, and a second resistor through which the variable voltage is applied to the other terminals of the above-mentioned capacitor, and that the resistance value of the second resistor is maintained greater than the resistance value of the first resistor.

The invention will be better understood from the following detailed description of the invention when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a circuit diagram of a sound level control device which constitutes one embodiment of the present invention;

FIG. 2 is a graphical representation of the output sound level versus key touch characteristic which is obtained in the embodiment of the invention; and

FIG. 3 is a graphical representation of the envelope characteristic of the output sound after the musical instrument is keyed on and then off.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 showing a circuit diagram of one embodiment of the present invention wherein a circuit associated with one key among a plurality of keys is indicated, it is clearly seen that the sound control device comprises a key K included in the keyboard, a permanent magnet M interlinked with the key K, a coil L which induces a positive voltage when the permanent magnet M approaches the coil L, diode D.sub.1 connected to one terminal of the coil L, a capacitor C.sub.1 which is charged by a forward current through the diode D.sub.1, a field effect transistor FET for switching the tone signal, a normally closed switch S.sub.1 interlinked with the key K and a variable resistor VR.sub.1 to serve as a variable voltage source, a resistor R.sub.2 and a series connected resistor R.sub.1 and switch S.sub.1. There are further provided with a manually operable switch S.sub.2 for changing the decaying characteristics as an additional improvement, resistors R.sub.3 through R.sub.5, a diode D.sub.2 connected between the switch S.sub.1 and the switch S.sub.2 for circuit isolation and a variable resistor VR.sub.2. The switch S.sub.2 and the variable resistors VR.sub.1 and VR.sub.2 are respectively provided one in common for a plurality of circuits associated with a plurality of keys.

The sound control device described above with reference to FIG. 1 operates as follows.

When the key K is depressed, the normally closed switch S.sub.1 is opened, and the permanent magnet M is simultaneously brought nearer to the coil L inducing a positive voltage in the coil L. This voltage charges the capacitor C.sub.1 through the diode D.sub.1.

The charged voltage is then applied to the gate G of the field effect transistor FET so as to render the transistor conductive. When the charged voltage of the capacitor C.sub.1 applied to the gate terminal G of the field effect transistor FET exceeds a certain threshold value, a tone signal having a certain positive DC level and applied to an input terminal I will pass through the resistor R.sub.5, the drain D and the source S, and the signal thus conducted through the transistor FET is thereafter delivered from an output terminal To passing through the capacitor C.sub.2.

In the conventional sound control device, since one terminal of the capacitor C.sub.1 has been directly grounded without employing the resistor R.sub.2 and the variable resistor VR.sub.1, the potential of the gate G does not go up to a value sufficient to operate the field effect transistor FET (this value is hereinafter called a threshold value) if the key K is depressed by a light touch, and the potential of the gate G exceeds the threshold value only when the key K is depressed more quickly so that the field effect transistor FET conducts the tone signal to the output terminal To. For this reason, the conventional sound control device has made it possible to provide only the characteristic curves as indicated by (a) and (b) in FIG. 2.

According to the present invention, the resistor R.sub.2 and a variable resistor VR.sub.1 (serving as a variable voltage source) are provided between the ground side terminal of the capacitor C.sub.1 and the ground, and, furthermore, the hot side terminal of the capacitor C.sub.1 is connected through a smaller resistance R.sub.1 than that of the resistor R.sub.2 and a switch S.sub.1, a diode D.sub.2, and a switch S.sub.2, to a cutting-off potential point, so that a variable key touch versus sound level characteristic can be obtained.

More specifically, the terminals a and b of the variable resistor VR.sub.1 are connected to a positive voltage source +V and the ground, and if the sliding contact c of the variable resistor is not rotated completely to the ground side, a certain positive voltage will be created at the sliding contact c. This positive voltage is applied to the circuit point d and superposed as a bias voltage to the charged voltage in the capacitor C.sub.1. When the key K is not depressed, the switch S.sub.1 is maintained in a closed state, whereby the above-mentioned bias voltage appearing at the gate G through the coil L and the diode D.sub.1 is bypassed (shunted) through the resistor R.sub.1 of a smaller resistance than that of the resistor R.sub.2, the switch S.sub.1, the diode D.sub.2, and the switch S.sub.2, and thus the potential of the gate terminal G of the field effect transistor does not reach the above-mentioned threshold voltage.

When the key K is depressed, the discharging circuit is broken because of the opening operation of the switch S.sub.1 , and the bias voltage is superposed on the charged voltage of the capacitor C.sub.1 which is charged from the induced positive voltage in the coil L through the diode D.sub.1. As a result, the gate potential reaches the threshold voltage in an earlier stage of depressing of the key. If the resistance between the sliding contact c and one terminal b of the variable resistor VR.sub.1 is suitably selected so that a voltage required for rendering a low but certain level of sound can be obtained even if the touch force on the key is weak, as shown by the curves (d) and (e) in FIG. 1.

Furthermore, if the forward voltage drop of the diode D.sub.1, which is approximately in range of from 0.2 to 0.6 volt, is compensated for by the voltage created across the sliding contact c of the variable resistor VR.sub.1 and the ground, a key touch versus sound level characteristic as indicated by (c) in FIG. 2 can be obtained. This characteristic corresponds to that of the guitar or harp. When the sliding contact c is rotated completely to the end b, the potential at the d side terminal of the capacitor C.sub.1 is equalized with the ground potential whereby the key touch versus sound level characteristic of the sound control device can be represented by (a) or (b) in FIG. 2.

As is apparent from the description above, all of the characteristic curves represented by (a) through (e) in FIG. 2 can be obtained by suitably adjusting the position of the sliding contact c of the variable resistor VR.sub.1. It should be noted that a negative voltage is induced in the coil L when a key K is released, but this voltage is blocked by the diode D.sub.1 so that no current is thereby created through the circuit consisting of the coil L, capacitor C.sub.1 and other components. During this time, the capacitor C.sub.1 is discharged through the resistor R.sub.1, switch S.sub.1, diode D.sub.2, and the switch S.sub.2.

In addition to the main feature of the present invention, FIG. 1 also shows an additional improvement at the cutting-off potential portion. And then, the decaying characteristics of the sound after the time the key K is released can be varied by adjusting the position of the sliding contact e of a variable resistor VR.sub.2. That is, by varying the resistance value of the variable resistor VR.sub.2, the discharge characteristic of the capacitor C.sub.1 can be varied, whereby the decaying characteristic of the sound can be changed. FIG. 3 shows in a diagrammatic manner also the portions of characteristics after the key-off time. In the diagram, A--a, B--a indicate characteristics when the switch S.sub.2 is changed over to the ground side, and A--b, B--b indicate characteristics when the switch S.sub.2 is changed over to the variable resistor side (connected to the sliding contact e of the variable resistor VR.sub.2), and the sliding contact e is moved completely to the P side terminal. It is also apparent that any characteristic between the above-mentioned A--a and B--b can be obtained by suitably selecting the position of the sliding contact e of the variable resistor VR.sub.2.

Although in the above description a sound control device has been described with respect to one representative key, it will be apparent that the controls may be provided for all keys included in the keyboard in a similar manner as described above, and that the circuit including the variable resistor VR.sub.1 employed for adjusting the sound level at the initial part of the sound level versus keying speed characteristic and also the circuit including the switch S.sub.2 and the variable resistor VR.sub.2 for adjusting the decaying characteristic after the key is released may be commonly used for all keys as illustrated in FIG. 1.

Furthermore, it will also be apparent that various minor modifications or changes may be carried out without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

I claim:

1. In an electronic musical instrument of keyboard type, a sound level control device comprising:

a plurality of coils and magnets respectively associated with keys in the keyboard to induce a voltage in one of said coils by an associated magnet moving when a corresponding key in the keyboard is depressed, each said coil having a first terminal and a second terminal;

a diode;

a capacitor having a first terminal and a second terminal, the first terminal of the capacitor being connected to the first terminal of said coil through said diode and the second terminal of the capacitor being connected to the second terminal of said coil;

a semiconductor switching element having a signal input electrode and a signal output-electrode, and a control electrode connected to the first terminal of said capacitor;

a cutting-off potential source connected to provide a voltage which renders said switching element nonconductive when applied to said control electrode;

a series-connected circuit which comprises a first resistor and a normally closed switch interlinked with the key in the keyboard and is connected between said cutting-off potential source and the first terminal of said capacitor;

a variable voltage source; and

a second resistor connected between said second terminal of said capacitor and said variable voltage source, the resistance value of said second resistor being substantially greater than the resistance value of said first resistor.

2. A sound level control device according to Claim 1, wherein said cutting-off potential source is adjustable for providing a variable voltage for adjusting the discharge characteristic of said capacitor.