JPS5832390B2 - Touch response circuit for electronic keyed instruments - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a touch response circuit for detecting the strength of a keystroke as a voltage level in a keyed electronic musical instrument such as an electronic piano.

First, an actual example of a conventional touch response circuit will be explained based on FIGS. 1 and 2.

In FIG. 1, 1 is a keyboard, and 2 is a transfer switch that is interlocked with the keyboard 1 and has a movable contact 2a, a break contact 2b, and a make contact 2c.

A capacitor 3 has a discharging circuit formed by a resistor 4 connected in parallel, and a part of a charging circuit is formed by connecting a cap end to a movable contact 2a.

Bo is a power source and forms part of a charging circuit for the capacitor 3.

5 is a resistor, 6 is a transistor, and 7 is a capacitor, which constitute a sampling and holding circuit.

8 is an output terminal of the sampling and holding circuit, 9 is a gate circuit for obtaining an output musical tone signal proportional to the output voltage of the sampling and holding circuit, and 10 is an input terminal of the gate circuit to which a musical tone signal is applied.

11 is a musical tone signal output terminal.

The operation of the previous embodiment will be described below based on the same figure.

When the keyboard 1 is left alone, the movable contact 2a of the transformer 7' earth switch 2, which is linked to it, becomes the break contact 2b.
It is connected to the.

Therefore, power supply B from capacitor 3.

A charging circuit is formed, and the capacitor 3 is charged until its terminal voltage becomes equal to the power supply voltage.

Now, when the keyboard 1 is pressed down, the movable contact 2a of the transfer switch 2, which is interlocked with this, leaves the break contact 2b and jumps toward the make contact 2c.

At this time, the charging path for the capacitor 3 no longer exists from the moment the movable contact 2a leaves the break contact 2b.
The charge accumulated in the capacitor 3 is discharged through the resistor 4.

It is well known that the decreasing tendency of the terminal voltage of the capacitor 3 due to such discharge is expressed by an exponential function, as shown in FIG.

Therefore, the terminal voltage of the capacitor 3 at the moment when the movable contact 2a reaches the make contact 2c causes the movable contact 2a to
The contact jump time of a can be expressed.

Now, after pressing the keyboard 1, the movable contact 2a changes to the make contact 2c.
, the terminal voltage of capacitor 3 at that moment is applied to resistor 5.

Therefore, capacitor 7, which together with transistor 6 constitutes an emitter follower, is rapidly charged until its terminal voltage becomes approximately equal to the terminal voltage of resistor 5.

The charge accumulated in the capacitor 7 is held until an effective discharge circuit is formed.

The terminal voltage of the capacitor 3 is determined by the movable contact 2a being the make contact 2.
Since the contact jump time up to c is expressed as an exponential function of the reciprocal of the keyboard speed, this voltage is applied to the output terminal 6.
By extracting the signal from the input signal and applying it to the gate circuit 9, an output musical tone signal expressed by an exponential function of the reciprocal of the keyboard speed can be obtained at the musical tone signal output terminal 11.

What kind of functional relationship should be maintained between the contact jump time and the terminal voltage of the capacitor 3, that is, the output voltage of the sampling and holding circuit, has long been a concern in this technical field.

In the above embodiment, the relationship between the two is limited to an exponential function.

However, with regard to conventional mechanical keyboards used for pianos, it is known from experience that, under normal use, the volume of the keyboard is proportional to the force applied by the fingers when pressing down on the keyboard.

Now, since the contact jump time t is inversely proportional to the keyboard speed X, A relationship is established.

However, on the other hand, the keyboard speed Because it is proportional to the old root 1 is a constant.

The force F that pushes down A relationship is also established.

However, K2 is a constant. Therefore, if the output voltage V of the sampling and holding circuit maintains a relationship that is inversely proportional to the square of the contact jump time t, the following relationship holds true.

However, K is a constant. Therefore, it can be seen that in order to obtain a volume proportional to the force F with which the keyboard 1 is pressed, the output voltage V of the sampling and hold circuit should be held in a relationship inversely proportional to the square of the contact jump time t.

Additionally, it is known from experience that when expressing the strength of a musical tone using the sense of volume on a piano using a weak tone pedal or on a harpsichord, a specific functional relationship is required between the two. .

However, in the conventional embodiment, since the relationship between the two is limited to an exponential function, the sense of volume when operating the keyboard is inconsistent with that of a mechanical keyboard, and the strength of the musical tones especially in pianissimo and fortessimo becomes unnatural. There were drawbacks.

In addition, a piano using a weak tone pedal, or...
-It was difficult to express the strength and weakness of musical tones in psichords, etc.

In order to eliminate the above-mentioned drawbacks, the present invention maintains the output voltage V of the sunfling hold circuit in a relationship inversely proportional to the square of the contact jump time t and other necessary functional relationships, thereby providing a sense of volume during keyboard operation. To provide a touch response circuit which can match that of a mechanical keyboard and can faithfully express the strength of a musical tone on a piano or harpsichord using a weak tone pedal.

A first embodiment of the present invention will be described below with reference to FIGS. 3 to 9.

In FIG. 3, 13 is a capacitor corresponding to 3 in FIG. 1, 14 is a resistor, and 15 is a switching transistor, which forms part of a discharge circuit for the capacitor 13.

16 is a resistor, and the switching transistor 15
This is to maintain the 0 base current at an appropriate value.

17 is a discharge control signal generation circuit.

The other components are the same as in the previous embodiment shown in FIG.

The operation of this embodiment differs from that of the previous embodiment in the following points.

That is, the electric charge charged in the capacitor 13 is transferred to the switching transistor 15 and the resistor 1 at the same time when the keyboard 1 is pressed.
It is discharged through a discharge path consisting of 4.

At this time, the switching transistor 15 operates as a switching element driven by a discharge control signal of a specific waveform applied from the discharge control signal generation circuit 17.

More specifically, since the base current flows through the resistor 16 only during the period when the base potential of the switching transistor 15, which changes according to the discharge control signal, is negative with respect to the emitter potential, the switching transistor 15 is in a conductive state. As a result, a discharge path for the capacitor 13 is formed.

Therefore, since the discharge current of the capacitor 13 is controlled by the period during which the switching transistor 15 is in a conductive state, the discharge curve of the capacitor 13 can be changed by selecting the waveform of the discharge control signal.

- As an example, the operation when a waveform having a square curve as shown in FIG. 4 and FIG. 1 is used as a discharge control signal will be described below.

In FIG. 4, the horizontal axis represents time, the vertical axis represents voltage, and the value on the vertical axis is the peak value V of the discharge control signal waveform.

It has been standardized. A is a half period of the waveform, and B is an arbitrary value that intersects the vertical axis and is half the length of the interval between the intersections of a straight line parallel to the horizontal axis with respect to the waveform.

Now, the terminal voltage V of the capacitor 13 is the peak voltage V of a waveform having a square curve.

When it is higher, the switching transistor 15 is in a conductive state, so that the capacitor 13 is connected to the resistor 14.
A discharge path is formed through the discharge path.

Therefore, the terminal voltage V of the capacitor 13 is not affected by the discharge control signal within the time range from the moment when the movable contact 2a leaves the break contact 2b to the time when v>V□ is established (see Fig. 5). The potential decreases toward zero while maintaining an exponential relationship with time, as shown by curve C in FIG.

This discharge curve is C: Capacity of capacitor 13 R: resistance value of resistor 14 t: Time after starting discharge It is.

On the other hand, the terminal voltage V of the capacitor 13 is the peak value V of the discharge control signal.

When it becomes smaller than , the discharge current is controlled by turning on and off the switching transistor 150, so that the discharge curve, as shown by the solid line in FIG. 5, differs from the exponential function curve shown by the dotted line. Transition to the right.

More specifically, the terminal voltage V of the capacitor 13 is the peak value V of the discharge control signal.

When it becomes smaller than, in Fig. 4, v/V□<1
The duty ratio of the switching transistor 15 changes in accordance with the decreasing value of the terminal voltage V.

For example, in FIG. 4, when the terminal voltage V is Vl, the duty ratio of the switching transistor 15 is B, /A.

In this state, the discharge of the capacitor 13 is intermittent at the duty ratio B, /A, so the time required per unit drop in the terminal voltage V due to discharge is extended by A/B times, and as a result, The downward slope of the terminal voltage V is B, /
It becomes a gentle slope of A times.

Furthermore, when the terminal voltage V decreases, the duty ratio of the switching transistor 15 changes, and the rate of change (multiplying factor) of the downward slope also changes sequentially.

As mentioned above, the terminal voltage V, which drops along the exponential curve, is stretched by the falling time according to a specific function (determined by the discharge control signal waveform) of the value of the terminal voltage V, as indicated by the solid line in FIG. As shown, for example, when the voltage is corrected to drop along a square inverse proportional curve, the relationship between the above-mentioned exponential curve and the above-mentioned specific function, that is, the discharge control signal waveform, will be explained below. .

Now, as shown in FIG. 6, when the value of the contact jump time represented on the horizontal axis is standardized by the minimum value of the contact jump time, correction can be performed in the region where the value on the horizontal axis is 1 or more.

This is because the minimum value of the contact jump time is the value when the keyboard is pressed at the maximum speed expected during performance.
This is because a contact jump time with a value less than this cannot exist.

Furthermore, the value of the terminal voltage V of the capacitor 13 represented on the vertical axis is the peak value V of the discharge control signal.

When normalized to V, the terminal voltage ■ is the peak value V.

When the transistor 150 becomes smaller than
Since the off-state is started, the correction will be performed in the area (2), that is, the area where V/Vo is 1 or less.

FIG. 5 is a drawing in which only the areas to be corrected in FIG. 6 are extracted.

By the way, in order for the corrected curve to be a square inverse proportional curve, the slope of the curve when passing through its starting point, that is, the value 1 on the horizontal axis and the value I on the vertical axis, must be -2. is necessary.

That is, assuming that the now modified discharge curve is a squared inverse proportionality curve represented by Since V=t at i, the constant 1 must be multiplied by 1 in equation (1).

Therefore, from the group of inversely proportional square curves, The curve represented by must be selected.

However, the first derivative of this curve is Therefore, the slope at t=i is This is why it is necessary.

On the other hand, for an exponential curve, It's 2 It is expressed as Its first derivative is becomes.

However, in order to be continuously connected to the above-mentioned square inverse proportional curve at V=1 and t=i, the slope must be -2 at V=1 and t=i, so in the end, In the equation (4×5), the constant 2 must be multiplied by 2.

Therefore, the curve expressed by the exponential curve group must be selected, and since this curve has V=e2 at 1=0, in the end, v
As an exponential curve that is continuously connected to the square inverse proportionality curve at =i, t=1, e2 (7, 39
), it can be seen that those that intersect should be selected.

Now, the first derivative of the exponential curve selected as above can be expressed by substituting equation (4) into equation (5), so in equation (7), if K2-2, then I will leave it at that.

On the other hand, the first derivative of the square inverse proportionality curve as the discharge curve to be corrected can be expressed as follows by transforming equation (3) using equation (2).

Therefore, by comparing equations (8) and (9), we can see that the first derivative of the corrected square inverse proportionality curve is jv times the first derivative of the exponential curve. Recognize.

Therefore, it is only necessary to modify the slope of the exponential curve selected as described above by a factor of 11 in accordance with the change in the terminal voltage V of the capacitor 13.

In other words, by obtaining a curve with a slope obtained by multiplying the slope of an exponential function by jv, an exponential curve can be converted into a square inverse proportional curve.

However, as mentioned above, since the slope of the discharge curve intermittent at the duty ratio B/A is times B/A, it is necessary to maintain the following relationship.

Therefore, it can be seen that the following relationship is established, and the waveform of the discharge control signal only needs to have a square curve as shown in FIGS. 4 and 7.

Similarly, in FIG. 7, a is a discharge control signal waveform for a harpsichord, and C is a discharge control signal waveform for a piano using a soft pedal.

Moreover, d is a triangular wave as the original waveform of various discharge control signal waveforms.

FIG. 8 shows a group of discharge curves modified by these discharge control signals.

In the same figure, the discharge curves a, b, c, and d are the seventh
This is modified by the discharge control signals a, b, c, and d in the figure.

Next, the discharge control signal generation circuit 17 in FIG. 3 will be explained.

In FIG. 9, 17a is an operational amplifier and 17b.

17c and 17d are level shift resistors, 17e is F
ET, 17f is an input terminal, 17g is an output terminal, and 17h is a bias adjustment resistor.

Now, when a triangular wave that changes linearly with time is applied to the input terminal 17f, the relationship between the gate voltage and drain current of the FET 17e is a quadratic function, so the operational amplifier 17a
A current that changes in a square curve with respect to time flows through the input.

If this is converted into a voltage by the operational amplifier 17a, a discharge control signal waveform having a square curve is obtained at the output terminal 17g.

Also, by operating the bias adjustment resistor 17h, the FET
By adjusting the bias voltage supplied to the gate of I7e, the operating point of FET 17e can be changed, so in addition to the discharge control signal waveform having a square curve as shown in FIG. It is also possible to obtain a discharge control signal waveform suitable for a psichord or a piano using a soft pedal, as shown in Figures 1 and 7C.

By the way, the discharge control signal waveform is not limited to the above waveform, but can be changed by operating the bias adjustment resistor 17h.
By changing the operating point of the FET 17e, various discharge control signals can be obtained, and thereby discharge curves according to various functions can also be obtained.

Furthermore, the triangular wave to be supplied to the input terminal 17f of the discharge control signal generation circuit 170 directly controls the transistor 1.
5 may be intermittent.

Note that level shift resistors 17b and 17c.

17d compensates for the downward shift of the waveform due to the presence of the base-emitter potential of the transistor 150.

Next, a second embodiment of the present invention will be described based on FIG. 10.

In the same figure, 13 is a capacitor, 14 is a resistor, and 18 is a capacitor.
is a diode and forms part of the discharge circuit of the capacitor 13.

17 is a discharge control signal generation circuit corresponding to 11 in FIG.

Other components are the same as in the first embodiment.

In the range where the terminal voltage of the capacitor 13 is larger than the peak value of the discharge control signal, the diode 18 becomes conductive,
A discharge path is formed by the resistor 14 and the discharge control signal generation circuit 17 with low output impedance.

Therefore, the discharge curve of the capacitor 13 in this range becomes an exponential function as in the case of the first embodiment.

In the range where the terminal voltage of the capacitor 13 is smaller than the peak value of the discharge control signal, the diode 18 operates as a switching element and the discharge current is limited, so that the discharge curve changes as in the first embodiment. Corrected to a function curve other than an exponential function.

As described above, according to the present invention, a switching transistor is provided in a part of the discharge path of the capacitor, and the duty ratio of the switching transistor is controlled by a discharge control signal having various waveforms including a waveform having a square curve. Alternatively, by inserting a diode and a low output impedance discharge control signal generation circuit in series in a part of the discharge path of the capacitor, the duty ratio of the diode can be determined from various waveforms including waveforms having a square curve. By controlling the discharge control signal using a discharge control signal, the discharge curve can be modified to obtain a discharge curve other than an exponential function curve, such as a square inverse proportional curve.

As a result, when pressing a key, it is possible to obtain a musical sound output proportional to the force applied, so that the strength of the musical sound can be faithfully expressed with the same volume sensation as a mechanical keyboard.

In addition, by setting the slope of the discharge curve to a specific value within a range smaller than that of the square inverse proportionality curve, the volume of the harpsichord changes more slowly in response to the force of pressing down on the keyboard. In addition, by setting the slope of the discharge curve to a specific value within a range larger than that of the 2-modulus inverse proportionality curve, a weak tone pedal was used that caused the volume to change more steeply in response to the force of pressing the keyboard. The strength and weakness of musical tones can be faithfully expressed using the sense of volume of a piano.

As described above, the touch response circuit according to the present invention can obtain musical tones that have an arbitrary functional relationship with the strength of keystrokes with a simple circuit configuration, and can realize appropriate musical expression with a keyed electronic musical instrument. It is valid.

[Brief explanation of drawings]

1 and 2 relate to a conventional touch response circuit, with FIG. 1 being a circuit diagram thereof, and FIG. 2 being an exponential curve showing the relationship between the terminal voltage of the capacitor 3 and the jump time of the contact 2a. 3 to 9 relate to an embodiment of the present invention, FIG. 3 is a circuit diagram thereof, and FIG. 4 is a waveform diagram showing a discharge control signal waveform for obtaining a square inverse proportional curve as a discharge curve. , Figure 5 is a waveform diagram showing the relationship between the discharge curve and the discharge control signal waveform, Figure 6 is a waveform diagram showing a square inverse proportional curve as a discharge curve in comparison with an exponential curve, and Figure 7 is a typical discharge curve. FIG. 8 is a waveform diagram showing a control signal waveform, FIG. 8 is a waveform diagram showing a typical discharge curve, and FIG. 9 is a circuit diagram showing the configuration of a discharge control signal generation circuit. FIG. 10 is a circuit diagram showing the configuration of a second embodiment of the present invention. 1...Keyboard, 2...Transfer switch, 2a...Movable contact, 2b...
Break contact, 2c...Make contact, Bo...
...Power supply, 13...Capacitor, 14...
... Resistor, 15 ... Switching transistor, 16 ... Resistor, 17 ... Discharge control signal generation circuit, 18 ... Switching diode.

Claims (1)

[Claims] 1. A means for charging a capacitor, a means for discharging the charged capacitor for a specific period corresponding to the pressing speed of the keyboard, and a method based on the terminal voltage of the capacitor at the time when the pressing of the keyboard is completed. , means for generating an output voltage expressed as a specific function of the pressing speed of the keyboard; and a switching means inserted into a part of the discharge path of the capacitor to connect and disconnect the discharge path; A touch response circuit for an electronic musical instrument, comprising discharge control means for changing the duty ratio of the switching means in response to a terminal voltage of a capacitor during discharge. 2. A switching transistor that is inserted into a part of the discharge path of the capacitor and connects and disconnects the discharge path in response to a discharge control signal, and a discharge device that supplies discharge control signals of various waveforms, including a waveform having a square curve, to the switching transistor. A touch response circuit for an electronic musical instrument according to claim 1, further comprising control signal generating means. 3. A switching diode that is inserted into a part of the discharge path of the capacitor and connects and disconnects the discharge path in response to a discharge control signal, and a discharge control signal generating means that supplies the discharge control signal to the switching diode. A touch response circuit for an electronic musical instrument according to claim 1.