JPS6323559B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an envelope generation circuit for an electronic musical instrument, in which the pulse generator oscillates regardless of the position of a variable resistor that variably adjusts the duty ratio and frequency of the output pulse of the pulse generator. To provide an envelope generating circuit for an electronic musical instrument, which can stably operate and can effectively obtain changes in decay time by greatly increasing the variable ratio of the duty ratio and frequency of output pulses to the variable ratio of a variable resistor. With the goal.

FIG. 1 shows a circuit diagram of an example of an output circuit of a general electronic musical instrument. In the figure, a sound source signal e ₁ having a certain sound frequency that has entered a terminal 1 is supplied to a sound source signal switching circuit 2 . On the other hand, the power supply V _cc of terminal 3 is connected to the second switch S, which opens and closes in response to the pressing of the key.
The key-on signal _VK shown in FIG. A is supplied to the envelope generating circuit 4 via the resistor R _U.

The envelope generating circuit 4 is provided with a pulse generator 5, from which a pulse V _P having a long H level period T ₁ and a short L level period T ₂ as shown in FIG. 2B is taken out. . (Pulse V _P H
level voltage) > (H level voltage of key-on signal V _K ), R ₂ << R ₁ , so the period T ₂
, the voltage at point A is τ ₂ ≒ through resistors R ₁ and R ₂
It is discharged with a time constant of R ₂ C, while the period T ₁
The voltage at point A is _{τ 1 =}
It is discharged with a time constant of R ₁ C. This results in
The envelope generating circuit 4 generates an envelope signal V _ENV as shown in C in the figure (the broken line indicates its average value).
is taken out and supplied to the switching circuit 2. terminal 1
The sound source signal e ₁ is switched in the switching circuit 2 according to _the envelope V _ENV from the envelope generating circuit 4 to become a signal e ₀ as shown in FIG. It is taken out from the terminal 6.

The duty ratio of the output pulse V _P of the pulse generator 5 is variously varied by a variable resistor R ₃ whose resistance value is varied according to the operation of a tone selection lever provided on the operation panel as described later. By varying the duty ratio of this pulse generation V _P , the attenuation waveform of the envelope V _ENV shown in Figure C is varied (in other words, the attenuation rate of the envelope is varied), and the tones of various instruments can be selectively extracted. It is said to be composed of Envelope attenuation generally needs to be varied over a wide range.

Here, the pulse generator 5 of the conventional envelope generating circuit 4 is constituted by a well-known free-run multivibrator as shown in FIG. ₃ , and the period _{T 1} ,
As is well known, T ₂ is T ₁ ≒ R ₃・C ₁・_lo 2, T ₂ ≒
Determined by R ₄・C ₂・l _o 2.

However, when adjusting the variable resistor _R3 ,
For example, if the resistance value is maximized, the transistor
The base current of Q ₂ stops flowing and the pulse V _P becomes H.
There is no guarantee whether it will stop at low level or low level, and the operation is unstable.
Also, if the resistance value is minimized, the transistor
_Q2 had drawbacks such as its large base current, which could potentially destroy it.

By the way, let us consider changes in the duty ratio and frequency of the pulse V _P and changes in the decay time of the envelope. Generally, it is necessary to change the waveform of the envelope signal over a wide range, but even if the duty ratio and frequency of the pulse V _P are changed slightly, for example, the attenuation waveform of the envelope signal V _ENV will change little; To the ear, the change in decay time is difficult to hear. For this reason, it is generally possible to more effectively obtain changes in the decay time by changing the duty ratio and frequency at a relatively large rate relative to the variable rate of the resistor _R3 . However,
In this conventional circuit, the rate of variable adjustment of the resistance value of the resistor R ₃ and the rate of variation of the duty ratio and frequency of the pulse V _P are linear, so it is not possible to effectively obtain changes in decay time, etc. There were some shortcomings.

The present invention eliminates the above drawbacks, and the fourth
An example will be described below with reference to the drawings.

FIG. 4 shows a circuit diagram of a main part (pulse generator) of an embodiment of an envelope generating circuit for an electronic musical instrument according to the present invention. In the figure, 7 is an amplifier whose inverting input terminal is grounded _via a capacitor C ₃ and connected to the power supply V _CC1 via a resistor R ₅ . and is connected to output terminal 5 _2a . The non-inverting input terminal of amplifier 7 is connected to the power supply via resistor R ₆ and variable resistor R ₃ .
While it is connected to V _CC2 , it is also connected to the output terminal 5 _2a via a diode D ₂ in the forward direction. Note that it is set such that V _CC2 > V _CC1 .

In the same figure, the voltage from the power supply V _CC1 is connected to the resistor R ₅
The voltage is applied to the capacitor _C3 through the capacitor _C3 to charge it. During the period when the capacitor C3 is being charged, the relationship between the two input terminal voltages Va and Vb of the amplifier 7 is Vb>Va, and the voltage Va is The waveform becomes as shown in FIG. 5A. On the other hand, the voltage Vb is initially an H level voltage as shown in FIG. 5B depending on the adjustment position of the resistor _R3 , and an H level voltage as shown in FIG. _5C is taken out from the output terminal 52a.

When the capacitor _C3 is gradually charged and the voltage Va reaches the voltage Vb, the state of the amplifier 7 is reversed, the output Vp of the output terminal _52a is set to the L level, and the voltage Vb is also set to the L level as shown in Figure B. be done. Due to the inversion of amplifier 7, the charge on capacitor C ₃ becomes diode
The voltage Va is discharged through _D1 , and the voltage Va gradually decreases as shown in A of the figure. When the voltage Va drops to the L level of the voltage Vb, the amplifier 7 is inverted again and returns to its original state, and the output Vp of the output terminal _52a is set to the H level again.

The above operations are repeated, and a pulse Vp having a predetermined duty ratio and frequency is taken out from the output terminal _52a .

Here, in order to vary the duty ratio, resistor R ₃
Adjust the voltage Vb to, for example, the voltage Vb' (Figure 5A)
Suppose you set it to . As in the case above, the voltage
When Va reaches the voltage Vb', the amplifier 7 is inverted, and the voltages Vb' and Vp' become L level as shown in D and E of the same figure, and when the voltage Va reaches the L level voltage Vb', the amplifier 7 is inverted. The amplifier 7 is inverted again, and as a result, a pulse Vp' as shown in FIG. 5E is taken out from the output terminal _52a . Other voltages (Vb″, Vb, …)
Similarly, when the voltage is set, a pulse Vp whose level is inverted at a timing corresponding to the set voltage is extracted.

In this case, the time it takes for the voltage Va to reach the voltage (Vb, Vb′, Vb″, ...) set by the resistor R ₃ differs depending on each set voltage (periods T ₁ , T ₁ ′,
On the other hand, since the discharge time of the capacitor C ₃ is approximately constant (period T ₂ ), it is possible to obtain pulses with different duty ratios and frequencies depending on the set voltage. Moreover, since the voltage Va is a curve that changes exponentially,
The duty ratio can be changed exponentially by setting the voltage.

Next, let us consider the operational stability of this pulse generator ₅₂ . Minimum resistance value of resistor R ₃ (voltage
Vbmin), in Figure 5A,
The voltage Vbmin is on a low level line, and the duty ratio of the pulses Vbmin and Vp is, for example, close to 50%, and the oscillation operation is repeated stably in this state. Alternatively, depending on the value of voltage Vbmin, Vbmin and Vp remain at the L level. When set in this way, the circuit is more stable than the conventional circuit shown in FIG. 3, in which the base current of transistor Q ₂ becomes large.

On the other hand, when the resistor R ₃ is set to the maximum (voltage Vbmax), the voltage Vbmax in FIG. It remains as it is. This setting is more stable than the conventional circuit in which no current flows to the base of the transistor _Q2 and there is no guarantee whether the output pulse will stop at the H level or the L level.

As described above, the envelope generating circuit for an electronic musical instrument according to the present invention connects a pulse generator to an inverting input terminal of an amplifier to a charging circuit that is charged with a voltage from a power supply, and also connects a charging circuit to an inverting input terminal of the amplifier. A power supply with a voltage higher than the voltage of the power supply is connected to the amplifier through a variable resistor that varies the duty ratio and frequency of the output pulse, and the voltage is connected between the inverting input terminal and the output terminal of the amplifier, and the non-inverting input terminal and Since a diode is connected in the forward direction between each of the output terminals, the resistor of the variable resistor is made small and the voltage at the non-inverting input terminal of the amplifier is changed to the charging voltage of the charging circuit, that is, the voltage at the inverting input terminal of the amplifier. If set to a certain level, the amplifier repeats the inverting operation alternately, thereby extracting pulses with a certain duty ratio, or if the non-inverting input terminal voltage is set to less than the inverting input terminal voltage, the amplifier repeats the inverting operation alternately. If no inverting operation is performed and the output remains at L level, and on the other hand, if the resistance value of the variable resistor is maximized, the non-inverting input terminal voltage of the amplifier will be higher than the inverting input terminal voltage, and the output of the amplifier will be It remains at the H level, and in this way, no matter which position the variable resistor is adjusted to, the oscillation operation is in a stable state, which is more stable than the conventional circuit using a free-run multivibrator. Since the amplifier compares the charging voltage of the charging circuit, that is, the voltage that changes exponentially, with the voltage set by the variable resistor, the duty ratio and frequency of the pulse can be changed exponentially depending on the set voltage. , whereby the attenuation ratio of the envelope can be greatly changed with respect to the variable ratio of the variable resistor,
By using the variable resistor of the free-run multivibrator, it is possible to effectively obtain changes in decay time compared to conventional circuits in which the adjustment ratio, output pulse duty ratio, and frequency change ratio can only be obtained linearly. It has the following features.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an example of an output circuit of a general electronic musical instrument, Fig. 2 A to D are signal waveform diagrams for explaining the operation of the circuit shown in Fig. 1, and Fig. 3 is a circuit diagram of an example of a conventional pulse generator. , FIG. 4 is a circuit diagram of a main part of an embodiment of the circuit of the present invention, and FIGS. 5A to 5E are signal waveform diagrams for explaining the operation of the circuit shown in FIG. 4. 4... Envelope generation circuit, 5, 5 ₂ ... Pulse generator, 5 _2a ... Output terminal, 7... Amplifier,
V _CC1 , V _CC2 ... power supply, R ₃ ... variable resistor, R ₁ ,
R ₂ , R ₅ , R ₆ ... Resistor, C, C ₃ ... Capacitor,
D ₁ , D ₂ ...diodes.

Claims (1)

[Claims] 1. A pulse generator equipped with a variable resistor that variably adjusts the duty ratio and frequency of the output pulse is equipped with two pulse generators that discharge with a certain time constant during the H level period and the L level period of the output pulse from the pulse generator, respectively. In an envelope generation circuit for an electronic musical instrument that connects a discharge circuit and generates an attenuation envelope by repeating each discharge, the pulse generator is charged to an inverting input terminal of an amplifier with a voltage from a power source. At the same time, a power source with a voltage higher than the voltage of the power source is connected to the non-inverting input terminal of the amplifier via the variable resistor, and the voltage between the inverting input terminal and the output terminal of the amplifier and the non-inverting 1. An envelope generating circuit for an electronic musical instrument, comprising a diode connected in a forward direction between an input terminal and an output terminal.