JPH0640264B2 - Envelope generator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an envelope generator for generating a musical tone envelope of an electronic musical instrument.

Conventional Technology As a means to realize a conventional envelope generator,
There is one utilizing the discharge characteristic of the time constant circuit. This utilizes a voltage change when the time constant circuit is charged with a constant voltage as an attack envelope of a musical tone and a voltage change when discharging the time constant circuit as a decay envelope of a musical tone.

Problems to be Solved by the Invention However, in the envelope generator as described above,
The accuracy of the resistors and capacitors that form the time constant circuit is directly reflected in the envelope curve. That is, different envelope curves are generated due to changes in ambient temperature and variations in constants. Further, in order to obtain a complicated envelope curve, it is necessary to prepare a plurality of time constant circuits and switch them at the same time, resulting in a complicated circuit configuration. Further, a method of converting the envelope curve into a digital value and storing it in a memory and then reading it out at any time to convert it into an analog voltage to obtain an envelope curve, or when the tone formation is also a digital signal, read out from the memory. There is also a method of digitally multiplying the envelope digital signal and the musical tone digital signal. In either case, a large-capacity memory is required to store the digital signal of the envelope, and in particular, the latter requires a digital multiplier, which is expensive.

It is an object of the present invention to provide an envelope generator having a simple circuit configuration, by improving the instability of a time constant circuit composed of a resistor and a capacitor and the disadvantages of the digital method that are large-scale and expensive.

Means for Solving the Problems The present invention effectively utilizes respective merits of analog processing and digital processing in order to achieve the above object. That is, only the time axis direction is discretized,
The amplitude direction has a circuit configuration in which a signal converted into an analog signal as a reference voltage of the multiplying D / A converter is delayed and input through a sample and hold circuit.
The amplitude can be controlled by analog processing without using a digital multiplier, and the circuit can be integrated into a small scale by means of the signal cyclic processing means.

Example An example of the present invention will be described. FIG. 1 is a circuit diagram showing a main part of an embodiment of the envelope generator of the present invention. FIG. 2 is a timing chart showing the circuit operation of this embodiment. This shows an embodiment configured to generate an envelope of a decaying tone type musical instrument such as a piano or a guitar. The clock controller 1 in FIG. 1 instructs the master clock 1a and ON or OFF of the sound generation. The ON / ▲ ▼ signal from switch 1b is input and S
The signals of H ₁ , SH ₂ , and ▲ ▼ are output, and the timing between these signals is shown in FIG. A concrete circuit for controlling such timing is shown in FIG. 1 (b). Since the structure of this circuit is general and can be easily understood, description thereof will be omitted. Next, the selector 4 outputs the value input to the input terminal A when the select signal S is "H" and the value input to the input terminal B to the output terminal Y when the select signal S is "L". is there. The signal appearing at the output terminal Y is the digital value K of N bits. K becomes an input of the multiplication type D / A converter 5. Register A of 2 has a digital value of N bits
Register B having K ₁ and 3 also stores an N-bit digital value K ₂ . The output voltage of the multiplying D / A converter 5 is input to a first sample-and-hold circuit including a switch SW ₁ , a capacitor C ₁ and a buffer A ₁ . The output Vout of the first sample-and-hold circuit and the output voltage Vr of the constant voltage source 6 are selected by two switches SW ₃ and SW ₄ which operate alternately, and a switch SW ₂ , a capacitor C ₂ and a buffer A _{2 are selected.}
Is input to the second sample and hold circuit. The output of this second sample-and-hold circuit is the reference voltage Vref of the multiplying D / A converter 5.
Becomes Now, let us assume that it is in a completely initial state.
That is, Vout = 0 [V], and ON or OF of pronunciation
The ON / ▲ ▼ signal that indicates F is also “L”. Therefore, K = K ₂ . Also, the ▲ ▼ signal is "H".
Therefore, the switch SW ₃ is open, the switch SW ₄ is conductive, and Vout, that is, 0 [V] is sampled and held in the second sample-and-hold circuit. That is, Vref = 0 [V]. The output voltage of the multiplying D / A converter 5 depends on the reference voltage input Vref and the N-bit digital input K. Since Vref is 0 [V], it is 0 at this time.
[V]. Next, as shown in FIG. 2, it is assumed that the ON / ▲ ▼ signal becomes “H” at time t _{1 and the} sounding is instructed. Then, the select signal S of the selector 4 is "H".
Therefore, K = K ₁ . Also, from time t ₂ to t ₆
Until ▲ ▼ signal is generated, the switch SW ₃ becomes conductive and the switch SW ₄ is released, so that the output voltage Vr [V] of the constant voltage source 6 is from the time t ₂ to the time t _{3 in} the second sample and hold circuit. It is sampled for a period of time and is held for a period of time t ₃ to t ₆ . Therefore, at this time, the multiplying D / A converter 5
The output voltage of Becomes Then, the first sample and hold circuit samples from time t ₄ to t ₅ and holds it from time t ₅ to t ₈ . If the output at this time is Vout (1) Is. At time t ₆ , the ▲ ▼ signal returns to "H" again, so switch SW ₃ is released and switch SW ₄ becomes conductive.
Vout (1) is a sample between the second sample and hold circuit t ₇ from the time t _6, the is held between t ₁₀ from the time t _7. Therefore, at this time, the output voltage of the multiplying D / A converter 5 is Becomes It is held between t ₁₂ from between the sampled time t ₉ of t ₉ from the time t ₈ in the first sample-and-hold circuit. If the output at this time is V _out (2) Is. In this way, the output voltage Vout is updated for each SHZ signal after the ON / ▲ ▼ signal becomes “H”.
Output voltage Vout (i) at the time of the second SHZ signal
Is Becomes Here, in the range of 2 ^N −1> K ₁ > 0, the digital value K ₁
If is set Therefore, Vr> Vout (1)> Vout (2)>...> Vout (i-1)> Vout (i). That is, the output voltage Vout is monotonically decreasing. Moreover, Therefore, it can be seen that when the output voltages Vout are arranged in time series, they match the exponential function discretized in the time axis direction, and a natural attenuation characteristic is obtained.

Here, it can also be seen that the digital value K is a constant that determines the speed of attenuation. Therefore, if a digital value different from K ₁ is stored in register B3 as K ₂ , ON / ▲
▼ An envelope can be formed when the signal reaches “L”, that is, when released.

The above is a basic operation example of the present invention. The envelope of a natural musical instrument does not always match the exponential curve, but it can be approximated by switching a plurality of curves with different attenuation rates in time. For that purpose, a plurality of registers for storing the digital value K may be provided, and these may be switched at any time during the decay. Moreover, if the output voltage of the second sample and hold circuit is appropriately amplified, Therefore, it is possible to obtain an increasing characteristic with an arbitrary increasing rate.

EFFECTS OF THE INVENTION Since the reference voltage changes depending on the output voltage as described above, an effect such as compression or expansion can be obtained, and sufficient resolution can be obtained even with a configuration having a small number of bits.

[Brief description of drawings]

FIG. 1 (a) is a block diagram showing an embodiment of the present invention.
FIG. 2B is a circuit example of the clock controller 1, and FIG. 2 is a diagram showing a timing chart. 1 ... Clock controller, 2 ... Register A, 3 ...
… Register B, 4 …… Selector, 5 …… Multiplying D / A converter, 6 …… Constant voltage source, SW ₁ , C ₁ , A ₁ … First sample and hold circuit, SW ₁ … Analog switch , C ₁ …… Capacitor, A ₂ …… Buffer, SW ₂ , C ₂ , A ₂
…… Second sample and hold circuit, SW ₂ ……
Analog switch, C ₂ ... capacitor, A ₂ ... buffer, SW ₃ , SW ₄ ... analog switch, 7 ... shift register, 8, 9 ... D-FlipFlop.

Claims (3)

[Claims] 1. A storage device for storing a predetermined digital value in a sound source circuit of an electronic musical instrument for forming a musical tone by controlling the amplitude of a continuous sound source waveform with an envelope signal, and the stored digital signal. Multiplying D / A that converts the value into an analog voltage by comparing with the read reference voltage
A converter, and a first sample-and-hold circuit that samples and holds the output voltage of the D / A converter converted into an analog voltage at regular intervals, and outputs the sample-and-hold circuit.
A constant voltage source that outputs a certain constant voltage, and a second sample and hold circuit that switches the output of the first sample and hold circuit and the output of the constant voltage source at a predetermined timing to sample and hold this. An envelope generator comprising the output of the second sample-and-hold circuit as the reference voltage. 2. A plurality of digital values stored in a storage device are switched at a predetermined timing to be read by a multiplying D / A converter, and an output envelope is deformed. An envelope generator according to the paragraph. 3. An envelope generator according to claim 1, wherein the reference voltage is amplified to a value at which the output of the second sample-and-hold circuit is amplified and the envelope has an increasing characteristic. .