JPS59114B2 - Tone formation circuit for electronic musical instruments - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a musical tone forming circuit for an electronic musical instrument whose tone color changes with the passage of time after a key is pressed.

In a natural musical instrument, when a musical tone rises suddenly and then gradually decays, the frequency spectrum changes over time, creating a tone unique to that instrument. For example, when keys are struck quickly on a percussion instrument such as a piano, the rise of the sound contains many harmonics, and as the amplitude decreases thereafter, the number of harmonics contained decreases. Furthermore, when keys are pressed slowly, the harmonic multiples are reduced from the beginning.
On the other hand, in conventional electronic musical instruments, musical tones are obtained by appropriately containing harmonic components using an electronic circuit. FIG. 1 shows a conventional configuration of an electronic musical instrument. When the key KY is pressed, the touch response circuit TRS obtains an output corresponding to the speed or intensity of the key depression, and the envelope/signal forming circuit EVP obtains a Ξ-gonal envelope signal. The rectangular wave from the tone generator circuit TG is subjected to amplitude control by an envelope signal at a gate GT, and then converted into a desired musical tone by a musical tone conversion circuit TCV including a filter. In such a musical tone forming circuit, when the rectangular wave from the tone source TG has a symmetrical waveform, it does not contain even-order harmonics, and as can be seen from the output waveform diagram of the gate GT, the amplitude changes with the passage of time after the key is pressed. Therefore, no change occurs in the odd-numbered harmonic content. Furthermore, even if the key press is weak, the amplitude only decreases unilaterally from the initial small amplitude rectangular wave as shown by the broken line, so it is possible to obtain a musical tone whose timbre changes as time passes after the key press. It had become monotonous. SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks and to provide a musical tone forming circuit for an electronic musical instrument that has a relatively simple configuration and whose tone color changes with the passage of time after a key is pressed. Embodiments of the present invention shown in the drawings will be described below.

FIG. 2 is a diagram showing the first embodiment of the present invention, where KSW is a key press switch, TRS is a touch response circuit, EVP is an envelope signal forming circuit, TG is a sound source, DFC is an occupancy ratio changing circuit, and GT is a gate circuit. shows. The touch response signal obtained by charging and discharging the CR element forming the touch response circuit TRS is sent to the envelope signal forming circuit EVP.
A triangular envelope waveform is obtained by a known operation using the diode and the CR element. The occupancy ratio changing circuit DFC includes a capacitor Cd forming a differential circuit,
The gate circuit G consists of a resistor Rd, a diode D that extracts only the lower half of the waveform, and signal application coupling resistors Re and Rc.
T is composed of a transistor Qg and a resistor Rg.
FIG. 3 shows a waveform diagram for operating settings.

In Figure 3 Hata, the solid line is a rectangular wave differentiated by Cd and Rd, the dashed line is the envelope waveform obtained by pressing the key quickly, with the positive and negative reversed, and the dashed-dotted line is the envelope waveform obtained by pressing the key slowly. It is shown reversed. Then, at the base electrode of the transistor Qg, an operation is performed such that the voltage value of the differential waveform and the voltage value of the envelope waveform cancel each other out. The differential pulse generated at time TO has the same value at time T1 when compared with the envelope signal obtained by pressing the key quickly, and after T1, the envelope signal has a higher voltage, so transistor Qg becomes conductive. (Base when transistor Qg is conductive)
Since the emitter voltage is a small value, it is ignored in the calculation. )
Transistor Qg is therefore non-conducting only during TOTl, resulting in a first short pulse Pll as shown in FIG. 3B. It is clear from the relationship with the envelope signal indicated by the dashed dotted line that when the key is pressed late, the first long pulse P2l has a width between time TO and T2 as shown in FIG. 3C. Third
The second short pulse Pl2 shown in FIG. B is an envelope signal as shown by the broken line, and thus has a slightly wider width than Pll. After Pl3, the pulse becomes wide in the same way.
The second long pulse P22 shown in FIG.
It is clear that the range becomes even wider after 3. Since the envelope signal is applied to the collector electrode of the transistor Qg via the resistor Rg, the waveform obtained from the collector electrode becomes an amplified output whose voltage is controlled by the envelope waveform, and becomes Pll, Pl2, Pl3, . . . ...
, P2l, P22P23, . . . are each obtained with an envelope waveform as shown in FIG.

When a desired musical tone is obtained by the musical tone exchange circuit TCV from such an asymmetric rectangular waveform whose occupation ratio gradually changes, the harmonic content also changes over time, and a tone closer to that of a natural musical instrument is obtained. FIG. 4 is a diagram showing a second embodiment of the present invention, in which the occupancy ratio changing circuit includes transistors Qd and Q.
A positive half wave obtained by differentiating a rectangular wave is applied to the base electrode of the transistor Qd by emitter-coupling each other.

Therefore, the emitter potentials of transistors Qd and Qe change depending on the base electrode of transistor Qd, and
Since an envelope signal is applied to the base electrode of transistor Qe, the output of the collector electrode of transistor Qe has the waveform shown in the figure. This signal may be amplified by the AC amplifier AMP and then applied to the musical tone conversion circuit TCV. This embodiment is a case in which the occupancy ratio changing circuit and the amplitude controlling circuit are integrated. FIG. 5 is a diagram showing a third embodiment of the present invention.

The occupancy ratio changing circuit DFC in FIG.
A common emitter resistor of d-Qe is connected to a negative power supply, and constitutes a differential amplification circuit for the differential output of the rectangular wave and the envelope signal. Therefore, the collector output of the transistor Qe has a waveform as shown in B or C in FIG. 3, and the gate circuit GT in FIG. 5 functions as a voltage-controlled amplifier to obtain a waveform controlled by the envelope waveform. In this way, according to the present invention, the occupation ratio of the rectangular wave from the sound source is changed according to the envelope waveform and the strength and speed of the key depression using a relatively simple configuration. As time passes, the harmonic components contained in the musical sound output change, and the degree of change varies depending on the state of key depression, resulting in changes in tone similar to those of a natural musical instrument.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration and waveforms of a conventional musical tone forming circuit in an electronic musical instrument, Fig. 2 is a diagram showing the configuration and waveforms of the first embodiment of the present invention, and Fig. 3 is an explanatory diagram of the operation of Fig. 2. , FIG. 4, and FIG. 5 are diagrams showing the configurations of second and third embodiments of the present invention. KY...Key, KSW...Key switch,
TRS...Touch response circuit, EVP...
...Envelope signal forming circuit, DFC...
・occupancy ratio change circuit, GT... gate circuit, TC
V...Musical tone conversion circuit, TG...Sound source.

Claims (1)

[Claims] 1 Musical tone formation for an electronic musical instrument that obtains an output according to the speed or intensity of a key press from a touch response circuit output to form an envelope signal, and obtains a musical tone by controlling the amplitude of a rectangular wave from a sound source using the envelope signal. The circuit includes an occupation ratio changing circuit that converts a rectangular wave from the sound source into a rectangular wave having an occupation ratio corresponding to an output signal level from the envelope forming circuit, and the output of the occupation ratio changing circuit is applied to a circuit for amplitude control. A musical tone forming circuit characterized by: