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Triangle Sound Simulation Circuit


This project, a triangle sound simulation circuit from 1970,  shows a simple transistor circuit that simulates the sound of a triangle. It uses two oscillators to achieve a natural sound effect.



Executive Summary of the Triangle Sound Simulation Circuit

A triangle sound simulating device to be employed in an electronic musical instrument is composed of a fundamental sound signal oscillator, at least one additional sound signal oscillator for generating an additional sound signal of lower frequency than that of the fundamental sound frequency, the output level of the additional sound signal being selected to be lower than the output level of the fundamental sound signal obtained from the fundamental sound signal oscillator, and a switching circuit of nonlinear characteristic which, upon reception of the output signals can create a difference frequency sound signal of a frequency equal to the difference between those of the output signals each time the switching circuit is switched.

Background of the Triangle Sound Simulation Circuit

This design relates to an electronic device for simulating the sounds generated from musical triangles. In electronic musical instruments, by employing combinations of active circuit elements such as electron tubes and transistors and passive circuit elements such as resistors, capacitors, and inductors, various circuits are combined to constitute sound effect generators which simulate sounds of various kinds of natural musical instruments.

Although it is comparatively easy to obtain electronic devices for simulating artificially, sounds generated from string musical instruments and wind instruments, the sounds of percussion instruments which are more complicated have not been successfully simulated with sufficient naturalness of auditory sensation.

Conventional devices for simulating percussion instruments, more specifically the sound of a triangle, have been composed of merely a single oscillator and a tone-color circuit for shaping the output of the oscillator. However, because merely a fundamental frequency and some of the higher harmonics thereof are generated from the single oscillator, the sound thus simulated by such an arrangement of the circuit is too simple and lacks naturalness in auditory sensation, although the organization thereof is simple and thereby advantageous.

Summary of the Triangle Sound Simulation Circuit

Therefore, the primary object of the present design is to provide a device for simulating the natural sound of a triangle whereby the above described drawbacks of the conventional sound simulating devices can be substantially eliminated.

Another object of the present design is to provide a novel device for simulating the sound of a triangle which can generate a sound far closer to the natural sound of a triangle.

Still another object of the present design is to provide a novel device for simulating the sound of a triangle which is simple in organization and can be easily produced. These and other objects of the present design can be achieved by a novel device for simulating the sound of a triangle which comprises an oscillator for generating a fundamental sound signal, at least one additional sound oscillator for generating an additional sound signal having a lower frequency than that of the fundamental sound signal, and a switching circuit of nonlinear characteristic which can receive all of the above mentioned fundamental and additional signals simultaneously and create sound signal having frequencies equal to the differences between the frequencies of these signals, the sound level of the additional sound signal being selected to be at a lower level than that of the fundamental sound signal.

The nature, principle, and utility of the present design will be more clearly understood from the following detailed description with reference to the accompanying drawing.


Figure 1 : Is a block diagram for an explanation of the principle of the present invention for the triangle sound simulation circuit



Description of the Triangle Sound Simulation Circuit

Referring now to FIG. 1 which shows a basic concept of the present design, the device shown comprises an oscillator 1 for generating a fundamental sound signal having a frequency f1, an additional sound oscillator 2 for generating an additional sound signal having a frequency f2 lower than the frequency f1 of the fundamental sound signal, a switching circuit 3, and a tone-color circuit 4.

With the above described organization of the simulating device of a triangle sound, the output of the fundamental sound oscillator 1 of the frequency f1 and the output of the additional sound oscillator 2 of the frequency f2 are mixed at an appropriate level ratio before entering a switching circuit 3 and the output thus obtained is applied to the tone-color circuit 4.

The switching circuit 3 is one having a nonlinear characteristic represented for example, by a curved gain, and may exhibit a saturation and a class C amplification as is inherent with such nonlinearly operated devices, a difference sound signal is produced by same having a frequency equal to the difference between f1 of the fundamental sound signal and f2 of the additional sound signal.


Figure 2 : Is an electric circuit diagram showing a device for simulating the sound of a triangle, which constitutes a preferred embodiment of the present invention for the triangle sound simulation circuit



The switched output comprises this difference frequency sound signal, the above described fundamental sound signal, and the additional sound signal, these signals being mixed again and applied to the tone-color circuit 4 so that the natural sound of the triangle can be simulated. FIG. 2 illustrates a circuit diagram of a device simulating the sound of a triangle, which constitutes one embodiment of the present design.

In this circuit, there are provided a fundamental sound oscillator 1 including transistors Tr1 and Tr2 ; an additional sound oscillator 2 including transistors Tr3 and Tr4 ; a switching circuit 3 including a transistor Tr5, a resistor R3, and a capacitor C3 ; and a tone-color circuit 4 including a capacitor C4 and a resistor R4.

The output signals from the oscillators 1 and 2 including a considerable amount of higher harmonics are reduced respectively to appropriate levels through series connected circuits, one of which consists of a resistor R1 and a capacitor C1, and the other of which consists of a resistor R2 and a capacitor C2. The signals thus reduced to suitable levels are then mixed at the input side of the switching circuit 3. In the switching circuit 3, the mixed signal is then applied to the base electrode of a transistor Tr5.

When a switch S2 inserted in the emitter circuit of the transistor Tr5 is opened after it has been closed, the bias voltage of the transistor Tr5 is varied in accordance with a time constant determined by a resistor R3 and a capacitor C3, whereby the output signal passing through the switching circuit 3 is decayed.

At this time, because of the inherent nonlinear characteristic of the switching circuit 3, a difference frequency signal is created, so that as the output of the switching circuit 3, a mixed signal consisting of the above described two signals and the difference frequency signal can be obtained.

When the output signal thus mixed is thereafter passed through the tone-color circuit 4 consisting of a resistor R4 and capacitor C4, a desired sound simulating a triangle can be obtained. As a result of various experiments, I have found that, when the frequencies f1 and f2 of the fundamental sound and the additional sound are 4 KHz and 1.35 kHz, respectively (difference frequency f1 -f2 =2.65 KHz), and the mixing level ratio of the fundamental sound to the additional sound is 1:0.03, a sound creating an extremely natural auditory sensation of a triangle can be obtained.

The preferable ranges of the fundamental sound frequency, the additional sound frequency and the mixing level ratio thereof are, respectively, from 3 kHz to 5 kHz, from 1 kHz to 2 kHz and from 1:0.02 to 1:0.04, and the fundamental sound frequency should not be of the just integer multiple of the additional sound frequency.

Although, in the embodiment described hereinbefore, merely a fundamental sound oscillator and an additional sound oscillator are employed, it will be apparent that more than two oscillators may also be employed in the circuit, and when the number of the oscillators are thus increased, a sound producing an even more natural sensation in simulating the sound of a triangle can be obtained.


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