Apparatus for producing a plurality of audio sound effects such as shots, explosions, and airplane and car sounds, used in electronic games utilizes a variable clock driving a variable digital noise generator whose audio output amplitude is shaped by either of two types of control units. In one type the density or duty cycle is varied by selectively ANDing together outputs from a polynomial counter. In a second embodiment a digital to analog converter utilizing gated resistive summing provides the amplitude control the gates being driven by a four bit data register which in turn is driven by the game control means.

This invention is an electronic siren producing a siren sound having a sound wave produced on a slowly rising and falling frequency. A major cycle is pulsed at intervals with variations in frequency. The variations in each major cycle represent minor cycles. The invention utilizes an electronic circuit to effect such major and minor frequency cycles with existing speaker equipment to project the sound.

An electronic pest-control device which includes a plurality of electrically energizable ultrasonic transducers, each of which is operable within a different range of ultrasonic frequencies. Circuitry is provided for simultaneously energizing the transducers, with each generating ultrasonic waves whose frequencies are continuously randomly varied throughout the transducer's operating range. The ultrasonic waves generated by the device are directed into an area desired to be kept free from infestation by pests, such as rats, which are sensitive and responsive to ultrasonic energy. Through the use of a plurality of different, continually changing frequencies, the pests cannot become acclimated to the ultrasonic waves and thus become immune to their effect.

A pest control apparatus and method for dispersing pests, e.g., rodents, from a designated area by the transmission into the area of high intensity ultrasonic sound waves having a primary frequency varying as a function of time and frequency modulating the sound waves with a secondary vibrato. The apparatus additionally provides periodic bursts of such ultrasonic power affording transducer rest periods maximizing the power handling capability of the transducer during "on" periods.

An electronic circuit for simulating the sound of a percussive bell struck at a predetermined repetition rate. A realistic electronically generated sound is produced by appropriately modulating two or more audio frequencies with a decaying exponential control signal and thereafter mixing the modulated frequencies. The system comprises a repetition rate generator; a modulation envelope generator; a high and low frequency oscillator; a modulator; and a mixer together with a loud speaker. The repetition rate generator determines the ringing frequency of the simulated bell sound. The modulation envelope generator generates two decaying control signals with differing time constants with the time constant of the low frequency generator usually being greater than the time constant of the high frequency generator. Filter networks may be used to eliminate some of the harmonics. Potentiometers may be provided to vary the magnitude of the low and high frequency components at the input to the mixer. An isolation transformer may be used and connected to an external amplifier for audio distribution of the electronically generated sound.