Synthetic Animal Sound Generator And Method

Abstract

A circuit for generating signals in the audio frequency range which signals contain effective parts of animal calls. Because the signals are of relatively narrow bandwidth, the apparatus is uncomplex.

Parent Case Text

This is a continuation of the now abandoned application Ser. No. 648,907 filed June 26, 1967.

Description

This invention relates to apparatus for generating sounds of the type to which animals will respond. The invention finds utilization in ridding an area of pest birds by generating signals that correspond to warning or alarm signals normally created by the birds themselves.

The present invention arose as a consequence of extension of the teachings set forth in U.S. Pat. No. 3.294,909. The cited patent concerns an analogue ear; tests conducted with such ear have indicated that synthetic sounds have equal or greater effectiveness than actual sounds such as have been achieved by tape recording natural animal sounds and replaying the recorded sounds over a public address audio system. An advantage of employing synthetic sounds according to the present invention is that the components of the sound signal can be readily varied as dictated by conditions and as required to avoid adaptation by the birds. Moreover, the equipment necessary for the generation of the sounds is much less complex than tape recording and playing equipment.

A system according to the present invention includes a generator or oscillator for producing a carrier signal in the range of about 500 hz to about 5,000 hz. The carrier signal is modulated by a lower frequency AC signal in the range of about 50-300 hz to form a composite signal. The composite signal is amplified to a magnitude sufficient to drive a loudspeaker. Because the carrier frequency generator and the modulator are simple circuits that employ conventional elements, the entire apparatus can be constructed in a lightweight portable device.

A feature of the present invention that contributes to its portability and effectiveness is that the frequencies employed are in the mid-audio range, a range in which state-of-the-art loudspeakers are most efficient. For example, one system designed according to the present invention employs a carrier frequency of 3,000 hz and uses a conventional lightweight loudspeaker and a small horn-type acoustic radiator for aiming the audio energy.

The objects, features and advantages of the present invention will be more apparent on referring to the following specification and accompanying drawing in which:

FIG. 1 is a schematic diagram of a system embodying the present invention; and

FIGS. 2A, 2B, and 2C are graphs of voltage versus time and showing wave forms at various points in the system of FIG. 1 under various modes of operation, the sinusoidal carrier of FIGS. 2A and 2C being shown schematically.

Referring more particularly to the drawing, a conventional carrier frequency generator 12 which embodies conventional audio oscillator circuitry is connected to an amplitude modulator 14 which is driven by a modulating frequency driver 16 to modulate the carrier produced by generator 12.

The modulated carrier at the output of modulator 14 is connected through a switch 18 and an audio amplifier 20 to an electroacoustic transducer, such as a loudspeaker 22. Associated with the loudspeaker is a horn 24 which directs or aims the acoustic output of speaker 22 along a path in a direction designated by arrows 26.

The operation of the invention can be appreciated most readily by considering a specific example that is useful for flushing starlings from a vineyard. A carrier generator 12 capable of producing a carrier signal at 3,000 hz is provided in such exemplary apparatus, and modulating frequency generator 16 is constructed to produce a modulating signal at 100 hz. In order to secure a periodic interruption simulating a chirping sound, switch 18 is pulsed on and off at a rate of about twice per second. Maximum effect is achieved by moving horn 24 about to direct path 26 directly at the starlings. The system is effective in flushing the starlings. It was found, after one or two days of conducting the tests, that the starlings appeared to adapt to the noise and to become less sensitive to it. Accordingly, a frequency sweeping or dithering circuit 28 is provided in association with modulating frequency generator 16 to alter periodically or randomly the modulating frequency. Specifically, sweeping or altering the modulating frequency between about 100 and 150 hz, or like limits in a ratio of an order of magnitude of about two-to-one, at an average rate of a few alterations per second inhibits adaptation to the signal. In FIG. 1, shown in broken lines at 30, is a second kind of dithering circuit connected to carrier generator 12 for dithering the carrier frequency. The amount of sweep or dithering is nominally comparable to the frequency produced by modulating frequency generator 16. Carrier frequency sweep or dither can sometimes be used as an alternative to modulating frequency dither, or it may be effected in addition.

The above exemplary system employs a generator 16 that produces an irregular modulating signal which may or may not overmodulate the carrier. The output thereof is shown in FIG. 2A. In using the present invention to divert red-winged blackbirds from a landing strip used by jet planes, a random frequency square wave signal is produced by modulating frequency generator 16, a 3,000 hz carrier signal being generated by generator 12 in such application of the invention. The output waveform in this case is shown in FIG. 2B in which the nominal sine wave carrier has been replaced with a square wave as an additional modification.

FIG. 2C shows a variation in which switch 18 turns "on" and "off" gradually rather than in a step function relationship as in FIGS. 2A and 2B. The chirp sound in this case does not achieve full amplitude until several modulating frequency periods have occurred. In this way the clicks which otherwise exist are softened, although these clicks may not necessarily reduce effectiveness of the sounds.

It is believed that the present invention is effective in accomplishing its intended purpose because so much of the information contained in a continuous frequency signal generated by a bird is redundant and is eliminated in the organs of the bird so that the cochlear system responds only to several frequencies and signal interrelationships.

In the course of evaluating various synthetic sounds produced in accordance with the invention, field experiments comparing animal responses to the synthetic sound and the recorded natural sounds were performed. In one case sparrows in groups could be flushed from the ground using a sequence of presumably alarm-like chirps with a 3,000 hz carrier and a 100-150 hz swept or dithered modulation. It was found that if the number of sparrows was too small (one or two) they would not react to the synthetic alarm sound. (It is assumed that sparrows require visual cues from their neighbors along with the auditory cues produced by apparatus of this invention.)

In another series of experiments in a vineyard, it was found that the starlings could be consistently flushed and caused to abandon the vineyard for at least a short time; such could be accomplished whether the birds were on the ground or in flight. In order to flush the starlings, sounds like those for sparrows were produced except that the chirps were longer. In another case, starlings in a mixture of starlings, blackbirds, and pigeons were flushed consistently with the other birds following the starlings after one to two days of intensive harassment. It appears in this situation that the other birds learn by watching the starlings until their natural behavior, one of immunity to the sound, is modified.

In still another test, millions of red-winged blackbirds adjacent a jet aircraft strip were diverted from the strip by production of synthetic sounds. The signal used was a 3,000 hz carrier and a 100 hz swept or dithered random square wave amplitude modulation signal. It is believed that such sound is similar to a navigational aiding signal produced by the birds when they are flying in large formations and that such navigational signal normally informs the bird of the proximity of the other birds.

The present invention, although specifically described hereinabove in connection with avian pests, is not limited to birds or to pests. The sounds would appear to have maximum efficiency in reaching the central nervous system of animals for purposes of message transmission. Different messages can be presented upon changing carrier and modulation frequencies or chirp rates or duration so as to form an entire vocabulary of sounds. Thus, it is envisaged that the sounds can be used for controlling other pest animals, such as deer. Furthermore, a group of sounds, when selected purposefully, can facilitate the training of such animals as dogs, cats, pigs and so forth. Inasmuch as the sounds produced in accordance with the invention have exceptional effectiveness in communicating to the animal brain, the use of the sounds can provide a communication medium that is capable of overriding unusual amounts of interference of natural or intentional types. Conversely, the sounds produced according to the invention have unusual effectiveness in preventing communications of others, that is to say, as jamming or masking signals.

Because of the masking effectiveness of the signals produced according to the present invention, the sounds are more bothersome to the hearer, whether it be animal or human, than other sounds of comparable intensity, a property that is very likely at least partly responsible for the effectiveness of the sounds against animals at a psychological level. For example, a gregarious species of birds or animals is believed to depend upon constant chatter for indication of well-being; denial of these sound cues by effective chatter-like masking causes the animals to abandon the treated area as an unpleasant and undesirable area.

It is emphasized that the foregoing explanatory material is in large part theoretical and is not intended to limit the present invention to the theory set forth hereinabove. Although one embodiment of the present invention has been shown and described, it will be obvious that other adaptations and modifications can be made without departing from the true spirit and scope of the invention.

Claims

1. Apparatus controlling animals by beaming irregular sound at them comprising means for generating a carrier signal in a frequency range of about 500 hz to about 5,000 hz, means for overmodulating the amplitude of the carrier signal to turn the carrier signal on and off at a rate in the range of about 50 to 300 hz, means for interrupting the carrier signal at a rate of at least about once per second, and an electroacoustic transducer for converting the modulated and intermittently interrupted

2. A synthetic animal sound generator for subjecting animals to irregular, nonrepetitive sound signals to affect the animals and prevent the adaptation of the animals to the sound comprising: means for generating a carrier signal in a frequency range of about 500 hz to about 5,000 hz, means for overmodulating the amplitude of the carrier signal at a frequency of between about 50 to about 300 hz so that the carrier signal is intermittently silenced to thereby generate a plurality of signal pulses, means for interrupting the modulated carrier signal at a rate in the range of about one to five times per second, and means for converting the modulated and intermittently interrupted carrier signal to a sound

3. Apparatus according to claim 2 wherein the interrupting means includes means for gradually interrupting and reinstating the modulated carrier

4. Apparatus according to claim 2 wherein the interrupting means includes means for maintaining transmission of the modulated carrier signal to the sound generating means for a period of time sufficient to transmit to said

5. Apparatus according to claim 3 including means for varying the frequency

6. Apparatus according to claim 2 including means for varying the frequency of the carrier signal over a frequency range of about the same order of magnitude as the frequency range of the overmodulated carrier signal.