Infrasound generator, infrasound transmission system, infrasound generation method, and infrasound transmission method

Abstract

To provide an infrasound generator capable of generating infrasound from human voice.SOLUTION: An infrasound generator (1) includes a frequency characteristic conversion unit (11) that generates a sound signal (B2) by increasing the low-frequency level and decreasing the high-frequency level based on the center frequency of the frequency band of a sound signal (B1), which is an audible sound, a slide processing unit (12) that generates a sound signal (B3) by sliding the sound signal (B2) to the infrasound band audible to the human ear, and an output processing unit (13) that outputs the sound signal (B3) from an infrasound speaker (3).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an infrasound generating device, an infrasound transmission system, an infrasound generating method, and an infrasound transmitting method. [Background technology]

[0002] Sound waves are used in various technical fields. For example, there is amplified sound technology that amplifies and transmits sounds in a frequency band audible to the human ear (audible sounds), and state detection technology that detects sounds generated from objects and determines the state of the objects. Audible sounds are in a wide frequency band, such as 20 to 20,000 Hz. In contrast, the effects of infrasound, which includes the lower limit of the audible frequency band, on the human body and buildings, etc. have not been fully elucidated, and its use is being considered. For example, Patent Document 1 describes a technology that makes the amplitude change of infrasound audible by multiplying the electrical waveform of infrasound by an electrical waveform equivalent to a reference audible sound and reproducing the electrical waveform after this multiplication. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 58-6423 Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the frequency band of human voice differs from person to person, conventional techniques have had the problem that it is difficult to convert human voice into infrasound. It should be noted that the conventional technology described in Patent Document 1 is capable of making infrasound audible, but is unable to convert human voice into infrasound.

[0005] The present disclosure is intended to solve the above-mentioned problems, and aims to provide an infrasound generator capable of generating infrasound from human voice. [Means for solving the problem]

[0006] The infrasound generating device according to the present disclosure includes a frequency characteristic conversion unit that acquires audible sound collected by an audible sound collecting unit and generates a sound signal with a higher low-frequency level and a lower high-frequency level based on the center frequency of the frequency band of the acquired audible sound, a slide processing unit that generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit to an infrasound band audible to the human ear, and an output processing unit that outputs the sound signal generated by the slide processing unit from an infrasound output unit. Effect of the Invention

[0007] According to the present disclosure, a sound signal is generated with a higher low-frequency level and a lower high-frequency level based on the center frequency of the frequency band of audible sound, the generated sound signal is shifted to an infrasonic frequency band audible to the human ear, and the generated sound signal is output from an infrasonic speaker. In this way, the infrasonic sound generator according to the present disclosure can generate infrasonic sound from human voice. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram showing a configuration example of an infrasound generating device according to a first embodiment. [Diagram 2] 4 is a graph showing a process of processing a sound signal from a human voice to generating an infrasound in the first embodiment. [Diagram 3] 3 is a flowchart showing an infrasound generating method according to the first embodiment. [Figure 4] 4A and 4B are block diagrams showing a hardware configuration for realizing the functions of the infrasound generating device according to the first embodiment. [Diagram 5] FIG. 11 is a block diagram showing a configuration example of an infrasound transmission system according to a second embodiment. [Figure 6]11 is a graph showing a process of processing a sound signal from a human voice to generating an infrasound in the second embodiment. [Figure 7] 11 is a graph showing a process of processing a sound signal from an infrasound to reproducing a human voice in the second embodiment. [Figure 8] 10 is a flowchart showing an infrasound generating method according to a second embodiment. [Figure 9] 11 is a flowchart showing a process of reproducing a human voice from an infrasound according to the second embodiment. [Figure 10] FIG. 13 is a block diagram showing the configuration of a modified example of the infrasound detection device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Embodiment 1 FIG. 1 is a block diagram showing an example of the configuration of an infrasound generating device 1 according to the first embodiment. In FIG. 1, the infrasound generating device 1 is a device that generates infrasound from the voice of a person A collected by a general-purpose microphone 2 and outputs the generated infrasound from an infrasound speaker 3. The infrasound output by the infrasound generating device 1 through the infrasound speaker 3 is a sound signal in a low frequency band on the lower limit side of the audible frequency band. For example, a sound signal in a frequency band of 20 Hz or more and less than 50 Hz, which is the lower limit of audibility, is considered. A sound signal of 20 Hz or more and 30 Hz or less is preferable.

[0010] Infrasound between 20 Hz and 30 Hz has the characteristic that it can be transmitted over a much longer distance than the normal voice of human A. For example, normal voice, with a reference sound of about 440 Hz, can be transmitted up to about 4 km, while audible sounds such as disaster sirens can be transmitted up to about 6 km. In contrast, infrasound between 20 Hz and 30 Hz can reach up to 30 to 40 km. In addition, the infrasound output from the infrasound speaker 3 has no directionality and propagates in all directions. By using the infrasound generator 1, human A can transmit his voice up to 30 to 40 km away, allowing him to communicate his intentions and call attention.

[0011] The general-purpose microphone 2 is an audible sound collecting unit for collecting analog voice signals in the audible frequency band. Person A collects voice using the general-purpose microphone 2. The infrasonic speaker 3 is an infrasonic sound output unit for outputting infrasonic sound of, for example, 30 Hz or less. In other words, the infrasonic speaker 3 outputs infrasonic sound in the audible frequency band.

[0012] The infrasound generator 1 generates a sound signal with a higher low-frequency level and a lower high-frequency level based on the center frequency of the audible frequency band. The infrasound generator 1 generates a sound signal by sliding the generated sound signal to the infrasound band audible to the human ear. The infrasound generator 1 then outputs the generated sound signal from the infrasound speaker 3.

[0013] The infrasound generating device 1 is realized, for example, by a computer including a calculation unit and a storage unit. The calculation unit controls the overall operation of the infrasound generating device 1. The calculation unit includes a frequency characteristic conversion unit 11, a slide processing unit 12, and an output processing unit 13. The calculation unit executes an infrasound generation processing application to realize the functions of the frequency characteristic conversion unit 11, the slide processing unit 12, and the output processing unit 13.

[0014] The storage unit stores an infrasound generation processing application and information used for the arithmetic processing of the arithmetic unit. The storage unit includes a storage such as a hard disk drive (HDD) or a solid state drive (SSD), or the memory 104 of FIG. 4. The storage unit may be provided outside the infrasound generator 1 as long as it is accessible by the infrasound generator 1.

[0015] 1 shows a configuration in which the infrasound generating device 1 includes, as components, a frequency characteristic conversion unit 11, a slide processing unit 12, and an output processing unit 13, but any of these components may be included in another device. For example, an external device that is provided separately from the infrasound generating device 1 and can communicate with the infrasound generating device 1 may include the frequency characteristic conversion unit 11, and the infrasound generating device 1 may generate infrasound from a sound signal obtained by the external device.

[0016] The frequency characteristic conversion unit 11 acquires audible sound, which is the voice of human A, collected by the general-purpose microphone 2, and generates a sound signal in which the low-frequency level is increased and the high-frequency level is decreased based on the center frequency of the frequency band of the acquired audible sound. For example, the frequency characteristic conversion unit 11 digitally converts an audible sound, cuts both ends of the frequency band of the digitally converted audible sound, and increases the low-frequency level and decreases the high-frequency level of the sound signal with both ends of the frequency band cut.

[0017] 2 is a graph showing a process of processing a sound signal from a human voice to generating an infrasound in the first embodiment. In the sound signal in the audible frequency band of the voice of human A, the amplitude is generally attenuated at both ends of the low and high frequencies of the frequency band. The frequency characteristic conversion unit 11 cuts out components whose amplitude is equal to or less than a threshold at both ends of the low and high frequencies of the frequency band from the sound signal acquired from the general-purpose microphone 2. The frequency characteristic conversion unit 11 attenuates the sound signal such that the amount of attenuation is smaller as the amplitude of the sound signal with both ends of the frequency band cut is larger, and as shown in FIG. 2(a), the amplitude of each partial frequency component contained in the sound signal B1 is flattened, and the amplitude of the sound signal B1 is set to a constant width.

[0018] Next, the frequency characteristic conversion unit 11 detects the center frequency fo of the frequency band of the sound signal B1, and generates a sound signal B2 by increasing the low-frequency side level of the sound signal B1 based on the center frequency fo and decreasing the high-frequency side level of the sound signal B1 as shown in Fig. 2(b). For example, by increasing the low-frequency side by about three times the original level and reducing the high-frequency side to one-quarter or one-fifth of the original level, the sound signal B1 is converted into a sound signal B2 having linear characteristics that pass through the center frequency fo and decrease from the low-frequency side to the high-frequency side. The sound signal B2 has a narrower frequency band than the sound signal B1, and therefore is a signal whose frequency can be easily changed by the slide processing unit 12.

[0019] As shown in Fig. 2(c) and Fig. 2(d), the slide processing unit 12 generates a sound signal B3 by sliding the sound signal B2 generated by the frequency characteristic conversion unit 11 to an ultra-low frequency band audible to the human ear. For example, the slide processing unit 12 generates a sound signal B3 in the ultra-low frequency band by attenuating the sound signal B2 in a range of 3 to 4 octaves. A reference tone of 440 Hz becomes a sound signal of 55 Hz when lowered by 3 octaves, and becomes a sound signal of 27 Hz when lowered by 4 octaves. In other words, the sound signal B3 is a sound signal in the ultra-low frequency band that is within the audible frequency band but has a frequency lowered to near the audible limit.

[0020] In addition, simply lowering the frequency of the sound signal B2 in the audible frequency band to near the audible limit frequency may result in a stretched sound overall. Therefore, the slide processing unit 12 may adjust the pitch of the sound signal B3 to a pitch close to that of a normal sound by changing the pitch of the sound signal B3 based on the pitch of the sound signal B2.

[0021] The output processing unit 13 outputs the sound signal B3 generated by the slide processing unit 12 from the infrasonic speaker 3. For example, the output processing unit 13 converts the sound signal B3 into an analog signal, amplifies the analog-converted sound signal B3, and outputs it to the infrasonic speaker 3. The infrasonic speaker 3 outputs the sound signal B3 in all directions. The sound signal B3 is an infrasonic sound with a frequency of 20 Hz or more and 30 Hz or less, and is a sound signal that can be heard by the human ear.

[0022] For example, when transmitting voice to many people scattered on a coast or vast farmland, conventional loudspeakers output audible sounds with directionality and have a short transmission distance, so it was necessary to output the voice from multiple loudspeakers from multiple locations. In contrast, the infrasound generator 1 outputs infrasound with a long transmission distance in all directions, so the voice of person A can be transmitted to many people from one location.

[0023] Next, the infrasound generating method according to the first embodiment will be described. FIG. 3 is a flowchart showing the infrasound generating method according to the first embodiment. The frequency characteristic conversion unit 11 acquires the audible sound of the human A collected by the general-purpose microphone 2, and generates a sound signal B2 by increasing the low-frequency side level and decreasing the high-frequency side level based on the center frequency of the frequency band of the acquired audible sound (step ST1). The slide processing unit 12 generates a sound signal B3 by sliding the sound signal B2 generated by the frequency characteristic conversion unit 11 to the infrasonic frequency band audible to the human ear (step ST2). The output processing unit 13 outputs the sound signal B3 generated by the slide processing unit 12 from the infrasonic speaker 3 (step ST3). By executing this method, the infrasonic sound generating device 1 can generate infrasonic sound audible to the human ear from the voice of the human A.

[0024] Next, a hardware configuration for realizing the functions of the infrasound generating device 1 will be described. The functions of the frequency characteristic conversion unit 11, slide processing unit 12, and output processing unit 13 included in the infrasound generator 1 are realized by a processing circuit. That is, the infrasound generator 1 includes a processing circuit for executing each process from step ST1 to step ST3 shown in Fig. 3. The processing circuit may be dedicated hardware, or may be a CPU (Central Processing Unit) that executes a program stored in a memory.

[0025] Fig. 4A is a block diagram showing a hardware configuration for realizing the functions of the infrasound generator 1. Fig. 4B is a block diagram showing a hardware configuration for executing software for realizing the functions of the infrasound generator 1. In Figs. 4A and 4B, an input interface 100 is an interface for relaying a sound signal output from a general-purpose microphone 2 to a frequency characteristic conversion unit 11. An output interface 101 is an interface for relaying an infrasound signal output from an output processing unit 13 to an infrasound speaker 3.

[0026] When the processing circuit is the dedicated hardware processing circuit 102 shown in FIG. 4A, the processing circuit 102 may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. The functions of the frequency characteristic conversion unit 11, slide processing unit 12 and output processing unit 13 provided in the infrasound generating device 1 may be realized by separate processing circuits, or these functions may be realized together by a single processing circuit.

[0027] 4B, the functions of the frequency characteristic conversion unit 11, the slide processing unit 12, and the output processing unit 13 included in the infrasound generator 1 are realized by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in the memory 104.

[0028] The processor 103 realizes the functions of the frequency characteristic conversion unit 11, slide processing unit 12 and output processing unit 13 provided in the infrasound generating device 1 by reading and executing the program of an application for generating infrasound stored in the memory 104. For example, the infrasound generating device 1 includes a memory 104 for storing the above-mentioned program, which, when executed by the processor 103, results in the processing of steps ST1 to ST3 shown in Fig. 3 being executed. This program causes a computer to execute the procedure or method of the processing performed by the frequency characteristic conversion unit 11, the slide processing unit 12, and the output processing unit 13. The memory 104 may be a computer-readable storage medium in which a program for causing a computer to function as the frequency characteristic conversion unit 11, the slide processing unit 12, and the output processing unit 13 is stored.

[0029] Memory 104 may be, for example, a non-volatile or volatile semiconductor memory such as a Random Access Memory (RAM), a Read Only Memory (ROM), a flash memory, an Erasable Programmable Read Only Memory (EPROM), an Electrically-EPROM (EEPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a DVD, etc.

[0030] Some of the functions of the frequency characteristic conversion unit 11, slide processing unit 12, and output processing unit 13 included in the infrasound generating device 1 may be realized by dedicated hardware, and the remaining parts may be realized by software or firmware. For example, the output processing unit 13 has its function realized by a processing circuit 102, which is dedicated hardware, and the frequency characteristic conversion unit 11 and slide processing unit 12 have their functions realized by a processor 103 reading and executing a program stored in a memory 104. In this way, the processing circuit can realize the above functions by hardware, software, firmware, or a combination of these.

[0031] As described above, the infrasound generator 1 according to the first embodiment includes a frequency characteristic conversion unit 11 that generates a sound signal B2 by increasing the low-frequency level and decreasing the high-frequency level based on the center frequency of the frequency band of a sound signal B1, which is an audible sound, a slide processing unit 12 that generates a sound signal B3 by sliding the sound signal B2 to an infrasound band audible to the human ear, and an output processing unit 13 that outputs the sound signal B3 from the infrasound speaker 3. This allows the infrasound generator 1 to generate infrasound from human voice.

[0032] In the infrasound generator 1 according to the first embodiment, the frequency characteristic conversion unit 11 cuts both ends of the frequency band of the sound signal B1, which is an audible sound, and increases the low-frequency side level and decreases the high-frequency side level of the sound signal B1 with both ends of the frequency band cut. This allows the infrasound generator 1 to generate a sound signal whose frequency can be easily changed by the slide processing unit 12.

[0033] In the infrasound generator 1 according to the first embodiment, the slide processing unit 12 generates an infrasound band sound signal B3 by attenuating the sound signal B2 in the range of 3 to 4 octaves. This allows the infrasound generator 1 to generate an infrasound band sound signal B3 audible to the human ear.

[0034] The infrasound generating method according to the first embodiment includes step ST1 in which the frequency characteristic conversion unit 11 generates a sound signal B2 by increasing the low-frequency level and decreasing the high-frequency level based on the center frequency of the frequency band of a sound signal B1, which is an audible sound, step ST2 in which the slide processing unit 12 generates a sound signal B3 by sliding the sound signal B2 to the infrasound band audible to the human ear, and step ST3 in which the output processing unit 13 outputs the sound signal B3 from the infrasound speaker 3. By executing this method, the infrasound generating device 1 can generate infrasound audible to the human ear from the voice of human A.

[0035] Embodiment 2 Fig. 5 is a block diagram showing a configuration example of an infrasound transmission system 10 according to embodiment 2. In Fig. 5, the infrasound transmission system 10 outputs an infrasound band sound signal that cannot be heard by the human ear from an infrasound generator 1A, and makes the sound signal output from the infrasound generator 1A audible by an infrasound detector 4. Since the sound signal from when it is output from the infrasound generator 1A to when it is detected by the infrasound detector 4 is inaudible to the human ear, so-called secret calls are possible.

[0036] (Infrasound Generator; Transmission Side) The infrasound generator 1A is a device that generates infrasound from the voice of a person A collected by a general-purpose microphone 2 and outputs the generated infrasound from an infrasound speaker 3. The infrasound output by the infrasound generator 1A through the infrasound speaker 3 is a sound signal in an infrasound band below the lower limit of audibility and inaudible to the human ear. For example, a sound signal in a frequency band of 5 Hz or more and less than 20 Hz is considered.

[0037] Infrasound between 5 Hz and 20 Hz has the characteristic that it can transmit over a much longer distance than the normal voice of human A. For example, infrasound between 5 Hz and 20 Hz can reach a maximum distance of 30 to 40 km. Infrasound output from the infrasound speaker 3 is not directional and propagates in all directions. By using the infrasound generator 1A, human A can communicate secretly with a location 30 to 40 km away.

[0038] The infrasound generating device 1A includes a frequency characteristic conversion section 11, a slide processing section 12A, and an output processing section 13. The frequency characteristic conversion unit 11 acquires audible sound, which is the voice of human A, collected by the general-purpose microphone 2, and generates a sound signal in which the low-frequency level is increased and the high-frequency level is decreased based on the center frequency of the frequency band of the acquired audible sound. For example, the frequency characteristic conversion unit 11 digitally converts an audible sound, cuts both ends of the frequency band of the digitally converted audible sound, and increases the low-frequency level and decreases the high-frequency level of the sound signal with both ends of the frequency band cut.

[0039] Fig. 6 is a graph showing a process of processing a sound signal from a human voice to generating an infrasound in the second embodiment. The frequency characteristic conversion unit 11 cuts out components whose amplitude is equal to or less than a threshold value at both ends of the low and high frequency band of the sound signal acquired from the general-purpose microphone 2. The frequency characteristic conversion unit 11 attenuates the sound signal such that the amount of attenuation decreases as the amplitude of the sound signal after both ends of the frequency band are cut off increases, thereby flattening the amplitude of each partial frequency component contained in the sound signal C1 and aligning the amplitude of the sound signal C1 to a constant width, as shown in Fig. 6(a).

[0040] Next, the frequency characteristic conversion unit 11 detects the center frequency fo of the frequency band of the sound signal C1, and generates a sound signal C2 by increasing the low-frequency side level of the sound signal C1 based on the center frequency fo and decreasing the high-frequency side level of the sound signal C1 as shown in Fig. 6(b). For example, by increasing the low-frequency side by about three times the original level and reducing the high-frequency side to one-quarter or one-fifth of the original level, the sound signal C1 is converted into a sound signal C2 having linear characteristics that pass through the center frequency fo and decrease from the low-frequency side to the high-frequency side. The sound signal C2 has a narrower frequency band than the sound signal C1, and therefore is a signal whose frequency can be easily changed by the slide processing unit 12A.

[0041] The slide processing unit 12A is a transmission-side slide processing unit that generates a sound signal C3 by sliding the sound signal C2 generated by the frequency characteristic conversion unit 11 to an ultra-low frequency band that is inaudible to the human ear, as shown in Figures 6(c) and 6(d). For example, the slide processing unit 12A generates an ultra-low frequency band sound signal C3 by attenuating the sound signal C2 in the range of 4 to 5 octaves. A reference tone of 440 Hz becomes a sound signal of 27 Hz when lowered by 4 octaves, and becomes a sound signal of 13 Hz when lowered by 5 octaves. In other words, the sound signal C3 is a sound signal of an ultra-low frequency band whose frequency band is lowered almost to below the audible limit.

[0042] The output processing unit 13 is a transmission-side output processing unit that outputs the sound signal C3 generated by the slide processing unit 12A from the infrasonic speaker 3. For example, the output processing unit 13 converts the sound signal C3 into an analog signal, amplifies the analog-converted sound signal C3, and outputs it to the infrasonic speaker 3. The sound signal C3 is output in all directions from the infrasonic speaker 3.

[0043] (Infrasound detector; receiver) The infrasound detection device 4 detects infrasound collected by the infrasound microphone 5 from the infrasound generation device 1A, audibly converts the detected infrasound, and outputs it from the general-purpose speaker 6. The infrasound microphone 5 is an infrasound collection unit for collecting analog audio signals in the infrasound band that cannot be heard by the human ear. The general-purpose speaker 6 is, for example, an audible sound output unit for outputting audible sound.

[0044] For example, the infrasound detection device 4 acquires a sound signal collected by an infrasound microphone 5 from the infrasound generating device 1A, removes noise from the acquired sound signal, generates a sound signal by sliding the sound signal from which the noise has been removed into the audible frequency band, generates a sound signal with a lower low-frequency level and a higher high-frequency level based on the center frequency of the frequency band of the generated sound signal, and outputs the generated sound signal from a general-purpose speaker 6.

[0045] The infrasound detection device 4 is realized by, for example, a computer including a calculation unit and a storage unit. The calculation unit controls the overall operation of the infrasound detection device 4. The calculation unit includes a noise elimination unit 41, a slide processing unit 42, a frequency inverse conversion unit 43, and an output processing unit 44. The calculation unit executes an infrasound detection processing application to realize the functions of the noise elimination unit 41, the slide processing unit 42, the frequency inverse conversion unit 43, and the output processing unit 44.

[0046] The storage unit stores an infrasound detection processing application and information used for the arithmetic processing of the arithmetic unit. The storage unit includes a storage such as an HDD or SSD, or the memory 104 of Fig. 4. Note that the storage unit may be provided outside the infrasound detection device 4 as long as it is accessible by the infrasound detection device 4.

[0047] 1 shows a configuration in which the infrasound detection device 4 includes, as its components, the noise elimination unit 41, the slide processing unit 42, the frequency inverse conversion unit 43, and the output processing unit 44, but any of these components may be included in another device. For example, an external device that is provided separately from the infrasound detection device 4 and is capable of communicating with the infrasound detection device 4 may include the noise elimination unit 41, and the infrasound detection device 4 may detect infrasound from a sound signal obtained by the external device.

[0048] The noise elimination unit 41 acquires the sound signal C3 output from the infrasound speaker 3, and removes noise from the acquired sound signal C3. FIG. 7 is a graph showing the process of processing a sound signal from infrasound to reproduction of human voice in the second embodiment. For example, the noise elimination unit 41 is a low-pass filter (LPF), and as shown in FIG. 7(a), passes only the sound signal C3 and removes high-frequency noise contained in the sound signal C3. The sound signal C3 from which the high-frequency noise has been removed is output from the noise elimination unit 41 to the slide processing unit 42.

[0049] 7(b), the slide processing unit 42 is a receiving-side slide processing unit that generates a sound signal C2 by sliding the sound signal C3, from which the noise reduction unit 41 has removed noise, into the audible frequency band. For example, the slide processing unit 42 generates a sound signal C2 in the audible frequency band by raising the sound signal C3 in the range of 4 to 5 octaves. A 13 Hz infrasound becomes a 440 Hz sound signal by raising it by 5 octaves, and a 27 Hz infrasound becomes a 440 Hz sound signal by raising it by 4 octaves.

[0050] The frequency inverse conversion unit 43 generates a sound signal C4 by lowering the low-frequency side level and raising the high-frequency side level based on the center frequency fo of the frequency band of the sound signal C2 generated by the slide processing unit 42. For example, by lowering the low-frequency side by about one-third of the original level and raising the high-frequency side to four or five times the original level, as shown in Fig. 7(c), the sound signal C2 is converted into a sound signal C4 having linear characteristics that pass through the center frequency fo and decrease from the high-frequency side to the low-frequency side.

[0051] The output processing unit 44 is a receiving-side output processing unit that outputs the sound signal C4 generated by the frequency inverse conversion unit 43 from the general-purpose speaker 6. For example, the output processing unit 44 converts the sound signal C4 into an analog signal, thereby reproducing a sound signal C1 which is the voice of a person A, as shown in Fig. 7(d), and amplifies and outputs the sound signal C1 to the general-purpose speaker 6. The sound signal C1 is output from the general-purpose speaker 6 with directionality.

[0052] Next, an infrasound transmission method according to the second embodiment will be described. 8 is a flowchart showing an infrasound generating method. The frequency characteristic conversion unit 11 generates a sound signal C2 by increasing the low-frequency side level and decreasing the high-frequency side level based on the center frequency of the frequency band of audible sound (step ST1A). The slide processing unit 12A generates a sound signal C3 by sliding the sound signal C2 to an infrasound band that is inaudible to the human ear (step ST2A). The output processing unit 13 outputs the sound signal C3 from the infrasound speaker 3 (step ST3A). By executing this method, the infrasound generating device 1A can generate and output an infrasound that is inaudible to the human ear from the voice of human A.

[0053] FIG. 9 is a flowchart showing a process for reproducing a human voice from an infrasound. The noise elimination unit 41 acquires the sound signal C3 output from the infrasound speaker 3 and eliminates noise from the acquired sound signal C3 (step ST1B). The slide processing unit 42 generates a sound signal C2 by sliding the sound signal C3 from which noise has been removed to the audible frequency band (step ST2B). The frequency inverse conversion unit 43 generates a sound signal C4 by lowering the low-frequency side level and increasing the high-frequency side level based on the center frequency of the frequency band of the sound signal C2 (step ST3B). The output processing unit 44 outputs the sound signal C1 obtained by analog-converting the sound signal C4 from the general-purpose speaker 6 (step ST4B). By executing this method, the infrasound detection device 4 can detect infrasound and reproduce the voice of the person A from the detected infrasound.

[0054] The functions of the frequency characteristic conversion unit 11, slide processing unit 12A, and output processing unit 13 included in the infrasound generating device 1A are realized by, for example, the processing circuit shown in Fig. 4A or 4B. That is, the infrasound generating device 1A includes a processing circuit for executing the processes from step ST1A to step ST3A shown in Fig. 6. The processing circuit may be dedicated hardware, or may be a CPU that executes a program stored in a memory.

[0055] The functions of the noise removal unit 41, slide processing unit 42, frequency inverse conversion unit 43, and output processing unit 44 included in the infrasound detection device 4 are realized by, for example, the processing circuit shown in Fig. 4A or 4B. That is, the infrasound detection device 4 includes a processing circuit for executing the processes from step ST1B to step ST4B shown in Fig. 7. The processing circuit may be dedicated hardware, or may be a CPU that executes a program stored in a memory.

[0056] As described above, the infrasound transmission system 10 according to the second embodiment includes an infrasound generator 1A having a frequency characteristic conversion unit 11 that generates a sound signal with a higher low-frequency level and a lower high-frequency level based on the center frequency of the frequency band of audible sound, a slide processing unit 12A that generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit 11 to an infrasound band that is inaudible to the human ear, and an output processing unit 13 that outputs the sound signal generated by the slide processing unit 12A from the infrasound speaker 3, and the infrasound detection device 4 having a noise elimination unit 41 that acquires a sound signal output from the input terminal 1 and removes noise from the acquired sound signal; a slide processing unit 42 that generates a sound signal by sliding the sound signal from which the noise elimination unit 41 has been removed to the audible frequency band; a frequency inverse conversion unit 43 that generates a sound signal with a lower low-frequency level and a higher high-frequency level based on the center frequency of the frequency band of the sound signal generated by the slide processing unit 42; and an output processing unit 44 that outputs the sound signal generated by the frequency inverse conversion unit 43 from a general-purpose speaker 6. In this way, infrasound is transmitted from the infrasound generator 1A and detected by the infrasound detector 4, so that the infrasound transmission system 10 enables secret calls using infrasound that is inaudible to the human ear during transmission.

[0057] The infrasonic sound transmission method according to the second embodiment includes a step ST1A in which the frequency characteristic conversion unit 11 generates a sound signal with a higher low-frequency level and a lower high-frequency level based on a center frequency fo of an audible frequency band, a step ST2A in which the slide processing unit 12A generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit 11 to an infrasonic frequency band that is inaudible to the human ear, and a step ST3A in which the output processing unit 13 outputs the sound signal generated by the slide processing unit 12A from the infrasonic speaker 3, and a noise reduction unit 41 outputs the sound signal from the infrasonic speaker 3. The method includes step ST1B of acquiring a sound signal output from the sound processor 42 and removing noise from the acquired sound signal, step ST2B of the slide processing unit 42 generating a sound signal by sliding the sound signal from which the noise removal unit 41 has removed noise to the audible frequency band, step ST3B of the frequency inverse conversion unit 43 generating a sound signal with a lowered low-frequency level and an increased high-frequency level based on the center frequency fo of the frequency band of the sound signal generated by the slide processing unit 42, and step ST4B of the output processing unit 44 outputting the sound signal generated by the frequency inverse conversion unit 43 from the general-purpose speaker 6. The infrasound generating device 1A executes steps ST1A to ST3A, and the infrasound detection device 4 executes steps ST1B to ST4B, thereby enabling secret calls using infrasound that is inaudible to the human ear during transmission.

[0058] (Modification) Infrasound detection devices can be used in a variety of fields. Fig. 10 is a block diagram showing the configuration of an infrasound detection device 4A, which is a modified example of the infrasound detection device 4. In Fig. 10, the infrasound detection device 4A detects infrasound and analyzes the state of the source of the infrasound based on the result of comparing the detected infrasound with a reference signal. In addition, the infrasound detection device 4A can output a sound signal generated from the detected infrasound from a general-purpose speaker 6.

[0059] Furthermore, the infrasound detection device 4A is connected to a processing personal computer 7 (hereinafter, referred to as processing PC7) by wire or wirelessly, and is capable of communicating analysis result information regarding the state of the infrasound source. The analysis result information includes the state of the infrasound source as well as an alarm level according to that state. The processing PC7 records and displays the analysis result information, and is capable of communicating with a smartphone 8 to transmit the alarm level. The smartphone 8 functions as an alarm device that outputs an alarm according to the alarm level.

[0060] Sources of infrasound include, for example, large machines such as processing machines, engines of moving objects such as aircraft, housing sites built along roads, earthquake measurement sites, etc. These sources emit infrasound even in normal conditions, and the level of infrasound in normal conditions is set as a reference signal in the infrasound detection device 4A.

[0061] The infrasound detection device 4A digitally converts the infrasound collected from the source by the infrasound microphone 5, converts the digitally converted infrasound into, for example, an audible sound, and outputs it from the general-purpose speaker 6. The infrasound detection device 4A also compares the amplitude between a sound signal to be analyzed, which is obtained by converting the digitally converted infrasound into an audible sound, and a reference sound signal, which is obtained by converting the infrasound detected from the source in a normal state into an audible sound. The infrasound detection device 4A has various alarm levels set according to the magnitude of the difference in amplitude between the sound signal to be analyzed and the reference sound signal. For example, as an alarm form of the three alarm levels, at the first alarm level, a text message to call attention is displayed on the smartphone 8, and at the second alarm level, in addition to displaying the text message to call attention, vibration of the smartphone 8 is activated. Furthermore, at the third alarm level, it is possible to perform all of the following: displaying the text message to call attention on the smartphone 8, activating vibration, and outputting an alarm sound.

[0062] The infrasound detection device 4A outputs the analysis result information to the processing PC7. The processing PC7 is a computer equipped with a communication unit, a calculation unit, a display unit, an operation unit, and a storage unit, and receives the analysis result information from the infrasound detection device 4A through the communication unit. The processing PC7 records the analysis result information from the infrasound detection device 4A in the storage unit in chronological order. When the user instructs the display of the analysis result using the operation unit, the processing PC7 displays the analysis result recorded in the storage unit in chronological order on the display unit. The processing PC7 also transmits the analysis result information to the smartphone 8 through the communication unit. The smartphone 8 displays the analysis result information received through the processing PC7 on the display screen. Furthermore, the smartphone 8 performs an alarm operation according to the alarm level included in the analysis result information. In this way, the infrasound detection device 4A can support measures according to the state of the source of the infrasound.

[0063] The infrasound detection device 4A is realized, for example, by a computer including a calculation unit and a storage unit. The calculation unit controls the overall operation of the infrasound detection device 4A. The calculation unit includes a noise elimination unit 41, a slide processing unit 42, a frequency inverse conversion unit 43, and an analysis processing unit 45. The calculation unit executes an infrasound detection processing application to realize the functions of the noise elimination unit 41, the slide processing unit 42, the frequency inverse conversion unit 43, and the analysis processing unit 45.

[0064] The storage unit stores an infrasound detection processing application and information used for the arithmetic processing of the arithmetic unit. The storage unit includes a storage such as an HDD or SSD, or the memory 104 of Fig. 4. Note that the storage unit may be provided outside the infrasound detection device 4A as long as it is accessible by the infrasound detection device 4A.

[0065] 1 shows a configuration in which the infrasound detection device 4A includes, as components, the noise elimination unit 41, the slide processing unit 42, the frequency inverse conversion unit 43, and the analysis processing unit 45, but any of these components may be included in another device. For example, an external device that is provided separately from the infrasound detection device 4A and can communicate with the infrasound detection device 4A may include the noise elimination unit 41, and the infrasound detection device 4A may detect infrasound from a sound signal obtained by the external device.

[0066] The noise elimination unit 41 acquires the infrasound collected from the source by the infrasound microphone 5 and removes noise from the acquired infrasound. For example, the noise elimination unit 41 is an LPF that passes only the infrasound and removes high-frequency noise. The infrasound from which the high-frequency noise has been removed is output from the noise elimination unit 41 to the slide processing unit 42.

[0067] The slide processing unit 42 generates a sound signal by sliding the infrasound from which noise has been removed by the noise removal unit 41 to a predetermined frequency band. For example, the slide processing unit 42 generates an audible sound by raising the infrasound in a range of 4 to 5 octaves. The slide processing unit 42 may also change the frequency band of the infrasound to match the frequency band of the reference sound signal.

[0068] The frequency inverse conversion unit 43 generates a sound signal with a lowered low-frequency level and an increased high-frequency level based on the center frequency fo of the frequency band of the sound signal generated by the slide processing unit 42. For example, a sound signal having a linear characteristic that passes through the center frequency fo and descends from the high-frequency side to the low-frequency side is generated.

[0069] The analysis processing unit 45 analyzes the state of the source of the infrasound based on the result of comparing the sound signal generated by the frequency inverse conversion unit 43 with the reference signal. For example, the analysis processing unit 45 calculates the difference in amplitude between the analysis target sound signal, which is obtained by converting an infrasound into an audible sound, and a reference sound signal, which is obtained by converting an infrasound detected from a source under normal conditions into an audible sound, and compares the calculated difference value with a first threshold range. When the source is a large machine, the analysis processing unit 45 determines that an abnormality has occurred in the large machine when the difference in amplitude between the analysis target sound signal and the reference sound signal exceeds the upper limit of the first threshold range. Furthermore, when the difference value of the amplitude between the analysis target sound signal and the reference sound signal increases in a time series manner, the analysis processing unit 45 determines that the large machine is deteriorating with time. If the difference in amplitude between the analysis target sound signal and the reference sound signal is less than the lower limit of the first threshold range, the analysis processing unit 45 determines that the large machine is normal.

[0070] When the difference value of the amplitude between the analysis target sound signal and the reference sound signal exceeds the upper limit of the first threshold range, the analysis processing unit 45 compares the difference value with a second threshold range. When the difference value of the amplitude between the analysis target sound signal and the reference sound signal exceeds the upper limit of the second threshold range, the analysis processing unit 45 determines the warning level to be the highest, third stage warning level. When the difference value of the amplitude between the analysis target sound signal and the reference sound signal is within the second threshold range, the analysis processing unit 45 determines the warning level to be the second stage warning level. Furthermore, when the difference value of the amplitude between the analysis target sound signal and the reference sound signal is less than the lower limit of the second threshold range, the analysis processing unit 45 determines the warning level to be the lowest, first stage warning level.

[0071] The analysis processing unit 45 may use a machine learning model to determine the warning level. For example, when the amplitude information of the analysis target sound signal is input, the machine learning model infers and outputs a warning level for the source of the infrasound. The analysis processing unit 45 inputs the analysis target sound signal generated by the frequency inverse conversion unit 43 to the machine learning model, and outputs the warning level output by the machine learning model to the processing PC 7, including it in the analysis result information. This enables the analysis processing unit 45 to accurately determine the warning level for the source of infrasound.

[0072] The analysis processing unit 45 may also use a machine learning model to analyze the state of the source of the infrasound. For example, when amplitude information of the analysis target sound signal is input, the machine learning model infers and outputs the state of the source of the infrasound. The analysis processing unit 45 inputs the analysis target sound signal generated by the frequency inverse conversion unit 43 to the machine learning model, and outputs the state output by the machine learning model to the processing PC 7 by including it in the analysis result information. This enables the analysis processing unit 45 to accurately analyze the state of the source of the infrasound.

[0073] The flow of operations of the infrasound detection device 4A will be described. The noise elimination unit 41 acquires the infrasound collected by the infrasound microphone 5, and eliminates noise from the acquired infrasound. The slide processing unit 42 generates a sound signal by sliding the infrasound from which noise has been removed to a desired frequency band. The frequency inverse conversion unit 43 generates a sound signal by lowering the low-frequency side level and raising the high-frequency side level based on the center frequency of the frequency band of the sound signal. The analysis processing unit 45 analyzes the state of the source of the infrasound based on the comparison result between the sound signal generated by the frequency inverse conversion unit 43 and the reference signal. At this time, the analysis processing unit 45 may determine an alarm level according to the state of the source of the infrasound based on the comparison result, and set the determined alarm level in the smartphone 8 via the processing PC 7. By executing this method, the infrasound detection device 4A is able to detect infrasound and analyze the state of its source from the detected infrasound.

[0074] The functions of the noise elimination unit 41, the slide processing unit 42, the frequency inverse conversion unit 43, and the analysis processing unit 45 included in the infrasound detection device 4A are realized by, for example, the processing circuit shown in Fig. 4A or 4B. That is, the infrasound detection device 4A includes a processing circuit for executing the above-mentioned series of processes. The processing circuit may be dedicated hardware, or may be a CPU that executes a program stored in a memory.

[0075] Various aspects of the present disclosure are summarized below as appendices.

[0076] (Appendix 1) a frequency characteristic conversion unit that acquires the audible sound collected by the audible sound collection unit and generates a sound signal with a higher low-frequency level and a lower high-frequency level based on a center frequency of the frequency band of the acquired audible sound; a slide processing unit that generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit to an ultra-low frequency band audible to the human ear; an output processing unit that outputs the sound signal generated by the slide processing unit from a super low frequency sound output unit; An infrasound generating device characterized by: (Appendix 2) The frequency characteristic conversion unit cuts both ends of the frequency band of the audible sound, and increases the low-frequency side level and decreases the high-frequency side level of the sound signal with both ends of the frequency band cut. 2. The infrasound generating device according to claim 1, (Appendix 3) The slide processor generates a sound signal in a super-low frequency band by attenuating the sound signal in a range of 3 to 4 octaves. 3. The infrasound generating device according to claim 1 or 2, (Appendix 4) a frequency characteristic conversion unit that acquires the audible sound collected by the audible sound collection unit and generates a sound signal with a higher low-frequency level and a lower high-frequency level based on the center frequency of the frequency band of the acquired audible sound; a transmission-side slide processing unit that generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit to an ultra-low frequency band that is inaudible to the human ear; and a transmission-side output processing unit that outputs the sound signal generated by the transmission-side slide processing unit from an infrasonic sound output unit; a noise elimination unit that acquires a sound signal from the infrasound generating device collected by an infrasound collecting unit and eliminates noise from the acquired sound signal; a receiving-side slide processing unit that generates a sound signal by sliding the sound signal from which noise has been removed by the noise removal unit to an audible frequency band; a frequency inverse conversion unit that generates a sound signal with a lowered low-frequency level and a higher high-frequency level based on a center frequency of the frequency band of the sound signal generated by the receiving side slide processing unit; and and a receiving-side output processing unit that outputs the sound signal generated by the frequency inverse conversion unit from an audible sound output unit. 1. An infrasound transmission system comprising: (Appendix 5) The transmission side slide processing unit generates a sound signal in a super low frequency band by attenuating the sound signal in a range of 4 to 5 octaves. 5. The infrasound transmission system according to claim 4, characterized in that: (Appendix 6) A method for generating infrasound using an infrasound generator, comprising: A frequency characteristic conversion unit acquires the audible sound collected by the audible sound collection unit, and generates a sound signal in which the low-frequency side level is increased and the high-frequency side level is decreased based on the center frequency of the frequency band of the acquired audible sound; A step in which a slide processing unit generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit to an ultra-low frequency band audible to the human ear; An output processing unit outputs the sound signal generated by the slide processing unit from an ultra-low frequency sound output unit. A method for generating infrasound, comprising: (Appendix 7) A method for transmitting infrasound from an infrasound generating device to an infrasound detecting device, comprising: A frequency characteristic conversion unit acquires the audible sound collected by the audible sound collection unit, and generates a sound signal in which the low-frequency side level is increased and the high-frequency side level is decreased based on the center frequency of the frequency band of the acquired audible sound; A transmission side slide processing unit generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit to an extremely low frequency band that is inaudible to the human ear; A step in which a transmission-side output processing unit outputs the sound signal generated by the transmission-side slide processing unit from a super-low frequency sound output unit; A noise elimination unit acquires a sound signal from the infrasound generating device collected by an infrasound collection unit for infrasound frequencies, and eliminates noise from the acquired sound signal; A receiving side slide processing unit generates a sound signal by sliding the sound signal from which noise has been removed by the noise removal unit to an audible frequency band; A step in which a frequency inverse conversion unit generates a sound signal with a lowered low-frequency level and an increased high-frequency level based on a center frequency of the frequency band of the sound signal generated by the receiving side slide processing unit; a step in which a receiving side output processing unit outputs the sound signal generated by the frequency inverse conversion unit from an audible sound output unit. A method for transmitting infrasound comprising the steps of: (Appendix 8) a noise removal unit that acquires the infrasound collected by the infrasound collection unit and removes noise from the acquired infrasound; a slide processing unit that generates a sound signal by sliding the infrasound from which noise has been removed by the noise removal unit to a predetermined frequency band; a frequency inverse conversion unit that generates a sound signal with a lowered low-frequency level and an increased high-frequency level based on a center frequency of a frequency band of the sound signal generated by the slide processing unit; and an analysis processing unit that analyzes the state of a source of infrasound based on a comparison result between the sound signal generated by the frequency inverse conversion unit and a reference signal. An infrasound detection device characterized by: (Appendix 9) The analysis processing unit determines an alarm level according to a state of a source of infrasound based on a result of the comparison, and sets the determined alarm level in an alarm device that performs alarm processing according to the set alarm level. 9. The infrasound detection device according to claim 8, (Appendix 10) A method for detecting infrasound using an infrasound detection device, comprising: A noise elimination unit acquires the infrasound collected by the infrasound collection unit and eliminates noise from the acquired infrasound; A step in which a slide processing unit generates a sound signal by sliding the infrasound from which noise has been removed by the noise removal unit to a predetermined frequency band; A step in which a frequency inverse conversion unit generates a sound signal in which a low-frequency side level is lowered and a high-frequency side level is increased based on a center frequency of a frequency band of the sound signal generated by the slide processing unit; and a step of analyzing the state of the source of the infrasound based on a comparison result between the sound signal generated by the frequency inverse conversion unit and a reference signal by an analysis processing unit. A method for detecting infrasound comprising the steps of:

[0077] It is possible to combine the embodiments, modify any of the components of the embodiments, or omit any of the components of the embodiments. [Explanation of symbols]

[0078] 1,1A infrasound generator, 2 general-purpose microphone, 3 infrasound speaker, 4,4A infrasound detector, 5 infrasound microphone, 6 general-purpose speaker, 7 processing PC, 8 smartphone, 10 infrasound transmission system, 11 frequency characteristic conversion unit, 12,12A,42 slide processing unit, 13,44 output processing unit, 41 noise reduction unit, 42 slide processing unit, 43 frequency inverse conversion unit, 45 analysis processing unit, 100 input interface, 101 output interface, 102 processing circuit, 103 processor, 104 memory.

Claims

1. a frequency characteristic conversion unit that acquires the audible sound collected by the audible sound collection unit and generates a sound signal with a higher low-frequency level and a lower high-frequency level based on a center frequency of the frequency band of the acquired audible sound; a slide processing unit that generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit to an ultra-low frequency band audible to the human ear; an output processing unit that outputs the sound signal generated by the slide processing unit from a super low frequency sound output unit; An infrasound generating device characterized by:

2. The frequency characteristic conversion unit cuts both ends of the frequency band of the audible sound, and increases the low-frequency side level and decreases the high-frequency side level of the sound signal with both ends of the frequency band cut.

2. The infrasound generating device according to claim 1,

3. The slide processor generates a sound signal in a super-low frequency band by attenuating the sound signal in a range of 3 to 4 octaves.

3. The infrasound generating device according to claim 1 or 2.

4. a frequency characteristic conversion unit that acquires the audible sound collected by the audible sound collection unit and generates a sound signal with a higher low-frequency level and a lower high-frequency level based on the center frequency of the frequency band of the acquired audible sound; a transmission-side slide processing unit that generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit to an ultra-low frequency band that is inaudible to the human ear; and a transmission-side output processing unit that outputs the sound signal generated by the transmission-side slide processing unit from an infrasonic sound output unit; a noise elimination unit that acquires a sound signal from the infrasound generating device collected by an infrasound collecting unit and eliminates noise from the acquired sound signal; a receiving-side slide processing unit that generates a sound signal by sliding the sound signal from which noise has been removed by the noise removal unit to an audible frequency band; a frequency inverse conversion unit that generates a sound signal with a lowered low-frequency level and a higher high-frequency level based on a center frequency of the frequency band of the sound signal generated by the receiving side slide processing unit; and and a receiving-side output processing unit that outputs the sound signal generated by the frequency inverse conversion unit from an audible sound output unit.

1. An infrasound transmission system comprising:

5. The transmission side slide processing unit generates a sound signal in a super low frequency band by attenuating the sound signal in a range of 4 to 5 octaves.

5. The infrasound transmission system according to claim 4,

6. A method for generating infrasound using an infrasound generator, comprising: A frequency characteristic conversion unit acquires the audible sound collected by the audible sound collection unit, and generates a sound signal in which the low-frequency side level is increased and the high-frequency side level is decreased based on the center frequency of the frequency band of the acquired audible sound; A step in which a slide processing unit generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit to an ultra-low frequency band audible to the human ear; An output processing unit outputs the sound signal generated by the slide processing unit from an ultra-low frequency sound output unit. A method for generating infrasound, comprising:

7. A method for transmitting infrasound from an infrasound generating device to an infrasound detecting device, comprising: A frequency characteristic conversion unit acquires the audible sound collected by the audible sound collection unit, and generates a sound signal in which the low-frequency side level is increased and the high-frequency side level is decreased based on the center frequency of the frequency band of the acquired audible sound; A transmission side slide processing unit generates a sound signal by sliding the sound signal generated by the frequency characteristic conversion unit to an extremely low frequency band that is inaudible to the human ear; A step in which a transmission-side output processing unit outputs the sound signal generated by the transmission-side slide processing unit from a super-low frequency sound output unit; A noise elimination unit acquires a sound signal from the infrasound generating device collected by an infrasound collection unit for infrasound frequencies, and eliminates noise from the acquired sound signal; A receiving side slide processing unit generates a sound signal by sliding the sound signal from which noise has been removed by the noise removal unit to an audible frequency band; A step in which a frequency inverse conversion unit generates a sound signal with a lowered low-frequency level and an increased high-frequency level based on a center frequency of the frequency band of the sound signal generated by the receiving side slide processing unit; a step in which a receiving side output processing unit outputs the sound signal generated by the frequency inverse conversion unit from an audible sound output unit. A method for transmitting infrasound comprising the steps of:

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