JPH023126B2 - - Google Patents

Description

Detailed Description of the Invention This invention provides a sound source that can automatically measure and identify the type of sound source, that is, whether it is a ground sound source or a high-altitude sound source, and whether it is a fixed sound source or a moving sound source. The present invention relates to an automatic identification method and a device therefor.

As environmental issues related to sound sources become more prominent, there is an increasing need to not only measure the amount of noise but also clarify the types of noise sources. For example, if aircraft noise is to be measured, aircraft noise must be distinguished from other noises and only aircraft noise must be evaluated.

In this case, if the target to be identified is a very simple sine wave, or if a certain characteristic frequency component has a very high level, it may be possible to use a filter with the corresponding frequency, but If there are noises that have different components and have a large overall level, a simple filter will misidentify these noises and will not be able to distinguish them sufficiently. For this reason, further efforts have been made in the past.

Aircraft noise measurement usually involves monitoring a large number of measuring instruments placed around airports. In this case, according to the conventional method, aircraft noise can be identified by knowing in advance that the noise level is higher when an aircraft passes than at other times, and (1) the noise level increases, or (2)
Noise source identification and noise level measurement were performed based on the fact that the noise level exceeded a certain threshold for a certain period of time or more.

However, this conventional method lacks reliability. For example, if there is a road near the measurement point, it may not be possible to distinguish car noise from aircraft noise, or if the siren from a factory or police car continues at a certain level for a certain period of time, it will be mistaken for aircraft noise, making clear identification impossible. It was possible. Similar results were also caused by wind noise picked up by the microphone during strong winds. Moreover, because these factors have a complex effect, the conventional method of identifying the noise source as an aircraft or not has low reliability. Moreover, such a method cannot be used to distinguish between a fixed sound source, such as factory noise, and moving noise from a moving car.

This invention was made in an attempt to eliminate the above-mentioned drawbacks of the prior art, and it distinguishes between the type of noise source, whether it is on the ground or high in the air, and whether it is a fixed position or a moving one. It is an object of the present invention to provide an automatic sound source identification method and a device therefor that can clearly identify whether a sound source exists or not.

In order to achieve this object, according to the automatic sound source identification method of the present invention, the frequencies contained in the sound source to be identified and used for identification are displayed on substantially the same perpendicular line of the reflecting surface facing the sound source to be identified, and the A first sound receiving point is arranged at a first distance from the reflecting surface according to the angle of incidence of the sound source with respect to the reflecting surface, and the frequency included in the sound source to be identified and used for identification and the reflecting surface of the sound source are arranged. A second sound receiving point is disposed at a second distance from the reflecting surface that is smaller than the first distance according to an incident angle to the sound source, and the direct sound from the sound source and the sound reflected by the reflecting surface are A reflective surface is received at the first and second sound receiving points, and the sound pressure at each of these sound receiving points, the difference between the two sound pressures due to the presence or absence of interference, and the sound pressure Based on the temporal variation of the difference, the magnitude of the incident angle of the sound source from the sound receiving point to the reflecting surface and the presence or absence of movement are determined, thereby identifying the sound source.

In addition, the device according to the present invention is capable of detecting a frequency included in the sound source to be identified and used for identification on substantially the same perpendicular line to the reflecting surface facing the sound source to be identified and according to the incident angle of the sound source with respect to the reflecting surface. a first microphone disposed at a first distance from the reflecting surface; and the first distance corresponding to a frequency included in a sound source to be identified and used for identification and an incident angle of the sound source with respect to the reflecting surface. a second microphone disposed at a second smaller distance from the reflective surface; and a second microphone connected to these, and only a signal in a desired frequency band among the output signals of the first and second microphones. a pair of filters, a level difference detection circuit that outputs the difference between the output signal levels of these filters, a comparator that determines whether the output of the level difference detection circuit exceeds a certain level; A counter that counts the output of the comparator, a duration measurement circuit that integrates the operating time of this counter, and an output of the counter and an output of the duration measurement circuit are connected,
a discriminator circuit that identifies the type of the sound source from the outputs of both; a gate circuit whose signal passage/blocking is controlled by the output of the discriminator circuit; and one of the outputs of the first and second microphones and the gate circuit. A level holding circuit is connected between the gate circuits and holds a noise level signal, and when the discrimination circuit outputs, the gate circuit and the level holding circuit are controlled, and the noise level signal from the level holding circuit is transmitted to the gate circuit. It will be output via .

First, the principle of this invention will be explained.

In FIG. 1, M is a sound receiving point of a microphone or the like. The sound receiving point M is placed at a certain distance d ₁ from the reflector E having a horizontal reflecting surface in the sound source direction of the reflecting surface of the reflector. S is the target sound source. d ₂ is the distance of the sound source S from the reflector E.
Further, the angle between the straight line connecting the sound receiving point M and the sound S and the reflecting surface is defined as the angle of incidence (elevation angle). As the reflector, for example, the ground surface can be used (the ground surface can be considered as a perfect reflector of infinite size), or in the vertical direction, a fence, a side wall of a building, etc. can be used. , install a dedicated one if necessary.

In this way, when there is a reflective surface near the sound receiving point, the sound from the sound source S arriving at the sound receiving point M from the sound source is considered to be mainly divided into two paths of sound. In other words, the direct sound D that directly reaches the sound receiving point M from the sound source S
This is the reflected sound R that reaches the sound receiving point M after being reflected once by the reflector E. At the sound receiving point M, a combination of the direct sound D and the reflected sound R always exists. That is, the sound from the sound source S causes an interference phenomenon at the sound receiving point M due to the presence of the reflector. Although this interference phenomenon itself varies in degree, the sound source S
It occurs equally for all components of the sound generated from the . However, the effect of this interference phenomenon is especially remarkable for sound components that satisfy special conditions depending on the positional relationship between the reflector and the sound receiving point. That is, when considering the phase of these two sounds (sound waves) D and R, the distance d ₁ between the sound receiving point M and the reflector E, and the distance d ₂ from the sound source S to the reflector E, therefore, For specific wavelength components (thus, there are multiple) that are related to the path difference between direct sound and reflected sound (the path difference is an integer multiple of a half wavelength), there is a remarkable interference phenomenon that significantly changes the sound pressure level. arise.

In other words, if the angle of incidence of the sound source S, which is separated by d ₂ , is constant (d ₁ is constant), the path difference between the direct sound D and the reflected sound R from the sound source S is constant, and some Regarding the frequency components, see 2 above.
The sparse parts of the sound waves (concentration waves) that have passed through two paths,
As the dense parts overlap (become in phase) and strengthen each other, the sound pressure level at the sound receiving point doubles, increasing by 6 dB. In addition, for sound waves with other specific frequency components, the interference state is different even under the same conditions as above, and 2
As a result of the sparse and dense parts of the two sound waves overlapping (having opposite phases) and canceling each other out, the sound pressure at the sound receiving point becomes 0.

Furthermore, as a general characteristic of actual noise, the lower the frequency, the higher the energy, and the higher the frequency, the lower the energy. Among multiple frequency components exhibiting
It also has a large effect on the overall noise level.
Therefore, interference phenomena also occur with higher frequency components than the focused frequency component, and although significant interference effects occur under certain conditions, their level is small, and interference with the focused low frequency components occurs. It does not significantly disturb the effects of the phenomenon.

In addition, although actual noise is generally a mixture of many frequency components, due to the above-mentioned effects, the sound of frequency components corresponding to a certain fixed path difference that contributes to interference is The level is very different from that of . In other words, there is a kind of frequency selectivity. Therefore, when the sound source consists of frequency components within a narrow band of about 1/3 octave (such as the sound of an ambulance, amplified human voice broadcasts, or when some types of aircraft are the noise source), approximately An interference phenomenon substantially similar to that in the case of one frequency can be obtained. Note that when components near such frequencies are mixed, the interference state will not be completely stationary and will be accompanied by gradual level fluctuations.

Furthermore, even when the frequency of the sound source is accompanied by slight fluctuations (for example, noise from rotating machinery), the behavior is not significantly different from the one described above, and roughly the same phenomenon occurs.

As mentioned above, even if components other than the focused frequency are mixed, the interference effect that occurs in the sound of the focused frequency component is not significantly disturbed, and is almost the same as the effect that occurs when the sound has a single frequency. A similar effect can be obtained.

Note that in the case of a sound source that has sound components distributed over a wide range and is similar to so-called white noise, the desired effect cannot be obtained, but it is possible to identify noise sources in which specific frequency components are not significant. In this case, use a filter corresponding to the frequency of interest (e.g. 1/3 octave bandpass filter)
A desired effect can be obtained by attenuating unnecessary frequency components and further emphasizing the above-mentioned interference effect.

The characteristics of the signals obtained at the sound receiving point will be described below for different sound sources.

First, the sound source S is above the sound receiving point M (on the opposite side of the reflecting surface) and the distance d ₂ from the reflector E is the sound receiving point M.
is considered to be almost infinite compared to the distance d ₁ of the reflector E (d ₁ ≪ d ₂ ), and considering that it is stationary,
There is almost no difference in distance attenuation of sound between direct sound D and reflected sound R.
The sound pressure levels are almost the same.

Next, considering the path difference, since the sound source S is stationary, the mutual positional relationship of the sound receiving point M, the reflector E, etc. is constant, and the elevation angle from the sound receiving point (the direction from the sound receiving point to the sound source) is constant. The angle between the connecting straight line and the horizontal plane (incident angle)) Therefore, the path difference is also constant, so a certain interference effect occurs, and the sound pressure obtained at the sound receiving point M is steady and does not fluctuate. .

As mentioned above, when the sound source is far from the reflector (reflecting surface) and is fixed in position, an interference phenomenon occurs at the sound receiving point, and the resulting sound pressure is characterized by no fluctuation.

In reality, it is difficult to imagine a noise source that remains stationary at high altitude; generally, a noise source at high altitude is a moving sound source such as an aircraft. That is, the elevation angle of the sound source is the length of the path of the direct sound D and the indirect sound R (therefore,
The difference) will constantly change.

Next, a case will be described in which the sound source is far from the reflector and moves, so that the mutual positional relationship with the sound receiving point M, the reflector E, etc. is not constant.

In this case as well, it goes without saying that an interference phenomenon occurs with a certain frequency component of the sound wave from the sound source S, but in addition, since d ₁ is constant, the direct sound D and reflected sound R due to the value of d ₂ etc. The length of the path and therefore the path difference changes, and the interference state changes. Therefore, the sound source S
moves, and when d ₂ etc. change continuously, the sound pressure obtained at the sound receiving point as a result of the interference phenomenon will alternate between the two states described above, increasing by 6 dB. A certain sound pressure level can be obtained, or the sound pressure can become zero. In other words, fluctuations can be seen.

In this way, when the sound source is far from the reflector and its position moves, an interference phenomenon occurs at the sound receiving point, and the condition changes, so the resulting sound pressure changes. be.

Next, the sound source S is at approximately the same height as the sound receiving point M d ₂ (=d ₁ )
In other words, if we consider the case where the sound source S is close to the reflector E (the elevation angle is close to 0°), the path difference between the direct sound D and the reflected sound R becomes smaller and smaller than in the case described above. . Therefore, it can be considered that interference occurs only in the high frequency range, and almost no interference phenomenon occurs in the middle and low frequencies of the audible range that we deal with in noise measurements. In other words, in this case, there is no change due to increase or attenuation of sound pressure due to interference phenomena in the frequency band used in noise measurement, and therefore no fluctuations in sound pressure are observed even when the sound source moves. ing.

By the way, the above-mentioned phenomenon clearly appears when the sound source has only a single frequency, or when the level of sound at a specific frequency is particularly high. Therefore, when identifying such a sound source, we select and focus on frequency components of the sound source that are effective in identifying frequency components that are relatively high in level and are unique to the sound source. It is preferable to consider the setting of the sound receiving point and utilize the interference phenomenon that occurs near this frequency component.

Furthermore, since some actual noises are a mixture of various frequency components and are synthesized, the results of interference phenomena are often not clear. In this case, among the frequency components of the sound source, select and focus on frequency components that are effective in identifying the frequency components near the frequency components that are relatively high in level and are unique to the sound source, and at the same time take into account the setting of the sound receiving point. By selecting only this focused frequency using a filter and processing only the output signal of this filter, it is possible to cause the interference phenomenon to occur significantly and improve identification accuracy.

Although it is possible to identify the sound source to some extent based on the characteristics of each sound source obtained from a single sound receiving point as described above, depending on the noise, the level change may not be smooth and the level may vary. The overall level may change with small fluctuations.
In the case of such noise, if the presence or absence of an interference phenomenon is detected from changes in the output at one sound receiving point as described above, it is possible to clearly distinguish between the original level fluctuations of the noise and the level fluctuations caused by interference. There may also be cases where it is difficult to distinguish between the two.

Next, the principle for solving the above problem will be described.

As mentioned above, there is a fact that the interference state differs depending on the positional relationship between the sound receiving point, the sound source, and the reflector. A first sound receiving point is arranged at a first distance from the reflecting surface according to the frequency to be identified and the incident angle of the sound source to the reflecting surface, and the frequency included in the sound source to be identified and used for identification and the A second sound receiving point is disposed at a second distance from the reflecting surface that is smaller than the first distance according to the incident angle of the sound source with respect to the reflecting surface, and the direct sound from the sound source and the reflecting surface are The sound reflected by the reflective surface is received at the first and second sound receiving points, and the sound pressure at each of these sound receiving points, the difference between the two sound pressures due to the presence or absence of interference, and Based on the temporal variation of the difference in sound pressure, the magnitude of the incident angle of the sound source from the sound receiving point to the reflecting surface and the presence or absence of movement are determined, and this is used for identifying the sound source.

In this way, the level fluctuation inherent in the noise from the sound source as described above occurs equally at the two sound receiving points, and is therefore canceled out and not output as a difference.

On the other hand, since there is a difference in the path difference between the two direct and indirect sounds from the sound source to each sound receiving point, the degree of interference that occurs in a certain frequency component of interest at the two sound receiving points also differs. It turns out.
Therefore, when an interference phenomenon occurs, the sound pressure obtained from the two sound receiving points will be different, and the manner of fluctuation will also be different. Therefore, by comparing the sound pressures at the two sound receiving points, it is possible to determine whether or not an interference phenomenon is occurring. That is, if there is no difference between the sound pressures obtained at the two sound receiving points, there is no interference phenomenon, and if there is a difference between the sound pressures, it can be seen that an interference phenomenon has occurred. Further, if this difference is constant, it is determined that the sound source is a fixed sound source, and if both sound pressures vary, and therefore the difference varies, it can be determined that the sound source is a moving sound source. By installing two sound receiving points as described above, it becomes possible to more appropriately identify the sound source.

The reason for arranging the two sound receiving points on substantially the same perpendicular line of the reflecting surface facing the sound source is to ensure that for a sound source with a large elevation angle, the path difference between the two sound receiving points is greatly different, thus preventing interference. This is because the conditions are different and a large differential output can be obtained.

Above, we have described the principle of classifying and identifying sound sources by extracting the characteristics caused by the properties of the sound source when the reflecting surface is a horizontal surface.However, since exactly the same phenomenon occurs when the reflecting surface is a vertical surface, By using a reflector with a surface and arranging two sound receiving points on substantially the same perpendicular line to this reflective surface, it is possible to determine whether a sound source located at a long distance in the horizontal direction from this vertical reflective surface is a fixed sound source. Alternatively, depending on whether the source is a moving sound source, sound pressures having different characteristics can be obtained at the sound receiving point, making it possible to identify ground sounds in the same way as described above. In this case, a side wall or wall of a building is used as a vertical reflector, or a vertical reflective surface is appropriately installed.

As described above, according to the type of sound source, the interference effect may or may not occur depending on the positional relationship between the sound source, the sound receiving point, and the reflecting surface, and the degree of the interference phenomenon is constant. Focusing on the phenomenon of change in intensity, sound sources are classified and identified based on the magnitude of the angle of incidence with respect to a reflecting surface, or based on whether or not they move.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, identification of aircraft noise (in the case of a sound source moving over a long distance in a vertical direction) will be explained as an example. Aircraft normally fly at a considerable altitude. This invention is
When an aircraft approaches and moves away from this measurement point,
The difference in interference effect occurring at two microphone positions is utilized. This will be explained below with reference to FIG. The frequency components used for identification only need to be included in the sound source. If there is a frequency component with a relatively high level that is unique to the sound source, it is sufficient to focus on this frequency component, or as in this example, the frequency component used for identification may be However, if it is an aircraft and contains frequency components in a relatively wide range, focus on frequency components with relatively high levels among the frequency components included in the sound source, and use a bandpass filter that corresponds to this frequency. The interference phenomenon of this frequency component is then used for identification. In aircraft, it is generally known that frequency components near 200 Hz are strong, so in this embodiment, for example, attention will be paid to this 200 Hz frequency component.

Note that the frequency selection in such a case does not need to be very strict and can be selected as appropriate.

S is the aircraft that is the sound source, M ₁ and M ₂ are the first and second sound receiving points, respectively, and are arranged approximately on the same perpendicular line to the ground surface E (horizontal reflective surface) that serves as the reflector. Ru. D ₁ and D ₂ are direct sounds arriving at the respective sound receiving points, and R ₁ and R ₂ are similarly reflected sounds.

The distance from the reflecting surface where the two sound receiving points M ₁ and M ₂ are installed depends on the range of the elevation angle (angle of incidence) of the aircraft at the sound receiving point to be identified and the frequency used for the above-mentioned identification. to be determined.

For example, let's take a case where an aircraft is used to identify when an aircraft passes through an elevation angle of 20 degrees, passes through an elevation angle of 45 degrees, and then flies within an elevation angle of 20 degrees again, and the above-mentioned frequency component near 200 Hz is used for identification.

Further, the condition is that during this change in elevation angle, the nodal portion due to interference is observed at least once at each of the two sound receiving points, and the sound pressure at the sound receiving point becomes 0.

In this case, the first sound receiving point M ₁ at the top has a larger path difference than the second sound receiving point M ₂ at the bottom, and therefore, as the elevation angle increases, the 200 Hz interference phenomenon occurs first and the sound pressure decreases to 0. becomes. When the above-mentioned elevation angle is 20 degrees, the following condition is found: 2Hsinθ=λ/2.

Here, H is the distance between the sound receiving point and the reflecting surface.
Further, λ is the wavelength, which can be calculated as 1.7 m in the case of 200 Hz. Therefore, H is 1.2 m, and at a sound receiving point at this distance, interference occurs in the 200 Hz frequency component when the elevation angle is 20 degrees, and the sound pressure at the sound receiving point becomes 0. Therefore, the upper first sound receiving point _M1 is installed at a distance of 1.2 m or more from the reflecting surface.

In addition, at the second sound receiving point _M2 at the bottom, when the elevation angle is 45 degrees, an interference phenomenon occurs and the sound pressure becomes 0.
The distance of M ₂ from the reflective surface is as described above,
It can be calculated as 0.6m. Therefore, the second sound receiving point _M2 at the bottom may be installed at a distance of 0.6 m or less from the reflecting surface.

If the two sound receiving points M ₁ and M ₂ are installed in this manner, the sign of the difference output between the two sound receiving points will be reversed at least twice if the aircraft moves within the above-mentioned elevation angle range.

Now, the sound source S, which is an aircraft, is the microphone M ₁ ,
When located far away from M ₂ , the sound source appears to be close to the ground surface. That is,
The elevation angle of the sound source is small. For this reason, there is not much difference between the paths of direct sound and indirect sound that enter microphones M ₁ and M ₂ , respectively, and as explained in the principle above, the frequency at which direct sound and reflected sound interfere and influence becomes extremely high, and no significant interference phenomenon is observed in the 200Hz component that we are focusing on.

Furthermore, since the distance between the microphones M ₁ and M ₂ is negligibly small compared to the distance to the sound source S, the intensities of the sounds reaching the microphones M ₁ and M ₂ are almost the same. In other words, sound source S
The difference in distance attenuation between microphone M ₁ and microphone M ₂ is negligibly small. in the end,
There is almost no difference in sound pressure between the two sound receiving points.

Note that at this time, the noise level is not high and is not suitable for appropriate sound source determination.

Next, we will discuss the case where an aircraft approaches and approaches above the microphone while increasing its elevation angle.

At this time, each microphone M ₁ , M ₂
Because the path difference between the direct sound and the indirect sound increases, an interference phenomenon occurs. Also, microphones M ₁ and M ₂
Since the respective distances to the sound source S and S are different, the interference phenomena are also different. temporarily microphone
If the direct sound and reflected sound arrive at M ₁ in the same phase, and at this time, they arrive at microphone M ₂ in opposite phases, there will be interference between microphones M ₁ and M ₂ in a certain frequency range. A large difference occurs in the sound pressure level. Now, as the aircraft moves, the elevation angle becomes maximum.During this period, the interference condition changes from moment to moment, and therefore the level difference between the two microphones increases, decreases, or reverses as the aircraft moves. .

After that, the aircraft moves away again and the noise level decreases. This process is exactly the opposite of the process described above. That is, this is a process in which the elevation angle decreases from the maximum elevation angle.

Incidentally, since the aircraft that is the source of the sound is actually always moving in the sky, the above-mentioned state changes continuously. In other words, when the two microphones are located far away, there is no difference in sound pressure level between them, and as they get closer, the sound pressure level of one microphone becomes higher or lower than the other microphone. , this phenomenon is repeated. Further, after passing, the difference in sound pressure level between the two microphones disappears as the sound source moves farther away. Therefore, aircraft noise can be identified by comparing the outputs of the two microphones M ₁ and M ₂ separately to confirm the above-mentioned phenomenon. Furthermore, if the difference between the outputs of the two microphones M ₁ and M ₂ is taken, the above-mentioned phenomenon can be directly obtained as an output signal.

Figure 3A shows two such microphones M ₁ ,
This shows the difference in the output of M ₂ for the above case, and shows an aircraft coming from a distance, passing over the sound receiving point, and then flying away. Note that FIG. 3B shows, for example, the output of the microphone M ₁ recorded on a level recorder, and since it is difficult to extract the fluctuation of the interference phenomenon from this waveform, the difference between the outputs of the two microphones M ₁ and M ₂ is It takes .

In FIGS. 3A and 3B, there is almost no difference in sound pressure level between the microphones M ₁ and M ₂ until the time at point a because the aircraft, which is the sound source, is located far away. Between points a and b, there is a time when the aircraft approaches and a difference appears in the sound pressure level of microphones M ₁ and M ₂ , and the level difference between M ₁ and M ₂ becomes large or small many times. ing.
In other words, this is a time period in which a large amount of interference occurs and is also fluctuating. Further, at a time after point b, the aircraft moves away, and the level difference between the microphones M ₁ and M ₂ disappears, as in the area before point a.

For non-aircraft noise, the noise level is considered to be 3rd level.
Even if a waveform similar to that shown in Figure B is obtained, the signal (not shown) indicating the level difference between the microphones M ₁ and M ₂ at that time will not have a fluctuating waveform as shown in Figure 3A. It can be determined that there is no

Second, identification of vehicle noise traveling on the road (in the case of a ground-moving sound source) will be described.

Cars are also a type of moving sound source, and the direction of the reflecting surface, the installation position of the two sound receiving points (microphones),
Identification can be performed in the same way as in the case of the above-mentioned aircraft, if consideration is given to the frequency components used for identification and the range of change in the angle of incidence. That is, automobile noise has a sound source S near the ground and moves horizontally on the road. Therefore, in this measurement method, instead of using a horizontal reflecting surface, the reflector B is provided with the reflecting surface vertical as shown in FIG. 4 (the side wall surface of the building may also be used). In addition, two microphones M ₁ and M ₂ are installed near the reflecting surface on substantially the same perpendicular line (horizontal direction) to the reflecting surface of the reflector B, keeping an appropriate distance therebetween.

Specifically, as in the case of the aircraft mentioned above,
A 200Hz signal will be used for identification, and a first sound receiving point _M1 will be placed at a distance of 1.2 m or more above the reflecting surface B, and a second sound receiving point _M2 will be placed at a distance of 0.6 m above the reflecting surface B. Just set it up. Of course, this is just an example, and other frequencies and other sound receiving point distances may be selected.

The interference between direct sound and reflected sound when a car passes is similar to that of an aircraft, and the distance to the sound source, the car, is much larger than the distance between microphones M ₁ and M ₂ and the distance from each microphone to reflector B. For example, (if the angle of incidence from the sound source to the reflecting surface at the measurement point is relatively large), there will be a difference in sound pressure level due to interference between the microphones M ₁ and M ₂ due to the influence of the reflector B, and this level will increase as the sound source moves. The difference will change. Therefore, it can be identified in the same way as in the case of the aircraft described above.

Third, identification of fixed sound sources (factory noise or ground fixed sound sources such as factory sirens) will be explained.

A major issue may arise as to whether the noise level on the boundary line of a factory, as stipulated by the Noise Control Act, is factory noise or other noise, such as traffic noise. Here, various machines, sirens, etc. that are noise sources in the factory are fixed sound sources.

When it is desired to identify a fixed sound source on the ground in this manner, microphones M ₁ and M ₂ and a reflector B are installed in the same manner as shown in FIG. 4, similar to the identification of automobile noise. Of course, the reflector B may be a door or a wall of a factory.

As is clear from the above explanation of the principle, the angle of incidence is constant for a fixed sound source, and even if interference occurs, its fluctuation is not significant. Therefore, even if the absolute value of the noise level is large, the two microphones M ₁ and M ₂
There is almost no variation in the output difference. This makes it possible to identify fixed sound sources.

As is clear from the above description, according to the present invention, two microphones M ₁ and M ₂ and a reflecting surface are used, and the difference between the output levels of the two microphones is determined by paying attention to the installation direction of the reflecting surfaces, etc. By doing so, you can easily distinguish between moving sound sources and fixed sound sources, and between overhead noise and ground noise.

Based on the above facts, Figures 5A and 5B respectively show the level difference between the microphones and the output waveform of the reference microphone when the microphones M ₁ and M ₂ are installed as shown in Figure 2. This is an example where the purpose is to identify aircraft noise.

As shown in the figure, the noise level of the automobile noise X has a certain value, but the level difference does not vary much. Fixed sound source Z from factory siren
is the highest in terms of noise level, but hardly appears as a level difference. Aircraft noise Y has a noise level intermediate between the two noises X and Z, but it is the target moving noise source, and the fluctuation in the level difference is the most noticeable.By determining this characteristic, it is determined that it is aircraft noise. identify At the same time, other sound sources can be identified to some extent, although the accuracy is lower.

Incidentally, if, for example, it is desired to more clearly identify automobile noise, the settings as shown in FIG. 4 may be used, and in the case of automobile noise, the fluctuation in the level difference appears the largest.

FIG. 6 shows a specific embodiment of the present invention, and shows a specific configuration for outputting only the identified noise (for example, aircraft noise) based on the results shown in FIGS. 5A and 5B. There is.

According to the figure, two microphones 1, 1',
two filters 2, 2', a level difference detection circuit 3,
two comparators 4, 4', two counters 5, 5',
two duration measurement circuits 6, 6', a discrimination circuit 7,
A level holding circuit 8 and a gate circuit 9 are shown.

The microphones 1, 1' are set as shown in FIG. 2 or 4 depending on the sound source to be identified. That is, for example, when identifying aircraft noise, the reflector B is placed in parallel with an appropriate distance in the substantially perpendicular direction near the horizontal reflecting surface of the reflector E, and when identifying automobile noise, the reflector B is placed vertically. are placed in parallel in the vicinity of the front of the reflective surface of the reflector at an appropriate distance in the substantially perpendicular direction. The outputs of the microphones 1 and 1' are:
They are connected to filters 2 and 2', respectively, and the outputs of both filters are connected to a level difference detection circuit 3. Filters 2 and 2' use appropriate frequencies effective for identification (for example, 200Hz for aircraft identification).
Only the nearby signals are passed through, and the S/S of the identification signal is
This is to improve the N ratio and make the interference phenomenon more clear. Therefore, if the sound source to be identified is different, a signal near the frequency that is unique to the noise or the main component of the noise is passed through.

The level difference detection circuit 3 converts the outputs of both microphones into DC (output signal level) and then calculates the difference between the output of one microphone and the output of the other microphone, for example, as shown in Fig. 3A. This is what gets the output. For example, it can be configured to include a group of operational amplifiers.

The output of this level difference detection circuit passes through two systems of comparators 4, 4', counters 5, 5', and duration measuring circuits 6, 6', respectively. In principle, one system may be sufficient as these systems, but in this embodiment, two systems are provided in order to cope with the case where the output is biased toward the positive or negative side due to fluctuations at the zero level.
That is, the comparator 4 has a threshold value on the plus side of FIG. 3A, and determines when the input signal exceeds this threshold value, and outputs "1", which is sent to the counter. On the other hand, the comparator 4' has a threshold value on the negative side, and determines when the input signal exceeds this threshold value, and sends an output "1" to the counter.

The counters 5, 5' count the output circuits of the comparators 4, 4', respectively, and send the outputs of the comparators 4, 4' to the duration measuring circuits 6, 6'.

The duration measuring circuits 6, 6' are for detecting the presence or absence of the output of the counters 5, 5', and detecting the operating time of the counters and thus the period of the counted signal.

The discrimination circuit 7 discriminates whether the noise meets predetermined conditions based on the outputs of the counters 5, 5' and the duration measuring circuits 6, 6', and controls the gate circuit 9 to pass or block the signal. For example, the gate circuit 9 is opened only when the count value of the counter 5 is a certain value or more and the operation time of the counter by the duration measuring circuit 6 is a certain time or more (corresponding to the case where the signal is a certain frequency or less). Conditions are set so that the signal input to the gate circuit 9 is allowed to pass. The setting conditions are determined to be optimal for each sound source to be identified, such as aircraft or automobiles.

In the above description, the threshold levels of the comparators 4 and 4' and the discrimination conditions of the discrimination circuit 7 are determined empirically for each type of noise to be discriminated.

The level holding circuit 8 is a memory that stores and holds the output signal of the reference microphone 1 and hence the noise level, and works in conjunction with the gate circuit 9 to transmit the necessary noise level signal to the gate circuit when the discrimination circuit 7 determines that the noise is to be identified. 9. Note that this level holding circuit 8 continuously and sequentially stores noise level signals for a certain period of time at all times, and is controlled by a discrimination circuit to sequentially send out signals when the gate circuit 9 is opened to reproduce the waveform. It is configured as a circuit, and noise identified as a waveform is obtained from the output of the gate circuit 9.

Next, the operation of this embodiment will be explained.

Install microphones 1 and 1' as shown in Figure 2,
Assume that the input is as shown in FIG. 5B. At this time, the output of the level difference detection circuit 3 is as shown in FIG. 5A. Here, if the threshold levels of comparators 4 and 4' are set to +4 dB and -4 dB, respectively, then
Comparators 4, 4' operate only on the waveform Y portion of FIG. 5B, and therefore counters 5, 5' count only on the waveform Y portion of FIG. 5B.

By the way, for example, in the case of aircraft noise, the level difference between microphones 1 and 1' can be repeated within a few seconds, be positive,
Since it is known in advance that this will appear as a negative value, these conditions are set in the discrimination circuit 7. If you do this, counters 5 and 5' will be counted several times or more.
If the input signal appears on the positive or negative side at intervals of several seconds, the discrimination circuit 7 determines that the input signal is aircraft noise and gives an output command to the gate circuit 9. Therefore, the data stored in the level holding circuit 8 is taken out as an output via the gate circuit 9. This output may be recorded on recording paper or simply displayed on a meter or the like.

Note that the fluctuation state of the level of other microphones relative to the reference microphone and the repetition period are not necessarily constant depending on the installation location of the microphone and the flight course of the aircraft, so the conditions for the above-mentioned determination will be changed depending on the situation at the measurement location. There is a need.

Similarly, for ground moving sound sources such as automobiles, the configuration is exactly the same, except that the reflective surface, the installation state of the two microphones, and the discrimination conditions are changed. In addition, in the case of identifying a fixed sound source, it is sufficient to send out the value only when there is no change in the level difference between both microphones as a signal from the gate circuit 9, and block the part where the phenomenon occurs when the sound source is a moving one. .

In addition, if multiple sets of the above-mentioned reflective surface and a pair of microphones are installed in different juxtaposed directions, and the recording is made in multiple channels, it is possible to identify an aircraft, a car or not, and a train at the same point. Needless to say, it becomes possible to perform a wide variety of identifications at the same time.

This invention is not limited to the above embodiments, but includes various modifications within the scope of the technical idea of this invention.

The present invention has the above-described method and configuration.
It is possible to provide an automatic sound source identification method and a device therefor that can clearly identify the type of sound source based on its distance from a reflecting surface, whether it is a moving sound source, etc.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of this invention, Fig. 2 is an explanatory diagram of an embodiment of this invention, Figs. 3A and 3B.
The figures are an explanatory diagram of the operation of the embodiment of Fig. 2, Fig. 4 is an explanatory diagram of another embodiment of the invention, Figs.
Figure B is a comprehensive operational explanatory diagram of the embodiment shown in Figure 2, and Figure 6
The figure is a system diagram of a specific embodiment of the present invention. S...Sound source, M...Sound receiving point, D...Direct sound, R
...Indirect sound, E, B...Reflecting surface (reflector), 1,
1'...Microphone, 2, 2'...Filter, 3
...Level difference detection circuit, 4, 4'...Comparator, 5,
5'... Counter, 6, 6'... Continuation time measuring circuit, 7... Discrimination circuit, 8... Level holding circuit, 9
...gate circuit.

Claims (1)

[Scope of Claims] 1. On substantially the same perpendicular line to the reflecting surface facing the sound source to be identified, the above-mentioned sound source is included in the sound source to be identified and is based on the frequency used for identification and the angle of incidence of the sound source with respect to the reflective surface. a first distance from a reflective surface;
a second sound receiving point from the reflecting surface that is smaller than the first distance according to the frequency included in the sound source to be identified and used for identification and the angle of incidence of the sound source with respect to the reflecting surface; A second sound receiving point is arranged at a distance, and the direct sound from the sound source and the reflecting surface reflected by the reflecting surface are received at the first and second sound receiving points, respectively, and these are The incidence of the sound source on the reflecting surface from the sound receiving point is based on the sound pressure at each sound receiving point, the difference between the two sound pressures due to the presence or absence of interference, and the temporal fluctuation of the difference in sound pressure. An automatic sound source identification method that identifies the sound source by determining the size of the corner and the presence or absence of movement. 2. On substantially the same perpendicular line of the reflecting surface facing the sound source to be identified, a first beam from the reflecting surface corresponding to the frequency included in the sound source to be identified and used for identification and the angle of incidence of the sound source with respect to the reflecting surface. a first microphone disposed at a distance from the reflecting surface that is smaller than the first distance according to the frequency included in the sound source to be identified and used for identification and the angle of incidence of the sound source with respect to the reflecting surface. a second microphone disposed at a second distance from the first and second microphones, respectively connected to the first and second microphones;
a filter that allows only signals in a desired frequency band to pass among the output signals of the microphone; a level difference detection circuit that outputs a difference between the output signal levels of these filters; a comparator that determines whether or not the
A counter that counts the output of this comparator, a duration measurement circuit that integrates the operating time of this counter, and an output of the counter and an output of the duration measurement circuit are connected, and the type of the sound source is identified from the outputs of both. a discriminating circuit for detecting a noise level signal; a gate circuit for controlling passage/blocking of a signal by the output of the discriminating circuit; and a level holding circuit to hold the sound source, and when the discrimination circuit outputs, the gate circuit and the level holding circuit are controlled to output the noise level signal from the level holding circuit via the gate circuit. circuit.