JPH0286397A - Microphone array - Google Patents

Abstract

PURPOSE:To improve an S/N by arranging microphones in such a way that the widest interval between adjacent planes is a half or nearly a half the wavelength of a sound of the upper limit frequency of the frequency band of an input object. CONSTITUTION:Two microphones 1, 2 are arranged at an interval of (d) and the interval (d) is selected to a half the wavelength of the sound having the upper limit frequency of the frequency band of an input object. Then the microphones 1, 2 are arranged at a interval of d=lambda4k/2, where lambda4k is the wavelength of the sound at the limit frequency and the frequency band is 0-4kHz. When the interval (d) of the microphones is selected to be lambda4k/2 in this way, that is, the interval is a half the wavelength of the sound at the band upper limit frequency, the S/N improvement PF is best. Thus, the spatial areasing being the most effective factor of the improvement quantity of the S/N is prevented from being generated and the S/N improving quantity at a low frequency is best improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a microphone array in which a plurality of microphones are specially arranged and is suitable for a device that suppresses noise.

[Prior Art] Conventionally, microphone arrays and methods have been proposed that suppress noise by arranging a plurality of microphones.

One method is to place microphones at intervals of 1/2 the wavelength of the sound at the center frequency of the human-powered target signal (target signal), and sharpen the directivity with respect to the target signal. This is a microphone array that suppresses noise. The other one is from the document Kaneda: ASSP-34pp.
This method was proposed in 1391-1400 '86, and is a method of suppressing noise by forming a directional blind spot in the direction of noise arrival. This method detects the direction of arrival of noise by calculating the correlation between the human input signals of each microphone, and suppresses the noise by forming a directional blind spot in that direction.

[Problems to be Solved by the Invention] However, the microphone array in the above-mentioned conventional technology is effective when the target signal that is actually subject to human input has a relatively narrow band. However, there is a problem in that a sufficient effect cannot be obtained when the signal has a wide band. On the other hand, the conventional method of suppressing noise by forming a directional blind spot in the direction of noise arrival has the problem that it cannot be directly adapted to the microphone arrangement proposed so far.

The present invention was created to solve the above problems, and maximizes the performance (improvement of S/H) of a device that suppresses noise by forming a directional blind spot in the direction of noise arrival. The purpose of the present invention is to provide a microphone array for

[Means for Solving the Problems] The configuration of the microphone array of the present invention for achieving the above object is a microphone array in which a plurality of microphones are arranged linearly, in a plane, or in a three-dimensional shape, and one Assuming a group of planes that are parallel to each other and include the above-mentioned microphones, the distance between adjacent planes that is the widest among the planes corresponds to the upper limit frequency of the frequency band to be input. Each of the microphones is arranged so that the length thereof is half or approximately half the wavelength.

[Operation] The present invention is characterized in that the factor that reduces the performance (amount of improvement in S, /H) of a device that suppresses noise by forming a directional blind spot with respect to the direction of arrival of noise is the increase in spatial aliasing. We focused on the performance deterioration in the low frequency range and the performance deterioration in the low frequency range that occurs when the microphone spacing is narrow. It was discovered that the amount of sound is minimized when the length is half the wavelength of the sound, and when configuring a microphone array with multiple microphone elements, the above relationship or almost the above relationship can be obtained in at least a part of the microphone elements. By arranging the microphones, the occurrence of spatial aliasing is prevented, and the deterioration in low frequency performance is minimized, thereby maximizing the amount of improvement in S/N in the above device.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings. First, the basic structure and operation of the present invention will be described.

FIG. 1 is a basic layout diagram of a microphone array showing a first embodiment of the present invention. In this embodiment, two microphones 1.2 are arranged at an interval d, and the interval d is set to be half the wavelength of the sound at the upper limit frequency of the frequency band to be input (hereinafter referred to as band upper limit frequency). . Now, if the above frequency band is 0 to 4kHz and the wavelength of the sound at the upper limit frequency of the band is expressed as λ4, the microphone 1.2 will be d=λ4/2.
are arranged at intervals of

Figure 2 shows the microphone spacing and S/N in the first embodiment.
It is a relationship diagram of the amount of improvement, and in the first embodiment, the target signal S
The noise N comes from a direction at an angle θ from the line connecting microphones 1 and 2, and the noise N comes from a direction at an angle θ from the line. An example of measuring the improvement in signal-to-noise ratio S/N (ff1PF) when the microphone interval d is variously changed when the microphone is coming from the direction shown in FIG. The horizontal axis represents the ratio of the interval d to the wavelength λ4k, and each signal S, N is assumed to be white noise of 0 to 4 kHz. ○
Curve A plotted with marks is θ1=30°, θ0=160
Curve B, which shows the relationship between d/λ and PF [dB] when the angle is θ, is similarly plotted in the mouth.

=40°, θ. = 150°, the curve C plotted with Δ marks shows the cases when θ, = 140° and θ, = 60°. As is clear from the figure, the S/N improvement amount PF has the best value when the microphone interval d is d=λ4/2, that is, when it is half the wavelength of the sound of the band upper limit frequency. The difference in S/H improvement amount PF depending on the microphone spacing d is that when d>λ4/2, the amount of improvement in low-frequency S/H increases, and when d>λ4/2, the amount of improvement in high-frequency S/H. This is thought to be due to the dependence on Therefore, each cause is considered to be as follows.

■When d becomes small (d<λ4/2), in the low range,
Since the sensitivity in the direction of the target signal S decreases, the S/N improvement amount PF decreases.

■When d becomes large (d>λ, 2/2), in the high range,
Since spatial aliasing occurs, a directional blind spot that cannot be controlled other than the direction of noise arrival is formed, and the S/N improvement amount PF decreases.

It can be seen from the measurement results in Figure 2 that the influence of ■ is greater than that of ■. In the above measurement, the direction of arrival of the noise is actually θ. Considering the arrival time difference of sound waves with respect to the change in , the apparent microphone interval r (distance difference in the arrival direction of noise) is r = d・cos θ. It is expressed as In this case, d is the maximum value of r, and the condition in which spatial aliasing does not occur is that d as the maximum value of r is λ4/
2, and the condition in which the decrease in sensitivity of ■ does not occur is that d.
This is the case when d>λ4. That is, microphone 2
The interval d in the case of
2 is optimal.

Next, we will discuss the case where the number of microphones is increased and they are arranged in a straight line. FIG. 3 is a layout diagram of a linearly arranged microphone array showing a second embodiment of the present invention. In this embodiment, three microphones 1 and 2.3 are arranged in a straight line with microphone 3 located outside microphone 1.2, and the distance d between microphones 1.2 and 2.3 is d, respectively the band upper limit frequency (4
It is arranged so that it is half λ4 of the sound wavelength λ, which is assumed to be kHz.

Figure 4 shows the microphone spacing and S/N in the second embodiment.
It is a relational diagram of the amount of improvement, and shows the amount of improvement in S/N when the microphone interval d2 side is changed. In Fig. 3, the target signal S comes from a direction of 90 degrees to the microphone array, the noise N comes from a direction of 30 degrees, and the noise N is 18 degrees.
It is assumed that the light comes from the 0° direction. As is clear from this relationship diagram, microphone 3 is different from microphone 1.2.
It can be seen that the amount of improvement in S/N is the best if it is provided outside of , and d is set to λ4J2. At this time, microphone 3
If it is placed between 1.2, spatial aliasing does not occur, but since the microphones are placed very close to each other, the amount of improvement in low frequency S/H deteriorates. The same thing can be said even if the number of microphones increases. In other words, when microphones are arranged in a straight line, the distance between adjacent microphones is set to 1/1/2 of the wavelength of the sound at the upper limit frequency of the band.
It is best to set it to 2.

Furthermore, a case where microphones are arranged two-dimensionally in a plane will be described. FIGS. 5(a) and 5(b) show the third embodiment of the present invention.
FIG. 2 is a layout diagram of a microphone array arranged in a plane according to an embodiment. In a two-dimensional arrangement, assuming that the maximum value of the apparent distance between two adjacent microphones is dmax assuming all directions of sound arrival, the condition under which spatial aliasing does not occur is dmax<λ4 ni/2
It is.

The example (2L) shows a two-dimensional arrangement of microphones l2 and 3 on the third side, each of which is arranged at the apex of a triangle. In this case, the maximum value d m a x of the apparent distance between two adjacent microphones
is the distance between the line connecting microphones 2.3 and microphone l. In this way, the maximum value dmax of the apparent microphone spacing does not necessarily match the actual microphone spacing d.

As in the conventional method, the actual distance between each microphone d is λ.

If placed at /2, spatial aliasing will not occur, but
The array length becomes smaller than when dmax is set to λ4/2. However, for low frequencies, it is desirable to place the microphones as far apart as possible. Therefore, in order to arrange the microphones as far apart as possible under the condition that spatial aliasing does not occur in a two-dimensional arrangement, the maximum value of the apparent microphone spacing d m
It is optimal to set a x to 1/2 of the wavelength λ4 of the sound at the upper limit frequency of the band. That is, at this time, the amount of S/N improvement becomes maximum. (b) shows four microphones l, 2, 3.
4 shows a two-dimensional arrangement of three microphones 1.
This is an example of a two-dimensional arrangement in which microphones 2 and 3 are arranged at the vertices of a triangle and on the circumference, and the microphone 4 is arranged at the center of the circle. The maximum value of the apparent microphone spacing d m a x in this case is the spacing d between each microphone 1.2.3 and the microphone 4, and this spacing d corresponds to the sound wavelength λ4. Four microphones 1 and 23.4 are arranged so that the number of microphones is 1/2.

FIG. 6 shows a relationship between the microphone spacing and the S/N improvement amount in the third embodiment shown in FIG. 5(b). In FIG. 5(b), the target signal S comes from the 90@ direction (direction from microphone 1 to microphone 4), the noise N1 comes from the 30° direction, the noise N3 comes from the 30° direction, and the noise N3 comes from the 30° direction. It is assumed that the sound comes from the 90" direction. If the maximum value of the apparent microphone spacing dmax (=d) is changed, as is clear from the figure, d/λ4 = 0.5
It can be seen that the S/N improvement amount PF [dB] is the best when (= 1/2). The same can be said of the above even if the number of microphones increases, and also the same can be said of three-dimensional arrangement.

Hereinafter, representative examples of symmetrical two-dimensional (planar) arrangement and three-dimensional (three-dimensional) arrangement among the embodiments of the present invention will be shown. FIGS. 7(a) and 7(b) are layout diagrams showing an embodiment of the two-dimensional arrangement of the present invention, in which three microphones 1 and 2.3 are arranged in an equilateral triangle. When the noise N is coming from the direction shown in (a), the noise N first enters the microphone l, and then enters the microphone 2.3. Therefore, after entering microphone L, microphone 2.
The distance from which the light enters the light source 3 is d, respectively. Further, since noise is simultaneously incident on the microphones 2.3, the distance difference between the microphones 2.3 is zero. Further, when noise N arrives from the direction E as shown in (b), the noise N first enters the microphone l, then the microphone 2, and finally the microphone 3. Therefore, the apparent interval between each microphone with respect to the direction of arrival of the noise is d13+d3t as shown in the figure. This apparent microphone interval d ll+ d 3t changes depending on the arrival direction of the noise. Among the apparent microphone intervals that change in this way, the apparent interval between adjacent microphones becomes maximum when the noise N arrives from the direction shown in (a) in this embodiment. In other words, (2
), spatial aliasing will not occur if the maximum value d of the apparent microphone spacing is set to I/2 of the sound wavelength of the upper limit frequency of the frequency band used.

FIGS. 8(a) and 8(b) each show an example of a two-dimensional arrangement in the case of four microphones. (a) shows microphones 1, 2, and 3 arranged in an equilateral triangle shape, with microphone 4 placed in the center, and (b) shows microphone I.
, 2, 3.4 are arranged in a square shape. d m a x in the figure each represents the maximum value of the apparent distance between adjacent microphones among the apparent microphone distances mentioned above, and this distance is 1/2 of the wavelength of the upper limit frequency of the frequency band in which this distance is used. Make it.

Similarly, Fig. 9 is an example of a two-dimensional arrangement with five microphones, Figs. 1O (a) and (b) are an example of a two-dimensional arrangement with six microphones, and Fig. 11 is an example of a two-dimensional arrangement with eight microphones. This is an example of a two-dimensional arrangement in the case of microphones 1 to 5, respectively. 1 to 6. 1 to 8 are arranged in a regular polygonal shape, or arranged in a regular polygonal shape and one microphone is arranged in the center thereof. d m in each figure
a x is the maximum value of the apparent microphone spacing,
This dmax is assumed to be 1/2 of the wavelength of the sound at the upper limit frequency of the frequency band to be used.

FIG. 12 shows an embodiment of the present invention in the case of four microphones in a three-dimensional arrangement, with microphones 1.2, 3.4
are arranged in a regular triangular pyramid shape. In this case, the maximum value of the apparent microphone spacing dmax is the distance between the plan view including microphones 2 and 3.4 and microphone l, and this spacing dmax is set to 1/2 of the wavelength of the sound at the upper limit frequency of the band. .

FIG. 13 shows an example of five microphones in a three-dimensional arrangement, in which the microphones 1 and 2°3.4 are arranged in a regular triangular pyramid shape, and the microphone 5 is arranged at the center. In this case, the maximum value dmax of the apparent microphone spacing is the distance between each of the microphones 1 to 4 and the microphone 5, and the microphones are arranged so that this spacing dmax is 1/2 of the wavelength of the sound at the upper limit frequency of the band.

Generally speaking, the linear, planar, and three-dimensional microphone arrangements in the above microphone array embodiments are as follows:
When a sound wave enters each microphone in turn from a certain angle, and the difference in distance from the time it enters one microphone to the next microphone is taken as the apparent distance between the two microphones with respect to the direction of arrival of the sound wave, noise It can be said that the maximum value of the apparent spacing between these microphones, which changes depending on the direction of arrival of the sound, is half the wavelength of the sound at the upper limit frequency of the frequency band used. To be more specific, the microphone arrangement is based on the assumption that, when a group of parallel planes containing one or more microphones is assumed, the distance between adjacent planes is the input value for the widest distance between adjacent planes in the group of planes. It can be said that the length is half the wavelength of the sound at the upper limit frequency of the target frequency band.

In the above embodiment, the case where a plurality of microphones are arranged symmetrically is mainly taken as an example, but it goes without saying that the same effect can be obtained even when the microphones are arranged asymmetrically. In addition, in the microphone arrangement of the above embodiment, it was assumed that it is optimal to set the maximum value of the apparent microphone spacing dmax to 1/2 of the wavelength of the sound of the band upper limit frequency. Microphone spacing and S/ in Figure 6
As can be seen from the relational diagram of the amount of improvement in N, a considerable effect can be obtained even when the interval is close to 1/2, so if the amount of improvement in S/N is within the desired or allowable range, 1 /2
dmax may be set to other intervals. in this way,
The present invention can be applied in various ways in accordance with its gist and can take various embodiments.

[Effects of the Invention] As is clear from the above explanation, the microphone array of the present invention prevents the occurrence of spatial aliasing, which is the factor that most influences the amount of S/N improvement, and improves low-frequency S/N. This has the advantage of maximizing the amount of improvement in /N.

[Brief explanation of drawings]

FIG. 1 is a basic microphone array arrangement diagram showing the first embodiment of the present invention, FIG. 2 is a diagram showing the relationship between microphone spacing and S/N improvement amount in the first embodiment, and FIG. FIG. 4 is a diagram showing the relationship between microphone spacing and S/N improvement amount in the second embodiment, and FIGS. 5(a) and (b) are according to the present invention. FIG. 6 is a diagram showing the relationship between microphone spacing and S/N improvement amount in the third embodiment. FIG. 7 (a), <b) 8 Figures (a), (b), Figure 9, Figure 10 (a) (b),
FIG. 11 is a diagram showing a typical example of a two-dimensional arrangement among the embodiments of the present invention, and FIGS. 12 and 13 are diagrams showing typical examples of the two-dimensional arrangement among the embodiments of the invention. 1.2, 3.4...Microphone. 0.02 Q, 1 0.51 Figure 2 Figure 4 Figure 9 (b) Figure 5 Figure 6 Figure 11 Figure 12 Section Figure 13

Claims (1)

[Claims] (1) A microphone array in which a plurality of microphones are arranged linearly, in a plane, or in a three-dimensional manner, and when a plane group containing one or more of the above-mentioned microphones is assumed to be parallel to each other, within that plane group Each of the microphones is arranged so that the widest distance between adjacent planes is half or approximately half the wavelength of the sound at the upper limit frequency of the frequency band to be input. microphone array.