CN109714689B - Directional acoustic index obtaining method based on differential microphone linear array - Google Patents
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Abstract
The invention discloses a directional acoustic index obtaining method based on a differential microphone linear array. The method comprises the steps of firstly obtaining a multi-channel sound signal through small-sized portable acoustic testing equipment, then constructing a strong directional beam by utilizing a differential microphone linear array signal processing technology, realizing spatial filtering of field collected data, and finally calculating to obtain an acoustic index result. The method is particularly suitable for complex environments such as neighborhood and wild animal activity areas, namely boundary environments of the human activity areas and the wild animal activity areas, and can effectively inhibit adverse effects of various noises including human activity interference sounds from other directions, so that the finally obtained acoustic index calculation result can reflect the acoustic activity conditions of the wild animals in the monitored area corresponding to the expected direction more truly, and the method has very important significance for ecological environment acoustic monitoring research.
Description
Technical Field
The invention belongs to the technical field of differential microphone linear arrays and ecological environment monitoring, and particularly relates to a directional acoustic index acquisition method based on the differential microphone linear arrays.
Background
The promotion of urbanization construction gradually deepens the influence of human activities on the ecological environment, and ecological monitoring and assessment are increasingly emphasized. Acoustic activity in the ecological environment area is important content of ecological monitoring, wherein animal chirping activity is an important index of ecological monitoring and evaluation of ecological environment influence. The activity of animal chirping activities in the ecological region can reflect the biodiversity of the ecological region and the health degree of the ecological environment, and has important significance for ecological research.
With the popularization of acoustic monitoring technology and the development of sound-scene ecology, acoustic indexes are widely applied to ecological monitoring and environmental assessment as a method capable of rapidly assessing the biological diversity and health degree of ecological environment. However, the acoustic index is extremely sensitive to artificial sound and can only be used for monitoring and evaluation in an ecological region in a quieter environment. However, in the urban and rural areas, the vicinity of urban arterial roads with heavy traffic and the edge areas of urban parks, especially in the areas which are seriously affected by human activities and have large artificial noises, the acoustic index cannot reliably reflect the acoustic activity conditions in the areas.
Therefore, the existing acoustic index cannot be directly applied to ecological environment assessment and monitoring in an ecological area affected by human activities and artificial noise.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a directional acoustic index acquisition method based on a differential microphone linear array, which can be flexibly applied.
The technical solution for realizing the purpose of the invention is as follows: a directional acoustic index obtaining method based on a differential microphone linear array comprises the following steps:
and 3, acquiring animal sound signal data by using the differential microphone linear array animal sound acquisition system built in the step 2, processing the differential microphone linear array signals, and then obtaining an acoustic index result to complete the construction of the directional acoustic index.
Compared with the prior art, the invention has the following remarkable advantages: 1) the invention can effectively separate the animal sound data coming from the front hemisphere space from the strong interference and noise environment coming from the rear hemisphere space; 2) the invention can effectively improve the reliability of the acoustic index in strong interference and noise environments; 3) the invention adopts a differential microphone linear array passive monitoring mode with small volume, and has no influence on the activity of wild animals; 4) the method has the advantages of convenient calculation process, easy implementation and high flexibility.
The present invention is described in further detail below with reference to the attached drawing figures.
Drawings
Fig. 1 is a flowchart of a directional acoustic index acquisition method based on a linear array of a differential microphone according to the present invention.
FIG. 2 is a schematic view of a typical ecological environment area in an embodiment of the present invention.
Fig. 3 is a schematic diagram of a differential microphone linear array according to the present invention, wherein (a) is a schematic diagram of a first-order differential microphone linear array, and (b) is a schematic diagram of a second-order differential microphone linear array.
Fig. 4 is a schematic diagram of beam forming of differential microphone linear arrays in an embodiment of the present invention, where (a) is a first-order differential microphone linear array cardioid beam pattern, (b) is a first-order differential microphone linear array hypercardioid beam pattern, (c) is a second-order differential microphone linear array cardioid beam pattern, and (d) is a second-order differential microphone linear array hypercardioid beam pattern.
Fig. 5 is a schematic diagram of a bird sound signal and a noise signal required by a simulation experiment in an embodiment of the present invention, where (a) is a schematic diagram of a bird sound signal, and (b) is a schematic diagram of a noise signal.
FIG. 6 is a statistical diagram of the results of the acoustic entropy index of the simulation experiment in the embodiment of the present invention.
Detailed Description
With reference to fig. 1, the present invention provides a method for obtaining directional acoustic index based on a linear array of a differential microphone for an area affected by fixed incoming noise and interference, which includes the following steps:
And 2, building a differential microphone linear array animal sound acquisition system according to the interference including the human activity sound and the incoming range of the noise source obtained in the step 1.
Further, step 2 specifically comprises:
step 2-1, defining the central direction of a main beam of a differential microphone linear array as the arrangement direction of the differential microphone linear array, defining the central direction of the main beam as a positive axial direction, defining the opposite direction as a negative axial direction, and respectively defining a front hemispherical space and a rear hemispherical space according to the positive axial direction and the negative axial direction; setting the main beam width to cover the ecological area to be monitored, and simultaneously enabling the interference and noise source obtained in the step (1) to be in a rear hemisphere space; taking the 1 st array element at the head position of the middle end of the front hemisphere space of the differential microphone linear array as a main array element;
step 2-2, determining the number L of array elements of the linear array of the differential microphone according to the width of the main beam, wherein the smaller the width of the main beam is, the higher the array order of the correspondingly designed linear array of the differential microphone is; if an L-1 order differential microphone linear array needs to be constructed, at least L array elements are needed;
step 2-3, determining the distance d between the array elements of the differential microphone linear arrays, linearly arranging the array elements of the differential microphone linear arrays at equal distance d, and constructing the differential microphone linear arrays as shown in fig. 3;
step 2-4, constructing a K-order differential microphone linear array beam pattern, wherein the formula is as follows:
wherein, the order K is L-1, theta is the angle corresponding to the positive axial direction as 0 scale, BK(theta) is the amplitude response of the differential microphone line array beam at an angle theta, aK,KIs the real coefficient of the linear array of the differential microphone, and satisfies the following conditions:
where the first real coefficient is represented as:
step 2-5, utilizing directional gain DKAnd front-to-rear output power ratio FKThe two indexes are used for evaluating the performance of main beam enhancement, and specifically comprise the following steps:
(1) directive gain D of differential microphone linear arrayKThe specific formula is the ratio of the directivity pattern of the differential microphone linear array in the positive axial direction, that is, θ is 0 °, to the average directivity pattern distributed in the whole space:
directive gain DKThe gain is used for representing the gain of the signal acquisition in the positive axial direction compared with the gain acquired in the average distribution of the whole space, and the larger the numerical value is, the stronger the main beam gain is;
(2) front-to-back output power ratio F of differential microphone linear arrayKThe signal output power of the differential microphone linear array in the forward hemisphere space and the backward hemisphere space are in the same directionThe specific formula of the ratio of the output power of the signals is as follows:
front-to-rear output power ratio FKThe method is used for representing the signal acquisition energy ratio of the space of the front hemisphere and the space of the rear hemisphere of the beam and also used for representing the signal enhancement degree of the front hemisphere where the main beam is located, and the larger the numerical value is, the higher the signal enhancement degree of the front hemisphere where the main beam is located is.
Further, step 2-4 is to construct a K-order differential microphone linear array beam pattern, specifically:
step 2-4-1, determining the shape of a beam formed by the differential microphone linear array to be heart-shaped or super heart-shaped by combining the distribution condition of human activity areas; if the reverse axial direction of the differential microphone linear array has noise, setting the shape of a beam formed by the differential microphone linear array as a heart shape, and otherwise, setting the beam as a super-heart shape;
step 2-4-2, Pair αK，kRandom selection and adjustment are carried out to change the number and the position of the zero points of the wave beams, so that the noise from the direction of the zero points is suppressed;
take a linear array of first order differential microphones as an example, α1，1Has a value range of
The beam forming formula is as follows:
B1(θ)＝(1-α1，1)+α1，1cosθ
when in use
Forming a first-order cardioid beam, wherein the beam has a zero point and is positioned at the position of theta which is 180 degrees; when in use
When forming a first-order hypercardioid beam, two zeros are distributed at theta1∈ (90, 180) and θ2∈ (180 DEG, 270 DEG) by varying the coefficient α1，1Value of (2), adjusting the beam patternThe width of the middle main lobe, the width of the side lobe and the notch direction are controlled until the width of the main lobe covers the ecological area to be monitored, and the notch direction is aligned with the noise incoming direction;
take a second order differential microphone array as an example, α2，1And α2，2The value ranges of (1, 0) are all, and the beam forming formula is as follows:
B2＝(1-α2，1-α2，2)+α2，1cosθ+α2，2cos2θ
when in use
When the wave forms a second-order cardioid wave beam, it has a zero point, and its position is 180 deg. and when 0 < α2，1＜1，0＜α2，2When the value is less than 1, a second-order hypercardioid beam is formed, and the coefficient is changed α2，1，α2，2And adjusting the width and the notch direction of the main lobe and the side lobe in the beam pattern until the width of the main lobe covers the ecological region to be monitored, and aligning the notch direction with the noise incoming direction.
Meanwhile, the higher the order of the linear array of the differential microphone is, the narrower the width of a main lobe in a formed beam pattern is, the lower the amplitude of a side lobe is, the larger the main-side lobe ratio is, the more concentrated the energy is on the main lobe, and the better the suppression effect on the interference and noise from the side surface and the back surface is.
And 3, acquiring animal sound signal data by using the differential microphone linear array animal sound acquisition system built in the step 2, processing the differential microphone linear array signals, and then obtaining an acoustic index result to complete the construction of the directional acoustic index.
Further, step 3 specifically comprises:
step 3-1, performing acoustic monitoring in the ecological region to be monitored by using the differential microphone linear array animal sound acquisition system set up in step 2, and acquiring a multichannel actually-measured sound signal, wherein a sound signal C obtained by actually measuring the animal sound acquisition system is as follows:
C＝[c1，c2，…，cL]
in the formula, c*The sound signals collected for the "-" th channel,l is the number of array elements of the differential microphone array, namely the total number of channels; the signal that main array element gathered is 1 st channel signal, arranges according to the array element and is 2 ~ L channel signal in proper order, and the signal of the L channel is expressed as:
cl＝alsl+v l1≤l≤L；
in the formula, slFor animal acoustic signals collected in the l channel, alTo attenuation coefficient, vlAdditive interference and noise for the l-th channel;
step 3-2, filtering the multi-channel signal of the step 3-1 and combining the channels to obtain a single-channel signal c0；
Step 3-3, the single-channel signal c in the step 3-2 is processed0And (4) as an acoustic signal input, calculating an acoustic index to obtain a final acoustic index result.
Further, in step 3-2, the multi-channel signal of step 3-1 is filtered and channel-combined to obtain a single-channel signal c0The method specifically comprises the following steps:
step 3-2-1, carrying out normalized least mean square adaptive filtering on the multichannel signal in the step 3-1;
(1) taking a first-order differential microphone linear array system as an example, taking a 1 st channel signal as a reference expected signal, setting an error signal e (n) in the adaptive filtering process as:
e(n)＝c1(n)-h(n)c2(n)
in the formula, c1(n) is the 1 st channel input value corresponding to the nth iteration, c2(n) is the 2 nd channel input value corresponding to the nth iteration, h (n) is the filter weight vector obtained by the nth iteration, and the iteration formula is represented as:
wherein g (n) is the gradient vector at the iteration, and the formula is:
in the formula, epsilon (n) is the mean square error of the iteration and the energy e of the instantaneous error is utilized2(n) replacement of mean square error energy { e2(n), the above equation is transformed into:
in the formula (I), the compound is shown in the specification,
the normalized least mean square adaptive filter algorithm is expressed as:
h(n+1)＝h(n)+μ(n)e(n)c2(n)
where μ (n) is the step size used in the nth iteration, also called the convergence factor, which is expressed as:
wherein M is the length of the adaptive filter, α is a constant and 0 < α < 2,
the estimated signal power for the nth iteration is given by the formula:
in practice, to avoid the step size being too large, μ (n) is further set as:
wherein β is a small constant;
(2) with reference to the first-order differential microphone linear array system in (1), for a high-order differential microphone linear array system, setting an error signal e (n) in the adaptive filtering process as:
e(n)＝K*c1(n)-Hn×C′n
in the formula, K-L-1 is the order of the linear array of the differential microphone; c'nThe combination of signals of other channels except the 1 st channel is expressed as follows:
Hnfor the combination of the other channel filter weight vectors, it is expressed as:
Hn＝[h2(n) h3(n) … hL(n)]
and if other parameters are changed correspondingly, the normalized least mean square adaptive filtering algorithm formula is expressed as follows:
Hn+1＝Hn+μ(n)e(n)C′n
at this time, the length of the adaptive filter is expanded by K times, and the signal power
And the step size mu (n) is also adjusted accordingly:
step 3-2-2, solving an optimal differential microphone linear array adaptive beam forming coefficient according to the normalized least mean square adaptive filtering algorithm in the step 3-2-1, wherein the formula is as follows:
αK，k(n)＝1-hk(n) k＝1，2，...，K
step 3-2-3, carrying out normalized least mean square self-adaptationThe multi-channel signals to be filtered are combined to obtain a single-channel signal c after filtering0The formula is expressed as:
the present invention will be described in further detail with reference to examples.
Examples
The invention provides a method for acquiring directional acoustic index based on a differential microphone linear array, which is oriented to an acoustic monitoring task of ecological environment and aims at the problem of acoustic monitoring of the ecological environment influenced by interference and noise. The method comprises the steps of firstly obtaining a multi-channel sound signal through small-sized portable acoustic testing equipment, then constructing a strong directional beam by utilizing a differential microphone linear array signal processing technology, realizing spatial filtering of field collected data, and finally calculating to obtain an acoustic index result. The method is particularly suitable for complex environments (namely the boundary environment of the human activity area and the wild animal activity area) such as neighborhood of a residential area and the wild animal activity area, can effectively inhibit adverse effects of various noises including human activity interference sounds from other directions, enables the finally obtained acoustic index calculation result to reflect the acoustic activity condition of the wild animal in the monitoring area corresponding to the expected direction more truly, and has very important significance for the ecological environment acoustic monitoring research.
With reference to fig. 1, the method for obtaining directional acoustic index based on differential microphone linear array of the present invention has the following simulation experiment steps:
firstly, constructing sound data simulation of two channels to finish first-order differential microphone linear array signal acquisition, and assuming that a positive axial direction of a differential microphone linear array is over against an expected monitoring area, interference and noise come from a rear hemisphere where a reverse axial direction of the differential microphone linear array is located, wherein the process corresponds to the step 1 and the step 2;
and secondly, performing normalized adaptive filtering processing and first-order difference microphone linear array signal filtering processing on the constructed first-order difference microphone linear array acquisition signal to obtain single-channel data. The specific operation steps are as follows:
1) determining a differential microphone placement position according to the actual environment schematic diagram shown in FIG. 2;
2) the signal acquisition angle range of the linear array of the differential microphone is marked in fig. 2, with the arrow pointing in the positive axial direction; the main beam of the monitoring area is wide, and the incoming direction of interference and noise is distributed in the rear hemisphere area of the array beam, as shown in fig. 4, (a) is a first-order difference microphone cardioid beam, the main beam is wide, and meanwhile, the incoming direction interference of the rear hemisphere can be suppressed; (b) the main beam width is wider for the first-order difference microphone hypercardioid beam, and meanwhile, the anti-axial sound signal can be kept, and the interference of the zero point position in the incoming direction is only inhibited; (c) the main beam is wider for the second-order difference microphone cardioid beam, and meanwhile, the interference of the reverse axial direction and the zero point position in the incoming direction can be inhibited; (d) the two-order differential microphone hypercardioid beam has wider main beam width, can retain the sound signals in the reverse axial direction, increases the number of zero points compared with a first-order system, and inhibits the interference of the zero point position in the incoming direction.
In this embodiment, a first-order difference microphone linear array is used for data acquisition, and a first-order difference microphone linear array beam forming formula is as follows:
B1(θ)＝(1-α1，1)+α1，1cosθ
when in use
When a first order cardioid beam is formed, interference and noise from the rear hemisphere can be eliminated to the maximum extent.
At this time, a directivity gain D of the differential microphone array is calculatedKAnd front-to-rear output power ratio FKCalculating formula and result:
according to the main beam gain and the front-to-back output power ratio of the differential microphone linear array, the main beam enhancement performance of the first-order differential microphone linear array cardioid beam is stronger, and the capability of effectively inhibiting interference and noise in an anti-axial region is achieved.
3) Bird sound data with the signal-to-noise ratio of 40dB and the white noise data with the same duration are constructed by bird singing, wherein the signal-to-noise ratio of the bird sound data and the noise data is 7dB, and the waveforms are shown in FIG. 5; supposing that the bird sound signal comes from the front hemisphere space of the differential microphone linear array and the noise signal comes from the rear hemisphere space, two channels of noisy signals are obtained by delay aliasing and addition of the bird sound signal and the noise signal, wherein the two channels of noisy signals are respectively c1And c2Acquiring the obtained signals corresponding to the designed first-order differential microphone linear array;
4) to c1And c2Normalized least mean square adaptive filtering is performed, with a filter length M i6 and an error signal expressed as:
e(n)＝c1(n)-h(n)c2(n)
the normalized least mean square adaptive filtering algorithm formula can be expressed as:
h(n+1)＝h(n)+μ(n)e(n)c2(n)
where μ (n) is the step size used in the nth iteration, and is expressed as:
wherein the content of the first and second substances,
the estimated signal power for time n is expressed as:
in the simulation experiment β ═ 1e-4 and α ═ 0.05.
5) Local optimal differential microphone linear array beam forming coefficient α can be obtained according to normalized least mean square adaptive filtering algorithm1，1Sequentially carrying out differential microphone linear array signal processing on the multi-channel signals subjected to normalized least mean square adaptive filtering to obtain combined single-channel data c0It can be expressed as:
and thirdly, respectively calculating and comparing the acoustic index results of the pure bird sound data, the bird sound data added with noise (the noise is white noise from a semi-hemispherical space) and the sound data after the self-adaptive filtering and array signal processing.
By utilizing the method, 100 groups of simulation experiments are designed, wherein each group of experiments comprises three sections of sound data, namely pure bird sound data, bird sound data added with noise (the noise is white noise from a rear hemisphere space) and data after adaptive filtering and array signal processing. Each group of data is tested by taking an acoustic entropy index (H) in common acoustic indexes as an example, and the index result is shown in fig. 6; and performing performance evaluation on 100 groups of experimental results by adopting mean absolute percentage error (MAPD) and mean square percentage error (MSPD), wherein the definitions are as follows:
table 1 gives MAPD and MSPD for 100 sets of simulation experiments. As can be seen from fig. 6 and the results in table 1, the method provided by the present invention can effectively reduce the influence of noise on the result of the acoustic index.
TABLE 1100 MAPD and MSPD from simulation experiments
The method is oriented to an ecological environment acoustic monitoring task, the construction of a field animal sound acquisition system is carried out by utilizing a differential microphone linear array, then the acquired multi-channel sound data is subjected to adaptive filtering processing, and finally the calculation of an acoustic index is completed. The method can effectively reduce the influence of noise on the result of the acoustic index, so that the acoustic index more truly reflects the actual situation of the ecological environment monitoring area, the robust application of the acoustic index is realized, and the method has very important significance on ecological research.
Claims (3)
1. A directional acoustic index obtaining method based on a differential microphone linear array is characterized by comprising the following steps:
step 1, obtaining the interference including human activity sound and the incoming range of a noise source according to an ecological area to be monitored and a human activity area;
step 2, building a differential microphone linear array animal sound acquisition system according to the interference including the human activity sound and the incoming range of the noise source obtained in the step 1; the method specifically comprises the following steps:
step 2-1, defining the central direction of a main beam of a differential microphone linear array as the arrangement direction of the differential microphone linear array, defining the central direction of the main beam as a positive axial direction, defining the opposite direction as a negative axial direction, and respectively defining a front hemispherical space and a rear hemispherical space according to the positive axial direction and the negative axial direction; setting the main beam width to cover the ecological area to be monitored, and simultaneously enabling the interference and noise source obtained in the step (1) to be in a rear hemisphere space; taking the 1 st array element at the head position of the middle end of the front hemisphere space of the differential microphone linear array as a main array element;
step 2-2, determining the number L of array elements of the linear array of the differential microphone according to the width of the main beam, wherein the smaller the width of the main beam is, the higher the array order of the correspondingly designed linear array of the differential microphone is; if an L-1 order differential microphone linear array needs to be constructed, at least L array elements are needed;
2-3, determining the distance d between array elements of the differential microphone linear arrays, and linearly arranging the array elements of the differential microphone linear arrays at equal intervals d to construct the differential microphone linear arrays;
step 2-4, constructing a K-order differential microphone linear array beam pattern, wherein the formula is as follows:
wherein, the order K is L-1, theta is the angle corresponding to the positive axial direction as 0 scale, BK(theta) is the amplitude response of the differential microphone line array beam at an angle theta, aK，kIs the real coefficient of the linear array of the differential microphone, and satisfies the following conditions:
where the first real coefficient is represented as:
step 2-5, utilizing directional gain DKAnd front-to-rear output power ratio FKThe two indexes are used for evaluating the performance of main beam enhancement, and specifically comprise the following steps:
(1) directive gain D of differential microphone linear arrayKThe specific formula is the ratio of the directivity pattern of the differential microphone linear array in the positive axial direction, that is, θ is 0 °, to the average directivity pattern distributed in the whole space:
directive gain DKThe gain is used for representing the gain of the signal acquisition in the positive axial direction compared with the gain acquired in the average distribution of the whole space, and the larger the numerical value is, the stronger the main beam gain is;
(2) front-to-back output power ratio F of differential microphone linear arrayKThe specific formula is the ratio of the output power of the incoming signal of the front hemisphere space of the differential microphone linear array to the output power of the incoming signal of the rear hemisphere space:
front-to-rear output power ratio FKThe method is used for representing the signal acquisition energy ratio of the space of the front hemisphere and the space of the rear hemisphere of the beam and also representing the signal enhancement degree of the front hemisphere where the main beam is located, and the larger the numerical value is, the higher the signal enhancement degree of the front hemisphere where the main beam is located is;
step 3, collecting animal sound signal data by using the differential microphone linear array animal sound collection system built in the step 2, processing the differential microphone linear array signals, then obtaining an acoustic index result, and completing the acquisition of directional acoustic indexes, wherein the specific steps are as follows:
step 3-1, performing acoustic monitoring in the ecological region to be monitored by using the differential microphone linear array animal sound acquisition system set up in step 2, and acquiring a multichannel actually-measured sound signal, wherein a sound signal C obtained by actually measuring the animal sound acquisition system is as follows:
C＝[c1，c2，…，cL]
in the formula, clFor the sound signal collected by the L-th channel, L is the number of array elements of the differential microphone array, namely the total number of channels; the signal that main array element gathered is 1 st channel signal, arranges according to the array element and is 2 ~ L channel signal in proper order, and the signal of the L channel is expressed as:
cl＝alsl+vl1≤l≤L；
in the formula, slFor animal acoustic signals collected in the l channel, alTo attenuation coefficient, vlAdditive interference and noise for the l-th channel;
step 3-2, filtering the multi-channel signal of the step 3-1 and combining the channels to obtain a single-channel signal c0；
Step 3-3, the single-channel signal c in the step 3-2 is processed0And (4) as an acoustic signal input, calculating an acoustic index to obtain a final acoustic index result.
2. The method for obtaining directional acoustic index based on linear array of differential microphone according to claim 1, wherein the step 2-4 of constructing the beam pattern of the linear array of differential microphone of K order is specifically as follows:
step 2-4-1, determining the shape of a beam formed by the differential microphone linear array to be heart-shaped or super heart-shaped by combining the distribution condition of human activity areas; if the reverse axial direction of the differential microphone linear array has noise, setting the shape of a beam formed by the differential microphone linear array as a heart shape, and otherwise, setting the beam as a super-heart shape;
step 2-4-2, Pair αK，kRandom selection and adjustment are carried out to change the number and the position of the zero points of the wave beams, so that the noise from the direction of the zero points is suppressed;
for first order differential microphone linear array, a1，1Has a value range of
The beam forming formula is as follows:
B1(θ)＝(1-α1，1)+α1，1cosθ
when in use
Forming a first-order cardioid beam, wherein the beam has a zero point and is positioned at the position of theta which is 180 degrees; when in use
When forming a first-order hypercardioid beam, two zeros are distributed at theta1∈ (90, 180) and θ2∈ (180 DEG, 270 DEG) by varying the coefficient α1，1Adjusting the width of a main lobe and a side lobe and the notch direction in the beam pattern until the width of the main lobe covers the ecological region to be monitored, and aligning the notch direction with the noise incoming direction;
for a second order differential microphone array, α2，1And α2，2The value ranges of (1, 0) are all, and the beam forming formula is as follows:
B2＝(1-α2，1-α2，2)+α2，1cosθ+α2，2cos2θ
when in use
When the wave forms a second-order cardioid wave beam, it has a zero point, and its position is 180 deg. and when 0 < α2，1＜1，0＜α2，2When the value is less than 1, a second-order hypercardioid beam is formed, and the coefficient is changed α2，1，α2，2And adjusting the width and the notch direction of the main lobe and the side lobe in the beam pattern until the width of the main lobe covers the ecological region to be monitored, and aligning the notch direction with the noise incoming direction.
3. The method as claimed in claim 1, wherein the step 3-2 is performed by filtering the multi-channel signals of the step 3-1 and combining the channels to obtain a single-channel signal c0The method specifically comprises the following steps:
step 3-2-1, carrying out normalized least mean square adaptive filtering on the multichannel signal in the step 3-1;
(1) for a first-order difference microphone linear array system, a 1 st channel signal is a reference expected signal, and an error signal e (n) in the adaptive filtering processing process is set as follows:
e(n)＝c1(n)-h(n)c2(n)
in the formula, c1(n) is the 1 st channel input value corresponding to the nth iteration, c2(n) is the 2 nd channel input value corresponding to the nth iteration, h (n) is the filter weight vector obtained by the nth iteration, and the iteration formula is represented as:
wherein g (n) is the gradient vector at the iteration, and the formula is:
wherein ε (n) is the mean square error of the iteration,using instantaneous error energy e2(n) replacement of mean square error energy { e2(n), the above equation is transformed into:
in the formula (I), the compound is shown in the specification,
the normalized least mean square adaptive filter algorithm is expressed as:
h(n+1)＝h(n)+μ(n)e(n)c2(n)
where μ (n) is the step size used in the nth iteration, also called the convergence factor, which is expressed as:
wherein M is the length of the adaptive filter, α is a constant and 0 < α < 2,
the estimated signal power for the nth iteration is given by the formula:
μ (n) is further set to:
wherein β is a constant;
(2) with reference to the first-order differential microphone linear array system in (1), for a high-order differential microphone linear array system, setting an error signal e (n) in the adaptive filtering process as:
e(n)＝K*c1(n)-Hn×C′n
in the formula, K-L-1 is the order of the linear array of the differential microphone; c'nThe combination of signals of other channels except the 1 st channel is expressed as follows:
Hnfor the combination of the other channel filter weight vectors, it is expressed as:
Hn＝[h2(n) h3(n) … hL(n)]
and if other parameters are changed correspondingly, the normalized least mean square adaptive filtering algorithm formula is expressed as follows:
Hn+1＝Hn+μ(n)e(n)C′n
at this time, the length of the adaptive filter is expanded by K times, and the signal power
And the step size mu (n) is also adjusted accordingly:
step 3-2-2, solving an optimal differential microphone linear array adaptive beam forming coefficient according to the normalized least mean square adaptive filtering algorithm in the step 3-2-1, wherein the formula is as follows:
αK，k(n)＝1-hk(n) k＝1，2，...，K
step 3-2-3, the multi-channel signals subjected to the normalized least mean square adaptive filtering are subjected to combined processing to obtain filtered single-channel signalsc0The formula is expressed as:
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