1. A helicopter sound signal identification method based on auditory spectrum feature extraction is characterized by comprising the following steps:

step 1: segmented windowing: dividing original helicopter acoustic signals collected by a microphone into a plurality of signal segments with the length of L to obtain segmented acoustic signals，(ii) a Segmenting the acoustic signalMultiplication by a window functionObtaining a windowed acoustic signal；

Step 2: FFT analysis: to the result in step 1With windowed acoustic signalsPerforming FFT analysis to obtain a frequency spectrum of the windowed sound signal, and further obtaining an amplitude spectrum by taking an absolute value of the frequency spectrum of the windowed sound signal;

and step 3: and (3) scale transformation: in the frequency analysis rangeInner, center frequency of auditory filter bank under nonlinear frequency scale transformation is calculated，；The lower bound frequency of the frequency analysis range is larger than the lowest frequency of FFT analysis;is the upper bound frequency of the frequency analysis range, and is less than the maximum frequency and Nyquist frequency of FFT analysisThe minimum value of (a) is determined,sampling frequency for the acoustic signal; the auditory filter bank comprises a Mel filter bank or a Gamma filter bank; the nonlinear scale transformation comprises Mel scale transformation or ERB scale transformation or Bark scale transformation;

and 4, step 4: auditory filtering: firstly, the center frequency obtained by solving according to the step 3Determining an expression of an auditory filter, performing band-pass filtering processing on the amplitude spectrum obtained in the step (2) by using an auditory filter group, and outputting the amplitude spectrum after filtering processing;

and 5: logarithmic compression: carrying out logarithmic compression on the amplitude spectrum output by the auditory filter bank in the step 4;

step 6: and (3) calculating an average value: solving the mean value of the logarithmic compression result obtained in the step 5 to obtain the final auditory spectrum characteristic;

and 7: classification and identification: respectively obtaining the auditory spectrum characteristics of the training set and the test set according to the steps 1-6; the auditory spectrum features of the training set are firstly sent to a classifier for training, and then the auditory spectrum features of the test set are sent to the classifier for recognition to determine the type of the helicopter.

2. The method of claim 1, wherein the window function is a helicopter acoustic signal recognition method based on auditory spectrum feature extractionComprising a Hamming window; window functionComprises the following steps:

，

n is a sum of the segmented acoustic signalsThe corresponding discrete points in time are,(ii) a L is the length of the segmented acoustic signal.

3. The helicopter acoustic signal identification based on auditory spectrum feature extraction as claimed in claim 1A method of discriminating between said Mel scale and said center frequencyThe corresponding relation is as follows:

；

wherein the content of the first and second substances,which is the lower bound frequency of the frequency analysis range,i represents the serial number of the filter,n is the number of filters;representing the center frequencyThe corresponding Mel scale;to analyze the Mel scale corresponding to the lower bound frequency of the range,the Mel scale corresponding to the upper bound frequency of the analysis range;

the ERB scale transformation and center frequencyThe corresponding relation is as follows:

；

wherein the content of the first and second substances,which is the lower bound frequency of the frequency analysis range,i represents the serial number of the filter,n is the number of filters;representing the center frequencyThe corresponding ERB scale;to analyze the ERB scale corresponding to the lower bound frequency of the range,ERB scale corresponding to upper-bound frequency of analysis range;

the Bark scale transformation and center frequencyThe corresponding relation is as follows:

；

wherein the content of the first and second substances,which is the lower bound frequency of the frequency analysis range,i represents the serial number of the filter,n is the number of filters;representing the center frequencyThe corresponding Bark scale;to analyze the Bark scale corresponding to the lower bound frequency of the range,the Bark scale corresponding to the upper bound frequency of the analysis range.

4. A helicopter acoustic signal identification method based on auditory spectral feature extraction as claimed in claim 1 wherein the transfer function of said Mel filter is:

；

wherein, i represents the serial number of the filter, i =1, …, and N is the number of the filters;represents the transfer function of the Mel-filter;for a certain frequency of the analysis to be,，。

5. the helicopter acoustic signal identification method based on auditory spectrum feature extraction as claimed in claim 1, wherein the time domain expression of the Gammatone filter is:

；

wherein the content of the first and second substances,is a time domain expression of the Gamma atom filter, A is the gain of the filter; m is the order of the filter;is the filter bandwidth;is the center frequency and t is time.

6. The helicopter acoustic signal identification method based on auditory spectral feature extraction as claimed in claim 1, characterized in that said classifier comprises a Euclidean distance based nearest neighbor classifier.

7. The helicopter acoustic signal identification method based on auditory spectral feature extraction as claimed in claim 1, characterized in that said non-linear frequency scale transformation is combined with an auditory filter bank to obtain auditory spectral feature extraction algorithms comprising M-M, E-M, B-M, M-G, E-G and B-G algorithms; the M-M algorithm is an auditory spectrum feature extraction algorithm consisting of Mel scale transformation and Mel filters; the E-M algorithm is an auditory spectrum feature extraction algorithm consisting of ERB scale transformation and a Mel filter; the B-M algorithm is an auditory spectrum feature extraction algorithm consisting of Bark scale transformation and a Mel filter; the M-G algorithm is an auditory spectrum feature extraction algorithm consisting of Mel scale transformation and a Gamma-tone filter; the E-G algorithm is an auditory spectrum feature extraction algorithm consisting of ERB scale transformation and a Gamma atom filter; the B-G algorithm is an auditory spectrum feature extraction algorithm consisting of Bark scale transformation and a Gamma-tone filter.

8. The method of claim 1, wherein the length L of the segmented acoustic signal is such that the frequency resolution of FFT analysis isThe fundamental frequency is the same order of magnitude as that of a helicopter;is the acoustic signal sampling frequency and L is the segmented acoustic signal length.

9. The method of claim 1, wherein the number N of filters in the auditory filter bank is such that the minimum frequency resolution of the scaling is of the same order of magnitude as the fundamental frequency of the helicopter.

Background

Helicopters have gained increasing use in disaster relief, local blow and first-out maneuvers because of their unique vertical take-off and landing, high maneuverability and low altitude penetration capability. With the increasing prominence of the "black fly" problem and the increasing importance of low-altitude defense, there has been increasing interest and research into how to detect, identify, locate and track helicopters. Helicopter acoustic signals, particularly strong middle and low frequency noise generated by periodically disturbing air by main propellers and tail propellers of the helicopter acoustic signals, are important characteristics for identifying the helicopter.

The identification of the acoustic signals of the helicopter can effectively make up the defects of traditional detection and identification means such as radar, infrared and optics under severe weather conditions and high shielding conditions (such as cloud, mountains, jungles and the like), and the key link is to effectively extract the individual characteristics which are hidden in the acoustic signals and can reflect the type of the target of the helicopter. Typical helicopter acoustic signal feature extraction methods are roughly classified into a time domain method, a frequency domain method, a time-frequency domain method, a cepstrum domain method, and the like. The time domain feature extraction directly carries out statistical analysis on the original time domain acoustic signals acquired by the microphone, extracts the multi-dimensional features such as zero crossing rate, peak position, waveform structure and the like, and has the advantages of high speed and good real-time performance, but the feature extraction is difficult and the recognition performance is rapidly reduced under the low signal-to-noise ratio and the complex environment. Other feature extraction methods are essentially based on spectral characteristic analysis, and the improvement of spectral feature extraction capability has important significance on the performance improvement of the methods.

Disclosure of Invention

The invention aims to provide a helicopter sound signal identification method based on auditory spectrum feature extraction aiming at the problems.

A helicopter sound signal identification method based on auditory spectrum feature extraction comprises the following steps:

step 1: segmented windowing: dividing original helicopter acoustic signals collected by a microphone into a plurality of signal segments with the length of L to obtain segmented acoustic signals，(ii) a Segmenting the acoustic signalMultiplication by a window functionObtaining a windowed acoustic signal；

Step 2: FFT analysis: to the windowed signal obtained in step 1Performing FFT analysis to obtain a frequency spectrum of the windowed sound signal, and further obtaining an amplitude spectrum by taking an absolute value of the frequency spectrum of the windowed sound signal;

and step 3: and (3) scale transformation: in the frequency analysis rangeInner, center frequency of auditory filter bank under nonlinear frequency scale transformation is calculatedf _i ，；The lower bound frequency of the frequency analysis range is larger than the lowest frequency of FFT analysis;is the upper bound frequency of the frequency analysis range, and is less than the maximum frequency and Nyquist frequency of FFT analysisThe minimum value of (a) is determined,sampling frequency for the acoustic signal; the auditory filter bank comprises a Mel filter bank or a Gamma filter bank; the nonlinear scale transformation comprises Mel scale transformation or ERB scale transformation or Bark scale transformation;

and 4, step 4: auditory filtering: firstly, the center frequency obtained by solving according to the step 3Determining an expression of an auditory filter, performing band-pass filtering processing on the amplitude spectrum obtained in the step (2) by using an auditory filter group, and outputting the amplitude spectrum after filtering processing;

and 5: logarithmic compression: carrying out logarithmic compression on the amplitude spectrum output by the auditory filter bank in the step 4;

step 6: and (3) calculating an average value: solving the mean value of the logarithmic compression result obtained in the step 5 to obtain the final auditory spectrum characteristic;

and 7: classification and identification: and (3) respectively obtaining the auditory spectrum characteristics of the training set and the test set according to the steps 1-6, firstly sending the auditory spectrum characteristics of the training set into a classifier for training, then sending the auditory spectrum characteristics of the test set into the classifier for recognition, and determining the type of the helicopter.

Preferably, the window functionComprising a Hamming window; window functionComprises the following steps:

，

n is a sum of the segmented acoustic signalsThe corresponding discrete points in time are,(ii) a L is the length of the segmented acoustic signal.

Preferably, the Mel scale transformation and center frequencyThe corresponding relation is as follows:

；

wherein the content of the first and second substances,which is the lower bound frequency of the frequency analysis range,i represents the serial number of the filter,n is the number of filters;representing the center frequencyThe corresponding Mel scale;to analyze the Mel scale corresponding to the lower bound frequency of the range,the Mel scale corresponding to the upper bound frequency of the analysis range;

the ERB scale transformation and center frequencyThe corresponding relation is as follows:

；

wherein the content of the first and second substances,which is the lower bound frequency of the frequency analysis range,i represents the serial number of the filter,n is the number of filters;representing the center frequencyThe corresponding ERB scale;to analyze the ERB scale corresponding to the lower bound frequency of the range,ERB scale corresponding to upper-bound frequency of analysis range;

the Bark scale transformation and center frequencyThe corresponding relation is as follows:

；

wherein the content of the first and second substances,which is the lower bound frequency of the frequency analysis range,is frequency ofThe upper frequency of the analysis range, i denotes the filter number,n is the number of filters;representing the center frequencyThe corresponding Bark scale;to analyze the Bark scale corresponding to the lower bound frequency of the range,the Bark scale corresponding to the upper bound frequency of the analysis range.

From the above formula, the center frequency at the corresponding scale can be calculated by inverse transformation。

Preferably, the transfer function of the Mel filter is:

；

wherein, i represents the serial number of the filter, i =1, …, and N is the number of the filters;represents the transfer function of the Mel-filter;for a certain frequency of the analysis to be,，。

preferably, the time domain expression of the Gammatone filter is as follows:

；

wherein the content of the first and second substances,is a time domain expression of the Gamma atom filter, A is the gain of the filter; m is the order of the filter;is the filter bandwidth;is the center frequency and t is time.

Preferably, the classifier comprises a euclidean distance based nearest neighbor classifier.

Preferably, the non-linear frequency scale transformation and the auditory filter bank are combined to obtain an auditory spectrum feature extraction algorithm, wherein the auditory spectrum feature extraction algorithm comprises an M-M algorithm, an E-M algorithm, a B-M algorithm, an M-G algorithm, an E-G algorithm and a B-G algorithm; the M-M algorithm is an auditory spectrum feature extraction algorithm consisting of Mel scale transformation and Mel filters; the E-M algorithm is an auditory spectrum feature extraction algorithm consisting of ERB scale transformation and a Mel filter; the B-M algorithm is an auditory spectrum feature extraction algorithm consisting of Bark scale transformation and a Mel filter; the M-G algorithm is an auditory spectrum feature extraction algorithm consisting of Mel scale transformation and a Gamma-tone filter; the E-G algorithm is an auditory spectrum feature extraction algorithm consisting of ERB scale transformation and a Gamma atom filter; the B-G algorithm is an auditory spectrum feature extraction algorithm consisting of Bark scale transformation and a Gamma-tone filter.

Preferably, the length L of the segmented acoustic signal is such that the frequency resolution of the FFT analysis isThe fundamental frequency of the helicopter is the same numberMagnitude;is the acoustic signal sampling frequency and L is the segmented acoustic signal length.

Preferably, the number N of filters in the auditory filter bank is such that the minimum frequency resolution of the scaling is of the same order of magnitude as the fundamental frequency of the helicopter.

Compared with the prior art, the beneficial effects of adopting the technical scheme are as follows: the nonlinear frequency scale transformation and the auditory filter are introduced between FFT analysis and logarithmic compression, and by means of the nonlinear frequency selection capability of an auditory calculation model and stronger medium-low frequency resolution and analysis processing capability, the characteristics of the sound signals which are not easy to perceive are exposed in a plurality of analysis frequency bands, so that the identification effectiveness and robustness of the helicopter are improved.

Drawings

Fig. 1 is a helicopter acoustic signal identification process based on conventional spectral feature extraction.

Fig. 2 is a flow of helicopter acoustic signal identification based on auditory spectrum feature extraction according to the present invention.

Fig. 3 is a diagram of center frequencies corresponding to each filter in a non-linear frequency scale transform.

FIG. 4 is a graph of helicopter acoustic signal spectra at different signal-to-noise ratios.

FIG. 5 is a cloud image of recognition rate at different segment lengths based on the present invention.

FIG. 6 shows different lower bound frequencies obtained according to the present inventionCloud images of the recognition rate of time.

FIG. 7 shows different upper bound frequencies obtained according to the present inventionCloud images of the recognition rate of time.

FIG. 8 is a cloud chart of the recognition rate of different numbers of filters obtained based on the present invention, where the nonlinear frequency scale transformation uses Mel scale, and the filter bank uses Mel filter bank.

FIG. 9 is a cloud chart of the recognition rate of different numbers of filters obtained based on the present invention, where the nonlinear frequency scale transformation uses the Mel scale and the filter bank uses the Gamma filter bank.

FIG. 10 is a cloud chart of the recognition rate of different numbers of filters obtained based on the present invention, where the ERB scale is used for the nonlinear frequency scale transformation, and the Mel filter bank is used for the filter bank.

FIG. 11 is a cloud chart of the recognition rate of different numbers of filters obtained based on the present invention, where the ERB scale is used for the nonlinear frequency scale transformation, and the Gamma filter bank is used for the filter bank.

FIG. 12 is a cloud chart of the recognition rate of different numbers of filters obtained based on the present invention, wherein Bark scale is used for nonlinear frequency scale transformation, and Mel filter bank is used for the filter bank.

FIG. 13 is a cloud chart of the recognition rate for different numbers of filters obtained based on the present invention, wherein Bark scale is used for nonlinear frequency scale transformation, and Gamma filter bank is used for filter bank.

Fig. 14 is a graph of minimum frequency resolution and recognition accuracy of the scaling with the number of filters.

Fig. 15 is a graph showing the frequency resolution of scaling as a function of the filter number.

FIG. 16 is a graph of the coefficient curves of the Mel filter and the Gamma filter as a function of frequency.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

As shown in fig. 1, a helicopter acoustic signal identification process based on conventional spectral feature extraction. Fast Fourier Transform (FFT) is carried out on time domain acoustic signal data subjected to segmented windowing, sound pressure level frequency spectrum is obtained through logarithmic compression, then the frequency spectrum average value of each segment of data is obtained to obtain spectral features to be identified, and finally the spectral features are sent to a classifier to identify the type of a target，Is the acoustic signal sampling frequency and L is the segmented acoustic signal length.

As shown in fig. 2, a helicopter acoustic signal identification method based on auditory spectrum feature extraction includes the following steps:

step 1: segmented windowing: dividing original helicopter acoustic signals collected by a microphone into a plurality of signal segments with the length of L to obtain segmented acoustic signals，(ii) a Segmenting the acoustic signalMultiplication by a window functionTo reduce the 'frequency spectrum leakage' caused by the discontinuity of the head and the tail of the segmented signal and obtain the windowed sound signal(ii) a In order to avoid excessive signal variation between adjacent data segments, a 50% overlap region is typically provided;

step 2: FFT analysis: for the windowed acoustic signal obtained in step 1Performing FFT analysis to obtain a frequency spectrum of the windowed sound signal, and further obtaining an amplitude spectrum by taking an absolute value of the frequency spectrum of the windowed sound signal;

and step 3: and (3) scale transformation: in the frequency analysis rangeInner, center frequency of auditory filter bank under nonlinear frequency scale transformation is calculated，；The lower bound frequency of the frequency analysis range is larger than the lowest frequency of FFT analysis;is the upper bound frequency of the frequency analysis range, and is less than the maximum frequency and Nyquist frequency of FFT analysisThe minimum value of (a) is determined,sampling frequency for the acoustic signal; the auditory filter bank comprises a Mel filter bank or a Gamma filter bank; the nonlinear scale transformation comprises Mel scale transformation or ERB scale transformation or Bark scale transformation;

and 4, step 4: auditory filtering: firstly, the center frequency obtained by solving according to the step 3f _i Determining an expression of an auditory filter, performing band-pass filtering processing on the amplitude spectrum obtained in the step (2) by using an auditory filter group, and outputting the amplitude spectrum after filtering processing;

and 5: logarithmic compression: carrying out logarithmic compression on the amplitude spectrum output by the auditory filter bank in the step 4 to obtain the sound pressure level representation of the auditory spectrum;

step 6: and (3) calculating an average value: solving the mean value of the logarithmic compression result obtained in the step 5 to obtain the final auditory spectrum characteristic;

and 7: classification and identification: and (3) respectively obtaining the auditory spectrum characteristics of the training set and the test set according to the steps 1-6, firstly sending the auditory spectrum characteristics of the training set into a classifier for training, then sending the auditory spectrum characteristics of the test set into the classifier for recognition, and determining the type of the helicopter.

The window functionComprising a Hamming window; the window functionComprises the following steps:

，

n is a sum of the segmented acoustic signalsThe corresponding discrete points in time are,(ii) a L is the length of the segmented acoustic signal.

The Mel scale transformation and center frequencyThe corresponding relation is as follows:

；

wherein the content of the first and second substances,which is the lower bound frequency of the frequency analysis range,i represents the serial number of the filter,n is the number of filters;representing the center frequencyThe corresponding Mel scale;to analyze the Mel scale corresponding to the lower bound frequency of the range,the Mel scale corresponding to the upper bound frequency of the analysis range;

the ERB scale transformation and center frequencyThe corresponding relation is as follows:

；

wherein the content of the first and second substances,which is the lower bound frequency of the frequency analysis range,i represents the serial number of the filter,n is the number of filters;representing the center frequencyThe corresponding ERB scale;to analyze the ERB scale corresponding to the lower bound frequency of the range,for analysisERB scale corresponding to the upper range frequency;

the Bark scale transformation and center frequencyThe corresponding relation is as follows:

；

wherein the content of the first and second substances,which is the lower bound frequency of the frequency analysis range,i represents the serial number of the filter,n is the number of filters;representing the center frequencyThe corresponding Bark scale;to analyze the Bark scale corresponding to the lower bound frequency of the range,the Bark scale corresponding to the upper bound frequency of the analysis range.

From the above formula, the nonlinear frequency scale transformation and the actual frequency are usedThe central frequency under the corresponding scale can be back calculated by inverse transformation of the relational expression(ii) a Non-linear frequency scale transformation and actual frequencyThe relationship of (A) is as follows:

mel scale transformation and actual frequencyIs a relational expression ofComprises the following steps:

；

ERB scaling and actual frequencyIs a relational expression ofComprises the following steps:

；

bark scaling and actual frequencyIs a relational expression ofComprises the following steps:

。

analyzing the range [0, F ] by frequency_S/2]（F_S=44100Hz is the sampling frequency of the helicopter acoustic signal), 100 filters are examples (every 5 show 1 centerFrequency) to find the center frequency corresponding to each filter under three scale transformations, as shown in fig. 3; as can be seen from fig. 3, the perceptual frequencies after the scaling all have a nonlinear relationship with the common frequency, and the three scaling have different frequency characteristics: under the same filter number, the Mel scale corresponds to the highest center frequency but the change is more gradual, while the Bark scale corresponds to the lower center frequency but the filter corresponding to the high frequency band is steeper.

It should be noted that, in order to simulate dynamic and nonlinear impulse response and amplitude-frequency characteristics of human ears, a Mel filter bank or a Gammatone filter bank is adopted, which is a commonly used band-pass acoustic filter bank.

The transfer function of the Mel-filter is:

；

wherein, i represents the serial number of the filter, i =1, …, and N is the number of the filters;represents the transfer function of the Mel-filter;for a certain frequency of the analysis to be,，。

the time domain expression of the Gamma atom filter is as follows:

；

wherein the content of the first and second substances,time domain expression for a Gamma-tone filterA is the filter gain; m is the order of the filter;in order to be the bandwidth of the filter,is the center frequency, t is time; it should be noted that when m =4, the auditory characteristics of the human ear can be more simulated.

The classifier adopts a nearest neighbor classifier based on Euclidean distance, but is not limited to the nearest neighbor classifier.

The non-linear frequency scale transformation and the auditory filter bank are combined to obtain an auditory spectrum feature extraction algorithm, which comprises an M-M algorithm, an E-M algorithm, a B-M algorithm, an M-G algorithm, an E-G algorithm and a B-G algorithm.

It should be noted that the M-M algorithm refers to an auditory spectrum feature extraction algorithm composed of Mel scale transformation and Mel filters; the E-M algorithm is an auditory spectrum feature extraction algorithm consisting of ERB scale transformation and a Mel filter; the B-M algorithm is an auditory spectrum feature extraction algorithm consisting of Bark scale transformation and Mel filter; the M-G algorithm is an auditory spectrum feature extraction algorithm consisting of Mel scale transformation and a Gamma-tone filter; the E-G algorithm is an auditory spectrum feature extraction algorithm consisting of ERB scale transformation and a Gamma atom filter; the B-G algorithm is an auditory spectrum feature extraction algorithm consisting of Bark scale transformation and a Gamma-tone filter.

The length L of the segmented acoustic signal is such that the frequency resolution of the FFT analysis isThe fundamental frequency is the same order of magnitude as that of a helicopter;is the acoustic signal sampling frequency and L is the segmented acoustic signal length.

The number N of the filters in the auditory filter bank needs to enable the minimum frequency resolution of the scale transformation to be in the same order of magnitude as the fundamental frequency of the helicopter.

It should be noted that the minimum frequency resolution of the scaling is not enough, which is of the same order of magnitude as the fundamental frequency of the helicopter, and needs to be substantially equal to the fundamental frequency or slightly smaller. If the fundamental frequency is 20Hz, the minimum frequency resolution needs to be around 10-25 Hz.

Example 1

By adopting the helicopter acoustic signal identification method based on auditory spectrum feature extraction, the effectiveness and robustness in a noise environment are inspected.

Firstly, sound signal data radiated by a main rotor, a tail rotor, an engine and the like when 10 helicopters of different models fly in the field are acquired by using a microphone, and the sampling rate and the sampling time are H_S=44100Hz and t =18 s; and dividing the acoustic signal of each type of helicopter into data of non-overlapping 1s time periods to obtain 180 data samples.

Secondly, randomly selecting 50% of data from the total samples as a training set, and using the remaining 50% of data as a test set, wherein the number of samples in the training set and the test set is 90.

Finally, Gaussian white noise interferences with different intensities are added into the total sample, and a power spectral density graph of a certain section of helicopter sound signal under different signal-to-noise ratios as shown in FIG. 4 is obtained.

As can be seen from fig. 4, the energy of the helicopter acoustic signal is concentrated in the mid-low frequency band below 1000 Hz, and particularly, the energy of the sound with sharp and high amplitude is at the fundamental frequency of the rotor noise (about 20 Hz) and the frequency corresponding to the harmonic thereof. As the Signal-to-Noise Ratio (SNR) of noisy data decreases from SNR =40 dB to SNR = -40dB, the amplitude of the acoustic Signal spectrum tends to decrease as a whole. When the signal-to-noise ratio reaches SNR = -20 dB and SNR = -40dB, the sound energy of the high frequency band gradually exceeds the middle and low frequency bands, the rotor noise fundamental frequency and the harmonic frequency thereof can not be obviously sensed from the frequency spectrum, and the individual characteristics of the helicopter are gradually submerged in the noise.

Example 2

By adopting the helicopter acoustic signal identification method based on auditory spectrum feature extraction, the influence degree of the segment length on the helicopter acoustic signal identification effectiveness and robustness is examined, and the identification rate cloud charts under different segment lengths as shown in fig. 5 are obtained.

As shown in fig. 5, the cloud images of the recognition rate at different segment lengths L are given. As can be seen from fig. 5, as the signal-to-noise ratio decreases, the recognition rate also gradually decreases; however, under all segment lengths L, when SNR is more than or equal to 0dB, the identification accuracy rate is more than 60%. On the other hand, as the segment length increases, the recognition rate tends to increase; however, the larger L is, the better L is, but a proper intermediate value exists, namely under the condition of high signal-to-noise ratio, when L = 1024-4096, the identification accuracy rate is close to 100%. The reason for this is that: when the segment length is small, the useful information contained in the segment data is small and the frequency resolution of the FFT is low, (see table 1, F_SThe larger the/L value, the lower the frequency resolution), whereas the fundamental frequency of a typical helicopter is usually only a few tens of Hz, which results in spectral characteristics before scaling that do not effectively distinguish different helicopters; although non-linear scaling and auditory filtering can improve resolution, the recognition rate cannot be significantly improved when the FFT basis is poor. On the other hand, when the segment length is large, the segment data is more likely to change from approximately stationary to non-stationary, thereby affecting the feature extraction and identification performance. When the length of L is such that the frequency resolution F_SWhen the/L is in the same order of magnitude as the fundamental frequency of the helicopter, namely dozens of Hz, the recognition rate is higher.

TABLE 1 frequency resolution at different data segment lengths

L	Frequency resolution
		64	689.06
128	344.53
		256	172.27
512	86.13
		1024	43.07
2048	21.53
		4096	10.77
8192	5.38
		16384	2.69

It should be noted that, in embodiment 2, the nonlinear frequency scale transform uses Mel scale, and the filter bank uses Mel filter bank.

Example 3

By adopting the helicopter acoustic signal identification method based on auditory spectrum feature extraction, the influence degree of the frequency analysis range on the helicopter acoustic signal identification effectiveness and robustness is examined, and identification rate cloud charts in different frequency analysis ranges as shown in fig. 6-7 are obtained.

As shown in fig. 6-7, the lower bound of the different frequency analysis ranges is givenAnd upper boundAnd (5) setting a cloud graph of the identification rate. As can be seen from the figure, the lower frequency boundThe influence on the recognition rate is larger than the upper frequency boundAlthough its maximum parameter variation range 2560 Hz is much smaller than the maximum parameter variation range 12800 Hz of the latter. The main characteristics of the helicopter acoustic signal identification are high energy, slow attenuation and long propagation of strong middle and low frequency signals. It can also be seen from fig. 6 that the lower bound with frequencyThe recognition rate tends to decrease, particularlyAbove 1000 Hz, the decrease in recognition rate is very significant. On the other hand, with the frequency upper boundThe recognition rate is slightly improved. The reason for this is that: lower bound of frequency analysisWhen the helicopter identification data is increased, the signal characteristics of the medium-low frequency band are discarded by scale transformation and auditory filtering, and the individual characteristics of the helicopter contained in the data are gradually reduced, so that the identification rate is reduced; and the upper bound of frequency analysisWhen the signal is reduced, the high-frequency signal which is easily affected by interference is discarded, and the effective signal of the medium-low frequency is reserved, so that the recognition rate is not greatly affected, but is slightly improved.

It should be noted that the nonlinear frequency scale transform in embodiment 3 uses Mel scale, and the filter bank uses Mel filter bank.

Example 4

By adopting the helicopter acoustic signal identification method based on auditory spectrum feature extraction, the influence degree of the number of the filters on the helicopter acoustic signal identification effectiveness and robustness is examined, and identification rate cloud charts of different scale transformations and filter groups are applied when the number of the filters is different, as shown in fig. 8-13, are obtained.

As can be seen from fig. 8 to 13, the recognition accuracy rate tends to increase rapidly and then gradually become stable as the number of filters increases.

As shown in fig. 14, in order to change the minimum frequency resolution and the recognition accuracy of the scaling with the number of filters, the minimum frequency resolution and the recognition accuracy of the scaling are just opposite to each other: as the number of filters is increased from 1 to 200, the frequency resolution of the scaling is rapidly reduced from 3000 Hz to within 100Hz and stabilizes in the order of tens of Hz in a large range of the number of filters. This is consistent with the original intention of introducing nonlinear scale transformation in auditory spectrum feature extraction, namely strengthening the medium and low frequency resolution of helicopter acoustic signals: when the number of the filters is small, the frequency resolution of the scale transformation is also poor, and the resolution of the spectrum analysis cannot be improved when the filters are coupled with the FFT spectrum; meanwhile, when the number of the filters is small, the auditory spectrum features for classification and identification obtained after auditory filtering are also few, so that the identification accuracy is obviously low. On the other hand, when the number of the filters is large enough, the ability of improving the medium and low frequency resolution by the scale transformation and enhancing the medium and low frequency analysis by the auditory filtering is gradually shown, so that the recognition rate is increased.

It can also be seen from fig. 8-13 that, overall, the Bark scale recognition rate is slightly better than the ERB scale, and both are better than the Mel scale; meanwhile, the recognition rate of the Mel filter bank is superior to that of the Gamma filter bank.

As shown in fig. 15, in order to change the frequency resolution of the scaling with the filter number, the number N =100 of filters, and it can be known from the figure that, in the same frequency analysis range and the same number of filters, the Bark scale sacrifices the resolution of the high frequency band (when the filter number is large, the resolution value is large), so that the medium and low frequency resolution is lower than the ERB scale and the Mel scale. The resolution curve for the Mel scale is flat overall but in most cases the resolution is lower than for the other two scales.

As shown in fig. 16, in the case of the variation of the coefficient curves of the Mel filter and the Gammatone filter with frequency, the number of filters N =100, it can be seen that the Mel bandpass filter having a triangle shape has coefficients larger than 0 only between the center frequencies of two adjacent filters, while the Gammatone bandpass filter having a gamma function like the largest coefficient at the center frequency has a steep coefficient curve on both sides of the center frequency but a long tail. More importantly, the Mel filter coefficient curve is narrower under the condition that the filter serial numbers are the same, so that the Mel filter coefficient curve has sharper frequency selection capability.

The invention provides a helicopter acoustic signal identification method based on auditory spectrum feature extraction, wherein an auditory model is introduced into the spectrum feature extraction to improve the performance of the helicopter acoustic signal identification method; based on three non-linear frequency scale transformations (Mel scale, ERB scale and Bark scale) and two auditory filter banks (Mel filter and Gammatone filter), six specific auditory spectrum feature extraction algorithms are given: M-M, E-M, B-M, M-G, E-G, and B-G algorithms. The numerical simulation experiment verifies the effectiveness and robustness of the proposed algorithm, and provides guidance for parameter setting and further optimization of the algorithm:

(1) the length L of the data segments and the number N of the filter banks are properly selected so that when the frequency resolution is in the same order of magnitude as the fundamental frequency (about dozens of Hz) of the helicopter, the recognition rate and the noise robustness of the auditory spectrum feature extraction are high;

(2) frequency analysis rangeLower boundary of (1)The influence on the recognition rate and the noise robustness is larger than the upper boundCan be generally arranged、(Nyquist frequency of signal) to reduce the parameter;

(3) a calculation model closer to the auditory perception of a real human ear is designed, the medium and low frequency resolution of scale transformation and the sharpness of frequency selection of an auditory filter bank are enhanced, and the improvement of the recognition performance is facilitated.

The invention is not limited to the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification and any novel one, or any novel combination, of the steps of any method or process so disclosed. Those skilled in the art to which the invention pertains will appreciate that insubstantial changes or modifications can be made without departing from the spirit of the invention as defined by the appended claims.