Feedback active noise cancellation system with biquadratic error control

Abstract

A feedback-type active noise cancellation system with dual second-order error quantity control, comprising an error signal receiving device, an audio output device, an error shaper, and a feedback module. The error signal receiving device receives an error sound source signal and outputs an error signal. The audio output device outputs an audio signal. The input end of the error shaper is connected to the error signal receiving device to receive the error signal, and the error shaper eliminates high-frequency noise of the error signal and then outputs an error-shaped signal. The input end of the feedback module is connected to the output end of the error shaper and receives the audio signal, and the feedback module outputs a noise cancellation signal according to the error-shaped signal and the audio signal.

Description

Technical Field

[0001] This application belongs to the technical field of feedback active noise cancellation, and particularly relates to a feedback active noise cancellation system with dual second-order error quantity control. Background Art

[0002] Active Noise Control (ANC) is a device that can isolate specified noise without affecting other sounds. The main principle is to receive the specified noise through a sound source receiving device and use a sound transmitting device to send out sound waves with exactly opposite phases, so that the two sound waves can cancel each other out, thereby filtering out the noise. Currently, active noise control technology has been widely applied to sound insulation speakers on airplanes and fighter jets, as well as noise-canceling headphones.

[0003] Traditional feedback active noise control technology mainly converts the received error signal into a corresponding reverse signal through a filter (FIR filter) to filter out noise. However, the high frequency of the input error signal may cause the adaptive operation at the front end of the filter (FIR filter) to diverge, resulting in poor noise reduction effect. Summary of the Invention

[0004] The embodiment of this application provides a feedback active noise cancellation system with dual second-order error quantity control, which can improve the noise reduction effect.

[0005] In a first aspect, an embodiment of the present application provides a feedback-type active noise cancellation system with dual second-order error amount control, including: an error signal receiving device, an audio output device, an error shaper, and a feedback module. The error signal receiving device receives an error sound source signal and outputs an error signal. The audio output device outputs an audio signal. The input end of the error shaper is connected to the error signal receiving device to receive the error signal. The error shaper includes a noise bandwidth detector, a coefficient corrector with an input end connected to the noise bandwidth detector, and a first to Nth order biquadratic filter with an input end connected to the coefficient corrector. The noise bandwidth detector calculates the bandwidth of the error signal. The coefficient corrector corrects the coefficients of the first to Nth order biquadratic filter according to the bandwidth of the error signal. The first to Nth order biquadratic filter eliminates the high-frequency noise of the next sampled error signal according to the corrected coefficients and outputs an error-shaped signal. The input end of the feedback module is connected to the output end of the error shaper and receives the audio signal. The output end of the feedback module is connected to the audio output device. The feedback module includes a mixer, an LMS calculator with input ends respectively connected to the output end of the error shaper and the output end of the mixer, and an adaptive filter with input ends respectively connected to the output end of the LMS calculator and the output end of the mixer. The input end of the mixer is connected to the output end of the error shaper and receives the audio signal. The mixer mixes the error-shaped signal with the audio signal and outputs a mixed signal. The LMS calculator updates the weight coefficients of the adaptive filter according to the received error-shaped signal and the mixed signal. The adaptive filter filters the mixed signal according to the updated weight coefficients and outputs a noise-canceling signal to the audio output device.

[0006] Therefore, compared with the prior art, the present application can reduce the high-frequency noise of the error signal, and can adjust the eliminated high-frequency noise according to requirements. Further, it can avoid the operation divergence of the adaptive filter and reduce the noise cancellation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0008] Figure 1 is a block diagram of a feedback-type active noise cancellation system with dual second-order error amount control provided by an embodiment of the present application;

[0009] Figure 2 is a block diagram of an error shaper provided by an embodiment of the present application;

[0010] Figure 3It is a block diagram of a biquadratic filter provided by another embodiment of the present application;

[0011] Figure 4 It is a block diagram of a hierarchical configuration of a 1st to Nth order biquadratic filter provided by an embodiment of the present application;

[0012] Figure 5 It is a schematic diagram of the control logic of a feedback-type active noise cancellation system with biquadratic error control provided by an embodiment of the present application;

[0013] Figure 6 It is a schematic flowchart of a feedback-type active noise cancellation system with biquadratic error control provided by an embodiment of the present application.

[0014] Among them, the main reference signs in the figures are as follows:

[0015] 100 Feedback-type active noise cancellation system with biquadratic error control; 10 Error receiving device;

[0016] 12 Error microphone; 14 Preamplifier; 16 Anti-aliasing filter; 18 Analog-to-digital converter;

[0017] 20 Audio output device; 22 Digital-to-analog converter; 24 Reconstruction filter; 26 Power amplifier;

[0018] 28 Speaker; 30 Error shaper; 32 Noise bandwidth detector; 34 Coefficient corrector;

[0019] 36 1st to Nth order biquadratic filter; 361 - 36N Biquadratic filter; 40 Feedback module;

[0020] 41 First secondary path filter; 42 Mixer; 43 Second secondary path filter;

[0021] 44 LMS calculator; 46 Adaptive filter; NS Noise. Detailed implementation manners

[0022] The detailed description and technical content of the present application are described below in conjunction with the accompanying drawings. Furthermore, for the convenience of illustration, the scales of the drawings in the present application are not necessarily drawn according to the actual scales, and the multiple drawings and their scales are not used to limit the scope of the present application, which is hereby explained in advance.

[0023] The noise cancellation device or noise cancellation controller in the embodiments of the present application can be implemented in a personal listening system including a wired headset, a smart phone, a wireless headset, or other head-mounted audio devices, which is not limited in the present application.

[0024] In the present application, the "device", "apparatus", "module" and their corresponding functions can be executed collaboratively by a single chip or a combination of multiple chips. The number of chips configured is not within the scope defined by the present application. In addition, the chip can be, but is not limited to, a combination of devices such as a processor, a central processing unit (CPU), a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a programmable logic device (PLD), etc., and is not limited in the present application. In another embodiment of the present application, the "device", "apparatus", "module" or their combination can be a chip provided by an audio device (such as a mobile device, a wearable device), or an audio chip integrated or separated from a wired earphone, a wireless earphone or a head-mounted device. Multiple variations are not within the scope defined by the present application.

[0025] The following describes one embodiment of the present application. Please refer to Figure 1 , a block diagram of a feedback active noise cancellation system with a biquadratic error control provided by an embodiment of the present application is shown as follows:

[0026] Please refer to Figure 1 , this embodiment discloses a feedback active noise cancellation system 100 with a biquadratic error control, which mainly includes an error signal receiving device 10, an audio output device 20, an error shaper 30, and a feedback module 40.

[0027] The error signal receiving device 10 is mainly used to receive an error sound source signal. The error signal receiving device 10 is generally disposed at a position between a speaker and a human ear. The audio received by the error signal receiving device 10 mainly includes the difference between the noise NS and the sound output by the speaker. Here, this difference is defined as the error sound source signal. In the embodiment, the error signal receiving device 10 can be, for example, a microphone, a pickup, or other devices that can receive environmental sound waves and further convert them into analog or digital audio. In the embodiment, the error signal receiving device 10 includes an error microphone 12, a preamplifier 14 connected to the rear end of the error microphone 12, an anti-aliasing filter 16 connected to the rear end of the preamplifier 14, and an analog-to-digital converter 18 connected to the rear end of the anti-aliasing filter 16. Finally, the analog-to-digital converter 18 outputs an error signal to the error shaper 30.

[0028] The audio output device 20 described above is mainly used to output a noise reduction signal and an original audio for canceling the noise NS. In an embodiment, the audio output device 20 can be, for example, a speaker, a horn, and an audio processing chip correspondingly arranged, and devices of this kind for outputting sound. Herein, the output sound is defined as an audio signal. In an embodiment, the audio output device 20 sequentially includes a speaker 28, a power amplifier 26 connected to the front end of the speaker 28, a reconstruction filter 24 connected to the front end of the power amplifier 26, and a digital-to-analog converter 22 connected to the front end of the reconstruction filter 24. Among them, the digital-to-analog converter 22 receives the noise reduction signal and the original audio of the feedback module 40 (the input position is not shown in the figure). The original audio is music, human voice, or other sounds that have not entered the space and have not been affected by the noise NS, and is not limited in this application.

[0029] The error shaper 30 described above is mainly used to reduce the high-frequency noise of the error signal, and the error signal after reducing the high-frequency noise is defined as an error shaping signal. Please refer to Figure 2 , Figure 3 , Figure 4 , in this application, the block diagram of the error shaper 30, the biquadratic filter, and the block diagram of the hierarchical configuration of the 1st to Nth order biquadratic filters are shown as follows:

[0030] The input end of the error shaper 30 is connected to the output end of the error receiving device 10 to receive the error signal. In an embodiment, the error shaper 30 sequentially includes a noise bandwidth detector 32, a coefficient corrector 34 with its input end connected to the noise bandwidth detector 32, and a 1st to Nth order biquadratic filter 36 with its input end connected to the coefficient corrector 34. Among them, the input end of the noise bandwidth detector 32 is connected to the output end of the error receiving device 10; the other input end of the coefficient corrector 34 is connected to the error microphone 12, and a frequency detector (not shown in the figure) is provided between the coefficient corrector 34 and the error microphone 12; the input ends of the biquadratic filters in the 1st to Nth order biquadratic filter 36 are connected to the coefficient corrector 34. Specifically, the other input end of the 1st order biquadratic filter 361 of the 1st to Nth order biquadratic filter 36 is connected to the error receiving device 10. Finally, the error shaping signal is output from the Nth order biquadratic filter 36N of the 1st to Nth order biquadratic filter 36 to the feedback module 40.

[0031] The hierarchical configuration of the 1st to Nth order biquadratic filter 36 is as follows. Please refer to Figure 4: The output terminal of the first-order biquadratic filter 361 is connected to another input terminal of the second-order biquadratic filter 362; the output terminal of the second-order biquadratic filter 362 is connected to another input terminal of the third-order biquadratic filter 363, and so on. The output terminal of the (N - 1)-order biquadratic filter 36N-1 is connected to another input terminal of the N-order biquadratic filter 36N.

[0032] The input terminal of the feedback module 40 is connected to the error shaper 30 and receives the audio signal, which is used to perform an adaptive operation on the received audio signal and the error shaping signal, and use the generated reverse signal to cancel the noise to achieve a noise reduction effect. Here, the signal output by the feedback module 40 for canceling the noise NS is defined as the noise reduction signal. In one embodiment, please also refer to Figure 5 , the feedback module 40 includes a mixer 42, an LMS arithmetic unit 44 (Least Mean Square Filter) whose input terminal is connected to the output terminal of the mixer 42, and an adaptive filter 46 (Adaptive filter) whose input terminal is connected to the LMS arithmetic unit 44. Among them, another input terminal of the LMS arithmetic unit 44 is connected to the output terminal of the error shaper 30; another input terminal of the adaptive filter 46 is connected to the mixer 42, and the output terminal of the adaptive filter 46 is connected to the audio output device 20. In this embodiment, there is a first secondary path filter 41 between the path where the signal input to the speaker 28 is fed back to the mixer 42 to pre-filter the audio signal in advance; there is a second secondary path filter 43 between the output terminal of the mixer 42 and the input terminal of the LMS arithmetic unit 44 to pre-filter the mixed signal in advance. The first secondary path filter 41 and the second and path filters 43 are used to estimate the transfer function of the actual path, so that after the LMS arithmetic unit 44 adjusts the coefficients of the adaptive filter 46, a noise reduction signal with the same magnitude and opposite phase as the noise NS can be generated to the audio output device 20.

[0033] The above specifically describes the embodiments of the hardware architecture of the present application. The operation of the present application will be further described below. Please also refer to Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 , which are the block diagram of the hierarchical configuration of the biquadratic filter, the first to N-order biquadratic filters of the present application, and the control logic schematic diagram and flow schematic diagram of the feedback-type active noise cancellation system for biquadratic error amount control, as shown in the figure:

[0034] First, the noise NS and the audio signal are received by the error microphone 12 of the error signal receiver 10, and the noise NS and the audio signal are converted into a digital audio error signal by the error signal receiver 10 and sent to the error shaper 30 (step S201). When the system is started, the audio signal has not been processed for noise reduction, and the audio signal at this time is the original audio signal.

[0035] The noise bandwidth detector 32 of the error shaper 30 detects the bandwidth of the error signal and outputs a noise bandwidth signal with the same bandwidth as the center frequency of the error signal to the coefficient corrector 34 (step S202). The center frequency is obtained by the noise bandwidth detector 32 from the error signal according to the following formula:

[0036]

[0037] where k = 0,..., M - 1; x(n) is the error signal input by the error signal receiver at the nth stage, f(k) is the center frequency output by the noise bandwidth detector 32, and there are M outputs of f(k), where M is a preset number of outputs.

[0038] The coefficient corrector 34 receives the error microphone signal and the noise bandwidth signal, and calculates a coefficient correction signal for adjusting the coefficients of the biquadratic filters to the 1st to Nth order biquadratic filters 36, so that the 1st to Nth order biquadratic filters 36 correct the coefficients according to the bandwidth of the error signal (step S203). In other words, the coefficients of the 1st to Nth order biquadratic filters 36 of the present application can be corrected by the coefficient corrector 34 to adjust the high-frequency noise to be corrected. Please refer to Figure 3 The coefficient corrector 34 corrects the coefficients of each of the biquadratic filters 361 - 36N according to the following formula:

[0039]

[0040]

[0041]

[0042]

[0043]

[0044] where w0 is the center angular frequency value, α is the natural frequency parameter, and b0, b1, b2, a1, a2 are the coefficients of each of the biquadratic filters 361 - 36N.

[0045] The aforementioned center angular frequency value w0 and the natural frequency parameter α are obtained by the coefficient corrector 34 according to the following formula:

[0046]

[0047]

[0048] wherein, f k is the center frequency input by the noise bandwidth detector 32, F s is the frequency of the error microphone signal input by the error microphone 12, Q is a preset quality parameter, w0 is the value of the central angular frequency, and α is the natural frequency parameter. The aforementioned quality parameter Q is determined based on the quality factor; the natural frequency parameter α is determined based on the natural frequency factor.

[0049] Furthermore, the 1st to Nth order biquadratic filters 36 correct the bandwidth correction coefficient of the received error signal, and after eliminating the high-frequency noise of the error signal of the next sample according to the corrected coefficient (x(n - 1) and x(n - 2) are regarded as known parameters), the error shaping signal is output by the Nth order biquadratic filter 36N (step S204). Each of the biquadratic filters 361 - 36N filters the error signal according to the following formula:

[0050] y(n) = b0 × x(n) + b1 × x(n - 1) + b2 × x(n - 2) - a1 × y(n - 1) - a2 × y(n - 2);

[0051] wherein, x(n), x(n - 1), and x(n - 2) are the error signals received at the nth, (n - 1)th, and (n - 2)th time points respectively, y(n), y(n - 1), and y(n - 2) are the error shaping signals output at the nth, (n - 1)th, and (n - 2)th time points respectively, and b0, b1, b2, a1, and a2 are the coefficients of each of the biquadratic filters 361 - 36N.

[0052] Furthermore, the audio signal that has passed through the first secondary path filter 41 and the error shaping signal are mixed by the mixer 42 of the feedback module 40 and a mixed signal is output (step S205).

[0053] The LMS calculator 44 receives the error shaping signal and the mixed signal that has passed through the second secondary path filter 43 to update the weight coefficients of the adaptive filter 46, so that the adaptive filter 46 adjusts the received mixed signal into a noise reduction signal with the same magnitude and opposite phase as the noise NS, and the adaptive filter 46 outputs the noise reduction signal to the audio output device 20 (step S206).

[0054] Finally, the audio output device 20 uses the received noise reduction signal to eliminate the noise NS of the next stage, and converts the noise reduction signal and the original audio into an audio signal that is output as an analog audio (step S207). In other words, the audio signal achieves a noise reduction effect through the noise reduction signal of the previous stage, so that the original audio in the audio signal can enter the human ear without being affected by the noise NS.

[0055] In summary, compared with the prior art, the present application can reduce the high-frequency noise of the error signal compared with the prior art, and can adjust the eliminated high-frequency noise according to requirements. Furthermore, it can avoid the operation divergence of the adaptive filter and reduce the noise reduction effect.

[0056] The present application has been described in detail above. However, the above description is only an embodiment of the present application, and the scope of implementation of the present application cannot be limited thereby. That is, all equivalent changes and modifications made according to the scope of the patent application of the present application should still fall within the scope covered by the patent of the present application.

Claims

1. A feedback-type active noise cancellation system with double second-order error quantity control, characterized in that, The system includes: An error signal receiving device that receives an error sound source signal and outputs an error signal; An audio output device that outputs an audio signal; An error shaper, the input end of the error shaper is connected to the error signal receiving device to receive the error signal. The error shaper includes a noise bandwidth detector, a coefficient corrector with its input end connected to the noise bandwidth detector, and a 1st to Nth order biquadratic filter with its input end connected to the coefficient corrector. The noise bandwidth detector calculates the bandwidth of the error signal. The coefficient corrector corrects the coefficients of the 1st to Nth order biquadratic filter according to the bandwidth of the error signal. The 1st to Nth order biquadratic filter eliminates the high-frequency noise of the next sampled error signal according to the corrected coefficients and outputs an error-shaped signal; and A feedback module, the input end of the feedback module is connected to the output end of the error shaper and receives the audio signal. The output end of the feedback module is connected to the audio output device. The feedback module includes a mixer, an LMS calculator with its input ends respectively connected to the output end of the error shaper and the output end of the mixer, and an adaptive filter with its input ends respectively connected to the output end of the LMS calculator and the output end of the mixer. The input end of the mixer is connected to the output end of the error shaper and receives the audio signal. The mixer mixes the error-shaped signal with the audio signal and outputs a mixed signal. The LMS calculator updates the weight coefficients of the adaptive filter according to the received error-shaped signal and the mixed signal. The adaptive filter filters the mixed signal according to the updated weight coefficients and outputs a noise-reduced signal to the audio output device; The coefficient corrector corrects the coefficients of each of the biquadratic filters according to the following formula: ; ; ; ; ; where, is the central angular frequency value, is the natural frequency parameter, , , , , are the coefficients of each of the biquadratic filters; the coefficient trimmer corrects the coefficients of each of the biquadratic filters to adjust the high-frequency noise to be corrected, the central angular frequency value is determined by the central frequency of the input noise bandwidth signal and the frequency of the input error microphone signal, and the natural frequency parameter is determined by the central angular frequency value and a preset quality parameter.

2. The system according to claim 1, wherein The error signal receiving device includes an error microphone, a preamplifier connected to the rear end of the error microphone, an anti-aliasing filter connected to the rear end of the preamplifier, and an analog-to-digital converter connected to the rear end of the anti-aliasing filter.

3. The system according to claim 1, wherein The audio output device includes a speaker, a power amplifier connected to the front end of the speaker, a reconstruction filter connected to the front end of the power amplifier, and a digital-to-analog converter connected to the front end of the reconstruction filter.

4. The system according to claim 2, wherein The input end of the noise bandwidth detector is connected to the error signal receiving device to detect the bandwidth of the error signal and output a noise bandwidth signal with the same bandwidth as the center frequency of the error signal; Wherein, the input end of the coefficient corrector is connected to the error microphone to receive the error microphone signal, and calculates and outputs a coefficient correction signal for adjusting the coefficients of the biquadratic filter to the 1st to Nth order biquadratic filter according to the error microphone signal and the noise bandwidth signal; Wherein, the input end of the 1st order biquadratic filter in the 1st to Nth order biquadratic filter is connected to the error signal receiving device to receive the error signal. The 1st to Nth order biquadratic filter updates the coefficients according to the coefficient correction signal, corrects the next sampled error signal according to the coefficients, and then the Nth order biquadratic filter in the 1st to Nth order biquadratic filter outputs the error-shaped signal.

5. The system according to claim 4, wherein Each of the biquadratic filters filters the error signal according to the following formula: ； Among them, and and are the error signals received at the -th, -th, and -th time points, and and are the error integer signals output at the -th, -th, and -th time points, and and and and are the coefficients of each of the said biquadratic filters.

6. The system according to claim 5, wherein The central angular frequency value and the natural frequency parameter are obtained by the coefficient modifier according to the following formula: ； ； Among them, is the center frequency input by the noise bandwidth detector, is the frequency input by the error microphone, and Q is a preset quality parameter, is the central angular frequency value, is the natural frequency parameter.

7. The system according to claim 6, wherein The center frequency is obtained from the error signal by the noise bandwidth detector according to the following formula: Among them, is the error signal input by the error signal receiving device in the nth stage, is the center frequency output by the noise bandwidth detector, There are M outputs in total, and M is the preset number of outputs.

8. The system according to claim 6, wherein The quality parameter is determined based on the quality factor, and the natural frequency parameter is determined based on the natural frequency factor.

9. The system according to claim 1, wherein There is a first secondary path filter between the output end of the audio output device and the input end of the mixer; there is a second secondary path filter between the output end of the mixer and the input end of the LMS calculator.

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