CN111724762B - Noise reduction method and device for vehicle - Google Patents
Noise reduction method and device for vehicle Download PDFInfo
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- CN111724762B CN111724762B CN202010541688.XA CN202010541688A CN111724762B CN 111724762 B CN111724762 B CN 111724762B CN 202010541688 A CN202010541688 A CN 202010541688A CN 111724762 B CN111724762 B CN 111724762B
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1785—Methods, e.g. algorithms; Devices
- G10K11/17853—Methods, e.g. algorithms; Devices of the filter
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1787—General system configurations
- G10K11/17879—General system configurations using both a reference signal and an error signal
- G10K11/17883—General system configurations using both a reference signal and an error signal the reference signal being derived from a machine operating condition, e.g. engine RPM or vehicle speed
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
- H04R3/02—Circuits for transducers, loudspeakers or microphones for preventing acoustic reaction, i.e. acoustic oscillatory feedback
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
Abstract
The invention discloses a noise reduction method for a vehicle, which comprises the following steps: s1, respectively measuring a loudspeaker of each sound reproduction channel of a vehicle-mounted audio system to obtain the undistorted maximum output amplitude of a signal corresponding to each frequency point on a frequency domain; s2, generating a reference signal, and filtering the reference signal through a self-adaptive filter to generate a control signal; s3, comparing the control signal with the maximum output amplitude, if the control signal is not greater than the maximum value of the maximum output amplitude, directly converting the control signal into an analog signal, and feeding the analog signal to the loudspeaker of each corresponding sound reproduction channel through a power amplifier; and if the control signal is larger than the maximum value of the maximum output amplitude, performing power compression on the control signal, converting the control signal subjected to power compression into an analog signal, and feeding the analog signal to the loudspeaker of each corresponding sound reproduction channel through a power amplifier. The invention can solve the possibility of divergence of the active noise control system and avoid abnormal sound as early as possible.
Description
Technical Field
The invention belongs to the technical field of vehicle-mounted noise reduction, and relates to a noise reduction method and device for a vehicle.
Background
With the improvement of vehicle intelligence, the requirements of drivers and passengers on the acoustic environment in the vehicle are more and more strict. The noise in the automobile can reduce the comfort of drivers and passengers, and cause the dysphoria and fatigue of passengers in the automobile; the definition of communication and even the perception of the driving to the signal sound outside the automobile can be influenced, and the traffic hidden trouble is increased. Automotive NVH (Noise, vision, harshness) is an important concern for automotive plants. By modifying the structural design, damping materials are added or damping springs and other devices are used for reducing noise, which is generally called passive noise control. The passive noise control method has a good noise reduction effect on middle and high frequency noise, but the method has a poor effect on low frequency noise, particularly noise of an engine in a carriage, road noise caused by collision friction of a road surface and tires, and even airflow wind noise, and the noise is often concentrated on low frequency. In addition, passive noise control requires a long training time and is difficult to control cost.
The scheme of actively making an uproar utilizes on-vehicle audio system, effectively reduces the interior noise of carriage, but can hardly give the car increase extra counter weight, helps reducing exhaust emissions, is the solution of a green energy-conservation. From the consideration of integration level and cost, the conventional vehicle-mounted audio system on a vehicle is used by a general vehicle-mounted active noise reduction system and comprises a door panel loudspeaker, a subwoofer loudspeaker, a vehicle-mounted power amplifier and the like. Consider the nonlinear characteristics of components such as power amplifiers and speakers. The voltage amplitude of the audio signal cannot be too large in consideration of the dynamic range of components such as a power amplifier and a speaker. In particular, for a loudspeaker, such as a commonly used moving coil loudspeaker, when the voltage amplitude is too large, the voice coil displacement deviates from the middle position too much, and the magnetic field force changes, which causes a nonlinear problem, causes distortion, affects the quality of reproduced sound, not only affects the control effect of active noise reduction, but also causes the whole control system to diverge, and generates abnormal sound or even larger noise.
In the prior art, EP1143411A2 detects a noise return value by a microphone, which is higher than a predetermined threshold value, and deactivates a noise control unit. CN104081451B sets a threshold value to ensure that the amplitude of a control signal cannot amplify noise especially for an active noise reduction system in a feedback control mode; setting the amplitude of the control signal to a threshold value when the amplitude of the control signal exceeds the threshold value; the threshold is considered to be determined for different engine speeds and loads (in other words, speed RPM). These thresholds are stored in a table, indexed by the engine RPM value. CN109587618A collects the noise signal after control, compares whether the sound pressure difference before and after the moment exceeds the set value; the active noise reduction system is reset if the set value is exceeded. The prior method has the following defects:
1. the current technology mainly considers the divergence risk of an active control system and judges the divergence risk of the system by detecting the change of a noise field in real time; such a treatment requires careful teaching of relevant parameters;
2. the control is carried out by detecting the noise field change, the control has the inevitable delay characteristic, and abnormal sound can be avoided because the control can be carried out only when the sound pressure rises and the divergent sign appears;
3. control by detecting noise field variations, which if prematurely suppressed, may have an effect on the noise reduction performance of the active noise reduction system;
4. after detecting the risk of divergence of the active noise reduction system, a method of resetting the active control system is often adopted; under certain acoustic conditions, the risk of system divergence is not eliminated and the system will re-enter the brute force of divergence; the whole active control system is caused to generate periodic high-low intermittent buzzing sound; this is also a problem with current mass production solutions.
Disclosure of Invention
In view of the above technical problems, the present invention aims to provide an improved noise reduction method and apparatus for a vehicle.
To achieve the above object, a first aspect of the present invention provides a noise reduction method for a vehicle, comprising the steps of:
s1, respectively measuring a loudspeaker of each sound reproduction channel of a vehicle-mounted audio system to obtain the undistorted maximum output amplitude of a signal corresponding to each frequency point on a frequency domain;
s2, generating a reference signal, and filtering the reference signal through a self-adaptive filter to generate a control signal;
s3, comparing the control signal with the maximum output amplitude, if the control signal is not greater than the maximum value of the maximum output amplitude, directly converting the control signal into an analog signal, and feeding the analog signal to the loudspeaker of each corresponding sound reproduction channel through a power amplifier; and if the control signal is larger than the maximum value of the maximum output amplitude, performing power compression on the control signal, converting the control signal after power compression into an analog signal, and feeding the analog signal to the loudspeaker of each corresponding sound reproduction channel through a power amplifier.
Further, the step S1 specifically includes the following steps:
s11, generating a frequency sweep signal, and feeding the frequency sweep signal to one channel of the sound reproduction system;
s12, synchronously acquiring output audio signals of the sound reproduction system, obtaining linear impulse response and higher harmonic impulse response of the sound reproduction system according to the output audio signals, and respectively converting the linear impulse response and the higher harmonic impulse response into frequency domains to obtain corresponding amplitude-frequency responses;
s13, constructing a relation between the total harmonic distortion of the sound reproduction system and the amplitude of the input signal of the sound reproduction system;
s14, solving a maximum output amplitude at each frequency point, wherein the maximum output amplitude meets the condition that the total harmonic distortion is smaller than a set value;
repeating steps S11 to S14 until the loudspeakers of all sound reproduction channels of the sound reproduction system are measured.
Furthermore, in step S12, output audio signals of the acoustic playback system are synchronously acquired through M microphones; in step S13, the relationship between the total harmonic distortion of the acoustic playback system and the amplitude of the input signal is as follows:
in the formula, THD ml (f) Represents total harmonic distortion, A ml(f) Representing the amplitude, H, of said input signal ml 1 、H ml 2 、H ml 3 、H ml 4 、H ml 5 The amplitude-frequency responses of the frequency domains of the linear impulse response, the second harmonic impulse response, the third harmonic impulse response, the fourth harmonic impulse response and the fifth harmonic impulse response of the sound reproduction system are respectively shown, and M =1, \ 8230m, L =1, \8230l, L indicates the number of sound reproduction channels.
Further, in step S13, a relationship between total harmonic distortion of the acoustic playback system and the amplitude of the input signal is constructed based on a one-dimensional Volterra filter model.
Further, in the step S14, the set value is 10%.
Further, in step S2, the control signal is as follows: c l (f) (= W X (f)), wherein C l (f) The control signal representing the L-th sound reproduction channel, L =1, \8230l, L represents the number of sound reproduction channels, W represents the adaptive filter, X (f) represents the reference signal.
Further, in step S3, if the control signal is greater than the maximum value of the maximum output amplitude, the coefficient of the adaptive filter is multiplied by a gain factor, where the gain factor is a ratio of the maximum value of the maximum output amplitude to the control signal.
Further, in step S3, the coefficients of the filter are updated in real time according to the following formula: w n+1 ＝W n +κ×ΔW(X k ,e m ,H ml 1 ) Wherein W is n+1 And W n Denotes the filter coefficients after and before updating, respectively, n denotes the sampling point in time, k denotes the gain factor, Δ W (X) k ,e m ,H ml 1 ) As a function of the transfer function of the reference signal, the secondary channel, the residual noise signal, X k 、e m 、H ml 1 Respectively representing the k reference signal, the residual noise picked up by the m microphone, and the linear transfer function from the l sound reproduction channel to the m microphone.
Further, the noise reduction method further comprises the step of adjusting the maximum output amplitude according to a noise field.
Further, the noise reduction method further comprises the step of adjusting the maximum output amplitude according to a subjective listening experience. The output amplitude threshold value of the active control system is further adjusted by combining subjective perception, so that the method is more suitable for practical application scenes and has more realistic engineering significance.
A second aspect of the present invention provides a noise reduction apparatus for a vehicle for performing the noise reduction method as described above, the noise reduction apparatus comprising:
the first signal generator is used for generating a frequency sweeping signal;
the analog-to-digital conversion module is used for converting the sweep frequency signal into an analog signal;
the power amplification module is used for amplifying the power of the simulated frequency sweeping signal and outputting the frequency sweeping signal;
the L sound reproduction channel switches are respectively in one-to-one correspondence with the L sound reproduction channels of the sound reproduction system, only the sound reproduction channel switch of the current test sound reproduction channel is switched on, and the other sound reproduction channel switches are in a disconnected state;
the plurality of loudspeakers are used for converting the electric signals into acoustic signals according to the output of the power amplification module, and each acoustic playback channel is at least provided with one loudspeaker;
the microphone is used for acquiring the acoustic response signal of the loudspeaker in real time;
the analog-to-digital conversion module is used for converting the acoustic response signal into a digital signal;
the impulse response calculation module is used for obtaining the linear impulse response and the harmonic impulse response of the acoustic playback system according to the sweep frequency signal and the acoustic response signal converted by the analog-to-digital conversion module;
the amplitude-frequency response calculation module is used for carrying out Fourier transform on the linear impulse response and the harmonic impulse response of the time domain, and transforming the linear impulse response and the harmonic impulse response into the frequency domain to obtain the amplitude-frequency response of the frequency domain;
the total harmonic distortion calculation module is used for calculating and analyzing the relationship between the total harmonic distortion and the amplitude of each frequency point in the frequency band;
the maximum output calculation module is used for obtaining the maximum undistorted output amplitude of the signal corresponding to the frequency of each frequency point on the frequency domain, and the total harmonic distortion is less than a set value;
a second signal generator for generating a reference signal;
the adaptive filter is used for filtering the reference signal to generate a control signal;
a power monitoring module for comparing the control signal with the maximum output amplitude;
the power compression module is used for performing power compression on the control signal when the control signal is larger than the maximum value of the maximum output amplitude;
a gain control module for setting a gain factor of the adaptive filter to 1 when the control signal is not greater than a maximum value of the maximum output amplitude; when the control signal is larger than the maximum value of the maximum output amplitude, setting a gain factor of the adaptive filter as the ratio of the maximum value of the maximum output amplitude to the control signal;
a fixed coefficient filter for filtering the reference signal;
a multiplication module for multiplying the audio signal output by the analog-to-digital conversion module and the reference signal filtered by the fixed coefficient filter for coefficient update iteration of the adaptive filter;
the noise reduction device also comprises a mode selection switch, the noise reduction device has a normal operation mode and a parameter debugging mode, when in the normal operation mode, a signal output by the power compression module is fed to the analog-to-digital conversion module, and an acoustic response signal collected by the microphone is fed to the multiplication module; when the microphone is in the parameter modulation mode, the frequency sweep signal of the first signal generator is fed to the digital-to-analog conversion module, and the acoustic response signal collected by the microphone is fed to the impulse response calculation module.
Compared with the prior art, the invention has the following advantages by adopting the scheme:
according to the noise reduction method and device for the vehicle, the output of the noise reduction system is detected not to exceed the threshold value, monitoring is carried out from the source, and abnormal sounds are prevented from being generated as soon as possible; the nonlinear sound reproduction characteristic of the vehicle-mounted audio system is considered, so that the possibility of divergence of the noise reduction system is fundamentally solved, and a scientific theoretical basis is provided; after the output exceeds the threshold value, the parameters of the noise reduction system are properly adjusted instead of simply resetting, so that the system is ensured to have continuous output, but the sound pressure of a noise field is not increased.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a flow chart of a maximum output amplitude measurement according to an embodiment of the present invention;
FIG. 2 is a flow chart of the coefficient update of an adaptive filter according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a noise reduction apparatus according to an embodiment of the present invention.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the advantages and features of the invention may be more readily understood by those skilled in the art. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto.
The embodiment provides a noise reduction method for a vehicle, in particular to an active noise reduction method, which mainly comprises the following steps:
s1, respectively measuring a loudspeaker of each sound reproduction channel of a vehicle-mounted audio system to obtain the undistorted maximum output amplitude of a signal corresponding to each frequency point on a frequency domain;
s2, generating a reference signal, and filtering the reference signal through a self-adaptive filter to generate a control signal;
s3, comparing the control signal with the maximum output amplitude, if the control signal is not greater than the maximum value of the maximum output amplitude, directly converting the control signal into an analog signal, and feeding the analog signal to the loudspeaker of each corresponding sound reproduction channel through a power amplifier; and if the control signal is larger than the maximum value of the maximum output amplitude, performing power compression on the control signal, converting the control signal after power compression into an analog signal, and feeding the analog signal to the loudspeaker of each corresponding sound reproduction channel through a power amplifier.
The specific process is described below.
1. The microphone position is determined.
The microphones are arranged according to the distribution of the noise field. The microphone arrangement is based on: the position noise field has larger amplitude; the sound radiation response gain from the door panel loudspeaker to the microphone is large, and amplitude response valley points cannot be formed under the influence of a carriage sound field mode; the position is closer to the ears of the driver and passengers, and the distance is less than 1/10 wavelength of the noise frequency; the engineering installation is operable.
2. The number of microphones is determined.
And determining M microphones according to the noise reduction requirement. The noise reduction requirements are which locations need to be handled, and in this embodiment, M microphones are required at M driving locations of the vehicle.
3. A speaker channel is determined.
According to the configuration of the car audio system, the system-independent sound reproduction channel L is defined. It should be noted that the number of the sound reproduction channels is not completely equal to the number of the speaker units, for example, a plurality of speaker units are driven by one audio signal and belong to the same sound reproduction channel.
4. A frequency sweep signal is generated.
In a digital audio processor (DSP or MCU processor, etc.), a frequency sweep signal x (n) with any amplitude is generated, and for a specific method, reference may be made to patent document CN106199185B. And feeding the signal to a first path of sound reproduction channel of a sound reproduction system, wherein the first path of sound reproduction channel comprises a digital-analog conversion circuit, a power amplification circuit and a loudspeaker unit.
5. Acoustic response signals are acquired synchronously.
The microphones 1 to M synchronously acquire acoustic signals, and the linear impulse response [ h ] of the acoustic playback system is calculated 111 (n)…h M11 (n)] T And second, third, up to fifth harmonic impulse responses h 112 (n)…h M12 (n)] T …[h 115 (n)…h M15 (n)] T For a specific method, refer to patent document CN106331951B.
6. According to the set frequency domain sampling rate, the linear impulse response and the higher harmonic impulse response of the time domain are subjected to Fourier transform to obtain the amplitude-frequency response H of the frequency domain m1q (f) M =1, \ 8230, M, q =1, \ 8230, 5,f is the frequency.
7. Total Harmonic Distortion (THD) of whole sound reproduction system is constructed based on one-dimensional Volterra filter model m1 (f) And the input signal amplitude a, as follows:
8. at each frequency point f, solving the maximum output amplitude A to satisfy the inequality below, and obtaining the non-distorted maximum amplitude A of the signal corresponding to the frequency point f on each frequency point in the frequency domain m1 (f),m＝1，…M；
THD m1 (f)≤10％。
The mechanism of human ear subjective perception distortion is very complex, and the harmonic distortion is measured by subjective perception of distortion due to the fact that audio signal components are complex and masking effect in psychoacoustics and other factors can influence the distortion. Just how much percent distortion can be perceived is a hot spot of research to date. But it is generally considered that less than 1% distortion is not perceptible, i.e., inaudible, by the human ear. And more than 10% of the distortion can cause discomfort and the mind is irritated. Therefore, the set value of the present embodiment is selected to be 10%.
9. Repeating the third to eighth steps, feeding the sweep frequency signal to a second path of sound reproduction channel of the sound reproduction system, and calculating to obtain A m2 (f),m＝1，…M；
10. Repeating the steps until the loudspeakers of all channels of the vehicle-mounted audio system are measured to obtain A ml (f) M =1, \ 8230, M, L =1, \ 8230, L, see fig. 1.
11. A reference signal X (f) is generated.
The reference signal can be synthesized according to the information of the automobile speed, the engine speed, the gear, the load working condition and the like; the reference signal may also be obtained directly by a rotation speed sensor, an acceleration sensor, a vibration sensor, a microphone (microphone), or the like. The reference signal may be a single 1-channel signal or multiple K-channels of signals, denoted as X k (f),k＝1，…K。
12. The reference signal is filtered by the adaptive filter to generate a control signal C l (f)，C l (f) W X (f). The adaptive filter W is a multi-order FIR filter or IIR filter in single channel control. In general multi-channel control, it is a filter bank of L × K channels; each filter in the filter bank is a multiple order FIR or IIR filter. Adaptive filteringThe coefficients of the filter are varied and are determined by the reference signal, the transfer function of the secondary channel, the magnitude of the residual noise signal, etc. The adaptive filter may be an LMS, RLS, or the like filter.
13. Comparing the control signal C l (f) And the maximum output amplitude A measured before ml (f) M =1, \ 8230, M. If the control signal C l (f)≤max(A ml (f) And the output signal directly passes through a digital-analog conversion circuit without power compression and is fed to a loudspeaker unit through a power amplifier, wherein the gain factor kappa =1. If the control signal C l (f)>max(A ml (f) The output signal needs to be compressed by power at a compression ratio of C l (f)/max(A ml (f) The coefficients of the filter need to be gain varied, i.e. the filter coefficients are reduced, multiplied by a gain factor k = max (a) ml (f))/C l (f)。
14. The microphone picks up the residual noise signal in real time and records it as e m (n)，m＝1，…M。
15. As shown in fig. 2, the filter coefficients W are updated in real time n+1 ＝W n +κ×ΔW(X k ,e m ,H ml 1 ) Wherein Δ W (X) k ,e m ,H ml 1 ) Is a function of the reference signal, the transfer function of the secondary channel, the residual noise signal.
The noise reduction method further includes a sixteenth step of adjusting the maximum output amplitude according to a noise field. Considering the possibility that the basic parameters of the active control system are failed and divergence is caused due to the change of a great acoustic environment such as the full opening of a vehicle door and a vehicle window or a skylight, the amplitude of the maximum output can be A ml (f) Based on the noise field characteristics, some adjustments are made. The method comprises the following specific steps:
1. under actual working conditions, the M microphones arranged in the steps are used for collecting noise signals in a carriage in real time and recording the noise signals as D m (f) M =1, \ 8230; the actual working conditions comprise idle neutral gear rapid acceleration, idle neutral gear slow acceleration, full-throttle acceleration and half-throttle acceleration under various gears tested on the road surface, various load conditions and the like;
2. calculating outPossibly outputting a noise signal
Wherein η is a gain factor, generally speaking, η =1 can be taken, and in a physical sense, the amplitude of the output control sound signal is equivalent to that of the original noise; when the active noise control system is in an unstable or even divergent state, the phase of the output control sound signal is uncontrollable, and at the moment, the phase of the output control sound signal is possibly opposite to that of the original noise, so that a better noise reduction effect is achieved, or a certain phase difference is achieved, and a partial noise reduction effect is achieved; the worst case is in phase with the original noise, where the noise of the whole sound field increases by 6dB; but with the active noise control structure proposed in this embodiment, the noise increase will remain below 6dB; the gain factor eta can be adjusted to ensure that the noise increment under the worst condition is less than 6dB;
3. comparison
And A obtained in the above step ml (f) Is always smaller than ≥ the maximum amplitude of the output signal of the control system is always smaller than ≥>
And A ml (f) (ii) a In particular, if>
Taking the signal output amplitude threshold value as A ml (f) (ii) a Otherwise, the signal output amplitude threshold is taken as->
The noise reduction method further comprises a seventeenth step of adjusting the maximum output amplitude according to a subjective listening experience. The method comprises the following specific steps:
1. under actual working conditions, the M microphones arranged in the steps are used for collecting noise signals in a carriage in real time and recording the noise signals as D m (f) M =1, \ 8230; the actual working conditions comprise idle speed neutral gear rapid acceleration, idle speed neutral gear slow acceleration and road surface testFull throttle and half throttle acceleration under various gears, various load conditions and the like;
2. the control system outputs a signal in phase with the noise signal and having a magnitude of
Superimposing the noise field into the noise field; the physical significance behind the method lies in that the active noise control system is in an unstable or even divergent state, the phase of the output control sound signal is uncontrollable, and at the moment, the phase of the output control sound signal is possibly opposite to that of the original noise, so that a better noise reduction effect is achieved, or a certain phase difference is achieved, and a partial noise reduction effect is also achieved; the worst case is in phase with the original noise, where the noise of the entire sound field increases;
3. adjusting signal amplitude
Is evaluated subjectively, and in the case of an audible increase in noise, the final amplitude is recorded>
4. Comparison of
And A obtained in the above step ml (f) Is always smaller than ≥ the maximum amplitude of the output signal of the control system is always smaller than ≥>
And A ml (f) (ii) a In particular, if->
Taking the signal output amplitude threshold value as A ml (f) (ii) a Otherwise, the signal output amplitude threshold is taken as->
Referring to fig. 3, the present embodiment also provides a noise reduction apparatus for a vehicle for performing the noise reduction method as described above, the noise reduction apparatus including:
the first signal generator is used for generating a frequency sweeping signal;
the analog-to-digital conversion module is used for converting the digitized sweep frequency signal or the control signal into an analog signal;
the power amplification module is used for amplifying and outputting the power of the simulated frequency sweeping signal or the control signal;
the L sound reproduction channel switches are respectively in one-to-one correspondence with the L sound reproduction channels of the sound reproduction system, each sound reproduction channel comprises a sound reproduction channel switch, only the sound reproduction channel switch of the currently tested sound reproduction channel is switched on, and the other sound reproduction channel switches are in a disconnected state;
the plurality of loudspeakers are used for converting the electric signals into acoustic signals according to the output of the power amplification module, and each acoustic playback channel is at least provided with one loudspeaker;
the M microphones are used for acquiring the acoustic response signals of the loudspeaker in real time;
the analog-to-digital conversion module is used for converting the acoustic response signal into a digital signal;
the impulse response calculation module is used for obtaining the linear impulse response and the harmonic impulse response of the sound reproduction system according to the sweep frequency signal and the acoustic response signal converted by the analog-to-digital conversion module;
the amplitude-frequency response calculation module is used for carrying out Fourier transform on the linear impulse response and the harmonic impulse response of the time domain, converting the linear impulse response and the harmonic impulse response into the frequency domain, and analyzing the frequency band to be [0,2 pi ] to obtain the amplitude-frequency response of the frequency domain;
the total harmonic distortion calculation module is used for calculating and analyzing the relation between the total harmonic distortion and the amplitude of each frequency point in the frequency band;
the maximum output calculation module is used for obtaining the maximum undistorted output amplitude of the signal corresponding to the frequency of each frequency point on the frequency domain, and the total harmonic distortion is less than a set value (namely 10%);
a second signal generator for generating a reference signal as an input to the adaptive filter and simultaneously as an input to the fixed coefficient filter; can be according to the steamSynthesizing signals from information such as vehicle speed, engine speed, gear and load condition; signals can also be directly obtained through a rotating speed sensor, an acceleration sensor, a vibration sensor, a microphone (microphone) and the like; the reference signal may be a single 1-channel signal or multiple K-channels of signals, denoted as X k (f),k＝1，…K；
An adaptive filter for filtering the reference signal to generate a control signal, and a second signal generator for filtering the reference signal to generate a control signal C l (f)，C l (f) = W X (f); the adaptive filter W is a filter bank of L multiplied by K paths; each filter in the filter bank is a multi-order FIR or IIR filter; the coefficient of the adaptive filter is changed and is determined by the reference signal, the transfer function of the secondary channel, the size of the residual noise signal and the like; the adaptive filter can be LMS, RLS and other filters; updating filter coefficients W in real time n+1 ＝W n +κ×ΔW(X k ,e m ,H ml1 ) Wherein Δ W (X) k ,e m ,H ml1 ) Is a function of the reference signal, the transfer function of the secondary channel, the residual noise signal;
the power monitoring module is used for comparing the control signal with the maximum output amplitude;
the power compression module is used for performing power compression on the control signal when the control signal is larger than the maximum value of the maximum output amplitude; if the control signal C l (f)≤max(A ml (f) The output signal directly passes through a digital-analog conversion circuit without power compression and is fed to a loudspeaker unit through a power amplifier; if the control signal C l (f)>max(A ml (f) The output signal needs to be power compressed by C l (f)/max(A ml (f))；
The gain control module is used for setting the gain factor of the adaptive filter to be 1 when the control signal is not greater than the maximum value of the maximum output amplitude; when the control signal is larger than the maximum value of the maximum output amplitude, setting the gain factor of the self-adaptive filter as the ratio of the maximum value of the maximum output amplitude to the control signal; if the control signal C l (f)≤max(A ml (f) Indicating that the control signal is in the normal range, gain factor k =1; if the control signal C l (f)>max(A ml (f) The coefficients of the filter need to be gain varied, i.e. the filter coefficients are reduced, multiplied by a gain factor k = max (a) ml (f))/C l (f)；
The fixed coefficient filter is used for filtering the reference signal and filtering the reference signal generated by the second signal generator, the frequency response represented by the filter is a transfer function of the estimated secondary channel, and the coefficient of the filter is fixed and invariable; the filtered signal is fed to a multiplication module for use as a coefficient update iteration of the adaptive filter;
and the multiplication module is used for multiplying the audio signal output by the analog-to-digital conversion module and the reference signal filtered by the fixed coefficient filter so as to be used for the coefficient updating iteration of the adaptive filter.
The noise reduction device also comprises a mode selection switch, the noise reduction device is provided with a normal operation mode and a parameter debugging mode, when the noise reduction device is in the normal operation mode, a signal output by the power compression module is fed to the analog-to-digital conversion module, and an acoustic response signal acquired by the microphone is fed to the multiplication module; when the microphone is in the parameter modulation mode, the sweep frequency signal of the first signal generator is fed to the digital-to-analog conversion module, and the acoustic response signal collected by the microphone is fed to the impulse response calculation module. The number of the mode selection switches is two, one mode selection switch is electrically connected with the output end of the power compression module and the output end of the first signal generator and is electrically connected with the input end of the digital-to-analog conversion module, and the other mode selection switch is electrically connected with the M microphones and is electrically connected with the input end of the multiplication module and the input end of the impulse response calculation magic block.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and are preferred embodiments, which are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (9)
1. A noise reduction method for a vehicle, characterized by comprising the steps of:
s1, respectively measuring a loudspeaker of each sound reproduction channel of a vehicle-mounted audio system to obtain the undistorted maximum output amplitude of a signal corresponding to each frequency point on a frequency domain;
s2, generating a reference signal, and filtering the reference signal through a self-adaptive filter to generate a control signal;
s3, comparing the control signal with the maximum output amplitude, if the control signal is not greater than the maximum value of the maximum output amplitude, directly converting the control signal into an analog signal, and feeding the analog signal to the loudspeaker of each corresponding sound reproduction channel through a power amplifier; if the control signal is larger than the maximum value of the maximum output amplitude, performing power compression on the control signal, converting the control signal after power compression into an analog signal, and feeding the analog signal to the loudspeaker of each corresponding sound reproduction channel through a power amplifier;
in step S3, if the control signal is greater than the maximum value of the maximum output amplitude, the coefficient of the adaptive filter is multiplied by a gain factor, where the gain factor is a ratio of the maximum value of the maximum output amplitude to the control signal.
2. The noise reduction method according to claim 1, wherein the step S1 specifically comprises the steps of:
s11, generating a frequency sweep signal, and feeding the frequency sweep signal to one of the sound reproduction channels of the sound reproduction system;
s12, synchronously acquiring output audio signals of the sound reproduction system, obtaining linear impulse response and higher harmonic impulse response of the sound reproduction system according to the output audio signals, and respectively converting the linear impulse response and the higher harmonic impulse response into frequency domains to obtain corresponding amplitude-frequency responses;
s13, constructing a relation between the total harmonic distortion of the sound reproduction system and the amplitude of the input signal of the sound reproduction system;
s14, solving a maximum output amplitude at each frequency point, wherein the maximum output amplitude meets the condition that the total harmonic distortion is smaller than a set value;
repeating steps S11 to S14 until the loudspeakers of all sound reproduction channels of the sound reproduction system are measured.
3. The noise reduction method according to claim 2, wherein in step S12, output audio signals of the acoustic playback system are synchronously acquired by M microphones; in step S13, the relationship between the total harmonic distortion of the acoustic playback system and the amplitude of the input signal is as follows:
in the formula, THD ml (f) Represents total harmonic distortion, A ml(f) Representing the amplitude, H, of said input signal ml1 、H ml2 、H ml3 、H ml4 、H ml5 The amplitude-frequency responses of the frequency domains of the linear impulse response, the second harmonic impulse response, the third harmonic impulse response, the fourth harmonic impulse response and the fifth harmonic impulse response of the sound reproduction system are respectively shown, and M =1, \ 8230m, L =1, \8230l, L indicates the number of sound reproduction channels.
4. The noise reduction method according to claim 2, wherein in step S13, a relationship between total harmonic distortion of the acoustic playback system and the amplitude of the input signal is constructed based on a one-dimensional Volterra filter model.
5. The noise reduction method according to claim 2, wherein the set value is 10% in step S14.
6. The method of claim 1The noise reduction method is characterized in that in the step S2, the control signal is as follows: c l (f) (= W X (f)), wherein C l (f) The control signal representing the L-th sound reproduction channel, L =1, \8230l, L represents the number of sound reproduction channels, W represents the adaptive filter, X (f) represents the reference signal.
7. The noise reduction method according to claim 1, wherein in step S3, the coefficients of the filter are updated in real time according to the following formula: w n+1 ＝W n +κ×ΔW(X k ，e m ，H ml1 ) Wherein W is n+1 And W n Denotes the filter coefficients after and before updating, respectively, n denotes the sampling point in time, k denotes the gain factor, Δ W (X) k ，e m ，H ml1 ) As a function of the transfer function of the reference signal, the secondary channel, the residual noise signal, X k 、e m 、H ml1 Respectively representing the k reference signal, the residual noise picked up by the m microphone and the linear transfer function from the l sound reproduction channel to the m microphone.
8. The method of reducing noise according to claim 1, further comprising the step of adjusting the maximum output amplitude according to a noise field or a subjective listening experience.
9. A noise reduction device for a vehicle for performing the noise reduction method according to any one of claims 1 to 8, the noise reduction device comprising:
the first signal generator is used for generating a frequency sweeping signal;
the analog-to-digital conversion module is used for converting the sweep frequency signal into an analog signal;
the power amplification module is used for amplifying the power of the simulated frequency sweeping signal and outputting the frequency sweeping signal;
the L sound reproduction channel switches are respectively in one-to-one correspondence with the L sound reproduction channels of the sound reproduction system, only the sound reproduction channel switch of the current test sound reproduction channel is switched on, and the other sound reproduction channel switches are in a disconnected state;
a plurality of loudspeakers, which are used for converting the electric signals into acoustic signals according to the output of the power amplifier module, and each acoustic playback channel is provided with at least one loudspeaker;
the microphone is used for acquiring the acoustic response signal of the loudspeaker in real time;
the analog-to-digital conversion module is used for converting the acoustic response signal into a digital signal;
the impulse response calculation module is used for obtaining the linear impulse response and the harmonic impulse response of the acoustic playback system according to the sweep frequency signal and the acoustic response signal converted by the analog-to-digital conversion module;
the amplitude-frequency response calculation module is used for carrying out Fourier transform on the linear impulse response and the harmonic impulse response of the time domain, and transforming the linear impulse response and the harmonic impulse response into the frequency domain to obtain the amplitude-frequency response of the frequency domain;
the total harmonic distortion calculation module is used for calculating and analyzing the relation between the total harmonic distortion and the amplitude of each frequency point in the frequency band;
the maximum output calculation module is used for obtaining the maximum undistorted output amplitude of the signal corresponding to the frequency of each frequency point on the frequency domain, and the total harmonic distortion is less than a set value;
a second signal generator for generating a reference signal;
the adaptive filter is used for filtering the reference signal to generate a control signal;
a power monitoring module for comparing the control signal with the maximum output amplitude;
the power compression module is used for performing power compression on the control signal when the control signal is larger than the maximum value of the maximum output amplitude;
a gain control module for setting a gain factor of the adaptive filter to 1 when the control signal is not greater than a maximum value of the maximum output amplitude; when the control signal is larger than the maximum value of the maximum output amplitude, setting a gain factor of the adaptive filter as the ratio of the maximum value of the maximum output amplitude to the control signal;
a fixed coefficient filter for filtering the reference signal; and
a multiplication module for multiplying the audio signal output by the analog-to-digital conversion module and the reference signal filtered by the fixed coefficient filter for coefficient update iteration of the adaptive filter;
the noise reduction device also comprises a mode selection switch, the noise reduction device has a normal operation mode and a parameter debugging mode, when in the normal operation mode, a signal output by the power compression module is fed to the analog-to-digital conversion module, and an acoustic response signal collected by the microphone is fed to the multiplication module; when the microphone is in the parameter modulation mode, the sweep frequency signal of the first signal generator is fed to the analog-to-digital conversion module, and the acoustic response signal collected by the microphone is fed to the impulse response calculation module.
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