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CN111724762A - Noise reduction method and device for vehicle - Google Patents

Noise reduction method and device for vehicle Download PDF

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Publication number
CN111724762A
CN111724762A CN202010541688.XA CN202010541688A CN111724762A CN 111724762 A CN111724762 A CN 111724762A CN 202010541688 A CN202010541688 A CN 202010541688A CN 111724762 A CN111724762 A CN 111724762A
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signal
sound reproduction
control signal
frequency
amplitude
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CN111724762B (en
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沐永生
马登永
叶超
蔡野锋
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Zhongke Shangsheng Suzhou Electronics Co ltd
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Zhongke Shangsheng Suzhou Electronics Co ltd
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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
    • 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
    • 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
    • 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
    • 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

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
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  • Fittings On The Vehicle Exterior For Carrying Loads, And Devices For Holding Or Mounting Articles (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)

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 the vehicle-mounted audio system to obtain the undistorted maximum output amplitude of the signal corresponding to each frequency point on the frequency domain; s2, generating a reference signal, and filtering the reference signal through an adaptive filter to generate a control signal; s3, comparing the control signal with the maximum output amplitude, if the control signal is not larger 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 soon as possible.

Description

Noise reduction method and device for vehicle
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 general vehicle-mounted active noise reduction system uses the existing vehicle-mounted audio system on the vehicle, including 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 above a predetermined threshold, deactivating the noise control unit. CN104081451B especially aims at the active noise reduction system of feedback control mode, sets threshold value to ensure the amplitude of control signal can not amplify noise; 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, and compares whether the sound pressure difference before and after the time 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 is inevitably generated 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 schemes.
Disclosure of Invention
In view of the above technical problems, an object of the present invention is 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 the vehicle-mounted audio system to obtain the undistorted maximum output amplitude of the signal corresponding to each frequency point on the frequency domain;
s2, generating a reference signal, and filtering the reference signal through an adaptive filter to generate a control signal;
s3, comparing the control signal with the maximum output amplitude, if the control signal is not larger 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.
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 the 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.
Further, in step S12, the 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:
Figure BDA0002539163450000031
in the formula, THDml(f) Represents total harmonic distortion, Aml(f)Representing the amplitude, H, of said input signalml1、Hml2、Hml3、Hml4、Hml5The 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, M is 1, … M, L is 1, … L, and L represents 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: cl(f) W x (f), wherein Cl(f) Control signal representing the L-th sound reproduction channel, L ═ 1, … L, 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: wn+1＝Wn+κ×ΔW(Xk,em,Hml1) Wherein W isn+1And WnDenotes the filter coefficients after and before the update, respectively, n denotes the sampling point in time, k denotes the gain factor, Δ W (X)k,em,Hml1) As a function of the transfer function of the reference signal, the secondary channel, the residual noise signal, Xk、em、Hml1Respectively 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;
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;
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 can continuously 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 coefficient updating 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 the vehicle-mounted audio system to obtain the undistorted maximum output amplitude of the signal corresponding to each frequency point on the frequency domain;
s2, generating a reference signal, and filtering the reference signal through an adaptive filter to generate a control signal;
s3, comparing the control signal with the maximum output amplitude, if the control signal is not larger 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 specific process is described below.
Firstly, determining the position of a microphone.
The microphones are arranged according to the distribution of the noise field. The microphone arrangement is based on: the position noise field has large 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 the passengers, and the distance is less than 1/10 wavelengths of noise frequency; the engineering installation is operable.
And secondly, determining the number of the microphones.
And determining M microphones according to the noise reduction requirement. The noise reduction requirements are the locations that need to be handled, and in this embodiment, M microphones are required at M driving locations of the vehicle.
And thirdly, determining a loudspeaker channel.
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.
And fourthly, generating a frequency sweeping signal.
A sweep frequency signal x (n) with any amplitude is generated in a digital audio processor (DSP or MCU processor, etc.), and a specific method can refer to patent document CN 106199185B. 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.
And fifthly, synchronously acquiring acoustic response signals.
The microphones 1 to M synchronously acquire acoustic signals, and the linear impulse response [ h ] of the acoustic playback system is calculated111(n)…hM11(n)]TAnd second, third, up to fifth harmonic impulse responses h112(n)…hM12(n)]T…[h115(n)…hM15(n)]TFor a specific method, patent document CN106331951B is referred to.
Sixthly, 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 domainm1q(f) M1,. M, q 1,. 5, f is frequency.
Seventhly, constructing Total Harmonic Distortion (THD) of the whole sound reproduction system based on a one-dimensional Volterra filter modelm1(f) And the input signal amplitude a, as follows:
Figure BDA0002539163450000071
eighthly, at each frequency point f, solving the maximum output amplitude A to satisfy the inequality below, and obtaining the undistorted maximum amplitude A of the signal corresponding to the frequency point f on each frequency point on the frequency domainm1(f),m＝1，…M；
THDm1(f)≤10％。
The mechanism of human ear subjective perception distortion is complex, and the audio signal components are complex, so that the harmonic distortion measuring method based on subjective perception of distortion can be influenced by various factors such as masking effect in psychoacoustics. 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%.
Ninthly, repeating the steps from three to eight, feeding the sweep frequency signal to a second path of sound reproduction channel of the sound reproduction system, and calculating to obtain Am2(f),m＝1，…M；
Ten, repeating the steps until the vehicle-mounted sound is measuredLoudspeakers for all channels of the frequency system, get Aml(f) And M is 1, … M, L is 1, … L, see fig. 1.
Eleven, generating a reference signal X (f).
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 Xk(f),k＝1，…K。
Twelve, filtering the reference signal by a self-adaptive filter to generate a control signal Cl(f)，Cl(f) In general, in multi-channel control, L × K filter banks, each filter in the filter bank is a multi-order FIR or IIR filter.
Thirteen, comparing the control signal Cl(f) And the maximum output amplitude A measured beforeml(f) And M is 1, … M. If the control signal Cl(f)≤max(Aml(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, and the gain factor k is 1 at the moment. If the control signal Cl(f)>max(Aml(f) The output signal needs to be power compressed by Cl(f)/max(Aml(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))/Cl(f)。
Fourteen, the microphone picks up the residual noise signal in real time and records as em(n)，m＝1，…M。
Fifteen, as shown in FIG. 2, update the filter coefficient W in real timen+1＝Wn+κ×ΔW(Xk,em,Hml1)，Wherein Δ W (X)k,em,Hml1) 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 step sixteen of adjusting the maximum output amplitude according to the 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 Aml(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 Dm(f) M is 1, … M; 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 a probable output noise signal
Figure BDA0002539163450000091
η is a gain factor, generally speaking, η is 1, which means that the amplitude of the output control sound signal is equivalent to the original noise in the physical sense, when the active noise control system is in an unstable or even divergent state, the phase of the output control sound signal is uncontrollable, at this time, the phase of the output control sound signal is possibly opposite to the phase of the original noise, a better noise reduction effect is achieved, or a certain phase difference is achieved, and a partial noise reduction effect is also achieved, at worst, the phase of the output control sound signal is the same as the original noise, at this time, the noise of the whole sound field is increased by 6dB, but the noise increase is kept below 6dB under the active noise control structure provided by the embodiment, and the gain factor η can be adjusted to ensure that the noise increase is less than 6dB under the worst case;
3. comparison
Figure BDA0002539163450000092
And A obtained in the above stepml(f) The maximum amplitude of the output signal of the control system is always smaller than
Figure BDA0002539163450000093
And Aml(f) (ii) a In particular, if
Figure BDA0002539163450000094
Taking the signal output amplitude threshold value as Aml(f) (ii) a Otherwise, the signal output amplitude threshold is taken as
Figure BDA0002539163450000095
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 Dm(f) M is 1, … M; 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. the control system outputs a signal in phase with the noise signal and having a magnitude of
Figure BDA0002539163450000101
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
Figure BDA0002539163450000102
Is evaluated by subjective listening, and when the noise increase is heard, the final amplitude is recorded
Figure BDA0002539163450000103
4. Comparison
Figure BDA0002539163450000104
And A obtained in the above stepml(f) The maximum amplitude of the output signal of the control system is always smaller than
Figure BDA0002539163450000105
And Aml(f) (ii) a In particular, if
Figure BDA0002539163450000106
Taking the signal output amplitude threshold value as Aml(f) (ii) a Otherwise, the signal output amplitude threshold is taken as
Figure BDA0002539163450000107
As shown in 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 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 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 as an input to the fixed coefficient filter; signals can be synthesized according to information such as automobile speed, engine rotating speed, gear, load working condition and the like; 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 Xk(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 Cl(f)，Cl(f) W x X (f), the adaptive filter W is L × K filter bank, each filter in the filter bank is multi-stage FIR or IIR filter, the coefficient of the adaptive filter is variable and is determined by the reference signal, the transfer function of the secondary channel, the size of the residual noise signal, etc., the adaptive filter can be LMS, RLS, etc, the filter coefficient W is updated in real timen+1＝Wn+κ×ΔW(Xk,em,Hml1) Wherein Δ W (X)k,em,Hml1) 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 Cl(f)≤max(Aml(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 Cl(f)>max(Aml(f) The output signal needs to be power compressed by Cl(f)/max(Aml(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 Cl(f)≤max(Aml(f) Indicating that the control signal is in the normal range, the gain factor k is 1; if the control signal Cl(f)>max(Aml(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))/Cl(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 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 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 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 (10)

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 the vehicle-mounted audio system to obtain the undistorted maximum output amplitude of the signal corresponding to each frequency point on the frequency domain;
s2, generating a reference signal, and filtering the reference signal through an adaptive filter to generate a control signal;
s3, comparing the control signal with the maximum output amplitude, if the control signal is not larger 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.
2. The noise reduction method according to claim 1, wherein the step S1 specifically includes the steps of:
s11, generating a frequency sweep signal, and feeding the frequency sweep signal to one of the acoustic reproduction channels of the acoustic 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 the 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, the 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:
Figure FDA0002539163440000011
in the formula, THDml(f) Represents total harmonic distortion, Aml(f)Representing the amplitude, H, of said input signalml 1、Hml 2、Hml 3、Hml 4、Hml 5The 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, M is 1, … M, L is 1, … L, and L represents 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 in the step S14, the set value is 10%.
6. The noise reduction method according to claim 1, wherein in step S2, the control signal is as follows: cl(f) W x (f), wherein Cl(f) Control signal representing the L-th sound reproduction channel, L ═ 1, … L, 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, 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, and the gain factor is a ratio of the maximum value of the maximum output amplitude to the control signal.
8. The noise reduction method according to claim 7, wherein in step S3, the coefficients of the filter are updated in real time according to the following formula: wn+1＝Wn+κ×ΔW(Xk,em,Hml 1) Wherein W isn+1And WnRepresenting the filter coefficients after and before updating, respectively, n represents the sample point in time, k represents the gain factor, Δ W (X)k,em,Hml 1) As a function of the transfer function of the reference signal, the secondary channel, the residual noise signal, Xk、em、Hml 1Respectively 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.
9. 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.
10. A noise reduction apparatus for a vehicle for performing the noise reduction method according to any one of claims 1 to 9, 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;
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 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.
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