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CN109089203B - Multi-channel signal conversion method of automobile sound system and automobile sound system - Google Patents

Multi-channel signal conversion method of automobile sound system and automobile sound system Download PDF

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CN109089203B
CN109089203B CN201811072927.0A CN201811072927A CN109089203B CN 109089203 B CN109089203 B CN 109089203B CN 201811072927 A CN201811072927 A CN 201811072927A CN 109089203 B CN109089203 B CN 109089203B
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sound
signals
background
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CN109089203A (en
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叶超
蔡野锋
马登永
沐永生
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Zhongke Shangsheng Suzhou Electronics Co ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S7/00—Indicating arrangements; Control arrangements, e.g. balance control
    • H04S7/30—Control circuits for electronic adaptation of the sound field
    • H04S7/302—Electronic adaptation of stereophonic sound system to listener position or orientation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S7/00—Indicating arrangements; Control arrangements, e.g. balance control
    • H04S7/30—Control circuits for electronic adaptation of the sound field
    • H04S7/305—Electronic adaptation of stereophonic audio signals to reverberation of the listening space
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S2400/00—Details of stereophonic systems covered by H04S but not provided for in its groups
    • H04S2400/01—Multi-channel, i.e. more than two input channels, sound reproduction with two speakers wherein the multi-channel information is substantially preserved

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Abstract

The invention relates to an automobile sound system and a multi-channel signal conversion method thereof, which are specially used for an in-automobile multi-channel loudspeaker system and have better practicability and operability. The multi-channel signal conversion method comprises the following steps: A. processing the direct sound signal and the background sound signal through a mixing matrix to generate multi-channel signals of a plurality of channels in the vehicle; B. filtering the multi-channel signals of each channel to generate signals of each loudspeaker unit; C. the signals of each loudspeaker unit are subjected to position correction on the difference of hearing caused by different distances between the loudspeaker unit and the listening position through a position correction filter, and then the loudspeaker units are driven to sound; or, after further height correction is performed on the difference in audibility caused by the difference in height of the speaker units by the height correction filter, the speaker units are driven to sound.

Description

Multi-channel signal conversion method of automobile sound system and automobile sound system
Technical Field
The invention relates to the field of automobile sound systems, in particular to a method for converting stereo sound into multi-channel signals of an automobile sound system.
Background
In an automobile sound system, more loudspeakers are adopted to increase the performance of the sound system and improve the comfort of drivers and passengers in the automobile. However, most of the music signals are stereo two-channel signals, and thus the stereo signals need to be converted into multi-channel signals. However, most current methods of stereo to multi-channel signal conversion are for home theater, Soundbar, etc. systems where the listener position is substantially equidistant from the various speakers, whereas for car sound systems the listener position is not the optimal position, regardless of which listening position, one set of speakers is closest. And because of the limitation of the space in the vehicle, the installation position of the loudspeaker is not ideal, so the method of converting the multi-channel signal by stereo suitable for the environment in the vehicle needs to be adopted aiming at the particularity of the space in the vehicle so as to improve the sound reproduction performance of the sound system in the vehicle.
United states patent US6697491B1 by haman uses a time domain algorithm to divide into eight regions at 45 degree intervals in four directions, front-back and left-right, to redistribute the signal to five loudspeakers according to the energy relationship between the left and right channels. The calculation process is more complicated to divide eight regions.
U.S. Pat. No. 6496584B2 and chinese patent zl01802081.x are based on Principal Component Analysis (PCA), a weighting factor of a left channel and a right channel is calculated by a least mean square error method, speech sound and background sound are separated, a vector relation of sound signals under a three-dimensional coordinate is determined by calculating a correlation coefficient between the left channel and the right channel, the speech sound and the background sound are divided into four signals of a left signal, a middle signal, a right signal and a surround signal according to an energy conservation principle, and the surround signal is divided into a left rear surround signal and a right rear surround signal by a cross correlation filter, so that conversion from a dual channel to a 5 channel is realized. The method is simple and fast in operation speed, only one surround signal can be separated through PCA analysis, and a certain error is generated by the method of separating left rear surround and right rear surround by using a decorrelation filter.
The united states patent US8295493B2 converts the sound signal into the frequency domain by short-time fourier transform, estimates the direct sound signal and the background sound signal by the method of minimum mean square error, then equally divides the spatial angles of the original left and right speakers according to the spatial positions of the reproduced speakers, and distributes the direct sound signal to the newly added speakers to ensure the accurate localization of the spatial sound image. The method can realize the sound reproduction of any plurality of loudspeakers and can also be applied to a WFS system. However, the calculation process is complex, and the method of angle division cannot effectively determine the sound source position, which is easy to cause the sound image localization error.
Most of the prior patents are directed to a method for converting multi-channel signals by stereo under a common environment, and the method is relatively lacked under a special environment in a vehicle.
Disclosure of Invention
In view of the above problems, the present invention is directed to a multi-channel signal conversion method for an automobile audio system, which is specifically directed to an in-vehicle multi-channel speaker system and has better practicability and operability. The invention also aims to provide the automobile sound system based on the multi-channel signal conversion method of the automobile sound system.
According to the first aspect of the invention, the technical scheme adopted by the invention is as follows:
a multi-channel signal conversion method of an automobile sound system comprises the following steps:
A. processing the direct sound signal and the background sound signal through a mixing matrix to generate a multi-channel signal in the vehicle;
B. filtering the multi-channel signals to generate signals of each loudspeaker unit;
C. the signals of each loudspeaker unit are subjected to position correction on the difference of hearing caused by different distances between the loudspeaker unit and the listening position through a position correction filter, and then the loudspeaker units are driven to sound; or, the signals of each loudspeaker unit are subjected to position correction on the difference of the audibility caused by the different distances between the loudspeaker unit and the listening position through a position correction filter, and then are subjected to height correction on the difference of the audibility caused by the different heights of the loudspeaker unit through a height correction filter, and then are driven to generate sound.
In one embodiment, in step a, a multi-channel signal in the vehicle is generated, including a front left signal xFL(n), right front signal xFR(n), left rear signal xRL(n), right rear signal xRR(n), left surround signal xSL(n), right surround signal xSR(n) mid-set signal xCEN(n), subwoofer signal xSUB(n)。
Specifically, the multi-channel signal is represented by the following equation,
Figure GDA0002618586710000031
wherein W represents a conversion coefficient matrix, ω1、ω2、…ω18The conversion coefficients are respectively represented by a number of,
Figure GDA0002618586710000032
representing the direct sound signal,
Figure GDA0002618586710000033
Representing the background sound signal of the left channel,
Figure GDA0002618586710000034
representing the right channel background sound signal.
In one embodiment, in step B, the multi-channel signals of the channels are respectively high-pass, band-pass and low-pass filtered to generate signals of the high-pitch, middle-pitch and low-pitch loudspeaker units.
In an embodiment, in the step C, the position correction filter adjusts the phase of the signal of each speaker unit by using an all-pass system.
Specifically, the all-pass system HAP(z) is defined as follows:
|HAP(ejω)|＝A
wherein HAP(ejω) The frequency domain expression of the all-pass system is represented, e, j and omega respectively represent a natural constant, an imaginary number unit and an angular frequency, and a real constant A is the gain of the all-pass system;
to satisfy the above definition, HAP(z) each pole has a conjugate reciprocal zero paired with it, and a rational all-pass system has the general form:
Figure GDA0002618586710000035
wherein z, p, k respectively represent complex variables, | ak|<1, if there is one pole at z ═ akThen there is a zero point at
Figure GDA0002618586710000036
In an embodiment, in the step C, the height correction filter adopts a peak filter or a waveform filter.
In one embodiment, the direct sound signal and the background sound signal in step AWith signals of direct sound separated from the stereo binaural signal
Figure GDA0002618586710000037
Left channel background sound signal
Figure GDA0002618586710000038
And right channel background sound signal
Figure GDA0002618586710000041
The multi-channel signal conversion method further includes a direct sound and background sound extraction step.
Preferably, the direct sound and background sound extracting step:
s1, respectively converting the left channel signal xL(n) and a right channel signal xR(n) performing short-time Fourier transform to obtain X corresponding to the left channel signal and the right channel signal respectivelyL(m, k) and XR(m, k), where n represents time domain sample points, m and k represent discrete time and discrete frequency, respectively;
s2, introducing space factors, expressing the background sound signal as a signal generated by different transmission paths in the room, and respectively corresponding to XL(m, k) and XR(m, k) performing energy estimation to obtain energy P of left and right sound channelsL(m, k) and PR(m,k)；
S3, setting the value of the space factor, and carrying out signal separation to obtain the estimation of the direct sound signal of the time-frequency domain
Figure GDA0002618586710000042
Estimation of left channel background sound signal
Figure GDA0002618586710000043
And estimation of the right channel background acoustic signal
Figure GDA0002618586710000044
S4, obtaining the direct sound signal of the time domain through inverse Fourier transform
Figure GDA0002618586710000045
Left channel background sound signal
Figure GDA0002618586710000046
And right channel background sound signal
Figure GDA0002618586710000047
In the step S1, in the step S,
Figure GDA0002618586710000048
Figure GDA0002618586710000049
where J denotes the presence of J direct sound sources in space, sj(n) denotes the direct sound signal at a certain time instant,
Figure GDA00026185867100000410
respectively representing coefficients of the distribution of the direct sound signal to the left and right channel signals, nL(n) and nR(n) background signals representing left and right channels, respectively;
Figure GDA00026185867100000411
Figure GDA00026185867100000412
wherein S isj(m, k) represents a direct sound signal of a time-frequency domain,
Figure GDA00026185867100000413
time-frequency domain expressions, N, representing the coefficients of a direct sound signal assigned to the left and right channel signals, respectivelyL(m, k) and NR(m, k) represent time-frequency domain expressions of background signals of the left and right channels, respectively.
Step S2 specifically includes:
s21, at a certain time m andin a certain frequency band k, only one sound source S existsiThen, then
Figure GDA0002618586710000051
Figure GDA0002618586710000052
Figure GDA0002618586710000053
Wherein A isL、ARCoefficients representing the distribution of the direct sound signal to the left and right channel signals, respectively;
s22, introducing space factor BL(m, k) and BR(m, k) gives the following expression, NL(m,k)＝BL(m,k)N(m,k)，NR(m,k)＝BR(m,k)N(m,k)，
Figure GDA0002618586710000054
Figure GDA0002618586710000055
Figure GDA0002618586710000056
Figure GDA0002618586710000057
Where N (m, k) represents the background signal in the time-frequency domain, bL(m,k)、bR(m, k) respectively represent the magnitudes of the left and right channel spatial factors,
Figure GDA0002618586710000058
respectively representing the phases of the left and right channel spatial factors;
then, XL(m, k) and XR(m, k) are simplified to:
XL(m,k)＝AL(m,k)S(m,k)+BL(m,k)N(m,k)
XR(m,k)＝AR(m,k)S(m,k)+BR(m,k)N(m,k)
correlation coefficient between left and right channel signals
Figure GDA0002618586710000059
Wherein E { } represents the expectation of the signal;
s23, obtaining the energy P of the left and right channels from the energy angleL(m, k) and PR(m, k) are respectively:
Figure GDA0002618586710000061
Figure GDA0002618586710000062
Figure GDA0002618586710000063
step S3 specifically includes: setting the value b of the space factorL(m,k)＝bR(m,k)＝1，
Figure GDA0002618586710000064
To obtain PS(m,k)，PN(m,k)，AL(m,k)，ARThe analytical solutions of (m, k) were calculated to obtain the following formulas (1) and (2)
Figure GDA0002618586710000065
Figure GDA0002618586710000066
Space factor BL(m, k) and BR(m, k) are respectively substituted in formula (2) to obtain
Figure GDA0002618586710000067
And
Figure GDA0002618586710000068
according to a second aspect of the invention, the invention adopts the technical scheme that:
a car audio system further comprising a multi-channel signal conversion apparatus for performing the multi-channel signal conversion method as described above.
Compared with the prior art, the invention has the following advantages by adopting the scheme:
(1) because a group of loudspeakers is always closest to the listening position at any position in the car, the sound image can deflect towards the direction, and the group of loudspeakers are corrected through a position correction filter so as to correct the sound image deflection caused by the close-range loudspeakers;
(2) the automobile sound system with the loudspeakers being installed at different heights is characterized in that the loudspeakers are installed at different heights when the loudspeakers are installed in an automobile, for example, a low pitch loudspeaker is arranged at the bottom of a door panel, a middle pitch loudspeaker is arranged in the middle of the door panel, a high pitch unit is arranged at the joint of an A column or an instrument panel and a front windshield and the like, the different installation heights of the loudspeakers can cause the height of sound to be insufficient, and the loudspeakers can be corrected by adopting a height correction filter to improve the height of the sound;
(3) the system is specially used for the multi-channel loudspeaker system in the vehicle, and has better practicability and operability.
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 flowchart of a multi-channel signal conversion method according to the present invention;
FIG. 2 is a schematic diagram of a stereo converted multi-channel speaker array signal;
FIG. 3 is a schematic diagram of the location of a speaker unit and listening position in a vehicle;
FIG. 4 is a signal processing flow diagram of the direct sound and background sound extraction step;
fig. 5 shows left and right channel signals;
fig. 6 shows correlation coefficients of left and right channel signals at a certain time instant;
fig. 7a, 7b, 7c show the separated direct sound signal, left channel background sound signal, right channel background sound signal, respectively.
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. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The present embodiment provides a method for converting a multi-channel signal of an automobile audio system, and the specific flow is described with reference to fig. 1 and the following description.
1. After the direct sound and background sound separation step is carried out on the left and right sound channel signals of the stereo sound, direct sound signals are generated
Figure GDA0002618586710000071
Background sound signal
Figure GDA0002618586710000072
And
Figure GDA0002618586710000073
2. after the direct sound and the background sound signals are subjected to a mixing matrix, signals of eight sound channels in the vehicle are generated, including a left front signal xFL(n), right front signal xFR(n), left rear signal xRL(n), right rear signal xRR(n), left surround signal xSL(n), right surround signal xSR(n) mid-set signal xCEN(n), subwoofer signal xSUB(n)。
Figure GDA0002618586710000081
In which several multi-channel signals are generated which are related to only two adjacent signals, e.g. the front left channel signal xFLWith the left channel background signal only
Figure GDA0002618586710000082
And direct sound signal
Figure GDA0002618586710000083
Related to the background of the right channel
Figure GDA0002618586710000084
Irrelevant; the center signal and the subwoofer signal are related to the left and right channel background sound signals and the direct sound signals. The mixing matrix employed in the present invention is as described above. Some documents or patents have described the generation method of the mixing matrix specifically in the prior art, and are not described here again.
3. After generating the multi-channel signal, the respective channel signals are filtered to generate signals for the respective speakers. Specifically, high pass, band pass and low pass signal filtering is performed on each channel signal to generate signals for each of the treble, midrange and woofer units. The front left signal x is only exemplarily shown in fig. 1FLThe filter processing of the other seven channel signals and the left front signal xFLThe filtering process is the same and is not shown in detail. As shown in fig. 1, for the left front signal xFLAnd carrying out high-pass, band-pass and low-pass signal filtering to obtain signals of the high pitch loudspeaker unit, the middle pitch loudspeaker unit and the bass loudspeaker unit respectively.
4. For a home cinema system or loudspeaker array, the individual loudspeakers are positioned in a line or at the same height, as shown in fig. 2. Thus, if included in the stereo signal, the signal is located at P0Then only y is needed for reproduction with the loudspeaker array4And y5The speaker can be determined to be located at P0However, in the car audio system, since the distances from the listening positions of the speaker units are different and the heights thereof are also different, it is necessary to correct the speakers.
(1) First, the difference in the auditory sensation caused by the difference in the distance between the speaker unit and the listening position is corrected by using a position correction filter, and here, in order to collectively express the function of the correction filter, the position correction filter is passed through each speaker unit. The position correction filter can adopt an all-pass system to adjust the phase of the signal without affecting the amplitude.
All-pass system HAP(z) is defined as follows:
|HAP(ejω)|＝A
the gain of an all-pass system is a real constant a.
To satisfy the above definition, HAPEach pole of (z) has a conjugate reciprocal zero paired with it. A rational allpass system has the following general form:
Figure GDA0002618586710000091
wherein, | ak|<1. If there is one pole at z ═ akThen there is a zero point at
Figure GDA0002618586710000092
For example, there is a pole at ak＝rejθIt must have a zero point paired with it
Figure GDA0002618586710000093
(2) And secondly, correcting the difference of the audibility caused by the difference of the heights of the loudspeaker units by adopting a height correction filter, wherein the height correction filter is passed through each loudspeaker unit for uniformly expressing the function of the correction filter. The height correction filter can adopt a peak value filter or a slope filter to process a certain frequency band in the signal so as to improve the listening height of the sound.
The position correction and the height correction are exemplified in connection with the example shown in fig. 3. Fig. 3 shows a front row of loudspeaker systems in a vehicle (including left front treble and bass units, right front treble and bass units, and center loudspeakers), where the dashed circle positions can be considered as sweet spots, at almost the same distance from each loudspeaker unit, but in the vehicle interior this position is considered as a listening position, whereas the usual listening positions are left front (main ride) and right front (copilot) positions, as indicated by the circles, both listening positions being at different distances from each loudspeaker unit, always one set of loudspeakers being closest to the listening position. For example, if the right front speaker is closer to the right front (passenger) position than the left front speaker is to the right front position, the sound image is deflected to the right front direction when listening to the sound at the right front position. Similarly, in the front left position, the sound image is deflected in the front left direction due to the closer distance of the front left speaker. It is therefore necessary to modify the signals of the individual loudspeaker units to achieve a better listening result. By modifying each speaker unit with the position correction filter and the height correction filter, the sound image can be stabilized at a fixed position regardless of the position (front left or front right).
Further, the direct sound signal and the background sound signal in the present embodiment are direct sound signals separated from the stereo binaural signal
Figure GDA0002618586710000094
Left channel background sound signal
Figure GDA0002618586710000095
And right channel background sound signal
Figure GDA0002618586710000096
Referring to fig. 4, the step of separating the direct sound from the background sound specifically includes:
s1, respectively converting the left channel signal xL(n) and right channel informationNumber xR(n) performing Short Time Fourier Transform (STFT) to obtain X corresponding to the left channel signal and the right channel signal respectivelyL(m, k) and XR(m, k), where n represents time domain sample points, m and k represent discrete time and discrete frequency, respectively;
s2, introducing space factors, expressing the background sound signal as a signal generated by different transmission paths in the room, and respectively corresponding to XL(m, k) and XR(m, k) performing energy estimation to obtain energy P of left and right sound channelsL(m, k) and PR(m,k)；
S3, setting the value of the space factor, and carrying out signal separation to obtain the estimation of the direct sound signal of the time-frequency domain
Figure GDA0002618586710000101
Estimation of left channel background sound signal
Figure GDA0002618586710000102
And estimation of the right channel background acoustic signal
Figure GDA0002618586710000103
S4, obtaining the direct sound signal of the time domain through inverse Fourier transform (ISTFT)
Figure GDA0002618586710000104
Left channel background sound signal
Figure GDA0002618586710000105
And right channel background sound signal
Figure GDA0002618586710000106
As shown in fig. 5, the left and right channel signals are:
Figure GDA0002618586710000107
Figure GDA0002618586710000108
wherein s isj(n) denotes the direct sound signal at a certain time instant,
Figure GDA00026185867100001011
coefficient n representing the distribution of the direct sound signal to the left and right channel signalsL(n) and nR(n) represents the background signals of the left and right channels.
S1, obtaining the product after short-time Fourier transform (STFT)
Figure GDA0002618586710000109
Figure GDA00026185867100001010
Where m and k represent time and frequency, respectively.
S2, there are two assumptions:
s21, only one sound source S exists at a certain time m and a certain frequency band kiI.e. by
Figure GDA0002618586710000111
Thus, it is possible to provide
Figure GDA0002618586710000112
Figure GDA0002618586710000113
Figure GDA0002618586710000114
S22, introducing a space factor B, expressing the background sound signal into a signal generated by different transmission paths of the signal in a room, similar to the expression mode of the direct sound signal, namely NL(m,k)＝BL(m,k)N(m,k),NR(m,k)＝BR(m,k)N(m,k)
Figure GDA0002618586710000115
Figure GDA0002618586710000116
Figure GDA0002618586710000117
Figure GDA0002618586710000118
Thus, the above formula can be simplified to
XL(m,k)＝AL(m,k)S(m,k)+BL(m,k)N(m,k)
XR(m,k)＝AR(m,k)S(m,k)+BR(m,k)N(m,k)
The correlation coefficient between the left and right channel signals (as shown in FIG. 6) is defined as
Figure GDA0002618586710000119
S23, the energy of the left and right channels is obtained from the energy perspective:
Figure GDA00026185867100001110
Figure GDA0002618586710000121
Figure GDA0002618586710000122
s3, the background sound energy is smaller than the direct sound energy in general, and
Figure GDA0002618586710000123
so that the traditional method is neglectedSlightly PN(m, k) i.e.
Figure GDA0002618586710000124
Figure GDA0002618586710000125
Here, assume that the value of the spatial factor is bL＝bR＝1，
Figure GDA0002618586710000126
Not ignoring PNContribution of (m, k) such that P is obtainedS(m,k)，PN(m,k)，AL(m,k)，ARAnalytic solution of (m, k).
Thus, S (m, k), N (m, k) can be calculated
Figure GDA0002618586710000127
Figure GDA0002618586710000128
Then the space factor B is calculatedL(m, k) and BR(m, k) is substituted therein to obtain NL(m,k)，NR(m,k)。
S4, and finally performing inverse fourier transform to obtain direct sound signals as shown in fig. 7a, 7b, and 7c
Figure GDA0002618586710000129
Background sound signal
Figure GDA00026185867100001210
And
Figure GDA00026185867100001211
in the extraction step, (1) a space factor variable between left and right channel signals is defined to represent the difference between the left and right channels caused by room reverberation, space size and other factors in the sound propagation process of the background sound signal; (2) background sound signals of left and right sound channels can be separated, and only one background signal can be separated by the traditional method; (3) the calculation process after the spatial factor is added is simpler, and the analytic solution of the direct sound and the background sound can be obtained.
The present embodiment also provides a car audio system including a multi-channel signal conversion apparatus for performing the multi-channel signal conversion method as described above. With reference to fig. 1, the extracting apparatus specifically includes a direct sound and background sound separation module, and a mixing matrix module connected to the direct sound and background sound separation module, where the mixing matrix module is connected to multiple sets of filters, and the multiple sets of filters correspond to the multi-channel signals (e.g., eight filters shown in fig. 1). Each group of filters respectively comprises a high-pass filter, a band-pass filter and a low-pass filter, the high-pass filters, the band-pass filters and the low-pass filters are respectively connected with the mixing matrix module, each high-pass filter is respectively connected with one position correction filter, each position correction filter is respectively connected with one height correction filter, and the multi-channel signals after correction are output
Figure GDA0002618586710000131
And the like.
The direct sound and background sound separation module specifically comprises an STFT module, an energy estimation module, a signal separation module and an ISTFT module. Wherein, the input of the STFT module is a left channel signal xL(n) and a right channel signal xR(n) performing short-time Fourier transform and outputting X corresponding to the left channel signal and the right channel signalL(m, k) and XR(m, k); the energy estimation module receives X output by the STFT moduleL(m, k) and XR(m, k) and introducing space factors, expressing background sound signals as signals generated by different transmission paths of the signals in a room, and respectively corresponding to XL(m, k) and XR(m, k) performing energy estimation to obtain energy P of left and right sound channelsL(m, k) and PR(m, k) and AL、ARAnd output to the signal separation module; the signal separation module also sets the value of the space factor to carry outSignal separation to obtain
Figure GDA0002618586710000132
And
Figure GDA0002618586710000133
and output to the ISTFT module; the ISTFT modules respectively perform inverse Fourier transform and output direct sound signals
Figure GDA0002618586710000134
Left channel background sound signal
Figure GDA0002618586710000135
And right channel background sound signal
Figure GDA0002618586710000136
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.

Claims (8)

1. A multi-channel signal conversion method for an automobile sound system is characterized by comprising the following steps:
A. processing the direct sound signal and the background sound signal through a mixing matrix to generate a multi-channel signal;
B. filtering the multi-channel signals to generate signals of each loudspeaker unit;
C. the signals of each loudspeaker unit are subjected to position correction on the difference of hearing caused by different distances between the loudspeaker unit and the listening position through a position correction filter, and then the loudspeaker units are driven to sound; or, the signals of each loudspeaker unit are subjected to position correction on the auditory sense difference caused by different distances between the loudspeaker unit and the listening position through a position correction filter, and then subjected to height correction on the auditory sense difference caused by different heights of the loudspeaker unit through a height correction filter, and then each loudspeaker unit is driven to sound;
the direct sound signal and the background sound signal in the step A are separated direct sound signals in the independent stereo sound dual-channel signal
Figure FDA0002618586700000011
Left channel background sound signal
Figure FDA0002618586700000012
And right channel background sound signal
Figure FDA0002618586700000013
The multi-channel signal conversion method also comprises a direct sound and background sound extraction step;
the direct sound and background sound extraction step comprises the following steps:
s1, respectively converting the left channel signal xL(n) and a right channel signal xR(n) performing short-time Fourier transform to obtain X corresponding to the left channel signal and the right channel signal respectivelyL(m, k) and XR(m, k), where n represents time domain sample points, m and k represent discrete time and discrete frequency, respectively;
s2, introducing space factors, expressing the background sound signal as a signal generated by different transmission paths in the room, and respectively corresponding to XL(m, k) and XR(m, k) performing energy estimation to obtain energy P of left and right sound channelsL(m, k) and PR(m,k)；
S3, setting the value of the space factor, and carrying out signal separation to obtain the estimation of the direct sound signal of the time-frequency domain
Figure FDA0002618586700000014
Estimation of left channel background sound signal
Figure FDA0002618586700000015
And estimation of the right channel background acoustic signal
Figure FDA0002618586700000016
S4, warpObtaining a direct sound signal of a time domain through inverse Fourier transform
Figure FDA0002618586700000017
Left channel background sound signal
Figure FDA0002618586700000018
And right channel background sound signal
Figure FDA0002618586700000019
In the step S1, in the step S,
Figure FDA00026185867000000110
Figure FDA0002618586700000021
where J denotes the presence of J direct sound sources in space, sj(n) denotes the direct sound signal at a certain time instant,
Figure FDA0002618586700000022
respectively representing coefficients of the distribution of the direct sound signal to the left and right channel signals, nL(n) and nR(n) background signals representing left and right channels, respectively;
Figure FDA0002618586700000023
Figure FDA0002618586700000024
wherein S isj(m, k) represents a direct sound signal of a time-frequency domain,
Figure FDA0002618586700000025
time-frequency domain table representing coefficients of direct sound signal to be distributed to left and right channel signals, respectivelyD is NL(m, k) and NR(m, k) time-frequency domain expressions representing background signals of left and right channels, respectively;
step S2 specifically includes:
s21, only one sound source S exists at a certain time m and a certain frequency band kiThen, then
Figure FDA0002618586700000026
Figure FDA0002618586700000027
Figure FDA0002618586700000028
Wherein A isL、ARCoefficients representing the distribution of the direct sound signal to the left and right channel signals, respectively;
s22, introducing space factor BL(m, k) and BR(m, k) gives the following expression, NL(m,k)＝BL(m,k)N(m,k)，NR(m,k)＝BR(m,k)N(m,k)，
Figure FDA0002618586700000029
Figure FDA00026185867000000210
Figure FDA00026185867000000211
Figure FDA00026185867000000212
Where N (m, k) represents the background signal in the time-frequency domain, bL(m，k)、bR(m, k) respectively represent left and right channel spacesThe magnitude of the factor(s) is,
Figure FDA0002618586700000031
respectively representing the phases of the left and right channel spatial factors;
then, XL(m, k) and XR(m, k) are simplified to:
XL(m，k)＝AL(m，k)S(m，k)+BL(m，k)N(m，k)
XR(m，k)＝AR(m，k)S(m，k)+BR(m，k)N(m，k)
correlation coefficient between left and right channel signals
Figure FDA0002618586700000032
Wherein E { } represents the expectation of the signal;
s23, obtaining the energy P of the left and right channels from the energy angleL(m, k) and PR(m, k) are respectively:
Figure FDA0002618586700000033
Figure FDA0002618586700000034
Figure FDA0002618586700000035
step S3 specifically includes: setting the amplitude b of the spatial factorL(m，k)＝bR(m, k) 1, phase
Figure FDA0002618586700000036
Figure FDA0002618586700000037
According to PL(m，k)、PR(m, k) and Φ (m, k) to obtain PS(m，k)，PN(m，k)，AL(m，k)，ARThe analytical solutions of (m, k) were calculated to obtain the following formulas (1) and (2)
Figure FDA0002618586700000038
Figure FDA0002618586700000039
Space factor BL(m, k) and BR(m, k) are each independently substituted in formula (2) to give
Figure FDA00026185867000000310
Then using the expression
Figure FDA00026185867000000311
Obtaining the estimated value of the background sound of the left and right sound channels
Figure FDA00026185867000000312
And
Figure FDA00026185867000000313
2. the multi-channel signal conversion method according to claim 1, wherein in step a, a multi-channel signal is generated including a front left signal xFL(n), right front signal xFR(n), left rear signal xRL(n), right rear signal xRR(n), left surround signal xSL(n), right surround signal xSR(n) mid-set signal xCEN(n), subwoofer signal xSUB(n)。
3. The multi-channel signal conversion method according to claim 2, wherein the multi-channel signal is expressed by the following equation,
Figure FDA0002618586700000041
wherein W represents a conversion coefficient matrix, ω1、ω2、…ω18The conversion coefficients are respectively represented by a number of,
Figure FDA0002618586700000042
representing the direct sound signal,
Figure FDA0002618586700000043
Representing the background sound signal of the left channel,
Figure FDA0002618586700000044
representing the right channel background sound signal.
4. The multi-channel signal converting method according to claim 1, wherein in step B, the multi-channel signal is subjected to high-pass, band-pass and low-pass signal filtering, respectively, to generate signals for each of the high pitch, mid pitch and low pitch speaker units.
5. The multi-channel signal converting method according to claim 1, wherein in step C, the position correcting filter adjusts the phase of the signal of each speaker unit using an all-pass system.
6. The multi-channel signal conversion method as claimed in claim 5, wherein the all-pass system HAP(z) is defined as follows:
|HAP(ejω)|＝A
wherein HAP(ejω) The frequency domain expression of the all-pass system is represented, e, j and omega respectively represent a natural constant, an imaginary number unit and an angular frequency, and a real constant A is the gain of the all-pass system;
to satisfy the above definition, HAP(z) each pole has a conjugate reciprocal zero paired with it, and a rational all-pass system has the general form:
Figure FDA0002618586700000045
wherein z, p, k respectively represent complex variables, | ak|<1, if there is one pole at z ═ akThen there is a zero point at
Figure FDA0002618586700000046
7. The multi-channel signal converting method according to claim 1, wherein in step C, the height correcting filter employs a peak filter or a waveform filter.
8. A car audio system comprising a multi-channel signal conversion apparatus for performing the multi-channel signal conversion method according to any one of claims 1 to 7.
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