A loudspeaker phase equalization signal processing system and a pole parameter determination method thereof

Abstract

The application discloses a loudspeaker phase equalization signal processing system and a pole parameter determination method thereof, which equalizes the loudspeaker phase response in a set equalization frequency range to linear phase, and the system comprises a phase controller and a group delay equalizer in cascade; the phase controller is a first-order IIR all-pass filter; the group delay equalizer comprises S low-order IIR all-pass filters in cascade, wherein the first N1 low-order IIR all-pass filters are low-order causal IIR all-pass filters, and the last N2 low-order IIR all-pass filters are low-order non-causal IIR all-pass filters. The application can equalize the loudspeaker phase through the all-pass filter with low operation complexity and parameters, can significantly reduce the calculation amount required by low-frequency phase equalization, can improve the linear degree of the loudspeaker phase response, and can improve the sound quality and listening experience.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of audio signal processing, and relates to a loudspeaker phase equalization signal processing system and a pole parameter determination method thereof. BACKGROUND

[0002] As an electro-acoustic conversion device, a loudspeaker is not a perfect linear phase system. The components such as transducers, electronic signal processing and amplifiers will cause the phase response of the loudspeaker to be delayed and deviate from the ideal linear phase. Such nonlinear phase response will introduce distortion in the time-domain sound pressure output, making it difficult to accurately reproduce the original signal waveform. In loudspeaker response equalization, it is necessary to pre-compensate the phase.

[0003] An all-pass filter can adjust the phase response of a system without affecting its amplitude response. The form of the all-pass filter is divided into Finite Impulse Response (FIR) and Infinite Impulse Response (IIR) all-pass filters. By filtering the input signal, the output of the entire system is approximated to a linear phase response. However, for low-frequency loudspeaker phase equalization, the required IIR or FIR filter order is very high, resulting in a large filter operation cost, which is not easy to implement in a real-time signal processing system.

[0004] Prior art document 1 (201280068508.4) proposes to use an audio pre-compensation controller supporting a variable set of loudspeakers to design a FIR filter to achieve loudspeaker phase equalization, which requires a large number of filter coefficients to achieve the required frequency response, and has high computational complexity. Especially when equalizing the low-frequency phase of the loudspeaker, in order to ensure sufficient frequency resolution, a high-order FIR filter is required. SUMMARY

[0005] To solve the problems existing in the prior art, the present application provides a loudspeaker phase equalization signal processing system and a pole parameter determination method thereof. By using a low-complexity all-pass filter and its parameters, the phase of the loudspeaker is equalized, which can significantly reduce the calculation amount required for low-frequency phase equalization and improve the linearity of the loudspeaker phase response, thereby improving the sound quality and listening experience.

[0006] The present application adopts the following technical solutions.

[0007] The first aspect of the present application proposes a loudspeaker phase equalization signal processing system, which equalizes the phase response of the loudspeaker to a linear phase within a set equalization frequency range;

[0008] The system includes a phase controller and a group delay equalizer in cascade;

[0009] The phase regulator is a first-order IIR all-pass filter, and its transfer function is The pole parameter is a adj =ρ adj , where z = e jω , ω is the frequency, e is the natural constant, ρ adj is the extreme point diameter;

[0010] The group delay equalizer includes S cascaded low-order IIR all-pass filters, of which the first N1 are low-order causal IIR all-pass filters and the last N2 are low-order non-causal IIR all-pass filters. The corresponding transfer function is The pole parameters are {a1,a2,…,a S},in is m s Transfer function of the order IIR all-pass filter, m s =1 or m s =2; s is the index of the cascaded low-order IIR all-pass filter, and when it is 1 to N1, it corresponds to N1 low-order causal IIR all-pass filters, and when it is N1+1 to S, it corresponds to N2 low-order non-causal IIR all-pass filters.

[0011] Preferably, for m s Transfer function of an IIR all-pass filter of order

[0012] m s =1, for:

[0013] Among them, σ s is the pole diameter of the first-order IIR all-pass filter;

[0014] m s =2, for:

[0015] Among them, ρ s ,θ s They are the complex conjugate poles of the second-order IIR all-pass filter Polar diameter and polar angle.

[0016] Preferably, for the pole parameter a of the sth low-order IIR all-pass filter s :

[0017] m s =1, a s =σ s ,σ s is the pole diameter of the first-order IIR all-pass filter;

[0018] ms = 2, a s = [p s , q s ] T , p s and q s are the polar radius and polar angle of the complex conjugate pole of the second order IIR allpass filter.

[0019] Preferably, the signal processing procedure of the non-causal allpass filter is as follows:

[0020] Firstly, the input real-time signal is buffered and divided into continuous frames with length L, and the signal of the pth frame is:

[0021] b p = [b((p-1)·L+1), b((p-1)·L+2), …, b(p·L)] T .

[0022] wherein p is an integer, representing the index of the frame; b((p-1)·L+1), b((p-1)·L+2), b(p·L) represent the input real-time signal at discrete time (p-1)·L+1, (p-1)·L+2, p·L;

[0023] Then, each frame is time-reversed and combined with a zero vector 0 1×L of dimension 1xL to form an intermediate signal of dimension 2Lx1, and the intermediate signal of the pth frame is expressed as:

[0024] q p = [b(p·L), b((p-1)·L+L-1), …, b((p-1)·L+1), 0 1×L ] T .

[0025] Secondly, the intermediate signal [q1; q2; …] is filtered by the inverse function G2(z -1 ) of the non-causal allpass filter transfer function in turn, and then time-reversed to obtain an output signal of dimension 2Lx1;

[0026] Finally, the filtering result of the non-causal allpass filter on the input signal is obtained according to the output signal, and the expression of the filtering result y p of the pth frame is:

[0027]

[0028] wherein u p-1 (L+1:2L) is the last L elements of the output signal u p-1 of the pth-1 frame; u p (1:L) is the first L elements of the output signal u p ​u1(1:L) is the first L elements of the output signal u1 of the first frame.

[0029] A second aspect of the present invention provides a method for determining pole parameters applied to the loudspeaker phase equalization signal processing system, comprising:

[0030] Step 1: Perform acoustic measurements on the speaker to be compensated to obtain the speaker impulse response;

[0031] Step 2: Set the target angle φ t and the equalization frequency range [ω L ,ω H ], then the phase equalization goal is to obtain a linear phase where ω k is the kth discrete frequency, ω L ≤ω k ≤ω H , k=1,…,K, K=N / 2+1, N is the number of discrete Fourier transform points; ω L 、ω H They are the lower and upper limits of the equalization frequency range respectively; is the target group delay constant; at the same time, set the maximum order N max and frequency weighting function W=[W(ω1),…,W(ω K )], W(ω1) is the importance of discrete frequency ω1, W(ω K ) is the discrete frequency ω K the importance of

[0032] Step 3: Based on N max and W, calculate the pole parameters {a1, a2, …, a S The initial value of the speaker impulse response obtained in step 1 is approximately the phase response of the delay after filtering by the group delay equalizer using the initial value. Linear phase ω L ≤ω k ≤ω H , and then get the angle φ0;

[0033] Step 4: According to the angle φ0 and the target angle φ t Calculate the pole parameter a of the phase controller adj =ρ adj ;

[0034] Step 5: The speaker impulse response obtained in step 1 passes through the pole parameter a adj =ρ adj The phase response of the phase controller after filtering is used to determine the pole parameters of the group delay equalizer {a1, a2, ..., a S}Fine-tune the value.

[0035] Preferably, in step 3, the initial pole parameters {a1, a2, …, aN} of the group delay equalizer are calculated as follows: S} of the group delay equalizer are calculated as follows:

[0036] Step 301: Calculate the target group delay of the group delay equalizer: wherein, is the target group delay constant; τ0(ωk) represents the to-be-equalized group delay at the kth discrete frequency, which is the value after octave smoothing of the group delay of the loudspeaker impulse response; k

[0037] Step 302: Define the cost function J s (a s ) when cascading the s-th low-order IIR all-pass filter:

[0038]

[0039] wherein a s is the pole parameter of the s-th low-order IIR all-pass filter, is the group delay of the s-th low-order IIR all-pass filter at the kth discrete frequency, τ t (ω k ) is the target group delay at the kth discrete frequency, τ s-1 (ω k ) is the system group delay of the first s-1 low-order IIR all-pass filters before cascading at the kth discrete frequency;

[0040] Step 303: Determine the initial pole parameter value of the s-th low-order IIR all-pass filter to be cascaded by grid search and minimizing the cost function;

[0041] Step 304: Calculate the pole parameter of the s-th IIR all-pass filter to be cascaded based on the initial value by using the line search iterative algorithm;

[0042] Step 305: When the output condition based on the cost function or N max is met, output the current pole parameters of all low-order IIR all-pass filters to be cascaded as the initial pole parameters {a1, a2, …, aN} of the group delay equalizer. S

[0043] Preferably, in step 301, the target group delay constant is:

[0044]

[0045] wherein, [N e ,N e+1 ,…,N E ​​] T calculating the discrete frequency indices of the logarithmic distribution according to 1 / 24 octave resolution between the start index L and the end index H of the equalization frequency range;

[0046] τ0(ω H ) represents the group delay of the loudspeaker impulse response at the discrete frequency point the group delay of the loudspeaker impulse response at the discrete frequency point after the octave smoothing of the group delay of the loudspeaker impulse response; the value of the group delay of the loudspeaker impulse response at the discrete frequency point after the octave smoothing of the group delay of the loudspeaker impulse response;

[0047] median(·) is the median function;

[0048] {·} T is the vector transpose.

[0049] Preferably, the step 303 specifically comprises:

[0050] determining the initial values of the pole parameters of the low-order IIR allpass filters in the cascade by searching the discrete grid p = {p h}, h = 1,..., M, where h is the pole index and M is the total number of grid points;

[0051] the pole radius of the real pole in the discrete grid ranges from 1.0101 to 1.1765, the pole radius of the complex pole ranges from 0.78 to 0.96 and from 1.0417 to 1.2821, and the pole radius of the pole is linearly distributed within the pole radius range, and the pole angle of the complex pole is logarithmically distributed within the equalization frequency range;

[0052] the real pole in the discrete grid corresponds to the pole of the first-order IIR allpass filter, the complex pole corresponds to one of the poles of the second-order IIR allpass filter, the grid point within the unit circle corresponds to the pole of the causal IIR allpass filter, and the grid point outside the unit circle corresponds to the pole of the non-causal IIR allpass filter;

[0053] the grid point p h corresponds to the group delay of the filter the group delay of all filters corresponding to the discrete grid is traversed selecting the filter that minimizes the cost function, and the initial value of the pole parameter of the s-th low-order IIR allpass filter is the value of the grid point corresponding thereto:

[0054] the initial value of the pole parameter of the s-th low-order IIR allpass filter corresponding to the real pole is a s (0) = p s ;

[0055] the initial value of the pole parameter of the s-th low-order IIR allpass filter corresponding to the complex pole is a s (0) = [p s,θ s ] T .

[0056] Preferably, step 304 is specifically as follows:

[0057] With a s (0) As the initial condition, first find a search direction that reduces the cost function, then calculate the step size along this direction, iterate the pole parameters of the cascaded sth IIR all-pass filter to further reduce the cost function, and update the pole parameters of the sth IIR all-pass filter in each iteration. The update formula is:

[0058]

[0059] in, are the pole parameters of the sth IIR all-pass filter at the i+1th and ith iterations respectively; μ (i) is the step length, is the search direction;

[0060] When the iteration stop condition is met, the iteration stops and the pole parameter values ​​of the current sth IIR all-pass filter are saved.

[0061] Preferably, the step size is determined using Armijo's sufficient reduction condition, wherein Armijo's sufficient reduction condition is:

[0062]

[0063] in, It means that when the pole parameter of the sth IIR all-pass filter is The cost function value when It means that when the pole parameter of the sth IIR all-pass filter is The cost function value when , the coefficient γ∈(0,1), indicates that the reduction of the cost function value is sufficient and is consistent with μ (i) and proportional to;

[0064] The cost function is The gradient value at .

[0065] If the above conditions are not met, the step size is iteratively reduced using the reduction factor κ: μ (i) ←κμ (i) , until the above conditions are met, μ (i) The final value of .

[0066] Preferably, the search direction is:

[0067]

[0068] in, is the error matrix at the i-th iteration gradient;

[0069] H is the conjugate transpose;

[0070] is the group delay of the sth first-order IIR all-pass filter relative to the pole parameter σ at the i-th iteration s gradient;

[0071] are the group delay of the s-th second-order IIR all-pass filter relative to the pole parameter ρ at the i-th iteration. s ,θ s gradient;

[0072] for:

[0073]

[0074] in

[0075] m s =1, for

[0076] The group delay of the sth first-order IIR all-pass filter is relative to the pole parameter σ s The gradient of

[0077]

[0078] m s =2, for

[0079] The group delay of the sth second-order IIR all-pass filter with respect to the pole parameter ρ s and θ s The gradient of

[0080]

[0081] Preferably, the iteration stopping condition is: reaching the maximum number of iterations or α is the set tolerance.

[0082] Preferably, in step 305, based on the cost function or N max The output conditions are:

[0083] The cost function of cascading the sth low-order IIR all-pass filter increases to J s (a s )>J s-1 (as ), or, when the group delay equalizer order N gd Greater than N max -1.

[0084] Preferably, in step 4, ρ adj The calculation formula is:

[0085]

[0086] Where q is based on φ t The intermediate variable used to calculate the relationship between the magnitude of φ0 and φ0.

[0087] Preferably, step 5 is as follows:

[0088] With τ0'(ω k )=τ0(ω k )+τ adj (ω k ) is the group delay to be equalized, For the target group delay, the group delay equalizer pole parameters {a1, a2, …, a S}Specific calculation steps of the initial value to calculate the group delay equalizer pole parameters {a1, a2, ..., a S} fine-tuning value, where τ0(ω k ) is the group delay of the loudspeaker impulse response, τ adj (ω k ) is the pole parameter a adj =ρ adj The group delay of the phase modulator.

[0089] A third aspect of the present invention provides a terminal, comprising a processor and a storage medium; the storage medium is used to store instructions;

[0090] The processor is configured to operate according to the instructions to execute the steps of the method.

[0091] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the method when executed by a processor.

[0092] Compared with the prior art, the beneficial effects of the present invention include at least:

[0093] This paper proposes a phase equalization system and parameter determination method using a hybrid cascade of causal and non-causal infinite impulse response (IIR) all-pass filters. The non-causal IIR all-pass filters can generate negative group delay, replacing the FIR filter method commonly used in the prior art. Compared to the prior art, this paper implements a phase equalization system using lower-order IIR all-pass filters, reducing computational complexity.

[0094] The application designs an IIR filter to realize the phase equalization of a loudspeaker. Compared with an FIR filter, the IIR filter needs fewer filter coefficients to realize a required frequency response, and thus has lower calculation complexity. Especially when equalizing the low-frequency phase of a loudspeaker, in order to ensure sufficient frequency resolution, the application can design a low-order IIR filter to equalize the low-frequency phase of the loudspeaker, which can significantly reduce the calculation amount required for equalizing the low-frequency phase of the loudspeaker.

[0095] The application combines a non-causal filter when calculating the target group delay constant, so that the equalized target group delay constant can be less than the maximum value of the group delay to be equalized.

[0096] The application designs a cost function of a cascaded group delay equalizer according to the group delay, and solves a set of low-order IIR all-pass filter parameters instead of directly solving high-order all-pass filter parameters, which facilitates users to design a phase equalizer according to the use of a loudspeaker and an application scenario.

[0097] The application calculates the pole parameter a t of the phase controller according to the size relationship between φ adj and φ0 adj , and the designed phase controller can adjust the phase of the loudspeaker to a linear phase with the target angle φ t When a plurality of loudspeakers work in combination, the phases of the plurality of loudspeakers are consistent in the crossover frequency band, and the application can be applied to the phase equalization of the plurality of loudspeakers. BRIEF DESCRIPTION OF DRAWINGS

[0098] Figure 1 The application is a signal processing system for loudspeaker phase equalization;

[0099] Figure 1 The reference signs in the accompanying drawings are as follows: 101-phase controller, 102-causal IIR all-pass filter, 103-non-causal all-pass filter, 104-group delay equalizer, 105-phase equalization signal processing system;

[0100] Figure 2 The application is a flowchart for determining the initial value of the group delay equalizer;

[0101] Figure 3 The application is a flowchart for determining the fine adjustment value of the pole parameter of the group delay equalizer;

[0102] Figure 4 The application is the response of a bass loudspeaker;

[0103] Figure 5 The application is the group delay to be equalized;

[0104] Figure 6 The application is the target group delay;

[0105] ​Figure 7 is a discrete grid;

[0106] Figure 8 is the initial value group delay equalizer group delay;

[0107] Figure 9 is the phase equalization result;

[0108] Figure 10 is the group delay to be balanced;

[0109] Figure 11 Delay for the target group;

[0110] Figure 12 is the fine-tuned value group delay equalizer group delay;

[0111] Figure 13 is the phase equalization result. DETAILED DESCRIPTION

[0112] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without making creative efforts are all within the scope of protection of the present invention.

[0113] Embodiment 1 of the present invention proposes a loudspeaker phase equalization signal processing system that can equalize the loudspeaker phase response to a linear phase within a specified equalization frequency range. Linear phase means that the group delay is independent of frequency and remains constant. Specifically, the loudspeaker phase equalization signal processing system is described as follows:

[0114] like Figure 1 As shown, the phase equalization signal processing system 105 is composed of a phase regulator 101 and a group delay equalizer 104 connected in cascade.

[0115] Figure 1 The phase regulator 101 is a first-order IIR all-pass filter with a transfer function of The pole parameter of the phase regulator 101 is a adj =ρ adj , where z = e jω , ω is the frequency, e is the natural constant, ρ adj is the extreme point diameter.

[0116] Figure 1The middle group delay equalizer 104 is composed of a causal IIR all-pass filter 102 and a non-causal all-pass filter 103, i.e. a cascade of N1 low-order causal IIR all-pass filters and N2 low-order non-causal IIR all-pass filters.

[0117] The causal IIR all-pass filter 102 is a cascade of N1 low-order causal IIR all-pass filters, and the causal IIR all-pass filter 102 can be directly implemented.

[0118] The non-causal all-pass filter 103 is a cascade of N2 low-order non-causal IIR all-pass filters, and the non-causal all-pass filter 103 is unstable and cannot be directly filtered.

[0119] The non-causal all-pass filter 103 is a cascade of N2 low-order non-causal IIR all-pass filters, and the non-causal all-pass filter 103 is unstable and cannot be directly filtered. Since the non-causal all-pass filter 103 cannot be directly implemented, but the inverse function G2(z -1 ) of the transfer function G2(z) of the non-causal all-pass filter 103 is a causal filter transfer function and can be directly implemented. The filtering process of the non-causal all-pass filter 103 can be completed by the following steps:

[0120] First, the signal is time-reversed, then filtered by the inverse function G2(z -1 ) of the transfer function of the non-causal all-pass filter 103, and then time-reversed again.

[0121] Thus, the signal processing method of the non-causal all-pass filter 103 is:

[0122] First, the input real-time signal is buffered and divided into consecutive frames with a length of L, and the signal of the pth frame is:

[0123] b p = [b((p-1)·L+1), b((p-1)·L+2), …, b(p·L)] T .

[0124] Wherein, p is an integer, representing the index of the frame;

[0125] b((p-1)·L+1), b((p-1)·L+2), b(p·L) represent the input real-time signal at discrete time (p-1)·L+1, (p-1)·L+2, p·L ((p-1)·L+1 is the discrete time index, (p-1)·L+2 is one sampling time after (p-1)·L+1, and so on;

[0126] b p is a set of L input real-time signals at discrete time, for example, the first frame signal is:

[0127] b1 = [b(1), b(2), …, b(L)] T .

[0128] Then, each frame is time-reversed and combined with a zero vector of dimension 1 x L, 0 1×L to form an intermediate signal of dimension 2L x 1, the intermediate signal of the pth frame is denoted as:

[0129] q p = [b(pL), b((p-1)L+L-1), …, b((p-1)L+1), 0 1×L ] T .

[0130] For example, the intermediate signal of the 1st frame is: q1 = [b(L), b(L-1), …, b(1), 0 1×L ] T .

[0131] Secondly, the intermediate signal [q1; q2; …] is filtered by the inverse function G2(z -1 ) of the non-causal all-pass filter 103 transfer function in turn, and then time-reversed to obtain an output signal of dimension 2L x 1, the output signal of the pth frame is denoted as u p : u p = [u p ((p-1)L+1), u p ((p-1)L+2), …, u p (pL)] T For example, the output signal of the 1st frame is denoted as: u1 = [u1(1), u1(2), …, u1(2L)] T , u1(1), u1(2), …, u1(2L) are the output results filtered and time-reversed from the intermediate signal q1;

[0132] Finally, the filter results of the non-causal all-pass filter 103 processing the input signal are obtained by overlapping and adding, the filter result of the pth frame y p is expressed as:

[0133]

[0134] wherein u p-1 (L+1:2L) = [u p-1 (L+1), u p-1 (L+2), …, u p-1 (2L)] T are the last L elements of u p-1 ; u p (1:L) = [u p (1), u p (2), …, up (L)] T is the first L elements of u p ;

[0135] u1(1:L)=[u1(1),u1(2),…,u1(L)] T is the first L elements of u1.

[0136] That is, the above expression is: when the frame number p = 1, the first L elements of u1 are output

[0137] u1(1:L)=[u1(1),u1(2),…,u1(L)] T ;

[0138] When the frame number p > 1, the last L elements of u p-1 are output

[0139] u p-1 (L+1:2L)=[u p-1 (L+1),u p-1 (L+2),…,u p-1 (2L)] T and the first L elements u p (1:L)=[u p (1),u p (2),…,u p (L)] p of u T are overlapped and added to obtain the filtering result.

[0140] The group delay equalizer 104 transfer function A gd is expressed as

[0141]

[0142] Where s is the index of the cascaded low-order IIR all-pass filter;

[0143] m s is the order of the cascaded low-order IIR all-pass filter (m s = 1 or m s = 2);

[0144] S is the total number of low-order IIR all-pass filters cascaded into the group delay equalizer 104 (S = N1 + N2).

[0145] First-order IIR all-pass filter transfer function

[0146] Second-order IIR all-pass filter transfer function

[0147] a sis the pole parameter of the s-th cascaded low-order IIR all-pass filter:

[0148] If the order of the sth cascaded IIR all-pass filter is m s =1,a s =σ s ,σ s is the pole diameter of the first-order all-pass filter;

[0149] If the order of the sth cascaded IIR all-pass filter is m s =2,a s =[ρ s ,θ s ] T ,ρ s and θ s is the complex conjugate pole of the second-order all-pass filter Polar diameter and polar angle.

[0150] The pole parameters of the group delay equalizer 104 are {a1, a2, ..., a S}.

[0151] In summary, the transfer function A of the phase equalization system 105 is eq The expression is

[0152]

[0153] The pole parameters that need to be determined in the phase equalization system 105 according to the characteristics of the compensated loudspeaker are {a adj ,a1,a2,…,a S}.

[0154] Embodiment 2 of the present invention proposes a parameter determination method applicable to the above-mentioned loudspeaker phase equalization signal processing system, specifically determining the parameters of the phase equalization system according to the characteristics of the loudspeaker to be compensated:

[0155] Step 1: Perform acoustic measurements on the loudspeaker to obtain its impulse response.

[0156] Step 2: The user sets a constant angle φ t (-π≤φ t ≤π) and the equalization frequency range [ω L ,ω H ], the balanced phase target is delay Linear phase where ω k is the kth discrete frequency, ω L ≤ω k ≤ω H , k=1,...,K, K=N / 2+1, N is the number of discrete Fourier transform points; ω L 、ωH respectively, lower and upper limit of equalization frequency range; target group delay constant is the median of the log-sampled octave-smoothed response to be equalized. Meanwhile, the user can set the maximum order N of the phase equalization system max and a frequency weighting function W = [W(ω1),...,W(ω K )], W is a 1 x K matrix, which is used to give different importance to the discrete frequencies ω1,...,ω K . For example, W(ω1) is the importance of the discrete frequency ω1, W(ω1) is a constant, W(ω K ) is the importance of the discrete frequency ω K , W(ω K ) is a constant.

[0157] Step 3: determine the initial pole parameters {a1, a2,...,a S} of the group delay equalizer 104, the phase response of the loudspeaker impulse response filtered by the initial pole parameters of the group delay equalizer 104 is approximately a linear phase with a delay of Step 4: calculate the angle φ0, which is used for the calculation of step 5; Step 5: calculate the initial pole parameters {a1, a2,...,a S} of the group delay equalizer 104, and the phase response of the loudspeaker impulse response filtered by the initial pole parameters of the group delay equalizer 104 is approximately a linear phase with a delay of

[0158] In specific implementation, the group delay equalizer 104 is cascaded by S low-order IIR all-pass filters, and the value of S is determined by the calculation process.

[0159] The initial pole parameters {a1, a2,...,a s} of the group delay equalizer 104 are calculated in turn, and the specific process is shown in Figure 2 .

[0160] When ρ s < 1 in the pole parameter a s , the low-order IIR all-pass filter of the s-th cascade is a causal filter.

[0161] When ρ s > 1 in the pole parameter a S , the low-order IIR all-pass filter of the s-th cascade is a non-causal filter.

[0162] When the pole parameters {a1, a2,...,a s} of the group delay equalizer 104 are determined, the pole parameters a s are divided to obtain the pole parameters {a1, a2,...,a N1} of the causal all-pass filter 102 and the pole parameters {a N1+1 ,a N1+2 ,...,a S} of the non-causal all-pass filter 103.

[0163] Further preferably, the initial values ​​of the pole parameters of the group delay equalizer 104 {a1, a2, ..., a S The specific calculation steps of} are as follows:

[0164] Step 301: Calculate the target group delay τ of the group delay equalizer 104 t (ω k ): The target group delay is used to design the group delay equalizer 104. The group delay of the group delay equalizer 104 should be close to the target group delay. The cost function below uses the target group delay τ t (ω k );in, is the target group delay constant; τ0(ω k ) represents the group delay to be equalized at the kth discrete frequency, which is the value of the loudspeaker impulse response group delay after octave smoothing;

[0165] After the speaker impulse response is filtered by the group delay equalizer 104, the equalization frequency range [ω L ,ω H The phase response within ] is linear phase, and the group delay remains constant. The group delay of the causal filter can only be positive. Since the present invention combines a non-causal filter, the target group delay τ of the group delay equalizer 104 is t (ω k ) can be negative. Because Target group delay constant It does not need to be greater than the group delay to be equalized τ0(ω k ). The target group delay constant of the present invention The calculation formula is:

[0166]

[0167] Among them, [N e ,N e+1 ,…,N E ] T The logarithmically distributed discrete frequency index is calculated with a 1 / 24 octave resolution between the start index L and the end index H of the equalization frequency range;

[0168] τ0(ω H ) means in The group delay to be equalized at the discrete frequency point is the group delay of the loudspeaker impulse response after octave smoothing. The value of the discrete frequency point;

[0169] median(·) is the median function;

[0170] {·} TFor vector transposition.

[0171] The group delay of the equalized signal is the group delay of the loudspeaker plus the group delay of the phase equalizer, and the goal of the equalization is to make the response of the loudspeaker after filtering by the phase equalizer linear phase. The phase response and group delay expression of the linear phase signal are:

[0172]

[0173] where ω k is the discrete frequency (ω L ≤ω k ≤ω H ), and φ0 is a certain angle value (-π≤φ0≤π). That is, the response of the loudspeaker after filtering by the phase equalizer, the group delay is a constant Therefore, the target group delay τ t (ω k ) of the group delay equalizer 104 is:

[0174]

[0175] Step 302: define the cost function;

[0176] The derivation process of the cost function is:

[0177] The group delay τ1(ω k ) of the first-order IIR all-pass filter and the group delay τ2(ω k ) of the second-order IIR all-pass filter are

[0178]

[0179] The cost function is the sum of the squared errors of the group delay τ gd (ω k ) of the group delay equalizer 104 and the target group delay τ t (ω k ):

[0180]

[0181] where K=N / 2+1, and N is the number of points of the discrete Fourier transform.

[0182] The group delay of the group delay equalizer 104 is the sum of the group delays of the cascaded low-order filters, that is,

[0183]

[0184] Based on the minimization of the cost function, the initial value of the pole parameter {a1, a2, …} of each low-order IIR all-pass filter in the cascade is calculated in turn. The cost function when the s-th filter is cascaded is:

[0185]

[0186] where a s is the pole parameter of the s-th low-order IIR allpass filter, τ s-1 (ω k ) is the system group delay of the first s-1 low-order IIR allpass filters, τ t (ω k ) is the target group delay at the k-th discrete frequency, τ s-1 (ω k ) is the system group delay of the first s-1 low-order IIR allpass filters at the k-th discrete frequency.

[0187] Step 303: grid search to determine the initial value of the s-th low-order IIR allpass filter in the cascade;

[0188] The initial value of the pole parameter of the low-order IIR allpass filter in the cascade is determined by searching the discrete grid p = {p h}, h = 1,..., M, where M is the total number of grid points.

[0189] Suppose the pole radius of the real pole in the discrete grid ranges from 1.0101 to 1.1765 (1 / 0.99 to 1 / 0.85), and the pole radius of the complex pole in the discrete grid ranges from 0.78 to 0.96 and 1.0417 to 1.2821 (1 / 0.96 to 1 / 0.78).

[0190] The pole radius is linearly distributed within the pole radius range, with a distribution interval of 0.02.

[0191] The pole angle of the complex pole is logarithmically distributed within the normalized frequency corresponding to the equalization frequency range.

[0192] The real pole corresponds to the pole of a first-order allpass filter, and the complex pole corresponds to one of a pair of poles of a second-order allpass filter.

[0193] The grid points within the unit circle correspond to the poles of causal allpass filters, and the grid points outside the unit circle correspond to the poles of non-causal allpass filters.

[0194] The group delay of all filters corresponding to the discrete grid is traversed

[0195] The filter that minimizes the cost function J s (a s ) is selected, and the grid point p s = p s or

[0196] For real pole, the s-th low-order IIR all-pass filter pole parameter is initialized as a s (0) = p s .

[0197] For complex pole, the s-th low-order IIR all-pass filter pole parameter is initialized as a s (0) = [p s , q s ] T .

[0198] Step 304: the s-th filter pole parameter of the iterative cascade is updated by line search;

[0199] The initial condition of line search is a s (0) The line search first finds a search direction that makes the cost function J s (a s ) decrease, and then calculates the step size along the direction, the s-th filter pole parameter of the iterative cascade further reduces the cost function J s (a s ).

[0200] The s-th filter pole parameter is updated in each iteration as

[0201]

[0202] where i is the iteration number, μ (i) is the step size, is the search direction.

[0203] When the iteration stopping condition is met, the iteration is stopped, and the s-th filter parameter a s is saved.

[0204] The iteration stopping condition can be: the maximum iteration number, the change (α is the specified tolerance).

[0205] The cost function J s (a s ) allows the gradient to be calculated with respect to the filter parameters, and the search direction can be calculated by various methods, such as gradient descent method, Newton method and quasi-Newton method. The Gauss-Newton (GN) method calculates the search direction by expressing the derivative of the i-th iteration as the Jacobian matrix , and thus the search direction .

[0206] The error matrix of the i-th iteration is expressed as:

[0207]

[0208] where

[0209] The search direction of the i-th iteration is:

[0210]

[0211] where, is the gradient of the error matrix at the i-th iteration; H is the conjugate transpose;

[0212] is the gradient of the group delay of the s-th first-order IIR allpass filter with respect to the pole parameter s at the i-th iteration;

[0213] is the gradient of the group delay of the s-th second-order IIR allpass filter with respect to the pole parameters s and s at the i-th iteration;

[0214] m s = 1, for

[0215] the gradient of the group delay of the s-th first-order IIR allpass filter with respect to the pole parameter s at the i-th iteration is

[0216]

[0217] m s = 2, for

[0218] the gradient of the group delay of the s-th second-order IIR allpass filter with respect to the pole parameters s and s at the i-th iteration is

[0219]

[0220] The convergence speed of the line search also depends on the choice of the step size (i) , the present invention uses Armijo's sufficient decrease condition to determine the value of (i) . Armijo's sufficient decrease condition is:

[0221]

[0222] where, denotes the value of the cost function when the pole parameters of the s-th IIR allpass filter are , denotes the cost function value when the pole parameter of the s-th IIR all-pass filter is , γ ∈ (0, 1), indicates that the reduction of the cost function value is sufficient, and is proportional to μ (i) and ;

[0223] is the gradient value of J s (a s ) at .

[0224] If the Armijo condition is not satisfied, the step size (μ (i) ) is iteratively reduced using a reduction factor (κ (i) ).

[0225] The final value of μ (i) is obtained when the Armijo condition is satisfied.

[0226] Step 305: output all the low-order filter parameters of the cascade.

[0227] When the s-th filter is cascaded, the error function increases J s (a s ) > J s-1 (a s ), stop calculating the cascaded filter parameters, and output all the low-order filter pole parameters {a1, a2, …, a S} of the cascade. Or when the group delay equalizer order N gd is greater than N max -1, stop calculating the parameters of the cascaded filter, and output all the filter pole parameters {a1, a2, …, a S} of the cascade.

[0228] Step 4: determine the pole parameter a adj = p adj of the phase controller 101 according to the angle φ0 and the target angle φ t .

[0229] When the multi-channel loudspeaker combination works, it is necessary to ensure that the phases of the multi-channel loudspeakers remain consistent in the crossover frequency band. After the multi-channel loudspeakers are equalized by the group delay equalizer 104, the phase is linear The φ0 values of different loudspeakers may not be consistent, and the phase controller 101 is designed to ensure that the φ0 of the multi-channel loudspeakers remains consistent.

[0230] Further preferably, the target phase response is:

[0231]

[0232] where φt a constant target value ( -π≤φ t ≤π) is set for the user.

[0233] When φ t is not consistent with φ0, phase control filter is performed to solve the phase control 101 parameter a adj = p adj .

[0234] The phase control 101 is a first-order all-pass filter, whose phase variation range is 0~ -π. By multiplying the signal by -1, and then filtering through the phase control 101, the phase variation of -π~ -2π can be realized.

[0235] When φ t < φ0, the phase control is directly performed by filtering through the phase control 101.

[0236] When φ t > φ0, the phase control is performed by multiplying the signal by -1 and then filtering through the phase control 101.

[0237] According to φ t and φ0, the pole parameter a adj of the phase control 101 is calculated as p adj , and the calculation formula of p adj is:

[0238]

[0239] where ω L is the lower limit of the equalization frequency range, and q is an intermediate variable introduced when calculating p adj . The value of q is divided into two cases according to the size relationship between φ t and φ0:

[0240] The phase control has an impact on the phase of the entire frequency, and the above formula is a simple calculation method. If there is a slight deviation, p adj can be slightly adjusted.

[0241] Step 5: According to the phase response of the loudspeaker impulse response after filtering through the phase control 101, the fine adjustment value of the pole parameter {a1, a2, …, a S} of the group delay equalizer 104 is determined.

[0242] Further preferably, the impulse response of the loudspeaker is first filtered through the phase control 101, and then filtered through the group delay equalizer 104. The fine adjustment value of the pole parameter {a1, a2, …, a S} of the group delay equalizer 104 is calculated based on the signal after filtering the loudspeaker impulse response through the phase control 101.

[0243] In the calculation of the initial pole parameter values of the group delay equalizer 104, the group delay to be equalized is the group delay of the loudspeaker impulse response τ0(ω k ). The target group delay in the calculation of the initial pole parameter values of the group delay equalizer 104 is

[0244] The fine-tuned pole parameter values {a1, a2, …, a S} of the group delay equalizer 104 are calculated in turn, and the specific process is as shown in Figure 3

[0245] In the determination of the fine-tuned pole parameter values of the group delay equalizer 104, the group delay to be equalized is no longer the group delay of the loudspeaker impulse response, but the sum of the group delay of the loudspeaker impulse response τ0(ω k ) and the group delay τ adj (ω adj ) of the phase controller 101 with the pole parameter a adj = p k , that is, τ0'(ω k ) = τ0(ω k ) + τ adj (ω k ). The target group delay τ t (ω k ) in the calculation of the fine-tuned pole parameter values of the group delay equalizer 104 is Except that the group delay to be equalized is different, the specific calculation steps of the fine-tuned pole parameter values {a1, a2, …, a S} of the group delay equalizer 104 are the same as those of the initial pole parameter values {a1, a2, …, a S} of the group delay equalizer 104. That is, in the calculation of the fine-tuned pole parameter values of the group delay equalizer 104, in the specific calculation steps of the initial values {a1, a2, …, a S}, τ0'(ω k ) is replaced with τ0(ω k ) in the replacement step 301, and is replaced with

[0246] The implementation and verification of the above scheme are as follows:

[0247] Figure 4 The three subgraphs from top to bottom are the impulse response, the frequency domain amplitude response, and the frequency domain phase response of a bass loudspeaker. Now, phase equalization is performed thereon, the system sampling rate f s is set to 48 kHz, and the equalization frequency range is 0.0131-0.2618 rad (100 Hz-2 kHz). The discrete Fourier transform point number N = 8192, K = 4097, and the weighting function W = [0 18×1 ​;30·1 80×1 ;15·1 200×1 ;0 3798×1 ], frame length L = 1024.

[0248] Determination of initial pole parameters of group delay equalizer 104: the group delay to be equalized and the target group delay after 1 / 3 octave smoothing of the group delay of the low frequency speaker impulse response are shown in Figure 5 , Figure 6 and Figure 7 respectively. The generated discrete grid is shown in

[0249] The maximum number of iterations of parameters is 10, the tolerance α = 10 -6 , the initial step size μ (1) = 0.9, the constant γ = 0.9 of Armijo condition, and the reduction factor κ = 0.8. Finally, when the stop condition is met, the pole parameters of the cascaded filters are saved. The initial pole parameters of the group delay equalizer are shown in Table 1, and the group delay of the initial value group delay equalizer is shown in Figure 8 . The phase equalization result after the speaker response is filtered by the initial value group delay equalizer is shown in Figure 9 .

[0250] Table 1: Filter types and pole parameters of the cascaded filters

[0251] Filter class Second order causal First order non-causal Filter pole radius 0.9399 1.0101 Filter pole angle 0.2618 0

[0252] The equalization target φ t = 0, the pole parameter ρ adj of the phase controller = 0.993, and the signal is multiplied by -1. When the fine tuning value of the pole parameters of the group delay equalizer is determined, the group delay to be equalized and the target group delay are shown in Figure 10 , Figure 11 respectively.

[0253] The fine tuning value of the pole parameters of the group delay equalizer is shown in Table 2, and the group delay of the fine tuning value group delay equalizer is shown in Figure 12 .

[0254] Table 2: Filter types and pole parameters of the cascaded filters

[0255] Filter class Second order causal First order non-causal First order non-causal Filter pole radius 0.9000 1.1111 1.1111 Filter pole angle 0.2299 0 0

[0256] In summary, the phase equalization system of this example is a cascade of a phase controller (one first-order causal IIR all-pass filter ρ adj = 0.993) and a group delay equalizer (one second-order causal IIR all-pass filter and two first-order non-causal IIR all-pass filters). The phase equalization system of this example is a five-order IIR all-pass filter. The phase equalization result after the speaker response is filtered by the phase equalization system is shown inFigure 13 The target group delay constant is calculated according to the size relationship between φ

[0257] The FIR filter length is N, and the frequency resolution Δf = f s / N. In this example, the lower limit of the equalization frequency is 100 Hz, the frequency resolution is 5 Hz, and the FIR filter length N = 9600. In this example, the phase equalization system designed by the application is a five-order IIR all-pass filter. It can be seen that using the phase equalizer designed by the application can significantly improve the linearity of the phase response of the loudspeaker, and at the same time, compared with the prior art, the calculation amount required for low-frequency phase equalization is reduced.

[0258] Compared with the prior art, the application has at least the following beneficial effects:

[0259] The application designs a phase equalization system mixed and cascaded by causal and acausal infinite impulse response (IIR) all-pass filters and a parameter determination method thereof. The acausal IIR all-pass filter can produce negative group delay and can replace the commonly used FIR filter method in the prior art. Compared with the prior art, the application uses a lower-order IIR all-pass filter to realize the phase equalization system, thereby reducing the calculation amount.

[0260] The application uses an IIR filter to realize loudspeaker phase equalization. Compared with an FIR filter, the IIR filter needs fewer filter coefficients to realize the required frequency response, and thus has lower calculation complexity. Especially when equalizing the low-frequency phase of the loudspeaker, in order to ensure sufficient frequency resolution, the application can design a lower-order IIR filter to equalize the low-frequency phase of the loudspeaker, thereby significantly reducing the calculation amount required for equalizing the low-frequency phase of the loudspeaker.

[0261] The application combines the acausal filter when calculating the target group delay constant, so that the target group delay constant of the equalization can be less than the maximum value of the group delay to be equalized.

[0262] The application designs a cost function of the cascaded group delay equalizer according to the group delay, and solves a set of low-order IIR all-pass filter parameters instead of directly solving high-order all-pass filter parameters, thereby facilitating users to design a phase equalizer according to the use of the loudspeaker and the application scene.

[0263] The application calculates the phase controller pole parameter a t according to the size relationship between φ adj and φ0 adj = ρ t , and the designed phase controller can control the phase of the loudspeaker to be a linear phase with the target angle φ When a plurality of loudspeakers work in combination, the phases of the plurality of loudspeakers are consistent in the crossover frequency band, and the application can be applied to the phase equalization of the plurality of loudspeakers.

[0264] The present disclosure can be a system, a method, and / or a computer program product. The computer program product can include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present disclosure.

[0265] The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium can be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or punched tape, a

[0266] The computer readable program instructions described herein can be downloaded to respective computing / processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and / or a wireless network. The network can comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and / or edge servers. A network adapter card or network interface in each computing / processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing / processing device.

[0267] Computer readable program instructions for carrying out operations of the present disclosure can be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages such as the "C" programming language or similar programming languages. The computer readable program instructions can execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection can be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) can execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present disclosure.

[0268] Finally, it should be noted that the above-mentioned embodiments are merely used to illustrate the technical solutions of the present application, but not to limit it. Although the present application has been described in detail with reference to the above-mentioned embodiments, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced, and any modification or replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.

Claims

1. A loudspeaker phase equalization signal processing system, which equalizes a loudspeaker phase response to be linear phase in a set equalization frequency range, characterized in that: the system comprises a phase controller and a group delay equalizer cascaded; The phase controller is a first order IIR all-pass filter with a transfer function of The pole parameter is a adj = p adj , where z = e jω , ω is the frequency, e is the natural constant, p adj is the pole radius; The group delay equalizer comprises S cascaded low-order IIR all-pass filters, wherein the first N1 are low-order causal IIR all-pass filters and the last N2 are low-order non-causal IIR all-pass filters, and the corresponding transfer function is The pole parameters are {a1, a2, …, a S} and the zero parameters are {b1, b2, …, b The transfer function of the m s order IIR all-pass filter, m s =1 or m s =2; s is the index of the cascaded low-order IIR all-pass filter, and when s is 1 to N1, it corresponds to the N1 low-order causal IIR all-pass filters, and when s is N1+1 to S, it corresponds to the N2 low-order non-causal IIR all-pass filters. 2.The loudspeaker phase equalization signal processing system according to claim 1, characterized in that: For m s Transfer function of a stage IIR all-pass filter m s = 1, is: where σ s is the pole radius of the first-order IIR all-pass filter pole; m s = 2, = 2, where ρ s and θ s are the polar radius and polar angle of the complex conjugate pole of the second order IIR all-pass filter, respectively. where ρ s and θ s are the polar radius and polar angle of the complex conjugate pole of the second order IIR all-pass filter, respectively. 3.The loudspeaker phase equalization signal processing system according to claim 1, characterized in that: For the s-th low-order IIR all-pass filter, the pole parameter a s : m s = 1, a s = σ s , σ s is the pole radius of the first-order IIR all-pass filter pole. m s = 2, a s = [p s , θ s ] T , p s and θ s are the polar radius and polar angle of the complex conjugate pole of a second order IIR allpass filter . 4.The loudspeaker phase equalization signal processing system according to claim 1, characterized in that: the signal processing procedure of the non-causal all-pass filter is: first, buffer and divide the input real-time signal into continuous frames with length L, the signal of the p th frame is: b p = [b((p - 1) L + 1), b((p - 1) L + 2),..., b(p L)] T . where p is an integer, indicating the index of the frame; b ((p-1) ·L+1), b ((p-1) ·L+2), b (p·L) represent the input real-time signal at discrete time (p-1) ·L+1, (p-1) ·L+2, p·L; Next, each frame is time reversed and combined with a zero vector of dimension 1 x L, 0 1×L to form a vector of dimension the intermediate signal of 2L×1, the intermediate signal of the p th frame is represented as: q p = [b(p-L), b((p-l)L+L-l),..., b((p-l)L+l), 0 1×L ] T . Secondly, the intermediate signal [q1; q2; …] is filtered by the inverse function G2(z -1 ) of the non-causal all-pass filter transfer function in turn, and then time reversal is performed to obtain the output signal of dimension 2Lx1; Finally, according to the filtering result of the non-causal all-pass filter processing the input signal according to the output signal, the filtering result y p The expression is: wherein u p-1 (L+1:2L) is the last L elements of the (p-1)th frame output signal u p-1 (L+1:2L) is the last L elements of the (p-1)th frame output signal u p (1:L) is the first L elements of the pth frame output signal u p (1:L) is the first L elements of the pth frame output signal u 5. A pole parameter determination method applied to the loudspeaker phase equalization signal processing system of any one of claims 1-4, characterized in that, including: Step 1: acoustic measurement is performed on the compensated loudspeaker to obtain the loudspeaker impulse response; Step 2: Set target angle φ t and equalization frequency range [ω L ,ω H ], the phase equalization target is to get linear phase where ω k is the kth discrete frequency, ω L ≤ω k ≤ω H , k = 1, …, K, K = N / 2 + 1, N is the number of points of discrete Fourier transform; ω L , ω H are the lower and upper limits of the equalization frequency range respectively; is the target group delay constant; at the same time, set the maximum order N max and the frequency weighting function W = [W(ω1), …, W(ω K )], W(ω1) is the importance of the discrete frequency ω1, W(ω K ) is the importance of the discrete frequency ω K ; Step 3: Based on N max and W, the pole parameters {a1, a2, …, an} of the group delay equalizer are calculated S The phase response of the loudspeaker impulse response obtained in step 1 is approximately a delay linear phase ω L ≤ω k ≤ω H , and then the angle φ0 is obtained; Step 4: Calculate the target angle φt from the angle φ0 and the target angle φ t Calculate the pole parameter a of the phase controller adj = p adj ; Step 5: The pole parameters {a1, a2,..., an} of the group delay equalizer are determined by the phase response of the loudspeaker impulse response obtained in Step 1 after being filtered by the phase controller with the pole parameters a adj = p adj . S ​ 6.The pole parameter determination method according to claim 5, characterized in that: In Step 3, the initial values of the pole parameters {a1, a2,..., an} of the group delay equalizer are calculated as follows: S} of the pole parameters {a1, a2,..., an} of the group delay equalizer are calculated as follows: Step 301: Calculate the target group delay of the group delay equalizer: wherein, is the target group delay constant; τ0(ω k ) represents the group delay to be equalized at the kth discrete frequency, which is the value after the octave smoothing of the group delay of the loudspeaker impulse response. Step 302: define the cost function J when defining the s-th low-order IIR all-pass filter in the cascade s (a s ): where a s is the pole parameter of the s-th low-order IIR allpass filter, is the group delay of the s-th low-order IIR allpass filter at the k-th discrete frequency, τ t (ω k ) is the target group delay, τ s-1 (ω k ) is the system group delay of the first s-1 low-order IIR allpass filters at the k-th discrete frequency; Step 303: the initial value of the pole parameter of the s th low-order IIR all-pass filter in the cascade is determined by grid search and minimization of the cost function; Step 304: the pole parameter of the s th IIR all-pass filter in the cascade is calculated based on the initial value by using a line search iterative algorithm; Step 305: When the output condition based on the cost function or N max of the current cascade of all low-order IIR allpass filters as the pole parameters {a1, a2,..., an} of the group delay equalizer. S} initial values. 7.The pole parameter determination method according to claim 6, characterized in that: In step 301, the target group delay constant is: wherein [N e ,N e+1 ,…,N E ] T are discrete frequency indices calculated according to a 1 / 24 octave resolution between a start index L and an end index H of the equalization frequency range; representing in the value of the group delay to be equalized at the discrete frequency point, for the loudspeaker impulse response group delay after octave smoothing the value of the group delay to be equalized at the discrete frequency point median (·) is a median function; {·} T is the vector transpose. 8.The pole parameter determination method according to claim 6, characterized in that: Step 303 specifically includes: The initial values of pole parameters of the concatenated low-order IIR all-pass filters are determined by searching a discrete grid p = {p h}, h = 1, …, M, where h is the pole index and M is the total number of grid points. the polar radius of the real pole in the discrete grid ranges from 1.0101 to 1.1765, the polar radius of the complex pole ranges from 0.78 to 0.96 and from 1.0417 to 1.2821, and the polar radius of the pole is linearly distributed within the polar radius range, and the polar angle of the complex pole is logarithmically distributed within the equalization frequency range; the real pole in the discrete grid corresponds to the pole of a first-order IIR all-pass filter, and the complex pole corresponds to one of a pair of poles of a second-order IIR all-pass filter, the grid point within the unit circle corresponds to the pole of a causal IIR all-pass filter, and the grid point outside the unit circle corresponds to the pole of a non-causal IIR all-pass filter; grid point p h group delay of the corresponding filter traversing the discrete grid to obtain the group delay of all filters select the filter that minimizes the cost function, and the initial value of the pole parameter of the s-th low-order IIR all-pass filter is the value of the corresponding grid point The s-th low-order IIR all-pass filter pole parameter corresponding to the real pole point is initialized as a s (0) = p s ; The s-th low-order IIR all-pass filter pole parameter corresponding to the complex pole is initialized as a s (0) = [p s , θ s ] T . 9.The pole parameter determination method according to claim 8, characterized in that: Step 304 specifically includes: a s (0) As the initial condition, a search direction is first found to make the cost function descend, then a step along the direction is calculated, and the pole parameter of the s-th IIR all-pass filter in the cascade is iterated to further reduce the cost function. In each iteration, the pole parameter of the s-th IIR all-pass filter is updated, and the update formula is: wherein, are pole parameters of the s-th IIR allpass filter of the i+1-st, i-th iteration, respectively; μ (i) is a step size, is a search direction; when the iteration stop condition is met, the iteration is stopped, and the current pole parameter value of the s th IIR all-pass filter is saved. 10.The pole parameter determination method according to claim 9, characterized in that: the step length is determined using Armijo's sufficient decrease condition, wherein Armijo's sufficient decrease condition is: wherein, J (s) denotes a cost function value when the pole parameter of the s-th IIR allpass filter is J (s) denotes a cost function value when the pole parameter of the s-th IIR allpass filter is J (s) denotes a cost function value when the pole parameter of the s-th IIR allpass filter is J (s) denotes a cost function value when the pole parameter of the s-th IIR allpass filter is (i) and proportional to μ; the gradient value of the cost function at ; If the above condition is not satisfied, the step size is iteratively reduced using a reduction factor K: m (i) ← K m (i) until the above condition is satisfied, obtaining the final value of m (i) . 11.The pole parameter determination method according to claim 9, characterized in that: the search direction is: in, is the error matrix at the i-th iteration gradient; H is a conjugate transpose; the gradient of the group delay of the s-th first order IIR allpass filter for the i-th iteration with respect to the pole parameter σ s s. gradient of the group delay of the s-th second-order IIR allpass filter with respect to the pole parameter p at the i-th iteration s , θ s of the s-th second-order IIR allpass filter at the i-th iteration is: wherein m s = 1, for Group delay of the s-th first order IIR allpass filter with respect to pole parameter s s is m s = 2, for Group delay of the s-th second order IIR allpass filter with respect to pole parameter p s and the gradient of theta s is 12.The pole parameter determination method according to claim 9, characterized in that: The iteration stop condition is: reaching a maximum iteration number or α is a set tolerance. 13.The pole parameter determination method according to claim 6, characterized in that: In step 305, the output condition of the cost function or N max is that: The cost function of the cascaded s-th low-order IIR all-pass filter increases to J s (a s ) > J s-1 (a s ), or when the group delay equalizer order N gd is greater than N max -1.

14. The pole parameter determination method of claim 5, wherein: In step 4, p adj The formula for the calculation is: where q is an intermediate variable calculated from the magnitude relationship of φ t and φ0.

15. The pole parameter determination method of claim 5, wherein: Step 5 is specifically as follows: With τ0'(ω k )=τ0(ω k )+τ adj (ω k ) is the group delay to be equalized, For the target group delay, the group delay equalizer pole parameters {a1, a2, …, a S }Specific calculation steps of the initial value to calculate the group delay equalizer pole parameters {a1, a2, ..., a S } fine-tuning value, where τ0(ω k ) is the group delay of the loudspeaker impulse response, τ adj (ω k ) is the pole parameter a adj =ρ adj The group delay of the phase modulator.

16. A terminal comprising a processor and a storage medium; characterized in that: the storage medium is configured to store instructions; the processor is configured to operate according to the instructions to perform the steps of the method of any one of claims 5-15.

17. A computer readable storage medium having stored thereon a computer program, characterized in that The program, when executed by the processor, implements the steps of the method of any one of claims 5-15.

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