Patent Publication Number: US-11039261-B2

Title: Audio signal processing method, terminal and storage medium thereof

Description:
This application is a National Stage of International Application No. PCT/CN2018/118764, filed on Nov. 30, 2018, which claims priority to Chinese Patent Application No. 201711432680.4, filed on Dec. 26, 2017 and entitled “AUDIO SIGNAL PROCESSING METHOD AND APPARATUS, AND TERMINAL THEREOF”, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to the field of audio processing technology, and in particular, relates to an audio signal processing method and apparatus, and a terminal and a storage medium thereof. 
     BACKGROUND 
     In related art, an audio playback device plays a double-channel audio signal by an audio playback unit, such as a double-channel earphone or a double-channel speaker, such that a user may achieve a stereo effect. 
     SUMMARY 
     Embodiments of the present disclosure provide an audio signal processing method, a terminal and a storage medium thereof. 
     In an aspect, embodiments of the present disclosure provide an audio signal processing method. The method is performed by a terminal, and includes: 
     acquiring a first stereo audio signal; 
     splitting the first stereo audio signal into 5.1-channel audio signals; 
     obtaining processed 5.1-channel audio signals by processing the 5.1-channel audio signals based on a speaker box parameter of a three-dimensional surround 5.1-channel virtual speaker box; and 
     synthesizing the processed 5.1-channel audio signals into a second stereo audio signal. 
     In another aspect, embodiments of the present disclosure provide a terminal. The terminal includes a processor and a memory, wherein at least one instruction is stored in the memory, and loaded and executed by the processor to perform following processing: 
     acquire a first stereo audio signal; 
     split the first stereo audio signal into 5.1-channel audio signals; 
     obtain processed 5.1-channel audio signals by processing the 5.1-channel audio signals based on a speaker box parameter of a three-dimensional surround 5.1-channel virtual speaker box; and 
     synthesize the processed 5.1-channel audio signals into a second stereo audio signal. 
     In another aspect, embodiments of the present disclosure provide a computer-readable storage medium, wherein at least one instruction is stored in the storage medium, and loaded and executed by a processor to perform following processing: 
     following processing: 
     acquire a first stereo audio signal; 
     split the first stereo audio signal into 5.1-channel audio signals; 
     obtain processed 5.1-channel audio signals by processing the 5.1-channel audio signals based on a speaker box parameter of a three-dimensional surround 5.1-channel virtual speaker box; and 
     synthesize the processed 5.1-channel audio signals into a second stereo audio signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For clearer descriptions of the technical solutions in the embodiments of the present disclosure, the following briefly introduces the accompanying drawings required for describing the embodiments. Apparently, the accompanying drawings in the following description show merely some embodiments of the present disclosure, and a person of ordinary skill in the art may also derive other drawings from these accompanying drawings without any creative efforts. 
         FIG. 1  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 2  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 3  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 4  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 5  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 6  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 7  is a schematic diagram showing placement of a 5.1-channel virtual speaker box in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 8  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 9  is a schematic diagram showing HRTF data acquisition in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 10  is a block diagram of an audio signal processing apparatus in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 11  is a block diagram of an audio signal processing apparatus in accordance with an exemplary embodiment of the present disclosure; and 
         FIG. 12  is a block diagram of a terminal in accordance with an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     For clearer descriptions of the objectives, the technical solutions and the advantages of the present disclosure, the embodiments of the present disclosure are further described in detail hereinafter with reference to the accompanying drawings. 
     In related art, the double-channel audio signal is an audio signal formed by superimposing a left-channel audio signal over a right-channel audio signal. The audio playback unit plays the left-channel audio signal by a left-channel portion and plays the right-channel audio signal by a right-channel portion. The user obtains a stereo impression by a phase difference between the left-channel audio signal played by the left-channel portion and the right-channel audio signal played by the right-channel portion. 
     In the related art, the audio playback unit plays the left-channel audio signal and the right-channel audio signal such that the user obtains the stereo impression. Since sound travels in multiple directions, the stereo effect is relatively poor when only the two channels of audio signals are played. 
       FIG. 1  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure, which may solve the problem that the stereo effect is relatively poor when the left-channel audio signal and the right-channel audio signal are played by the audio playback unit. The method may be performed by a terminal with an audio signal processing function, and includes the following steps. 
     In step  101 , a first stereo audio signal is acquired. 
     The terminal reads a locally stored first stereo audio signal, or acquires the first stereo audio signal on a server by a wired or wireless network. 
     The first stereo audio signal is obtained by sound recording by a stereo recording device, which usually includes a first microphone on a left side and a second microphone on a right side. The stereo recording device records sound on the left side and sound on the right side by the first microphone and the second microphone respectively to obtain a left-channel audio signal and a right-channel audio signal. The stereo recording device superimposes the left-channel audio signal over the right-channel audio signal to obtain the first stereo signal. 
     Optionally, the received first stereo audio signal is stored in a buffer of the terminal and denoted as X_PCM. 
     The terminal stores the received first stereo audio signal in a built-in buffer area in the form of a sample pair of the left-channel audio signal and the corresponding right-channel audio signal and acquires the first stereo audio signal from the buffer area for use. 
     In step  102 , the first stereo audio signal is split into 5.1-channel audio signals. 
     The terminal splits the first stereo audio signal into the 5.1-channel audio signals by a preset algorithm. The 5.1-channel audio signals include a front left-channel signal, a front right-channel signal, a front center-channel signal, a low-frequency channel signal, a rear left-channel signal and a rear right-channel signal. 
     In step  103 , the 5.1-channel audio signals are processed based on a speaker box parameter of a three-dimensional surround 5.1-channel virtual speaker box to obtain processed 5.1-channel audio signals. 
     The terminal processes the 5.1-channel audio signals based on the speaker box parameter of the three-dimensional surround 5.1-channel virtual speaker box to obtain the processed 5.1-channel audio signals. 
     The processed 5.1-channel audio signals include a processed front left-channel signal, a processed front right-channel signal, a processed front center-channel signal, a processed low-frequency channel signal, a processed rear left-channel signal and a processed rear right-channel signal. 
     The three-dimensional surround 5.1-channel virtual speaker box is an audio model preset by the terminal, and simulates the playback effect of a 5.1-channel speaker box that surrounds a user in a real scene. 
     In the real scene, centered by the user and taking the direction in which the user faces towards as front, the 5.1-channel speaker box includes a front left speaker box at the left front side of the user, a front right speaker box at the right front side of the user, a front center speaker box right ahead the user, a low-frequency speaker box (not limited in location), a rear left speaker box at the left rear side of the user and a rear right speaker box at the right rear side of the user. 
     In step  104 , the processed 5.1-channel audio signals are synthesized into a second stereo audio signal. 
     The terminal synthesizes the processed 5.1-channel audio signals into the second stereo audio signal, which may be played by a common stereo earphone, a 2.0 speaker box or the like. The user may enjoy a 5.1-channel stereo effect upon hearing the second stereo audio signal of the common stereo earphone or the 2.0 speaker box. 
     In summary, according to the method provided by the embodiment, the first stereo audio signal is split into the 5.1-channel audio signals, which are processed and synthesized into the second stereo audio signal, and the second stereo audio signal is played by a double-channel audio playback unit, such that the user enjoys a 5.1-channel audio stereo effect. The present disclosure solves the problem in the related art that a relatively poor stereo effect is caused by only playing two channels of audio signals. Further, a stereo effect in audio playback is improved. 
     In the embodiment illustrated in  FIG. 1 , the process in which the first stereo audio signal is split into the 5.1-channel audio signals is divided into two stages. In the first stage, a 5.0-channel audio signal in the 5.1-channel audio signals is acquired, and the embodiments illustrated in  FIG. 2 ,  FIG. 3  and  FIG. 4  may explain splitting of the 5.0-channel audio signal from the first stereo audio signal. In the second stage, a 0.1-channel audio signal in the 5.1-channel audio signals is acquired, and the embodiment illustrated in  FIG. 5  may explain splitting of the 0.1-channel audio signal from the first stereo audio signal. In the third stage, the 5.0-channel audio signal and the 0.1-channel audio signal are synthesized into the second stereo audio signal. The embodiments illustrated in  FIG. 6  and  FIG. 8  provide methods for processing and synthesizing the 5.1-channel audio signals to obtain the second stereo audio signal. 
       FIG. 2  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure. The method may be performed by a terminal with an audio signal processing function and may be an optional implementation mode of step  102  and step  103  in the embodiment illustrated in  FIG. 1 . The method includes the following steps. 
     In step  201 , a first stereo audio signal is input into a high-pass filter for filtering to obtain a first high-frequency signal. 
     The terminal inputs the first stereo audio signal into the high-pass filter for filtering to obtain the first high-frequency signal. The first high-frequency signal is a superimposed signal of a first left-channel high-frequency signal and a first right-channel high-frequency signal. 
     Optionally, the terminal filters the first stereo signal by a 4-order IIR high-pass filter to obtain the first high-frequency signal. 
     In step  202 , a left-channel high-frequency signal, a center-channel high-frequency signal and a right-channel high-frequency signal are obtained by calculation based on the first high-frequency signal. 
     The terminal splits the first high-frequency signal into the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal. The left-channel high-frequency signal includes a front left-channel signal and a rear left-channel signal. The center-channel high-frequency signal includes a front center-channel signal. The right-channel high-frequency signal includes a front right-channel signal and a rear right-channel signal. 
     Optionally, the terminal obtains the center-channel high-frequency signal by calculation based on the first high-frequency signal. The center-channel high-frequency signal is subtracted from the first left-channel high-frequency signal to obtain the left-channel high-frequency signal. The center-channel high-frequency signal is subtracted from the first right-channel high-frequency signal to obtain the right-channel high-frequency signal. 
     In step  203 , the front left-channel signal, the front right-channel signal, the front center-channel signal, the rear left-channel signal and the rear right-channel signal in the 5.1-channel audio signals are obtained by calculation based on the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal. 
     The terminal obtains the front left-channel signal and the rear left-channel signal by calculation based on the left-channel high-frequency signal, obtains the front right-channel signal and the rear right-channel signal by calculation based on the right-channel high-frequency signal, and obtains the front center-channel signal by calculation based on the center-channel high-frequency signal. 
     Optionally, the terminal extracts first rear/reverberation signal data in the left-channel high-frequency signal, second rear/reverberation signal data in the center-channel high-frequency signal and third rear/reverberation signal data in the right-channel high-frequency signal, and calculates the front left-channel signal, the rear left-channel signal, the front right-channel signal, the rear right-channel signal and the front center-channel signal based on the first rear/reverberation signal data, the second rear/reverberation signal data and the third rear/reverberation signal data. 
     In step  204 , the front left-channel signal, the front right-channel signal, the front center-channel signal, the rear left-channel signal and the rear right-channel signal are respectively subjected to scalar multiplication with corresponding speaker box parameters to obtain a processed front left-channel signal, a processed front right-channel signal, a processed front center-channel signal, a processed rear left-channel signal and a processed rear right-channel signal. 
     Optionally, the terminal performs scalar multiplication on the front left-channel signal and a volume V 1  of a virtual front left-channel speaker box to obtain the processed front left-channel signal X_FL, on the front right-channel signal and a volume V 2  of a virtual front right-channel speaker box to obtain the processed front right-channel signal X_FR, on the front center-channel signal and a volume V 3  of a virtual front center-channel speaker box to obtain the processed front center-channel signal X_FC, on the rear left-channel signal and a volume V 4  of a virtual rear left-channel speaker box to obtain the processed rear left-channel signal X_RL, and on the rear right-channel signal and a volume V 5  of a virtual rear right-channel speaker box to obtain the processed rear right-channel signal X_RR. 
     In summary, according to the method provided by the embodiment, the first stereo audio signal is filtered to obtain the first high-frequency signal. The left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal are obtained by calculation based on the first high-frequency signal. The 5.0-channel audio signal is obtained by calculation based on the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal to further obtain the processed 5.0-channel audio signal. Thus, the first high-frequency signal is extracted from the first stereo audio signal and split into the 5.0-channel audio signal in the 5.1-channel audio signals to further obtain the processed 5.0-channel audio signal. 
       FIG. 3  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure. The audio signal processing method is applied to a terminal with an audio signal processing function and may be an optional implementation mode of step  202  in the embodiment illustrated in  FIG. 2 . The method includes the following steps. 
     In step  301 , fast Fourier transform (FFT) is performed on the first high-frequency signal to obtain a high-frequency real number signal and a high-frequency imaginary number signal. 
     The terminal performs FFT on the first high-frequency signal to obtain the high-frequency real number signal and the high-frequency imaginary number signal. 
     FFT is an algorithm for transforming a time-domain signal into a frequency-domain signal. In the present embodiment, the first high-frequency signal is subjected to FFT to obtain the high-frequency real number signal and the high-frequency imaginary number signal. The high-frequency real number signal includes a left-channel high-frequency real number signal and a right-channel high-frequency real number signal. The high-frequency imaginary number signal includes a left-channel high-frequency imaginary number signal and a right-channel high-frequency imaginary number signal. 
     In step  302 , a vector projection is calculated based on the high-frequency real number signal and the high-frequency imaginary number signal. 
     The terminal obtains a high-frequency real number signal by adding the right-channel high-frequency real number signal to the left-channel high-frequency real number signal in the high-frequency real number signal. 
     Exemplarily, the high-frequency real number signal is calculated by the following formula:
 
sum RE=X _HIPASS_ RE _ L+X _HIPASS_ RE _ R  
 
     X_HIPASS_RE_L is the left-channel high-frequency real number signal, X_HIPASS_RE_R is the right-channel high-frequency real number signal and sumRE is the high-frequency real number signal. 
     The terminal obtains a high-frequency imaginary number summary signal by adding the right-channel high-frequency imaginary number signal to the left-channel high-frequency imaginary number signal in the high-frequency imaginary number signal. 
     Exemplarily, the high-frequency imaginary number summary signal is calculated by the following formula:
 
sum IM=X _HIPASS_ IM _ L+X _HIPASS_ IM _ R  
 
     X_HIPASS_IM_L is the left-channel high-frequency imaginary number signal, X_HIPASS_IM_R is the right-channel high-frequency imaginary number signal and sumIM is the high-frequency imaginary number signal. 
     The terminal performs subtraction on the left-channel high-frequency real number signal and the right-channel high-frequency real number signal in the high-frequency real number signal to obtain a high-frequency real number difference signal. 
     Exemplarily, the high-frequency real number difference signal is calculated by the following formula:
 
differ= X _HIPASS_ RE _ L−X _HIPASS_ RE _ R  
 
     diffRE is the high-frequency real number difference signal. 
     The terminal performs subtraction on the left-channel high-frequency imaginary number signal and the right-channel high-frequency imaginary number signal in the high-frequency imaginary number signal to obtain a high-frequency imaginary number difference signal. 
     Exemplarily, the high-frequency imaginary number difference signal is calculated by the following formula:
 
diff IM=X _HIPASS_ IM _ L−X _HIPASS_ IM _ R  
 
     diffIM is the high-frequency imaginary number difference signal. 
     The terminal obtains a real number signal by calculation based on the high-frequency real number signal and the high-frequency imaginary number signal. 
     Exemplarily, the real number summary signal is calculated by the following formula:
 
sum Sq =sum RE *sum RE +sum IM *sum IM  
 
     sumSq is the real number signal. 
     The terminal obtains a real number difference signal based on a high-frequency real number difference signal and a high-frequency imaginary number difference signal. 
     Exemplarily, the real number difference signal is calculated by the following formula:
 
diff Sq =diff RE *diff RE +diff IM *diff IM  
 
     diffSq is the real difference signal. 
     The terminal calculates the vector projection based on the real number signal and the real number difference signal to obtain the vector projection that represents a distance between each virtual speaker box in the three-dimensional surround 5.1-channel virtual speaker box and the user. 
     Optionally, the vector protection is calculated by the following formula when the real number signal is a significant digit. That is, the vector protection is calculated by the following formula when the real number signal is not infinitely small or 0:
 
Alpha=0.5−SQRT(diff Sq /sum Sq )*0.5
 
     alpha is the vector projection, SQRT represents extraction of square root and * represents a scalar product. 
     In step  303 , inverse fast Fourier transform (IFFT) and overlap-add are performed on the product of the left-channel high-frequency real number signal in the high-frequency real number signal and the vector projection to obtain a center-channel high-frequency signal. 
     IFFT is an algorithm for transforming a frequency-domain signal into a time-domain signal. In the present disclosure, the terminal performs IFFT and overlap-add on the product of the left-channel high-frequency real number signal in the high-frequency real number signal and the vector projection to obtain the center-channel high-frequency signal. Referring to https://en.wikipedia.org/wiki/Overlap-add_method for details of the overlap-add which is a mathematical algorithm. The center-channel high-frequency signal may be calculated based on the left-channel high-frequency real number signal or the right-channel high-frequency real number signal. However, since most audio signals are gathered at a left channel if the first stereo signal only includes an audio signal of one channel, the center high-frequency signal may be calculated more accurately based on the left-channel high-frequency real number signal. 
     In step  304 , a difference between a left-channel high-frequency signal in the first high-frequency signal and the center-channel signal is taken as a left-channel high-frequency signal. 
     The terminals take the difference between the left-channel high-frequency signal in the first high-frequency signal and the center-channel signal as the left-channel high-frequency signal. 
     Exemplarily, the left-channel high-frequency signal is calculated by the following formula:
 
 X _PRE_ L=X _HIPASS_ L−X _PRE_ C  
 
     X_HIPASS_L is the left-channel high-frequency signal in the first high-frequency signal, X_PRE_C is the center-channel signal, and X_PRE_L is the left-channel high-frequency signal. 
     In step  305 , a difference between a right-channel high-frequency signal in the first high-frequency signal and the center-channel signal is taken as a right-channel high-frequency signal. 
     The terminal takes the difference between the right-channel high-frequency signal in the first high-frequency signal and the center-channel signal as the right-channel high-frequency signal. 
     Exemplarily, the right-channel high-frequency signal is calculated by the following formula:
 
 X _PRE_ R=X _HIPASS_ R−X _PRE_ C  
 
     X_HIPASS_R is the right-channel high-frequency signal in the first high-frequency signal, X_PRE_C is the center-channel signal and X_PRE_R is the right-channel high-frequency signal. 
     The sequence of step  304  and step  305  is not limited. The terminal may perform step  304  prior to step  305 , or perform step  305  prior to step  304 . 
     In summary, according to the method provided by the embodiment, FFT is performed on the first high-frequency signal to obtain the high-frequency real number signal and the high-frequency imaginary number signal. The center high-frequency signal is obtained by a series of calculations based on the high-frequency real number signal and the high-frequency imaginary number signal. Further, the left-channel high-frequency signal and the right-channel high-frequency signal are obtained by calculation based on the center-channel high-frequency signal. Thus, the left-channel high-frequency signal, the center high-frequency signal and the right-channel high-frequency signal are obtained by calculation based on the first high-frequency signal. 
       FIG. 4  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure. The audio signal processing method may be performed by a terminal with an audio signal processing function and may be an optional implementation mode of step  203  in the embodiment illustrated in  FIG. 2 . The method includes the following steps. 
     In step  401 , at least one moving window is obtained based on a sampling point in any of a left-channel high-frequency signal, a center-channel high-frequency signal and a right-channel high-frequency signal. Each moving window includes n sampling points, and n/2 sampling points of every two adjacent moving windows are overlapping. 
     The terminal obtains at least one moving window based on the sampling point in any of the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal by a moving window algorithm. If each moving window has n sampling points, n/2 sampling points of every two adjacent moving windows are overlapping, and n≥1. 
     The moving window is an algorithm similar to overlap-add, and it realizes only overlap but not addition. For example, data A include 1,024 sampling points, if a moving step length is 128 and an overlap length is 64, the following signals are output by the moving window every time: A[0-128] output firstly, A[64-192] output secondly, A[128-256] output thirdly, . . . . A is the moving window, and a serial number of the sampling point is inside the square brackets. 
     In step  402 , a low-correlation signal in the moving window and a start time point of the low-correlation signal are calculated. The low-correlation signal includes a signal of which a first decay envelope sequence in a magnitude spectrum and a second decay envelope sequence in a phase spectrum are unequal. 
     The terminal performs FFT on a sampling point signal in an i th  moving window to obtain a sampling point signal subjected to FFT, and i≥1. 
     The terminal performs the moving window algorithm and FFT on the left-channel high-frequency signal, the right-channel high-frequency signal and the center-channel signal respectively based on a preset moving step length and overlap length to sequentially obtain a left-channel high-frequency real number signal and a left-channel high-frequency imaginary number signal (denoted as FFT_L), a right-channel high-frequency real number signal and a right-channel high-frequency imaginary number signal (denoted as FFT_R), and a center-channel real number signal and a center-channel imaginary number signal (denoted as FFT_C). 
     The terminal calculates a magnitude spectrum and a phase spectrum of the sampling point signal subjected to FFT. 
     The terminal calculates a magnitude spectrum AMP_L and a phase spectrum PH_L of the left-channel high-frequency signal based on FFT_L, calculates a magnitude spectrum AMP_R and a phase spectrum PH_R of the left-channel high-frequency signal based on FFT_R and calculates a magnitude spectrum AMP_C and a phase spectrum PH_C of the center-channel signal. 
     In the followings, AMP_L, AMP_R and AMP_C are denoted as AMP_L/R/C, and PH_L, PH_R and PH_C are denoted as PH_L/R/C. 
     The terminal calculates a first decay envelope sequence of m frequency lines in the i th  moving window based on the magnitude spectrum of the sampling point signal subjected to FFT, calculates a second decay envelope sequence of the m frequency lines in the i th  moving window based on the phase spectrum of the sampling point signal subjected to FFT, determines a j th  frequency line as the low-correlation signal when the decay envelope sequence and the second decay envelope sequence of the j th  frequency line in the m frequency lines are different, and determines a start time point of the low-correlation signal based on a window number of the i th  moving window and a frequency line number of the j th  frequency line, wherein m≥1 and 1≤j≤m. 
     The terminal calculates the decay envelope sequences and relevancy of all the frequency lines for AMP_L/R/C and PH_L/R/C of all the moving windows. An effective condition is that the calculated decay envelope sequence of the moving window corresponds to the magnitude spectrum and the phase spectrum of the same moving window. 
     For example, when the decay envelope sequences of frequency spectra of No. 0 frequency lines corresponding to a moving window  1 , a moving window  2  and a moving window  3  are respectively 1.0, 0.8 and 0.6, and the decay envelope sequences of phase spectrums of No. 0 frequency lines corresponding to the moving window  1 , the moving window  3  and the moving window  3  are respectively 1.0, 0.8 and 1.0, it is believed that the No. 0 frequency line of the moving window  1  and the No. 0 frequency line of the moving window  2  are highly relevant, and the No. 0 frequency line of the moving window  2  and the No. 0 frequency line of the moving window  3  are less relevant. 
     The n sampling points may be subjected to FFT to obtain n/2+1 frequency lines. A window number and the frequency lines of a moving window corresponding to a signal with low correlation are taken. The start time point of the signal in X_PRE_L, X_PRE_R and X_PRE_C may be calculated based on the window number. 
     In step  403 , a target low-correlation signal that conforms to a rear/reverberation feature is determined. 
     Optionally, the terminal determines the target low-correlation signal that conforms to the rear/reverberation feature by the following means. 
     When magnitude spectrum energy of a very high frequency (VHF) line of the low-correlation signal is less than a first threshold and a decay envelope slope of a window adjacent to a window where the VHF line is greater than a second threshold, the terminal determines the low-correlation signal as the target low-correlation signal that conforms to the rear/reverberation feature. The VHF line is a frequency line of which a frequency band ranges from 30 MHz to 300 MHz. 
     Optionally, a method by which the terminal determines the target low-correlation signal that conforms to the rear/reverberation feature may include but not limited to the following steps. 
     When the magnitude spectrum energy of the VHF line of the low-correlation signal is smaller than the first threshold and a decay rate of a window adjacent to a window where the VHF line is larger than a third threshold, the terminal determines the low-correlation signal as the target low-correlation signal that conforms to the rear/reverberation feature. 
     In step  404 , an end time point of the target low-correlation signal is calculated. 
     Optionally, the terminal calculates the end time point of the low-correlation signal by the following means. 
     The terminal acquires a time point at which energy of a frequency line corresponding to the magnitude spectrum of the target low-correlation signal is smaller than a fourth threshold and uses the acquired time point as the end time point. 
     Optionally, the terminal calculates the end time point of the low-correlation signal by the following means. 
     The terminal determines a start time point of the next low-correlation signal as the end time point of the target low-correlation signal when energy of the target low-correlation signal is smaller than 1/n of energy of the next low-correlation signal. 
     In step  405 , the target low-correlation signal is extracted based on the start time point and the end time point, and the extracted target low-correlation signal is taken as rear/reverberation signal data in the corresponding channel high-frequency signal. 
     Optionally, the terminal extracts channel signal segments in the start time point and the end time point, performs FFT on the channel signal segments to obtain signal segments subjected to FFT, extracts a frequency line corresponding to the target low-correlation signal from the signal segments subjected to FFT to obtain a first portion signal, and performs IFFT and overlap-add on the first portion to obtain the rear/reverberation signal data in the corresponding channel high-frequency signal. 
     By the above steps, the terminal obtains first rear/reverberation signal data in the left-channel high-frequency signal, second rear/reverberation signal data in the center-channel high-frequency signal and third rear/reverberation signal data in the channel-channel high-frequency signal. 
     In step  406 , a front left-channel signal, a rear left-channel signal, a front right-channel signal, a rear right-channel signal and a front center-channel signal are calculated based on the first rear/reverberation signal data, the second rear/reverberation signal data and the third rear/reverberation signal data. 
     The terminal determines a difference between the left-channel high-frequency signal and the first rear/reverberation signal data acquired in the above step as the front left-channel signal. 
     The first rear/reverberation signal data is audio data included in the left-channel high-frequency signal and is audio data included in the rear left-channel signal of a three-dimensional surround 5.1-channel virtual speaker. The left-channel high-frequency signal includes the front left-channel signal and part of the rear left-channel signal. Thus, the front left-channel signal may be obtained by subtracting the part of the rear left-channel signal, namely, the first rear/reverberation signal data, from the left-channel high-frequency signal. 
     The terminal determines the sum of the first rear/reverberation signal data and the second rear/reverberation signal data, which are acquired in the above step, as the rear left-channel signal. 
     The terminal determines a difference between the right-channel high-frequency signal and the third rear/reverberation signal data acquired in the above step as the front right-channel signal. 
     The third rear/reverberation signal data is audio data included in the right-channel high-frequency signal and is audio data included in the rear right-channel signal of the three-dimensional surround 5.1-channel virtual speaker. The right-channel high-frequency signal includes the front right-channel signal and part of the rear right-channel signal. Thus, the front right-channel signal may be obtained by subtracting the part of the rear right-channel signal, namely, the third rear/reverberation signal data, from the right-channel high-frequency signal. 
     The terminal determines the sum of the third rear/reverberation signal data and the second rear/reverberation signal data, which are acquired in the above step, as the rear right-channel signal. 
     The terminal determines a difference between the center-channel high-frequency signal and the second rear/reverberation signal data acquired in the above step as the front center-channel signal. 
     The second rear/reverberation signal data is audio data included in the rear left-channel signal of the three-dimensional surround 5.1-channel virtual speaker box and is audio data included in the rear right-channel signal. The center-channel high-frequency signal includes the front center-channel signal and the second rear/reverberation signal data. Thus, the second rear/reverberation signal data may be subtracted from the center-channel high-frequency signal. 
     In summary, according to the method according to this embodiment, the rear/reverberation signal data in each channel high-frequency signal is extracted by calculating the start time and the end time of the rear/reverberation signal data in each channel high-frequency signal. The front left-channel signal, the rear left-channel signal, the front right-channel signal, the rear right-channel signal and the front center-channel signal are obtained by calculation based on the rear/reverberation signal data in each channel high-frequency signal. Thus, the accuracy is improved in obtaining the 5.1-channel audio signals by calculation based on the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal. 
       FIG. 5  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure. The audio signal processing method may be performed by a terminal with an audio signal processing function and may be an optional embodiment of step  102  in the embodiment illustrated in  FIG. 1 . The method includes the following steps. 
     In step  501 , a first stereo audio signal is input into a low-pass filter for filtering to obtain a first low-frequency signal. 
     The terminal inputs the first stereo audio signal into the low-pass filter for filtering to obtain the first low-frequency signal. The first low-frequency signal is a superimposed signal of a first left-channel low-frequency signal and a first right-channel low-frequency signal. 
     Optionally, the terminal filters the first stereo by a 4-order IIR low-pass filter to obtain the first low-frequency signal. 
     In step  502 , scalar multiplication is performed on the first low-frequency signal and a volume parameter of a low-frequency channel speaker box in a 5.1-channel virtual speaker box to obtain a second low-frequency signal. 
     The terminal performs the scalar multiplication on the first low-frequency signal and the volume parameter of the low-frequency channel speaker box in the 5.1-channel virtual speaker box to obtain the second low-frequency signal. 
     Exemplarily, the terminal calculates the second low-frequency signal by the following formula:
 
 X _ LFE _ S=X _ LFE*V 6
 
     X_LFE is the first stereo low-frequency signal, V 6  is the volume parameter of the low-frequency channel speaker box in the 5.1-channel virtual speaker box, X_LFE_S is the second low-frequency signal which is the superimposed signal of the first left-channel low-frequency signal X_LFE_S_L and the first right-channel low-frequency signal X_LFE_S_R, and * represents the scalar multiplication. 
     In step  503 , mono conversion is performed on the second low-frequency signal to obtain a processed low-frequency channel signal. 
     The terminal performs mono conversion on the second low-frequency signal to obtain the processed low-frequency channel signal. 
     Exemplarily, the terminal calculates the processed low-frequency channel signal by the following formula:
 
 X _ LFE _ M =( X _ LFE _ S _ L+X _ LFE _ S _ R )/2
 
     X_LFE_M is the processed low-frequency channel signal. 
     In summary, according to the method provided by the embodiment, the first stereo audio signal is filtered to obtain the first low-frequency signal. Mono conversion is performed on the first low-frequency signal to obtain the low-frequency channel signal in 5.1-channel audio signals. Thus, the first low-frequency signal is extracted from the first stereo signal and split into a 0.1-channel audio signal in the 5.1-channel audio signals. 
     In the method embodiments mentioned above, the first stereo audio signal is split and processed to obtain the 5.1-channel audio signals, including the front left-channel signal, the front right-channel signal, the front center-channel signal, the low-frequency channel signal, the rear left-channel signal and the rear right-channel signal. The following embodiment illustrated in  FIG. 6  and  FIG. 8  provides a method by which the 5.1-channel audio signals are processed and synthesized to obtain a second stereo audio signal. The method may be an optional embodiment of step  104  in the embodiment illustrated in  FIG. 1  and may also be an independent embodiment. A stereo signal obtained in the embodiments illustrated in  FIG. 6  and  FIG. 8  may be the second stereo audio signal in the above method embodiments. 
     The head related transfer function (HRTF) processing technology is a processing technology for producing a stereo surround sound effect. A technician may pre-establish an HRTF database, in which HRTF data, an HRTF data sampling point and a corresponding relationship between the HRTF data sampling point and position coordinates of a reference head are recorded. The HRTF data is a group of parameters for processing a left-channel audio signal and a right-channel audio signal. 
       FIG. 6  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment of the present disclosure. The audio signal processing method may be performed by a terminal with an audio signal processing function and may be an optional embodiment of step  104  of the embodiment illustrated in  FIG. 1 . The method includes the following steps. 
     In step  601 , a 5.1-channel audio signal is acquired. 
     Optionally, the 5.1-channel audio signal is the processed 5.1-channel audio signal which is obtained by splitting and processing the first stereo audio signal in the embodiment illustrated in  FIGS. 1 to 5 . Alternatively, the 5.1-channel audio signal is a 5.1-channel audio signal that is downloaded or read from a storage medium. 
     The 5.1-channel audio signal includes a front left-channel signal, a front right-channel signal, a front center-channel signal, a low-frequency channel signal, a rear left-channel signal and a rear right-channel signal. 
     In step  602 , HRTF data corresponding to each virtual speaker box in 5.1-channel virtual speaker boxes is acquired based on coordinates of the 5.1-channel virtual speaker boxes in a virtual environment. 
     Optionally, the 5.1 virtual speaker boxes include a front left-channel virtual speaker box FL, a front right-channel virtual speaker box FR, a front center-channel virtual speaker box FC, a bass virtual speaker box LFE, a rear left-channel virtual speaker box RL and a rear right-channel virtual speaker box RR. 
     Optionally, the 5.1 virtual speaker boxes have their respective coordinates in the virtual environment that may be a two-dimensional planar virtual environment or a three-dimensional virtual planar environment. 
     Exemplarily, referring to  FIG. 7  which is a schematic diagram of a 5.1-channel virtual speaker box in a 2D planar virtual environment. It is assumed that the reference head is located at a central point  70  in  FIG. 7  and faces towards the location of the center-channel virtual speaker box FC, and distances from all channels to the central point  70  where the reference head is located are the same, the channels and the central point are on the same plane. 
     A front center-channel virtual speaker box is located right ahead a direction that the reference head faces towards. 
     The front left-channel virtual speaker box FL and the front right-channel virtual speaker box FR are located at two sides of the front center-channel FC respectively, form an angle of 30° with the direction that the reference head faces towards respectively and are disposed symmetrically. 
     The rear left-channel virtual speaker box RL and the rear right-channel virtual speaker box RR are located behind two sides of the direction that the reference head faces towards respectively, form an angle of 100° to 120° with the direction that the reference head faces towards respectively and are disposed symmetrically. 
     Since the bass virtual speaker box LFE is relatively weaker in sense of direction, its locating place is not strictly required. In the text, a direction that the reference head faces away from is taken as an example for explanation. However, the angle formed by the bass virtual speaker box LFT and the direction that the reference head faces towards is not limited by the present disclosure. 
     It should be noted that the angle formed by each virtual speaker box in the 5.1-channel virtual speaker boxes and the direction that the reference head faces towards is merely exemplary. In addition, the distances between the virtual speaker boxes and the reference head may be different. When the virtual environment is a three-dimensional virtual environment, the virtual speaker boxes may be at different heights. Due to the different locating places of the virtual speaker boxes, sound signals may be different, which is not limited in the present disclosure. 
     Optionally, after a coordinate system is built for the two-dimensional virtual environment or the three-dimensional virtual environment by taking the reference head as an original point, coordinates of each virtual speaker box in the virtual environment may be obtained. 
     The HRTF database stored in the terminal includes a corresponding relationship between at least one HRTF data sampling point and the HRTF data. Each HRTF data sampling point has its own coordinates. 
     The terminal inquires the HRTF data sampling point nearest to an i th  coordinate from the HRTF database based on an i th  coordinate of an i th  virtual speaker box in the 5.1-channel virtual speaker boxes and determines HRTF data of the HRTF data sampling point nearest to the i th  coordinate as HRTF data of the i th  virtual speaker box, and i≥1. 
     In step  603 , the corresponding channel audio signal in the 5.1-channel audio signals is processed based on the HRTF data corresponding to each virtual speaker box to obtain the processed 5.1-channel audio signal. 
     Optionally, each piece of HRTF data includes a left-channel HRTF coefficient and a right-channel HRTF coefficient. 
     The terminal processes an i th  channel audio signal in the 5.1-channel audio signals based on the left-channel HRTF coefficient in the HRTF data corresponding to the i th  virtual speaker box to obtain a left-channel component corresponding to the processed i th  channel audio signal. 
     The terminal processes the i th  channel audio signal in the 5.1-channel audio signals based on the right-channel HRTF coefficient in the HRTF data corresponding to the i th  virtual speaker box to obtain a right-channel component corresponding to the processed i th  channel audio signal. 
     In step  604 , the processed 5.1-channel audio signals are synthesized into a stereo audio signal. 
     It should be noted that when the 5.1-channel audio signals in the present embodiment are the processed 5.1-channel audio signals obtained by splitting and processing the first stereo audio signal in the embodiment illustrated in  FIGS. 1 to 5 , the stereo audio signal in this step is the second stereo audio signal in the embodiment illustrated in  FIG. 1 . 
     In summary, according to the method provided by the present embodiment, the 5.1-channel audio signals are processed based on the HRTF data of all the 5.1-channel virtual speaker boxes, and the processed 5.1-channel audio signals are synthesized into the stereo audio signal, such that a user can play the 5.1-channel audio signals only using a common stereo earphone or a 2.0 speaker box and may also enjoy a better tone quality. 
       FIG. 8  is a flowchart of an audio signal processing method in accordance with an exemplary embodiment. The audio signal processing method may be performed by a terminal with an audio signal processing function and may be an optional embodiment of step  104  in the embodiment illustrated in  FIG. 1 . The method includes the following steps. 
     In step  801 , a series of at least one HRTF datum that takes a reference head as the center of a sphere are acquired from an acoustic room. Position coordinates of HRTF data sampling points corresponding to the HRTF data with respect to the reference head are recorded. 
     Referring to  FIG. 9 , a developer places the reference head  92  (made by simulating a human head) in the center of the acoustic room  91  (sound-absorbing sponge is disposed at the periphery of the room to reduce interference of echoes) in advance and disposes miniature omni-directional microphones in a left ear canal and a right ear canal of the reference head  92  respectively. 
     After finishing disposing of the reference head  92 , the developer disposes the HRTF data sampling points on the surface of a sphere that takes the reference head  92  as the center every preset distance and plays preset audios at the HRTF data sampling points by a speaker  93 . 
     The distance between the left ear canal and the speaker  93  is different from that between the right ear canal and the speaker  93 . The same audio has different audio features when reaching the left ear canal and the right ear canal because sound waves are affected by refraction, interference, diffraction, etc. Thus, the HRTF data at the HRTF data sampling points may be obtained by analyzing the difference between the audios acquired by the microphones and an original audio. The HRTF data corresponding to the same HRTF data sampling point includes a left-channel HRTF coefficient corresponding to a left channel and a right-channel HRTF coefficient corresponding to a right channel. 
     In step  802 , an HRTF database is generated based on the HRTF data, identifiers of the HRTF data sampling points and position coordinates of the HRTF data sampling points. 
     Optionally, a coordinate system is built by taking the reference head  92  as a central point. The coordinate system is built in the same way as a coordinate system of a 5.1-channel virtual speaker box. 
     When a virtual environment corresponding to the 5.1-channel virtual speaker box is a 2D virtual environment, a coordinate system may only be built for a horizontal plane where the reference head  92  is during acquisition of the HRTF data, and only the HRTF data of the horizontal plane are acquired. For example, on a circular ring that takes the reference head  92  as the center, a point is taken every 5° as the HRTF data sampling point. At this time, the HRTF data volume required to be stored in the terminal may be reduced. 
     When the virtual environment corresponding to the 5.1-channel virtual speaker box is a three-dimensional virtual environment, a coordinate system may be built for the three-dimensional environment where the reference head  92  is during acquisition of the HRTF data, and the HRTF data on the surface of the sphere that takes the reference head  92  as the center are acquired. For example, on the surface of the sphere that takes the reference head  92  as the center, a point is taken every 5° in a longitude direction and a latitude direction as the HRTF data sampling point. 
     Then, the terminal produces the HRTF database based on an identifier of each HRTF data sampling point, HRTF data of each HRTF data sampling point and the position coordinate of each HRTF data sampling point. 
     It should be noted that step  801  and step  802  may also be performed and implemented by other devices. The generated HRTF database is transmitted to a current terminal by a network or a storage medium. 
     In step  803 , a 5.1-channel audio signal is acquired. 
     Optionally, the terminal acquires the 5.1-channel audio signal. 
     The 5.1-channel audio signal is the processed 5.1-channel audio signal obtained by splitting and processing the first stereo audio signal in the embodiment illustrated in  FIGS. 1 to 5 . Alternatively, the 5.1-channel audio signal is a 5.1-channel audio signal that is downloaded or read from a storage medium. 
     The 5.1-channel audio signal includes a front left-channel signal X_FL, a front right-channel signal X_FC, a front center-channel signal X_FC, a low-frequency channel signal X_LFE_M, a rear left-channel signal X_RL and a rear right-channel signal X_RR. 
     In step  804 , the HRTF database is acquired and includes a corresponding relationship between at least one HRTF data sampling point and the HRTF data. Each HRTF data acquisition point has its own coordinates. 
     The terminal may read the HRTF database that is stored locally, or access the HRTF database stored on the network. 
     In step  805 , the terminal inquires the HRTF data sampling point nearest to an i th  coordinate from the HRTF database based on the i th  coordinate of an i th  virtual speaker box in the 5.1-channel virtual speaker boxes and determines HRTF data of the HRTF data sampling point nearest to the i th  coordinate as HRTF data of the i th  virtual speaker box. 
     Optionally, the coordinates of each virtual speaker box in the 5.1-channel virtual speaker boxes are pre-stored in the terminal, and i≥1. 
     The terminal inquires the HRTF data acquisition point nearest to a first coordinate from the HRTF database based on the first coordinate of a front left-channel virtual speaker box, and determines the HRTF data of the HRTF data acquisition point nearest to the first coordinate as HRTF data of the front left-channel virtual speaker box. 
     The terminal inquires the HRTF data acquisition point nearest to a second coordinate from the HRTF database based on the second coordinate of a front right-channel virtual speaker box, and determines the HRTF data of the HRTF data acquisition point nearest to the second coordinate as HRTF data of the front right-channel virtual speaker box. 
     The terminal inquires the HRTF data acquisition point nearest to a third coordinate from the HRTF database based on the third coordinate of a front center-channel virtual speaker box, and determines the HRTF data of the HRTF data acquisition point nearest to the third coordinate as HRTF data of the front center-channel virtual speaker box. 
     The terminal inquires the HRTF data acquisition point nearest to a fourth coordinate from the HRTF database based on the fourth coordinate of a rear left-channel virtual speaker box, and determines the HRTF data of the HRTF data acquisition point nearest to the fourth coordinate as HRTF data of the rear left-channel virtual speaker box. 
     The terminal inquires the HRTF data acquisition point nearest to a fifth coordinate from the HRTF database based on the fifth coordinate of a rear right-channel virtual speaker box, and determines the HRTF data of the HRTF data acquisition point nearest to the fifth coordinate as HRTF data of the rear right-channel virtual speaker box. 
     The terminal inquires the HRTF data acquisition point nearest to a sixth coordinate from the HRTF database based on the sixth coordinate of a low-frequency virtual speaker box, and determines the HRTF data of the HRTF data acquisition point nearest to the sixth coordinate as HRTF data of the low-frequency virtual speaker box. 
     The phrase “nearest to” means that the coordinate of the virtual speaker box and the coordinate of the HRTF data acquisition point are the same or the distance therebetween is the shortest. 
     In step  806 , primary convolution is performed on an i th  channel audio signal in the 5.1-channel audio signals using the left-channel HRTF coefficient in the HRTF data corresponding to the i th  virtual speaker box to obtain an i th  channel audio signal subjected to the primary convolution. 
     When the i th  channel audio signal in the 5.1-channel audio signals is set as X_i, Li=X_i*H_L_i, wherein * represents convolution, and H_L_i represents the left-channel HRTF coefficient in the HRTF data corresponding to the i th  virtual speaker box. 
     In step  807 , all the channel audio signals subjected to the primary convolution are superimposed to obtain a left-channel signal in a stereo audio signal. 
     The terminal superimposes 6 channel audio signals Li subjected to the primary convolution to obtain the left-channel signal L=L 1 +L 2 +L 3 +L 4 +L 5 +L 6  in the stereo audio signal. 
     In step  808 , secondary convolution is performed on the i th  channel audio signal in the 5.1-channel audio signals using the right-channel HRTF coefficient in the HRTF data corresponding to the i th  virtual speaker box to obtain an i th  channel audio signal subjected to the secondary convolution. 
     When the i th  channel audio signal in the 5.1-channel audio signals is set as X_i, Ri=X_i*H_R_i, wherein * represents convolution, and H_R_i represents the right-channel HRTF coefficient in the HRTF data corresponding to the i th  virtual speaker box. 
     In step  809 , all the channel audio signals subjected to the secondary convolution are superimposed to obtain a right-channel signal in the stereo audio signal. 
     The terminal superimposes 6 channel audio signals Ri subjected to the secondary convolution to obtain the right-channel signal R=R 1 +R 2 +R 3 +R 4 +R 5 +R 6  in the stereo audio signal. 
     In step  810 , the left-channel signal and the right-channel signal are synthesized into a stereo audio signal. 
     The synthesized stereo audio signal may be stored as an audio file or input into a playback device for playback. 
     It should be noted that when the 5.1-channel audio signal in the present embodiment is the processed 5.1-channel audio signal obtained by splitting and processing the first stereo audio signal in the embodiment illustrated in  FIGS. 1 to 5 , the stereo audio signal in this step is the second stereo audio signal in the embodiment illustrated in  FIG. 1 . 
     In summary, according to the method provided by the present embodiment, the 5.1-channel audio signals are processed based on the HRTF data of each 5.1-channel virtual speaker box, and the processed 5.1-channel audio signals are synthesized into the stereo audio signal. Thus, a user can play the 5.1-channel audio signals only by a common stereo earphone or a 2.0 speaker box and can enjoy a better playback tone quality. 
     In the method provided by the present embodiment, by convolution and superposition on the 5.1-channel audio signals based on the HRTF data of the 5.1-channel virtual speaker boxes, the stereo audio signal with a better three-dimensional surround sound effect may be obtained. The stereo audio signal has a better three-dimensional surround effect during playback. 
       FIG. 10  is a structural block diagram of an audio signal processing apparatus in accordance with an exemplary embodiment of the present disclosure. The apparatus may be a terminal or part of the terminal, and includes: 
     an acquiring module  1010 , configured to acquire a first stereo audio signal; 
     a processing module  1020 , configured to split the first stereo audio signal into 5.1-channel audio signals and to process the 5.1-channel audio signals based on a speaker box parameter of a three-dimensional surround 5.1-channel virtual speaker box to obtain processed 5.1-channel audio signals; and 
     a synthesizing module  1030 , configured to synthesize the processed 5.1-channel audio signals into a second stereo audio signal. 
     In an optional embodiment, the apparatus further includes a calculation module  1040 ; and 
     a processing module  1020 , configured to input the first stereo audio signal into a high-pass filter for filtering to obtain a first high-frequency signal. 
     The calculating module  1040  is configured to: obtain a left-channel high-frequency signal, a center-channel high-frequency signal and a right-channel high-frequency signal by calculation based on the first high-frequency signal; and obtain a front left-channel signal, a front right-channel signal, a front center-channel signal, a low-frequency channel signal, a rear left-channel signal and a rear right-channel signal in the 5.1-channel audio signals by calculation based on the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal. 
     In an optional embodiment, the calculating module  1040  is further configured to: perform FFT on the first high-frequency signal to obtain a high-frequency real number signal and a high-frequency imaginary number signal; calculate a vector projection based on the high-frequency real number signal and the high-frequency imaginary number signal; perform FFT on a product of a left-channel high-frequency real number signal in the high-frequency real number signal and the vector projection to obtain the center-channel high-frequency signal; take a difference between a left-channel high-frequency signal in the first high-frequency signal and the center-channel signal as the left-channel high-frequency signal; and take a difference between a right-channel high-frequency signal in the first high-frequency signal and the center-channel signal as the right-channel high-frequency signal. 
     The calculating module  1040  is further configured to: add the right-channel high-frequency real number signal to the left-channel high-frequency real number signal in the high-frequency real number signal to obtain a high-frequency real number signal; add the right-channel high-frequency imaginary number signal to the left-channel high-frequency imaginary number signal in the high-frequency imaginary number signal to obtain a high-frequency imaginary number signal; perform subtraction on the left-channel high-frequency real number signal and the right-channel high-frequency real number signal in the high-frequency real number signal to obtain a high-frequency real number difference signal; perform subtraction on the left-channel high-frequency imaginary number signal and the right-channel high-frequency imaginary number signal in the high-frequency imaginary number signal to obtain a high-frequency imaginary number difference signal; obtain a real number signal by calculation based on the high-frequency real number signal and the high-frequency imaginary number signal; obtain a real number difference signal based on the high-frequency real number difference signal and the high-frequency imaginary number difference signal; and calculate a vector projection based on the real number signal and the real number difference signal to obtain the vector projection. 
     In one optional embodiment, the calculating module  1040  is further configured to calculate the vector protection by the following formula when the real number signal is a significant digit:
 
alpha=0.5−SQRT(diff SQ /sum SQ )*0.5
 
     alpha is the vector projection, diffSq is the real number difference signal, sumSQ is the real number signal, SQRT represents extraction of square root and * represents a scalar product. 
     In one optional embodiment: 
     the processing module  1020  is further configured to extract first rear/reverberation signal data in the left-channel high-frequency signal, second rear/reverberation signal data in the center-channel high-frequency signal and third rear/reverberation signal data in the right-channel high-frequency signal. 
     The calculating module  1040  is further configured to: determine a difference between the left-channel high-frequency signal and the first rear/reverberation signal data as the front left-channel signal; determine a sum of the first rear/reverberation signal data and the second rear/reverberation signal data as the rear left-channel signal; determine a difference between the right-channel high-frequency signal and the third rear/reverberation signal data as the front right-channel signal; determine a sum of the third rear/reverberation signal data and the second rear/reverberation signal data as the rear right-channel signal; and determine a difference between the center-channel high-frequency signal and the second rear/reverberation signal data as the front center-channel signal. 
     In one optional embodiment, the acquiring module  1010  is further configured to obtain at least one moving window based on a sampling point in any of the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal. Each moving window includes n sampling points, and n/2 sampling points of every two adjacent moving windows are overlapping, n≥1. 
     The calculation module  1040  is further configured to: calculate a low-correlation signal in the moving window and a start time point of the low-correlation signal, wherein the low-correlation signal includes a signal of which a first decay envelope sequence in a magnitude spectrum and a second decay envelope sequence in a phase spectrum are unequal; determine a target low-correlation signal that conforms to a rear/reverberation feature; calculate an end time point of the target low-correlation signal; and extract the target low-correlation signal based on the start time point and the end time point, and take the extracted target low-correlation signal as rear/reverberation signal data in the corresponding channel high-frequency signal. 
     In one optional embodiment, the calculating module  1040  is further configured to: calculate a low-correlation signal in the moving window and a start time point of the low-correlation signal, wherein the low-correlation signal includes a signal of which a first decay envelope sequence in a magnitude spectrum and a second decay envelope sequence in a phase spectrum are unequal; determine a target low-correlation signal that conforms to a rear/reverberation feature; calculate an end time point of the target low-correlation signal; and extract the target low-correlation signal based on the start time point and the end time point, and take the extracted target low-correlation signal as rear/reverberation signal data in the corresponding channel high-frequency signal. 
     The calculating module  1040  is further configured to: perform FFT on a sampling point signal in an i th  moving window to obtain a sampling point signal subjected to FFT; calculate a magnitude spectrum and a phase spectrum of the sampling point signal subjected to FFT; calculate a first decay envelope sequence of m frequency lines in the i th  moving window based on a magnitude spectrum of the sampling point signal subjected to FFT; calculate a second decay envelope sequence of m frequency lines in the i th  moving window based on a phase spectrum of the sampling point signal subjected to FFT; determine a j th  frequency line as the low-correlation signal when the decay envelope sequence and the second decay envelope sequence of the j th  frequency line in the m frequency lines are different; and determine a start time point of the low-correlation signal based on a window number of the i th  moving window and a frequency line number of the j th  frequency line, wherein i≥1, m≥1, 1≤j≤m. 
     In one optional embodiment, the calculating module  1040  is further configured to: when magnitude spectrum energy of a VHF line of the low-correlation signal is smaller than a first threshold and a decay envelope slope of a window adjacent to a window where the VHF line is is larger than a second threshold, determine the low-correlation signal as a target low-correlation signal that conforms to a rear/reverberation feature; or when the magnitude spectrum energy of the VHF line of the low-correlation signal is smaller than the first threshold and a decay rate of a window adjacent to a window where the VHF line is larger than a third threshold, determine the low-correlation signal as the target low-correlation signal that conforms to the rear/reverberation feature. 
     In one optional embodiment, the calculating module  1040  is further configured to: acquire a time point at which energy of a frequency line corresponding to the magnitude spectrum of the target low-correlation signal is smaller than a fourth threshold and uses the acquired time point as the end time point; or determine a start time point of the next low-correlation signal as an end time point of the target low-correlation signal when energy of the target low-correlation signal is smaller than 1/m of energy of the next low-correlation signal. 
     In one optional embodiment, the acquiring module  1010  is further configured to extract channel signal segments in the start time point and the end time point. 
     The calculating module  1040  is further configured to: perform FFT on the channel signal segments to obtain signal segments subjected to FFT; extract a frequency line corresponding to the target low-correlation signal from the signal segments subjected to FFT to obtain a first portion signal; and perform IFFT and overlap-add on the first portion signal to obtain the rear/reverberation signal data in the corresponding channel high-frequency signal. 
     In one optional embodiment, the calculating module  1040  is further configured to perform scalar multiplication on the front left-channel signal and a volume of a front virtual left-channel speaker box to obtain the processed front left-channel signal, on the front right-channel signal and a volume of a front virtual right-channel speaker box to obtain the processed front right-channel signal, on the front center-channel signal and a volume of a front virtual center-channel speaker box to obtain the processed front center-channel signal, on the rear left-channel signal and a volume of a rear virtual left-channel speaker box to obtain the processed rear left-channel signal, and on the rear right-channel signal and a volume of a rear virtual right-channel speaker to obtain the processed rear right-channel signal. 
     In one optional embodiment, the 5.1-channel audio signals include a low-frequency channel signal. 
     The processing module  1020  is further configured to input the first stereo audio signal into a low-pass filter for filtering to obtain a first low-frequency signal. 
     The calculating module  1040  is further configured to perform scalar multiplication on the first low-frequency signal and a volume parameter of a low-frequency channel speaker box in the 5.1-channel virtual speaker box to obtain a second low-frequency signal, and perform mono conversion on the second low-frequency signal to obtain a processed low-frequency channel signal. 
     In one optional embodiment, the second low-frequency signal includes a left-channel low-frequency signal and a right-channel low-frequency signal. 
     The calculating module  1040  is further configured to superimpose the left-channel low-frequency signal over the right-channel low-frequency signal, then perform averaging, and use an averaged audio signal as the processed low-frequency channel signal. 
       FIG. 11  is a structural block diagram of an audio signal processing apparatus in accordance with an exemplary embodiment of the present disclosure. The apparatus may be a terminal or part of the terminal and includes: 
     a first acquiring module  1120 , configured to acquire 5.1-channel audio signals; 
     a second acquiring module  1140 , configured to acquire HRTF data corresponding to each virtual speaker box in 5.1-channel virtual speaker boxes based on coordinates of the 5.1-channel virtual speaker boxes in a virtual environment; 
     a processing module  1160 , configured to process the corresponding channel audio signal in the 5.1-channel audio signals based on the HRTF data corresponding to each virtual speaker box to obtain processed 5.1-channel audio signals; and 
     a synthesizing module  1180 , configured to synthesize the processed 5.1-channel audio signals into a stereo audio signal. 
     In one optional embodiment, the second acquisition module  1140  is configured to: acquire an HRTF database, wherein the HRTF database includes a corresponding relationship between at least one HRTF data sampling point and HRTF data, and each HRTF data sampling point has its own coordinates; and inquire the HRTF data sampling point nearest to an i th  coordinate from the HRTF database based on the i th  coordinate of an i th  virtual speaker box in the 5.1 virtual speaker boxes and determine HRTF data of the HRTF data sampling point nearest to the i th  coordinate as HRTF data of the i th  virtual speaker box, wherein i≥1. 
     In one optional embodiment, the apparatus further includes: 
     an acquiring module  1112 , configured to acquire a series of at least one HRTF datum that takes a reference head as the center of a sphere from an acoustic room and record position coordinates of HRTF data sampling points corresponding to each HRTF datum with respect to the reference head; and 
     a generating module  1114 , configured to generate an HRTF database based on the HRTF data, identifiers of the HRTF data sampling points and position coordinates of the HRTF data sampling points. 
     In one optional embodiment, the HRTF data include a left-channel HRTF coefficient. 
     The processing module  1160  includes: 
     a left-channel convoluting unit, configured to perform primary convolution on an i th  channel audio signal in the 5.1-channel audio signals using the left-channel HRTF coefficient in the HRTF data corresponding to the i th  virtual speaker box to obtain an i th  channel audio signal subjected to the primary convolution; and 
     a left-channel synthesizing unit, configured to superimpose all the channel audio signals subjected to the primary convolution to obtain a left-channel signal in a stereo audio signal. 
     In one optional embodiment, the HRTF data include a right-channel HRTF coefficient. 
     The processing module  1160  includes: 
     a right-channel convoluting unit, configured to perform secondary convolution on the i th  channel audio signal in the 5.1-channel audio signals using the right-channel HRTF coefficient in the HRTF data corresponding to the i th  virtual speaker box to obtain an i th  channel audio signal subjected to the secondary convolution; and 
     a right-channel synthesizing unit, configured to superimpose all the channel audio signals subjected to the secondary convolution to obtain a right-channel signal in the stereo audio signal. 
       FIG. 12  is a structural block diagram of a terminal  1200  according to an exemplary embodiment of the present disclosure. The terminal  1200  may be a smart phone, a tablet computer, a Moving Picture Experts Group Audio Layer III (MP3) player, a Moving Picture Experts Group Audio Layer IV (MP4) player, or a laptop or desktop computer. The terminal  1200  may also be referred to as a user equipment, a portable terminal, a laptop terminal, a desktop terminal, and the like. 
     Generally, the terminal  1200  includes a processor  1201  and a memory  1202 . 
     The processor  1201  may include one or more processing cores, such as a 4-core processor, an 8-core processor, or the like. The processor  1201  may be implemented by using at least one of hardware forms in DSP (Digital Signal Processing), an field-programmable gate array (FPGA) and a programmable logic array (PLA). The processor  1201  may also include a main processor and a co-processor. The main processor is a processor for processing data in an awaken state, and is also called as a central processing unit (CPU). The co-processor is a low-power processor for processing data in a standby state. In some embodiments, the processor  1201  may be integrated with a GPU (Graphics Processing Unit) which is responsible for rendering and drawing of content required to be displayed by a display. In some embodiments, the processor  1201  may also include an artificial intelligence (AI) processor for processing a calculation operation related to machine learning. 
     The memory  1202  may include one or more computer-readable storage media which may be non-transitory. The memory  1202  may also include a high-speed random-access memory, as well as a non-volatile memory, such as one or more disk storage devices and flash storage devices. In some embodiments, the non-transitory computer-readable storage medium in the memory  1202  is configured to store at least one instruction which is executable by the processor  1201  to implement following processing: 
     acquire a first stereo audio signal; 
     split the first stereo audio signal into 5.1-channel audio signals; 
     obtain processed 5.1-channel audio signals by processing the 5.1-channel audio signals based on a speaker box parameter of a three-dimensional surround 5.1-channel virtual speaker box; and 
     synthesize the processed 5.1-channel audio signals into a second stereo audio signal. 
     In a possible implement, the at least one instruction is executable by the processor  1201  to perform following processing: 
     obtain a first high-frequency signal by inputting the first stereo audio signal into a high-pass filter for filtering; 
     obtain a left-channel high-frequency signal, a center-channel high-frequency signal and a right-channel high-frequency signal by calculation based on the first high-frequency signal; and 
     obtain a front left-channel signal, a front right-channel signal, a front center-channel signal, a low-frequency channel signal, a rear left-channel signal and a rear right-channel signal in the 5.1-channel audio signals by calculation based on the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal. 
     In a possible implement, the at least one instruction is executable by the processor  1201  to perform following processing: 
     obtain a high-frequency real number signal and a high-frequency imaginary number signal by performing fast Fourier transform (FFT) on the first high-frequency signal; 
     calculate a vector projection based on the high-frequency real number signal and the high-frequency imaginary number signal; 
     obtain the center-channel high-frequency signal by performing FFT on a product of a left-channel high-frequency real number signal in the high-frequency real number signal and the vector projection; 
     determine a difference between a left-channel high-frequency signal in the first high-frequency signal and the center-channel high-frequency signal as the left-channel high-frequency signal; and 
     determine a difference between a right-channel high-frequency signal in the first high-frequency signal and the center-channel high-frequency signal as the right-channel high-frequency signal. 
     In a possible implement, the at least one instruction is executable by the processor  1201  to perform following processing: 
     extract first rear/reverberation signal data in the left-channel high-frequency signal, second rear/reverberation signal data in the center-channel high-frequency signal and third rear/reverberation signal data in the right-channel high-frequency signal; 
     determine a difference between the left-channel high-frequency signal and the first rear/reverberation signal data as the front left-channel signal; 
     determine a sum of the first rear/reverberation signal data and the second rear/reverberation signal data as the rear left-channel signal; 
     determine a difference between the right-channel high-frequency signal and the third rear/reverberation signal data as the front right-channel signal; 
     determine a sum of the third rear/reverberation signal data and the second rear/reverberation signal data as the rear right-channel signal; and 
     determine a difference between the center-channel high-frequency signal and the second rear/reverberation signal data as the front center-channel signal. 
     In a possible implement, the at least one instruction is executable by the processor  1201  to perform following processing: 
     obtain at least one moving window based on a sampling point in any of the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal, wherein each moving window comprises n sampling points, and n/2 sampling points of every two adjacent moving windows are overlapping, n≥1; 
     calculate a low-correlation signal in the moving window and a start time point of the low-correlation signal, wherein the low-correlation signal comprises a signal of which a first decay envelope sequence in a magnitude spectrum and a second decay envelope sequence in a phase spectrum are unequal; 
     determine a target low-correlation signal that conforms to a rear/reverberation feature; 
     calculate an end time point of the target low-correlation signal; and 
     extract the target low-correlation signal based on the start time point and the end time point, and taking the extracted target low-correlation signal as rear/reverberation signal data in the corresponding channel high-frequency signal. 
     In a possible implement, the at least one instruction is executable by the processor  1201  to perform following processing: 
     obtain a sampling point signal subjected to FFT by performing FFT on a sampling point signal in an i th  moving window, wherein i≥1; 
     calculate a magnitude spectrum and a phase spectrum of the sampling point signal subjected to FFT: 
     calculate a first decay envelope sequence of m frequency lines in the i th  moving window based on a magnitude spectrum of the sampling point signal subjected to FFT; 
     calculate a second decay envelope sequence of m frequency lines in the i th  moving window based on a phase spectrum of the sampling point signal subjected to FFT; 
     determine a j th  frequency line as the low-correlation signal when the decay envelope sequence and the second decay envelope sequence of the j th  frequency line in the m frequency lines are different, wherein 1≤j≤m; and 
     determine a start time point of the low-correlation signal based on a window number of the i th  moving window and a frequency line number of the j th  frequency line. 
     In a possible implement, the 5.1-channel audio signals comprise a low-frequency channel signal, the at least one instruction is executable by the processor  1201  to perform following processing: 
     input the first stereo audio signal into a low-pass filter for filtering to obtain a first low-frequency signal; and 
     the obtain processed 5.1-channel audio signals by processing the 5.1-channel audio signals based on a speaker box parameter of a three-dimensional surround 5.1-channel virtual speaker comprises: 
     obtain a second low-frequency signal by performing scalar multiplication of the first low-frequency signal and a volume parameter of a low-frequency channel speaker box in the 5.1-channel virtual speaker box; and 
     obtain a processed low-frequency channel signal by performing mono conversion on the second low-frequency signal. 
     In some embodiments, the terminal  1200  may optionally include a peripheral device interface  1203  and at least one peripheral device. The processor  1201 , the memory  1202  and the peripheral device interface  1203  may be connected to each other via a bus or a signal line. The at least one peripheral device may be connected to the peripheral device interface  1203  via a bus, a signal line or a circuit board. Specifically, the peripheral device includes at least one of a radio frequency circuit  1204 , a touch display screen  1205 , a camera assembly  1206 , an audio circuit  1207 , a positioning assembly  1208  and a power source  1209 . 
     The peripheral device interface  1203  may be configured to connect the at least one peripheral device related to input/output (I/O) to the processor  1201  and the memory  1202 . In some embodiments, the processor  1201 , the memory  1202  and the peripheral device interface  1203  are integrated on the same chip or circuit board. In some other embodiments, any one or two of the processor  1201 , the memory  1202  and the peripheral device interface  1203  may be practiced on a separate chip or circuit board, which is not limited in this embodiment. 
     The radio frequency circuit  1204  is configured to receive and transmit a radio frequency (RF) signal, which is also referred to as an electromagnetic signal. The radio frequency circuit  1204  communicates with a communication network or another communication device via the electromagnetic signal. The radio frequency circuit  1204  converts an electrical signal to an electromagnetic signal and sends the signal, or converts a received electromagnetic signal to an electrical signal. Optionally, the radio frequency circuit  1204  includes an antenna system, an RF transceiver, one or a plurality of amplifiers, a tuner, an oscillator, a digital signal processor, a codec chip set, a subscriber identification module card or the like. The radio frequency circuit  1204  may communicate with another terminal based on a wireless communication protocol. The wireless communication protocol includes, but not limited to: a metropolitan area network, generations of mobile communication networks (including 2G, 3G, 4G and 5G), a wireless local area network and/or a wireless fidelity (WiFi) network. In some embodiments, the radio frequency circuit  1204  may further include a near field communication (NFC)-related circuits, which is not limited in the present disclosure. 
     The display screen  1205  may be configured to display a user interface (UI). The UE may include graphics, texts, icons, videos and any combination thereof. When the display screen  1205  is a touch display screen, the display screen  1205  may further have the capability of acquiring a touch signal on a surface of the display screen  1205  or above the surface of the display screen  1205 . The touch signal may be input to the processor  1201  as a control signal, and further processed therein. In this case, the display screen  1205  may be further configured to provide a virtual button and/or a virtual keyboard or keypad, also referred to as a soft button and/or a soft keyboard or keypad. In some embodiments, one display screen  1205  may be provided, which is arranged on a front panel of the terminal  1200 . In some other embodiments, at least two display screens  1205  are provided, which are respectively arranged on different surfaces of the terminal  1200  or designed in a folded fashion. In still some other embodiments, the display screen  1205  may be a flexible display screen, which is arranged on a bent surface or a folded surface of the terminal  1200 . Even, the display screen  1205  may be further arranged to an irregular pattern which is non-rectangular, that is, a specially-shaped screen. The display screen  1205  may be fabricated from such materials as a liquid crystal display (LCD), an organic light-emitting diode (OLED) and the like. 
     The camera assembly  1206  is configured to capture an image or a video. Optionally, the camera assembly  1206  includes a front camera and a rear camera. Generally, the front camera is arranged on a front panel of the terminal, and the rear camera is arranged on a rear panel of the terminal. In some embodiments, at least two rear cameras are arranged, which are respectively any one of a primary camera, a depth of field (DOF) camera, a wide-angle camera and a long-focus camera, such that the primary camera and the DOF camera are fused to implement the background virtualization function, and the primary camera and the wide-angle camera are fused to implement the panorama photographing and virtual reality (VR) photographing functions or other fused photographing functions. In some embodiments, the camera assembly  1206  may further include a flash. The flash may be a single-color temperature flash or a double-color temperature flash. The double-color temperature flash refers to a combination of a warm-light flash and a cold-light flash, which may be used for light compensation under different color temperatures. 
     The audio circuit  1207  may include a microphone and a speaker. The microphone is configured to capture an acoustic wave of a user and an environment, and convert the acoustic wave to an electrical signal and output the electrical signal to the processor  1201  for further processing, or output to the radio frequency circuit  1204  to implement voice communication. For the purpose of stereo capture or noise reduction, a plurality of such microphones may be provided, which are respectively arranged at different positions of the terminal  1200 . The microphone may also be a microphone array or an omnidirectional capturing microphone. The speaker is configured to convert an electrical signal from the processor  1201  or the radio frequency circuit  1204  to an acoustic wave. The speaker may be a traditional thin-film speaker, or may be a piezoelectric ceramic speaker. When the speaker is a piezoelectric ceramic speaker, an electrical signal may be converted to an acoustic wave audible by human beings, or an electrical signal may be converted to an acoustic wave inaudible by human beings for the purpose of ranging or the like. In some embodiments, the audio circuit  1207  may further include a headphone plug. 
     The positioning assembly  1208  is configured to determine a current geographical position of the terminal  1200  to implement navigation or a local based service (LBS). The positioning assembly  1208  may be the global positioning system (GPS) from the United States, the Beidou positioning system from China, the Grenas satellite positioning system from Russia or the Galileo satellite navigation system from the European Union. 
     The power source  1209  is configured to supply power for the components in the terminal  1200 . The power source  1209  may be an alternating current, a direct current, a disposable battery or a rechargeable battery. When the power source  1209  includes a rechargeable battery, the rechargeable battery may support wired charging or wireless charging. The rechargeable battery may also support the supercharging technology. 
     In some embodiments, the terminal  1200  may further include one or a plurality of sensors  1210 . The one or plurality of sensors  1210  include, but not limited to: an acceleration sensor  1211 , a gyroscope sensor  1212 , a pressure sensor  1213 , a fingerprint sensor  1214 , an optical sensor  1215  and a proximity sensor  1216 . 
     The acceleration sensor  1211  may detect accelerations on three coordinate axes in a coordinate system established for the terminal  1200 . For example, the acceleration sensor  1211  may be configured to detect components of a gravity acceleration on the three coordinate axes. The processor  1201  may control the touch display screen  1205  to display the user interface in a horizontal view or a longitudinal view based on a gravity acceleration signal acquired by the acceleration sensor  1211 . The acceleration sensor  1211  may be further configured to acquire motion data of a game or a user. 
     The gyroscope sensor  1212  may detect a direction and a rotation angle of the terminal  1200 , and the gyroscope sensor  1212  may collaborate with the acceleration sensor  1211  to capture a three-dimensional action performed by the user for the terminal  1200 . Based on the data acquired by the gyroscope sensor  1212 , the processor  1201  may implement the following functions: action sensing (for example, modifying the UE based on an inclination operation of the user), image stabilization during the photographing, game control and inertial navigation. 
     The force sensor  1213  may be arranged on a side frame of the terminal and/or on a lowermost layer of the touch display screen  1205 . When the force sensor  1213  is arranged on the side frame of the terminal  1200 , a grip signal of the user against the terminal  1200  may be detected, and the processor  1201  implements left or right hand identification or perform a shortcut operation based on the grip signal acquired by the force sensor  1213 . When the force sensor  1213  is arranged on the lowermost layer of the touch display screen  1205 , the processor  1201  implement control of an operable control on the UI based on a force operation of the user against the touch display screen  1205 . The operable control includes at least one of a button control, a scroll bar control, an icon control, and a menu control. 
     The fingerprint sensor  1214  is configured to acquire fingerprints of the user, and the processor  1201  determines the identity of the user based on the fingerprints acquired by the fingerprint sensor  1214 , or the fingerprint sensor  1214  determines the identity of the user based on the acquired fingerprints. When it is determined that the identify of the user is trustable, the processor  1201  authorizes the user to perform related sensitive operations, wherein the sensitive operations include unlocking the screen, checking encrypted information, downloading software, paying and modifying settings and the like. The fingerprint sensor  1214  may be arranged on a front face a back face or a side face of the terminal  1200 . When the terminal  1200  is provided with a physical key or a manufacturer&#39;s logo, the fingerprint sensor  1214  may be integrated with the physical key or the manufacturer&#39;s logo. 
     The optical sensor  1215  is configured to acquire the intensity of ambient light. In one embodiment, the processor  1201  may control a display luminance of the touch display screen  1205  based on the intensity of ambient light acquired by the optical sensor  1215 . Specifically, when the intensity of ambient light is high, the display luminance of the touch display screen  1205  is up-shifted; and when the intensity of ambient light is low, the display luminance of the touch display screen  1205  is down-shifted. In another embodiment, the processor  1201  may further dynamically adjust photographing parameters of the camera assembly  1206  based on the intensity of ambient light acquired by the optical sensor. 
     The proximity sensor  1216 , also referred to as a distance sensor, is generally arranged on the front panel of the terminal  1200 . The proximity sensor  1216  is configured to acquire a distance between the user and the front face of the terminal  1200 . In one embodiment, when the proximity sensor  1216  detects that the distance between the user and the front face of the terminal  1200  gradually decreases, the processor  1201  controls the touch display screen  1205  to switch from an active state to a rest state; and when the proximity sensor  1216  detects that the distance between the user and the front face of the terminal  1200  gradually increases, the processor  1201  controls the touch display screen  1205  to switch from the rest state to the active state. 
     A person skilled in the art may understand that the structure of the terminal as illustrated in  FIG. 12  does not construe a limitation on the terminal  1200 . The terminal may include more components over those illustrated in  FIG. 12 , or combinations of some components, or employ different component deployments. 
     The present disclosure further provides a computer-readable storage medium. At least one instruction is stored in the storage medium and loaded and executed by a processor to implement following processing: 
     acquire a first stereo audio signal; 
     split the first stereo audio signal into 5.1-channel audio signals; 
     obtain processed 5.1-channel audio signals by processing the 5.1-channel audio signals based on a speaker box parameter of a three-dimensional surround 5.1-channel virtual speaker box; and 
     synthesize the processed 5.1-channel audio signals into a second stereo audio signal. 
     In a possible implement, the at least one instruction is executable by the processor  1201  to perform following processing: 
     obtain a first high-frequency signal by inputting the first stereo audio signal into a high-pass filter for filtering; 
     obtain a left-channel high-frequency signal, a center-channel high-frequency signal and a right-channel high-frequency signal by calculation based on the first high-frequency signal; and 
     obtain a front left-channel signal, a front right-channel signal, a front center-channel signal, a low-frequency channel signal, a rear left-channel signal and a rear right-channel signal in the 5.1-channel audio signals by calculation based on the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal. 
     In a possible implement, the at least one instruction is executable by the processor  1201  to perform following processing: 
     obtain a high-frequency real number signal and a high-frequency imaginary number signal by performing fast Fourier transform (FFT) on the first high-frequency signal; 
     calculate a vector projection based on the high-frequency real number signal and the high-frequency imaginary number signal; 
     obtain the center-channel high-frequency signal by performing FFT on a product of a left-channel high-frequency real number signal in the high-frequency real number signal and the vector projection; 
     determine a difference between a left-channel high-frequency signal in the first high-frequency signal and the center-channel high-frequency signal as the left-channel high-frequency signal; and 
     determine a difference between a right-channel high-frequency signal in the first high-frequency signal and the center-channel high-frequency signal as the right-channel high-frequency signal. 
     In a possible implement, the at least one instruction is executable by the processor  1201  to perform following processing: 
     extract first rear/reverberation signal data in the left-channel high-frequency signal, second rear/reverberation signal data in the center-channel high-frequency signal and third rear/reverberation signal data in the right-channel high-frequency signal; 
     determine a difference between the left-channel high-frequency signal and the first rear/reverberation signal data as the front left-channel signal; 
     determine a sum of the first rear/reverberation signal data and the second rear/reverberation signal data as the rear left-channel signal; 
     determine a difference between the right-channel high-frequency signal and the third rear/reverberation signal data as the front right-channel signal; 
     determine a sum of the third rear/reverberation signal data and the second rear/reverberation signal data as the rear right-channel signal; and 
     determine a difference between the center-channel high-frequency signal and the second rear/reverberation signal data as the front center-channel signal. 
     In a possible implement, the at least one instruction is executable by the processor  1201  to perform following processing: 
     obtain at least one moving window based on a sampling point in any of the left-channel high-frequency signal, the center-channel high-frequency signal and the right-channel high-frequency signal, wherein each moving window comprises n sampling points, and n/2 sampling points of every two adjacent moving windows are overlapping, n≥1; 
     calculate a low-correlation signal in the moving window and a start time point of the low-correlation signal, wherein the low-correlation signal comprises a signal of which a first decay envelope sequence in a magnitude spectrum and a second decay envelope sequence in a phase spectrum are unequal; 
     determine a target low-correlation signal that conforms to a rear/reverberation feature; 
     calculate an end time point of the target low-correlation signal; and 
     extract the target low-correlation signal based on the start time point and the end time point, and taking the extracted target low-correlation signal as rear/reverberation signal data in the corresponding channel high-frequency signal. 
     In a possible implement, the at least one instruction is executable by the processor  1201  to perform following processing: 
     obtain a sampling point signal subjected to FFT by performing FFT on a sampling point signal in an i th  moving window, wherein i≥1; 
     calculate a magnitude spectrum and a phase spectrum of the sampling point signal subjected to FFT; 
     calculate a first decay envelope sequence of m frequency lines in the i th  moving window based on a magnitude spectrum of the sampling point signal subjected to FFT; 
     calculate a second decay envelope sequence of m frequency lines in the i th  moving window based on a phase spectrum of the sampling point signal subjected to FFT; 
     determine a j th  frequency line as the low-correlation signal when the decay envelope sequence and the second decay envelope sequence of the j th  frequency line in the m frequency lines are different, wherein 1≤j≤m; and 
     determine a start time point of the low-correlation signal based on a window number of the i th  moving window and a frequency line number of the j th  frequency line. 
     In a possible implement, the 5.1-channel audio signals comprise a low-frequency channel signal, the at least one instruction is executable by the processor  1201  to perform following processing: 
     input the first stereo audio signal into a low-pass filter for filtering to obtain a first low-frequency signal; and 
     the obtain processed 5.1-channel audio signals by processing the 5.1-channel audio signals based on a speaker box parameter of a three-dimensional surround 5.1-channel virtual speaker comprises: 
     obtain a second low-frequency signal by performing scalar multiplication of the first low-frequency signal and a volume parameter of a low-frequency channel speaker box in the 5.1-channel virtual speaker box; and 
     obtain a processed low-frequency channel signal by performing mono conversion on the second low-frequency signal. 
     Optionally, the present disclosure further provides a computer program product including an instruction. A computer on which the computer program product runs executes the audio signal processing method described in the above aspects. 
     It is to be understood that the term “plurality” herein refers to two or more. “And/or” herein describes the correspondence of the corresponding objects, indicating three kinds of relationship. For example, A and/or B, may be expressed as: A exists alone, A and B exist concurrently, B exists alone. The character “/” generally indicates that the context object is an “OR” relationship. 
     The serial numbers of the above embodiments of the present application are merely for description, instead of indicating the merits or demerits of the embodiments. 
     Persons of ordinary skill in the art can understand that all or part of the steps described in the above embodiments may be completed by hardware, or by relevant hardware instructed by applications stored in a non-transitory computer readable storage medium, such as a read-only memory, a disk or a CD. 
     Described above are merely exemplary embodiments of the present disclosure, and are not intended to limit the present disclosure. Within the spirit and principles of the disclosure, any modifications, equivalent substitutions, or improvements are within the protection scope of the present disclosure.