Abstract:
This present invention discloses an audio-separating apparatus and operation method thereof. The audio-separating apparatus applies both blind source separation and noise reduction mechanisms. The audio-separating apparatus only uses one microphone to record mixed sound signals. After applying the noise reduction mechanism, noise reduced signals and the mixed sound signals are used as the inputs of the blind source separation. The method may avoid the spatial aliasing effect caused by using a microphone array to record the mixed sound signals. Besides, speech segment losses caused by processing the noise reduction will be effectively recovered, which may help the hearing impaired recognize target speech signals.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    (a) Field of the Invention 
         [0002]    The present invention relates to an audio-separating apparatus and an operation method thereof, and more particularly to an audio-separating apparatus applying both blind signal separation (BSS) and noise reduction mechanisms and an operation method thereof. 
         [0003]    (b) Description of the Prior Art 
         [0004]    Various noises, such as echoes, reverberations and the like, are omnipresent in people&#39;s daily lives, and all such noises would cause interference with sound signals. When sound signals are interfered by an interference source, the quality of the sound signals will degrade. For the hearing impaired who use hearing aids or cochlear implant, it is extremely difficult to recognize the sounds to be heard in a noise-filled environment without noise reduction or noise separation. Therefore, more and more emphases have been gradually put on noise reduction algorithms based on digital signal processing to obtain clearer sounds. 
         [0005]    In order to obtain clearer sounds, many noise reduction algorithms, such as independent component analysis (ICA), have been derived. The speech signals to be heard can be retrieved from a noise-filled environment by the algorithm to enhance the speech signals. In the prior art, the disclosure of US200713381 indicates that speech signals can be retrieved from a noise-filled environment via an ICA method. Nonetheless, conventional noise reduction algorithms and ICA still have some drawbacks. It is easy to lose portions of speech segments and produce musical noises during the processing in many conventional noise reduction methods. Such effect leads to reduced quality of speech; in other word, it is difficult to recognize speech signals. Furthermore, when ICA is used, at least two microphones are required to record sound signals. However, sound propagates at a substantially slower speed. If the microphones are placed at different positions, the time taken for a signal to be transferred from each sound source to each microphone is unequal. This causes the propagation delay between sampling points, referred to as the spatial aliasing effect. However, the spatial aliasing effect is not taken into consideration in the theoretical basis of ICA. Therefore, significant effect in the separation of sound signals by using ICA can not be well achieved. 
       SUMMARY OF THE INVENTION 
       [0006]    In view of the above-mentioned problems in the prior art, an object of the present invention is to provide an audio-separating apparatus and an operation method thereof for solving the spatial aliasing effect caused by using two microphones to record sound signals. 
         [0007]    According to one object of the present invention, there is provided an audio-separating apparatus comprising: a receiving unit, a first buffer unit, a second buffer unit, a noise reducing unit, a learning unit, and an audio-separating unit. The receiving unit is used to receive a mixed sound signal. The first buffer unit is connected to the receiving unit, and the mixed sound signal is stored as a first mixed sound signal therein. The second buffer unit is connected to the receiving unit, and the mixed sound signal is stored as a second mixed sound signal therein, and it has a buffer capacity different from that of the first buffer unit. The noise reducing unit is connected to the first buffer unit and the second buffer unit for receiving the first mixed sound signal and the second mixed sound signal, as well as uses a noise reduction algorithm to respectively generate a first noise reduced sound signal and a second noise reduced sound signal. The learning unit is connected to the first buffer unit and the noise reducing unit. The learning unit uses the first mixed sound signal and the first noise reduced sound signal to generate an audio separation parameter by means of a blind source separation algorithm. The audio-separating unit is connected to the noise reducing unit, the second buffer unit and the learning unit. The audio-separating unit uses the second mixed sound signal, the second noise reduced sound signal and the audio separation parameter to separate the mixed sound signal. 
         [0008]    The audio-separating apparatus further comprises an output unit for outputting a separated sound signal. The separated sound signal is a sound signal separated from the mixed sound signal and accordingly obtained. 
         [0009]    The buffer capacity of the first buffer unit is greater than the buffer capacity of the second buffer unit. 
         [0010]    The audio-separating unit processes the second mixed sound signal and the second noise reduced sound signal in real-time to separate the mixed sound signal in real-time. 
         [0011]    The blind source separation (BSS) algorithm further comprises an independent component analysis (ICA) algorithm to generate the audio separation parameter. 
         [0012]    The audio separation parameter is a matrix parameter. 
         [0013]    The receiving unit is a microphone for receiving the mixed sound signal. 
         [0014]    According to another object of the present invention, an operation method of an audio-separating apparatus is provided comprising the following steps. At first, a receiving unit is used to receive a mixed sound signal. Next, the mixed sound signal is stored as a first mixed sound signal in the first buffer unit. Next, the mixed sound signal is stored as a second mixed sound signal in the second buffer unit. The second buffer unit has a buffer capacity different from that of the first buffer unit. Next, the noise reducing unit receives the first mixed sound signal and the second mixed sound signal. Thereafter, the noise reducing unit uses a noise reduction algorithm to respectively generate a first noise reduced sound signal and a second noise reduced sound signal. Next, the learning unit uses the first mixed sound signal and the first noise reduced sound signal to generate an audio separation parameter by means of a blind source separation algorithm. At Last, the audio-separating unit uses the second mixed sound signal, the second noise reduced sound signal and the audio separation parameter to separate the mixed sound signal. Wherein the step of generating the audio separation parameter and the step of separating the mixed sound signal can be simultaneously performed, so that a separated sound signal can be output in real-time. 
         [0015]    The method further comprises a step of outputting a separated sound signal through an output unit. The separated sound signal is a sound signal separated from the mixed sound signal and accordingly obtained. 
         [0016]    The buffer capacity of the first buffer unit is greater than the buffer capacity of the second buffer unit. 
         [0017]    The audio-separating unit processes the second mixed sound signal and the second noise reduced sound signal in real-time to separate the mixed sound signal in real-time. 
         [0018]    The blind source separation (BSS) algorithm further comprises an independent component analysis (ICA) algorithm to generate the audio separation parameter. 
         [0019]    The audio separation parameter is a matrix parameter. 
         [0020]    When the receiving unit is a microphone, the microphone is used to receive the mixed sound signal. 
         [0021]    As described above, the audio-separating apparatus and the operation method thereof according to the present invention may have one or more of the following advantages: 
         [0022]    (1) The audio-separating apparatus and the operation method thereof only use one microphone to record mixed sound signals, so as to avoid the spatial aliasing effect caused by using a microphone array to record the mixed sound signals. 
         [0023]    (2) The audio-separating apparatus and the operation method thereof improve the signal-to-noise ratio (SNR). This helps the patients who use hearing aids or cochlear implant to hear clear sounds. 
         [0024]    (3) In the prior art, an independent component analysis (ICA) method needs more than two microphones to receive signals from signal sources. The audio-separating apparatus and the operation method thereof only use one microphone to record mixed sound signals through both blind source separation and noise reduction mechanisms. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a schematic view of an audio-separating apparatus according to the present invention; 
           [0026]      FIG. 2  is a flow chart showing the steps of an operation method of an audio-separating apparatus according to the present invention; 
           [0027]      FIG. 3  is a flow chart showing the steps of an operation method of an audio-separating apparatus according to another embodiment of the present invention; 
           [0028]      FIG. 4  is a signal diagram of two signal sources; 
           [0029]      FIG. 5  is a signal diagram of the signals from two signal sources, which signals being recorded respectively by using two microphones; 
           [0030]      FIG. 6  is a signal diagram of the signals recorded by a microphone through the application of a Wiener filter according to the prior art; 
           [0031]      FIG. 7  is a signal diagram of the signals recorded by a microphone, wherein the signals are analyzed by an independent component analysis (ICA) method according to the prior art; and 
           [0032]      FIG. 8  is a signal diagram of signals generated by an audio-separating apparatus according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Referring to  FIG. 1 , a schematic view of an audio-separating apparatus according to the present invention is illustrated. In this figure, the audio-separating apparatus  1  comprises a receiving unit  11 , a first buffer unit  12 , a second buffer unit  13 , a noise reducing unit  14 , a learning unit  15 , an audio-separating unit  16 , and an output unit  17 . 
         [0034]    The receiving unit  11  is a microphone for receiving mixed sound signals  111 . The mixed sound signals  111  can be sound signals from a plurality of signal sources. Since only one microphone is used to receive mixed sound signals, it is impossible to cause the spatial aliasing effect. 
         [0035]    The first buffer unit  12  is connected to the receiving unit  11 , and the mixed sound signals  111  are stored as first mixed sound signals  121  therein. The second buffer unit  13  is connected to the receiving unit  11 , and the mixed sound signals  111  are stored as second mixed sound signals  131  therein. The buffer capacity of the second buffer unit  13  is less than the buffer capacity of the first buffer unit  12 . As a result, longer mixed sound signals  111  can be stored in the first buffer unit  12 , and shorter mixed sound signals  111  are stored in the second buffer unit  13 . 
         [0036]    The noise reducing unit  14  is connected to the first buffer unit  12  and the second buffer unit  13  for receiving the first mixed sound signal  121  and the second mixed sound signal  131 , as well as uses a noise reduction algorithm  141  to respectively generate a first noise reduced sound signal  142  and a second noise reduced sound signal  143 . The goal of the noise reduction algorithm  141  is to reduce noises. Also, the mixed sound signals  111  can be processed by means of speech enhancement methods. 
         [0037]    The learning unit  15  is connected to the first buffer unit  12  and the noise reducing unit  14  for receiving the first mixed sound signal  121  and the first noise reduced sound signal  142 . The learning unit  15  uses a blind source separation algorithm  151  to generate a learning result from the first mixed sound signal  121  and the first noise reduced sound signal  142 . It is assumed that there are m sound sources (s) and n received mixed signals (x). The n received signals are used to separate the m sound sources under the condition that the signal characteristics are unknown; i.e. the blind source separation (BSS) algorithm. This can be represented by the mathematical expression as below: X nx1 =A nxm S mx1 , where A is a mixing matrix and influenced by environmental factors. In practical applications, it can be assumed that m sound sources are mutually independent. Therefore, the de-mixing matrix W≈A −1  can be obtained using an independent component analysis method, and is obtained a separated signal Y, which is similar to S and represented by the following equation: Y mx1 =W mxn X nx1 ≈S. Therefore, it can be assumed that the de-mixing matrix W=A −1 . At this time, the obtained separated signal Y=S is represented by the following equation: Y mx1 =W mxn X nx1 . Therefore, the learning unit  15  can generate an audio separation parameter  152  by means of the blind source separation algorithm  151 . The audio separation parameter  152  can be a matrix parameter, i.e. the de-mixing matrix W. 
         [0038]    The audio-separating unit  16  is connected to the second buffer unit  13 , the noise reducing unit  14  and the learning unit  15 , so the audio-separating unit  16  can receive the second mixed sound signal  131 , the second noise reduced sound signal  143  and the blind signal separation parameter  152  in order to obtain a separated signal. When the audio-separating unit  16  has not received an audio separation parameter  152  yet, a default parameter should be used or alternatively the signal is directly outputted without separation. The audio-separating unit  16  can use the second mixed sound signal  131  and the second noise reduced sound signal  143  to obtain a separated signal. When the audio-separating unit  16  receives an audio separation parameter  152 , the audio-separating unit  16  can obtain the de-mixing matrix W from the learning unit  15  and perform an operation on the mixed signal X to obtain a separated signal Y, as the above-mentioned Y mx1 =W mxn X nx1 . Therefore, the audio-separating unit  16  can use the second mixed sound signal  131 , the second noise reduced sound signal  143  and the audio separation parameter  152  to separate the mixed sound signal  111 . 
         [0039]    The audio-separating apparatus  1  further comprises an output unit  17  for outputting a separated sound signal  162 . The separated sound signal  162  is a sound signal separated from the mixed sound signal  111  and accordingly obtained. In the present invention, there are provided two buffer units of different sizes wherein the buffer capacity of the second buffer unit  13  is less than the buffer capacity of the first buffer unit  12 . The audio-separating unit  16  can process the second mixed sound signal  131  and the second noise reduced sound signal  143  in real-time, and outputs the separated sound signal  162  through the output unit  17  in real-time. Furthermore, in order that the learning unit  15  acquires a better learning result by learning for a longer duration of time, there can be provided a first buffer unit  12  which has a larger buffer capacity to generate better audio separation parameters so that the audio-separating unit  16  offers better audio separation ability. 
         [0040]    Referring to  FIG. 2 , a flow chart showing the steps of an operation method of an audio-separating apparatus according to the present invention is illustrated. In step S 1 , a receiving unit is used to receive a mixed sound signal. When the receiving unit only uses one microphone, the microphone can receive mixed sound signals to avoid the spatial aliasing effect caused by using a plurality of microphones in the prior art. In step S 2 , the mixed sound signal is stored as a first mixed sound signal in the first buffer unit. In step S 3 , the mixed sound signal is stored as a second mixed sound signal in the second buffer unit. The buffer capacity of the second buffer unit is different from that of the first buffer unit. In step S 4 , the noise reducing unit receives the first mixed sound signal and the second mixed sound signal. In step S 5 , the noise reducing unit uses a noise reduction algorithm to respectively generate a first noise reduced sound signal and a second noise reduced sound signal. In step S 6 , the learning unit uses the first mixed sound signal and the first noise reduced sound signal to generate an audio separation parameter by means of a blind source separation algorithm. In step S 7 , the audio-separating unit uses the second mixed sound signal, the second noise reduced sound signal and the audio separation parameter to separate the mixed sound signal. The method further comprises an output step S 8  for outputting a separated sound signal through an output unit. 
         [0041]    Referring to  FIG. 3 , a flow chart showing the steps of an operation method of an audio-separating apparatus according to another embodiment of the present invention is illustrated. In step S 11 , an initial value is set. In this step, the buffer length of the first mixed sound signal of the first buffer unit and the buffer length of the second mixed sound signal of the second buffer unit, as well as the duration of time in which the learning unit may learn, can be designated. The longer the learning time is, the better the learning result can be obtained, so as to generate more preferable audio separation parameters. 
         [0042]    In step S 12 , a receiving unit is used to receive a mixed sound signal. In step S 131 , the sound signal is stored in the first buffer unit. In step S 132 , the sound signal is stored in the second buffer unit. In step S 141 , it is determined whether or not the first buffer unit is full. When it is determined that the first buffer unit is full, the first mixed sound signals are processed. If not, then the sound signal continues to be stored in the first buffer unit. 
         [0043]    In step S 142 , it is determined whether or not the second buffer unit is full of the second mixed sound signals. When it is determined that the second buffer unit is full, the second mixed sound signals are processed. If not, the sound signal continues to be stored in the second buffer unit. In step S 151 , noise reduction is performed. This step can carried by the noise reducing unit, which uses a noise reduction algorithm to perform a noise reduction operation on the first mixed sound signals, so as to generate first reduced sound signals. In step S 152 , noise reduction is performed. This step can be carried out by the noise reducing unit, which uses a noise reduction algorithm to perform a noise reduction operation on the second mixed sound signals, so as to generate second reduced sound signals. 
         [0044]    In step S 16 , an audio separation parameter is generated. In this step, the learning unit uses the first mixed sound signal and the first noise reduced sound signal to generate an audio separation parameter by means of a blind source separation algorithm, and also transmits the new audio separation parameter to the audio-separating unit. The receiving unit continues to receive signals. When the first buffer unit is full, the procedures such as noise reduction and generation of audio separation parameters are conducted. As a result, the audio separation parameter is continuously updated so a new audio separation parameter is generated during each iterative process. 
         [0045]    In step S 17 , it is determined whether or not a new audio separation parameter is received. When the audio-separating unit determines that a new audio separation parameter is received, step S 18  is conducted to update the audio separation parameter. Also, step S 19  is conducted to separate the sound signal. An operation is performed on the updated audio separation parameter and the mixed sound signal to obtain a separated signal. When the audio-separating unit determines that the audio separation parameter has not been received yet, step S 19  is directly carried out to separate the sound signal. Step S 20  is conducted to determine whether or not the procedure ends. When the user intends to end the audio separation procedure, the audio-separating apparatus can be turned off and the operation ends at the same time. When the user continues to operate the audio-separating apparatus, it returns to step S 131  and S 132  to store sound signals in the first buffer unit and the second buffer unit. 
         [0046]    Referring to  FIG. 4 , a signal diagram of two signal sources is illustrated. In this figure, the upper signals are speech signals  41 , and the lower signals are noise signals  42 . Referring to  FIG. 5 , there is illustrated a signal diagram of the signals from two signal sources, wherein the signals are recorded respectively by using two microphones. According to this figure, the two microphones are placed only 1 centimeter apart. Thus, the signal diagrams of the signals recorded by the two microphones are similar. Referring to  FIG. 6 , there is illustrated a signal diagram of the signals (as illustrated in  FIG. 5 ) recorded by a microphone through the application of a Wiener filter according to the prior art. Compared to  FIG. 4 , it can be found that the filter has filtered out the noise signals  42 , but some segments of the speech signals  41  have also been lost. 
         [0047]    Referring to  FIG. 7 , there is illustrated a signal diagram of the signals recorded by a microphone, wherein the signals are analyzed by an independent component analysis (ICA) method according to the prior art. Herein two microphones are used to record the signals from two signal sources, and the signals from the two signal sources are speech signals  41  and noise signals  42 . Through the ICA method, two separated signals can be generated. Some of them are speech signals, and the others are noise signals. The signals represented in this figure are a part of the speech signals. Since the spatial aliasing effect is caused due to use of two microphones in recording, it is not significant for the noise reduction effect by directly using the ICA. Through the ICA method, both the noise signals  42  and the speech signals  41  are included in the signals. However, it is impossible to obtain better speech signals  41  because of excessive noise signals  42 . 
         [0048]    Referring to  FIG. 8 , a signal diagram of signals generated by an audio-separating apparatus according to the present invention is illustrated. Compared to  FIG. 4 , it can be found that all the original speech signals  41  occur in the signal diagram, and the noise signals  42  are effectively suppressed. Furthermore, compared to  FIG. 7 , the noise reduction effect is superior to the ICA method so that the hearing impaired can obtain better speech signals by way of this apparatus. 
         [0049]    The above description is illustrative only and is not to be considered limiting. Various modifications or changes can be made without departing from the spirit and scope of the invention. All such equivalent modifications and changes shall be included within the scope of the appended claims.