Patent Publication Number: US-10313789-B2

Title: Electronic device, echo signal cancelling method thereof and non-transitory computer readable recording medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Korean Patent Application No. 10-2016-0075165, filed on Jun. 16, 2016 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Field 
     Aspects of the exemplary embodiments relate to an electronic device, an echo signal cancelling method thereof and a non-transitory computer readable recording medium, and more particularly, to an electronic device capable of cancelling a residual echo additionally from a signal in which an echo is canceled through an adaptive filter firstly, an echo signal cancelling method thereof and a non-transitory computer readable recording medium. 
     Description of the Related Art 
     With respect to an electronic device such as a communication terminal, a voice of a far-end speaker is echoed by a surrounding environment and input through a near-end microphone. The phenomenon that the sound produced by a device is input to the device again is called an acoustic echo. 
     Recently, the development of the electronic device which operates by recognizing a voice has been increased. In addition, many display devices such as a smart TV often include a microphone to perform a voice recognition function. Accordingly, there is a growing need to develop a method to cancel an acoustic echo, which is available not only for a communication terminal but for electronic devices in a variety of fields. 
     There is an increasing necessity of a method to cancel an echo without using phase information because a vibration of an air pressure according to a speaker positioned near a microphone causes a confusion on a phase of a signal. According to the necessity, the method to convert a signal to a frequency domain has been developed, however, the efficiency of an adaptive filter is still low because of a use of a complex coefficient. 
     In addition, a residual echo still exists even after a sound is processed by the adaptive filter. Further, a dispersion value of a noise required for cancelling the residual echo may not be estimated appropriately. 
     SUMMARY 
     An aspect of the exemplary embodiment has been made to address the problems described above and to provide an electronic device capable of cancelling an echo with an adaptive filter (AF) and cancelling a residual echo with a residual echo suppressor (RES), an echo signal cancelling method thereof and a non-transitory computer readable recording medium. 
     According to an exemplary embodiment, there is provided an electronic device including a speaker configured to output a sound corresponding to a reference signal, a microphone configured to generate a microphone signal by obtaining a received sound and a filter configured to cancel an echo signal of the reference signal from the microphone signal, and the filter includes the first filter configured to estimate an echo signal of the reference signal and cancel the estimated echo signal from the microphone signal and the second filter configured to generate an adaptive gain to cancel a residual echo from the microphone signal in which the estimated echo signal is canceled, and generate an output signal by using the generated adaptive gain and the microphone signal in which the estimated echo signal is canceled. 
     According to an exemplary embodiment, there is provided an echo signal cancelling method of an electronic device including generating a microphone signal by obtaining a sound received by the electronic device, estimating an echo signal of a reference signal which is output from the electronic device and cancelling the estimated echo signal from the microphone signal, generating an adaptive gain to cancel a residual echo from the microphone signal in which the estimated echo signal is canceled and generating an output signal by using the generated adaptive gain and the microphone signal in which the estimated echo signal is canceled. 
     According to an exemplary embodiment, there is provided a non-transitory computer readable recording medium comprising a program to execute an echo signal cancelling method of an electronic device, the method including generating a microphone signal by obtaining a sound received by the electronic device, estimating an echo signal of a reference signal which is output from the electronic device and cancelling the estimated echo signal from the microphone signal, generating an adaptive gain to cancel a residual echo from the microphone signal in which the estimated echo signal is canceled, and generating an output signal by using the generated adaptive gain and the microphone signal in which the estimated echo signal is canceled. 
     According to yet another exemplary embodiment, an electronic device includes: a speaker configured to output a sound corresponding to a reference signal; a microphone configured to generate a microphone signal by obtaining the sound corresponding to the reference signal; and a filter configured to cancel an echo signal of the reference signal from the microphone signal, in which the filter includes: a first filter configured to estimate the echo signal of the reference signal and to cancel the estimated echo signal from the microphone signal; and a second filter configured to generate an adaptive gain to cancel a residual echo from the microphone signal in which the estimated echo signal is canceled, and generate an output signal by using the generated adaptive gain and the microphone signal, in which the estimated echo signal is canceled. 
     As described above, according to the diverse exemplary embodiments, the electronic device may cancel an echo signal occurred from the signal which is output from the electronic device itself, in two stages. In addition, the electronic device may cancel a residual echo by estimating an appropriate dispersion value of the residual echo. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a conceptual diagram of an electronic device according to an exemplary embodiment; 
         FIG. 2  is a block diagram provided to explain roughly a composition of an electronic device according to an exemplary embodiment; 
         FIG. 3  is a block diagram provided to explain a composition of an electronic device according to an exemplary embodiment; 
         FIG. 4  is a drawing provided to explain a process of cancelling an echo signal of an electronic device according to an exemplary embodiment; 
         FIG. 5  is a drawing provided to explain an echo signal cancelling method of an electronic device by a functional block according to an exemplary embodiment; 
         FIG. 6  is a drawing provided to explain a first filter of an electronic device according to an exemplary embodiment; 
         FIG. 7  is a drawing provided to explain a second filter of an electronic device according to an exemplary embodiment; and 
         FIGS. 8 and 9  are flowcharts provided to explain an echo signal cancelling method of an electronic device according to diverse exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments are described in detail with reference to the accompanying drawings. In describing the exemplary embodiments, well-known element structures and technologies are not described in detail since they would obscure the exemplary embodiments in unnecessary detail. Further, all terms used in the description are general terms that are widely used in consideration of their functions in the exemplary embodiments, but may differ depending on intentions of a person skilled in the art to which the exemplary embodiments belong, custom, or appearance of new technology. Accordingly, they should be defined on the basis of the contents of the whole description of the exemplary embodiments. 
     The term such as “first” and “second” used in various exemplary embodiments may modify various elements regardless of an order and/or importance of the corresponding elements, and does not limit the corresponding elements. The terms are used only to distinguish one element from other elements. For example, a first element may be named a second element without departing from the scope of right of various exemplary embodiments, and similarly, a second element may be named a first element. The term of and/or includes combination or one of a plurality of related items recited. 
     The terms used herein are solely intended to explain a specific exemplary embodiment, and not to limit the scope of the present disclosure. A singular expression includes a plural expression, unless otherwise specified. The terms, “include”, “comprise”, etc. of the description are used to indicate that there are features, numbers, operations, elements, parts or combination thereof, and they should not exclude the possibilities of combination or addition of one or more features, numbers, operations, elements, parts or combination thereof. 
       FIG. 1  is a conceptual diagram provided to explain the electronic device  100  according to an exemplary embodiment. The electronic device  100  according to an exemplary embodiment may be all kinds of devices including a strong speaker and a microphone placed at a close range. For example, the electronic device  100  may be realized as a device transmitting and receiving a voice signal such as a communication terminal. In addition, an electronic device  100  may be realized as a device capable of performing a voice controlling function such as a smartphone, a smart TV, a desktop, an audio device, an interactive voice recognition device, and a navigation device. The electronic apparatus  100  also may be realized as an IoT herb device which operates by a voice control. A microphone  120  receiving a voice of a user and a speaker  110  outputting a voice to the user are placed near the above devices, and thus an echo signal cancelling method according to an exemplary embodiment may be applied to the devices. 
     Referring to  FIG. 1 , the electronic device  100  may output a sound through the speaker  110 . The sound output from the speaker  110  corresponds to a signal generated from the electronic device  100 . The signal which is generated from the electronic device  100  and which will be output through the speaker  110  will be called a reference signal. In  FIG. 1 , the reference signal is recited as x(t). 
     The electronic device  100  may receive an utterance of a user s(t) through the microphone  120 . However, the microphone  120  receives not only an utterance of a user but an echo signal of the reference signal h(t)*x(t), which is output from the speaker  110 . The microphone  120  may generate a microphone signal d(t) by obtaining the received sound. 
     A purpose of the electronic device  100  according to an exemplary embodiment is to cancel the echo signal of the reference signal h(t)*x(t) from the microphone signal d(t) and obtain the signal of a near-end speaker s(t) only. Referring to  FIG. 1 , the electronic device  100  may cancel the echo signal of the reference signal by using a first filter  131  or an acoustic echo canceller (AEC), and a second filter  133  or a residual echo suppressor (RES). 
     According to the above, the electronic device  100  according to an exemplary embodiment may obtain a signal of a near-end speaker which is aimed to be received by cancelling the echo signal in two stages. The echo signal cancelling method in two stages will be described below in detail. 
       FIG. 2  is a block diagram provided to explain roughly a composition of the electronic device  100  according to an exemplary embodiment. Referring to  FIG. 2 , the electronic device  100  may include a speaker  110 , a microphone  120  and a filter  130 . The filter  130  may include a first filter  131  and a second filter  133 . 
     The speaker  110  may output a sound. For example, the speaker  110  may output the sound corresponding to a reference signal by processing the reference signal (or an audio signal). 
     The microphone  120  may obtain a sound around the electronic device  100 . In addition, the microphone  120  may generate a microphone signal (or an audio signal) by processing the obtained sound. 
     The filter  130  may cancel an echo signal of the reference signal from the microphone signal. The filter  130  may be composed of circuits performing respective functions and may perform a signal processing by using CPU, DSP and the like. 
     The filter  130  may include the first filter  131  which cancels an acoustic echo signal output from the speaker  110  by using an adaptive filter (AF), and the second filter  133  which cancels a residual echo which remains even after the processing of the first filter  131 . 
     In addition, the filter  130  may further include compositions such as a converter  134  which converts a signal into a frequency domain, a magnitude obtainer  135  which obtains a spectral magnitude from the signal converted into the frequency domain, a phase obtainer  136  which obtains a phase from the signal converted into the frequency domain, an inverter  137  which converts a signal into a time domain, and a synthesizer  138  which synthesizes the magnitude and the phase. 
     All the compositions performing respective functions in the above may be included in the filter  130 , or some of the functions may be performed in an additional composition. 
     The first filter  131  may estimate the echo signal of the reference signal and cancel the echo signal of the reference signal which is estimated from the microphone signal. The first filter  131  may be called an acoustic echo canceller (AEC). 
     For example, the first filter  131  may generate an estimated echo signal which traces the echo signal of the reference signal by renewing an adaptive filter (AF) coefficient. The first filter  131  may cancel a noise occurred by a voice signal of the electronic device  100  itself by cancelling the estimated echo signal generated by the microphone signal. 
     The first filter  131  may update an echo signal which is estimated successively to trace the echo signal of the reference signal. The signal which goes through the first filter  131  and in which the echo signal of the reference signal estimated from the microphone signal is canceled is called an error signal. For example, if the estimation is perfect, the estimated echo signal may coincide with an actual echo signal of the reference signal. However, the estimation may not be perfect in a practical operation, and thus the error signal which went through the first filter  131  may include a residual echo. 
     The second filter  133  may generate an output signal by cancelling a residual echo from the microphone signal (that is, the error signal) in which the estimated echo signal is canceled. For example, the second filter  133  may generate an adaptive gain to cancel the residual echo from the microphone signal in which the estimated echo signal is canceled. In addition, the second filter  133  may generate an output signal by using the microphone signal in which the generated adaptive gain and the estimated echo signal are canceled. A specific operation of the second filter  133  will be described below again. 
       FIG. 3  is a block diagram provided to explain a composition of the electronic device  100  according to an exemplary embodiment. The electronic device  100  may include additional compositions such as the speaker  110 , the microphone  120 , the filter  130 , a processor  140 , a communicator  150  and a voice recognizer  160 . In addition to the compositions illustrated in an exemplary embodiment of  FIG. 3 , additional compositions may be included according to an exemplary embodiment of the electronic device  100 . 
     The processor  140  may control an overall composition of the electronic device  100 . An exemplary embodiment of  FIG. 3  illustrates that the output signal generated in the filter  130  goes through the processor  140  and is transmitted to the communicator  150  or the voice recognizer  160 . However, the output signal may be transmitted directly to the composition such as the communicator  150 . 
     The communicator  150  may transmit the output signal which is generated through the filter  130  to an external device. For example, if the electronic device  100  is realized as a smartphone and performs a phone call on a speaker phone mode, the communicator  150  may cancel an echo signal of a voice of a person at the other end of the line which is output from the speaker  110 , and transmit the output signal in which the voice of the user only remains, to the device of the person at the other end of the line. 
     The communicator  150  may communicate with an external device through a wired and wireless network. For example, the communicator  150  may include a variety of communication modules such as a near-field wireless communication module (not illustrated) and a wireless communication module (not illustrated). Herein, the near-field wireless communication module refers to the module which communicates with an external device located nearly, according to a near-field wireless communication method such as Bluetooth, Zigbee and the like. In addition, the wireless communication module refers to the module which is connected to an external network according to a wireless communication protocol such as WiFi, IEEE and the like, and performs a communication. In addition to the above, the wireless communication module may further include a mobile communication module which accesses a mobile communication network according to a variety of mobile communication standards such as 3rd generation (3G), 3rd Generation Partnership Project (3GPP), Long Term Evolution (LTE) and LTE Advanced (LTE-A) and which performs a communication. 
     The communicator  150  may let the voice recognizer  160  to communicate with an external server and the like. For example, the communicator  150  may transmit a result of a voice recognition which is processed in the voice recognizer  160  to an external server, and receive corresponding information from an external device. 
     The voice recognizer  160  may perform a voice recognition by using an output signal generated in the filter  130 . The voice recognizer  160  may generate a control signal capable of controlling the electronic device  100  itself or an external device according to the result of the voice recognition. 
     For example, the voice recognizer  160  may detect and recognize a trigger word from the generated output signal and generate a result of a word and a sentence voice recognition from an output signal after the trigger word is recognized. 
       FIG. 4  is a drawing provided to explain a process of cancelling the echo signal of the electronic device  100  according to an exemplary embodiment. 
     In the exemplary embodiment of  FIG. 4 , x(n) refers to a reference signal. The reference signal generated in the electronic device  100  may be output as a sound corresponding to the reference signal through the speaker  110 . In addition, the reference signal may be input in the filter  130  and used to cancel an echo signal of the reference signal. 
     The microphone  120  may obtain a received sound and generate a microphone signal d(n). The microphone signal d(n) may include the echo signal of the reference signal. The filter  130  may perform an operation to cancel the echo signal of the reference signal included in the microphone signal. The electronic device  100  may preserve a voice signal of a near-end speaker by cancelling the echo signal of the reference signal. 
     The converter  134 - 1  and  134 - 2  may convert the reference signal x(n) and the microphone signal d(n) into a frequency domain respectively. In addition, the filter  130  may divide each of the microphone signal and the reference signal, which are converted into the frequency domain, into a magnitude and a phase. The magnitude obtainer  135 - 1  and  135 - 2  may respectively receive the microphone signal and the reference signal which are converted into the frequency domain, and obtain the magnitude only. The signal in which the phase is canceled and only the magnitude remains may be called spectral magnitude. The electronic device  100  according to an exemplary embodiment may solve a problem such as a release of an estimated value occurred due to a rapid change of a phase, by using the signal which is converted into a frequency domain and also of which phase is divided and only the magnitude remains. In addition, the phase obtainer  136  may receive the microphone signal converted into the frequency domain and obtain the phase only. 
     An exemplary embodiment of  FIG. 4  illustrates that the converter  134  converts the reference signal and the microphone signal into a frequency domain by using fast Fourier transform (FFT). l is a FFT frame index, and k is a frequency component index. However, the method that the electronic device  100  converts signals into the frequency domain may not be limited to FFT. For example, the converter  134  may use a method such as Short Time Fourier Transform (STFT). It may be more appropriate to use the method STFT than using the method FFT to prevent a signal distortion. 
     The first filter  131  may receive a spectrum magnitude of the converted reference signal, X(l,k), and a spectrum magnitude of the microphone signal, D(l,k). The first filter  131  or AEC may include a plurality of adaptive filters which operate in different frequency domains. Each of the plurality of adaptive filters may generate an estimated echo signal of frequency domains assigned respectively. Such AEC is called sub band AEC. 
     The first filter  131  may trace an echo signal of a reference signal while updating adaptive filter coefficient H(l,k). The first filter  131  generates an estimated echo signal of the reference signal F(l,k), by multiplying a reference signal of a previous time frame by an adaptive filter coefficient of a present time frame. In addition, the first filter  131  may cancel the echo signal of a reference signal estimated in a microphone signal. The signal that an echo signal estimated in the microphone signal is canceled is called error signal E(l,k). A detailed operation of the first filter  131  may be explained again in  FIG. 6 . 
     The second filter  133  may generate adaptive gain G(l,k) to cancel a residual echo from the microphone signal in which the estimated echo signal is canceled (that is, the error signal E(l,k)). The error signal E(l,k) may include both the residual echo and a voice signal of a near-end speaker. If the adaptive gain is multiplied by the error signal, only the voice signal of the near-end speaker is output. That is, the relation of the error signal and the adaptive gain is as follows.
 
 E =Signal+Noise, G·E =Signal
 
     The second filter  133  may estimate a dispersion value of the residual echo and generate the adaptive gain by using all frequency components of the dispersion value of the estimated residual echo and the error signal (the microphone signal in which an echo signal estimated in the first filter  131  is canceled). The second filter  133  may generate an adaptive gain by using one or more frequency components of the microphone signal in which the estimated echo signal is canceled. A detailed operation of the second filter  133  may be explained again in  FIG. 7 . 
     The synthesizer  138  may synthesize a spectrum magnitude that the error signal is multiplied by the adaptive gain, with a phase of the microphone signal. In addition, the inverter  137  may convert the synthesized signal into a time domain. 
       FIG. 5  is a drawing provided to explain an echo signal cancelling method of the electronic device  100  by a functional block according to an exemplary embodiment. 
     Referring to  FIG. 5 , the electronic device  100  may convert the reference signal and the microphone signal into a frequency domain respectively. In addition, the electronic device  100  may cancel a low frequency component by passing the reference signal which is converted into the frequency domain and the microphone signal respectively through a high pass filter. Since the low frequency component is a useless part in processing a voice, the electronic device  100  may use the high pass filter additionally in this stage. 
     A functional block expressed as sqrt( ) corresponds to the magnitude obtainer  135 , and obtains the reference signal and a spectrum magnitude of the microphone signal. A functional block expressed as e i atan  corresponds to the phase obtainer  136 , and obtains a phase component of the microphone signal. RLS functional block corresponds to the first filter  131 . It is called RLS functional block because the RLS functional block adapts a filter coefficient by using Recursive Least Squares (RLS) algorithm. RLS functional block may generate an estimated echo signal of the reference signal F(l,k) by using a spectrum magnitude of an input reference signal X(l,k) and an adaptive filter coefficient.
 
 F ( l,k )=Σ i=0   L−1   H   i ( l,k ) X ( l−i,k )
 
     In the above equation, L is a length of a filter. 
     Error signal E(l,k) corresponds to the value that the estimated echo signal of the reference signal is canceled from the microphone signal. The error signal may include a voice signal of a near-end speaker and a residual echo. 
     RES gain functional block corresponds to the second filter  133 . The RES gain functional block may estimate a dispersion value of a residual echo by using the reference signal, the microphone signal, the estimated echo signal of the reference signal and the error signal. In addition, the RES gain functional block may generate an adaptive gain from a dispersion value of an estimated residual echo. 
     The electronic device  100  may multiply the generated the adaptive gain G(l,k) by the error signal E(l,k) and obtain only a voice signal of a near-end speaker in which a residual echo is canceled. In addition, the electronic device  100  may use the phase obtained from the microphone signal as a phase of the voice signal of the near-end speaker. 
     The electronic device  100  may generate an output signal by multiplying the adaptive gain G(l,k), the error signal E(l,k) and a phase of the microphone signal e jφd(l,k) , and converting the same into a time domain. 
       FIG. 6  is a drawing provided to explain the first filter  131  of the electronic device  100  according to an exemplary embodiment.  FIG. 6  illustrates one of a plurality of adaptive filters comprising the first filter  131 . In different frequency domains, the plurality of adaptive filters may trace echo signals of reference signals of the corresponding frequency domains. 
     Referring to  FIG. 6 , the first filter  131  may estimate an echo signal of an input reference signal X(l,k) by using a vector of the adaptive filter coefficients, H(l,k). In order to decrease the error signal E(l,k), the first filter  131  may provide a feedback on the error signal and update the adaptive filter coefficient. The error signal corresponds to the signal that the estimated echo signal F(l,k) is canceled from the microphone signal D(l,k). The error signal E(l,k) may be calculated as the following equations.
 
 F ( l,k )=Σ i   H   i ( l,k ) X ( l−i,k )
 
 E ( l,k )= D ( l,k )− F ( l,k )
 
     The first filter  131  may output the adaptive filter coefficient, the estimated echo signal and the error signal, so the second filter  131  may use the adaptive filter coefficient, the estimated echo signal and the error signal to cancel a residual echo. 
       FIG. 7  is a drawing provided to explain the second filter  133  of an electronic device  100  according to an exemplary embodiment. The second filter  133  may generate the adaptive gain G(l,k) which is to be adapted to the microphone signal in which the estimated echo signal is canceled, in order to cancel a residual echo which remains in the microphone signal in which the estimated signal is canceled (that is, the error signal E(l,k)). 
     The second filter  133  may have to estimate a dispersion value of the residual echo first, in order to calculate the adaptive gain. According to an exemplary embodiment, the dispersion value of the residual echo may be calculated through information regarding an adaptive filter which reflects a reference signal and an acoustic environment. 
     The dispersion value of the residual echo λ d , may be calculated through the following equation.
 
λ d ( l,k )=α 2 ( l,k )λ d ( l− 1, k )+(1−α 2 ( l,k ))·| c ( l,k ) X   2 ( l,k )− F   2 ( l,k )|
 
     In the above equation, α(l,k) is a decaying coefficient of the adaptive filter coefficient H(l,k), c(l,k) is a coupling coefficient between a reference signal and a microphone signal, X(l,k) is the reference signal, F(l,k) is an estimated echo signal of the reference signal, l is a frame index, and k is a frequency component index. 
     First, the second filter  133  may calculate the coupling coefficient between the reference signal and the microphone signal c(l,k) as the following equation. 
     
       
         
           
             
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                 〈 
                 
                   
                     D 
                     2 
                   
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                     ( 
                     
                       l 
                       , 
                       k 
                     
                     ) 
                   
                 
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                 〈 
                 
                   
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     &lt; &gt; calculation corresponds to the calculation drawing a kind of an average by a frame unit. 
     After calculating the coupling coefficient c(l,k), the second filter  133  may calculate total energy of the reference signal c(l,k)X 2 (l,k) received in the microphone  120 , by multiplying the coupling coefficient by a square of the reference signal. In addition, the second filter  133  may calculate a residual reference energy c(l,k)X 2 (l,k)−F 2 (l,k) which remains in the error signal, by cancelling a square of the estimated echo signal F 2 (l,k) from the total energy of the reference energy. 
     The second filter  133  may reflect a residual echo energy of a previous frame by using a decaying coefficient of adaptive filter coefficient α(l,k). 
     The second filter  133  may calculate the decaying coefficient of adaptive filter coefficient α(l,k) by using the adaptive filter coefficient H(l,k). Components of the adaptive filter coefficient H(l,k) may be expressed as the following recursion on the assumption that the components decrease regularly.
 
| H   i ( l,k )|=α( l,k )| H   i−1 ( l,k )|
 
     The second filter  133  may calculate the decaying coefficient by using a recursive relation as the following equation.
 
α( l,k )=(| H   min ( l,k )|/| H   max ( l,k )|) 1/(i     min     −i     mzx   )
 
     In the above equation, H min  is a minimum filter coefficient, H max  is a maximum filter coefficient, and each of i min  and i max  are corresponding indexes. 
     The second filter  133  may generate the adaptive gain G(l,k) by using the dispersion value of the residual echo λ d  and the error signal E(l,k). In addition, the second filter  133  may generate an output signal by multiplying the generated adaptive gain by the error signal. 
     The electronic device  100  may multiply the generated output signal by the phase of the microphone signal, convert the same into a time domain, and output the converted signal.
 
{circumflex over ( Y )}( l,k )= G ( l,k ) E ( l,k ) e   jφ     d     (l,k)  
 
       FIG. 8  is a flowchart provided to explain an echo signal cancelling method of the electronic device  100  according to an exemplary embodiment. Referring to  FIG. 8 , the electronic device  100  may generate a microphone signal by obtaining a received sound in S 810 . The microphone signal may include an echo signal of a reference signal output from the electronic device  100  itself, and the purpose of the echo signal cancelling method according to an exemplary embodiment is to cancel the echo signal of the reference signal. 
     The electronic device  100  may estimate the echo signal of the reference signal by using the adaptive filter, and cancel the estimated echo signal from the microphone signal in S 820 . However, in the microphone signal in which the estimated echo signal is canceled by using the adaptive filter, a residual echo remains, and thus the electronic device  100  may generate an adaptive gain to cancel the residual echo in S 830 . In addition, the electronic device  100  may generate an output signal by using the microphone signal in which the generated adaptive gain and the estimated echo signal are canceled, in S 840 . 
       FIG. 9  is a flowchart provided to explain the echo signal cancelling method of the electronic device  100  according to an exemplary embodiment using other terms. Referring to  FIG. 9 , the electronic device  100  may obtain the microphone signal and the reference signal of a time domain in S 910 . The electronic device  100  may convert the microphone signal and the reference signal into a frequency domain in S 920 . The electronic device  100  may prevent a malfunction of the adaptive filter according to a confusion of the phase by converting the signals into the frequency domain. The electronic device  100  may cancel the echo signal from the microphone signal by using the adaptive filter in S 930 . In detail, the adaptive filter may estimate the echo signal of the reference signal, cancel the estimated echo signal from the microphone signal, and gain the error signal. 
     In order for the error signal, that is, the estimated echo signal to cancel the residual echo remains in the signal which is canceled from the microphone signal, the electronic device  100  may use a residual echo suppressor in S 940 . In detail, the residual echo suppressor may calculate the dispersion value of the residual echo from the information of the reference signal and the adaptive filter (acoustic environment), and calculate the adaptive gain to cancel the residual echo by using the calculated dispersion value of the residual echo. 
     Through the two stages of cancelling the echo signal, the electronic device  100  may obtain an output signal. In addition, the electronic device  100  may convert the output signal into the time domain again in S 950 . Successively, the electronic device  100  may output the output signal which is converted into the time domain, in S 960 . 
     The other exemplary embodiments of the echo signal cancelling method of the electronic device  100  are duplicated with the explanation of the electronic device  100 , and thus will be omitted. 
     As described above, the electronic device  100  may cancel the echo signal in two stages. In addition, the electronic device  100  may obtain the adaptive gain value to cancel the residual echo effectively, by calculating the dispersion value of the residual echo by using the reference signal and the acoustic environmental information. 
     The above explained methods may be realized in a program instruction formation which can be performed through a variety of computer means and recorded in a computer readable medium. The above computer readable medium may include one of or a combination of a program instruction, a data file, and a data structure and the like. The program instruction recorded in the medium may be planned and composed especially for the exemplary embodiment, or well-known and usable for those skilled in a computer software. The computer readable recording medium may include the examples such as a hard disk, a floppy disk, a magnetic media such as a magnetic tape, an optical media such as CD-ROM and DVD, a magneto-optical media such as a floptical disk, and a hardware apparatus especially configured to store and execute a program instruction, such as ROM, RAM and flash memory. An example of the program instruction may include a machine cod formed by a compiler, as well as a high-level language code which can be executed by a computer using an interpreter. The above hardware apparatus may be composed to be operated as more than one software module to perform an operation of the exemplary embodiment, and so is the reverse thereof. 
     While the present disclosure has been shown and described with reference to various exemplary embodiments and drawings thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein. Thus, the scope of the present disclosure should not be limited by the explained exemplary embodiments, and should be defined by the appended claims and their equivalents.