Abstract:
An audio signal processing method includes: receiving an audio signal comprising consecutive frames; generating a first encoding parameter corresponding to a first frame among the consecutive frames and a second encoding parameter corresponding to a second frame adjacent to the first frame; and generating at least one interpolated parameter based on the first encoding parameter and the second encoding parameter.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/371,294 filed on Aug. 6, 2010, and Korean Patent Application No. 10-2011-0069495, filed on Jul. 13, 2011 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    Methods and apparatuses consistent with exemplary embodiments relateto an audio signal processing method, an encoding apparatus therefor, and a decoding apparatus therefor, and more particularly, to an audio signal processing method of generating encoding parameters and an encoding apparatus therefor, and an audio signal processing method of generating interpolated frames by using encoding parameters, and a decoding apparatus therefor. 
         [0004]    2. Description of the Related Art 
         [0005]    To compress and transmit an audio signal including a plurality of frames, receive the compressed audio signal, and restore the original audio signal, an encoder is used in a transmission end, and a decoder is used in a reception end. The transmission end and the reception end compress and restore, respectively, an audio signal in accordance with a predetermined standard. 
         [0006]    The encoder extracts a predetermined parameter from each frame during a process of compressing an audio signal. In this regard, the predetermined parameter is a parameter value used to receive the compressed audio signal in the decoder and restore the received audio signal to the original audio signal. The predetermined parameter is hereinafter referred to as an encoding parameter. 
         [0007]    The encoding parameter may be generated in a frame unit. The encoder analyzes one frame that is an audio signal reproduced for a predetermined period of time, and generates a single encoding parameter. 
         [0008]    A single frame has the same value of encoding parameters. Therefore, if a sound image changes in a single frame, an audio signal reflecting such a change cannot be output. In this regard, the sound image indicates a point perceived by a user as a location where sound is produced. 
         [0009]    Therefore, if a sound image formed in a single frame is greatly different from a sound image formed in an adjacent frame, the user perceives unnatural sound. Accordingly, an audio signal processing method and an apparatus therefor are necessarily provided to reproduce naturally connected sound and enhance audio quality. 
       SUMMARY OF THE INVENTION 
       [0010]    One or more exemplary embodiments provide an audio signal processing method capable of generating interpolated frames located between originals frames, an encoding apparatus therefor, and a decoding apparatus therefor. 
         [0011]    More specifically, one or more exemplary embodiments provide an audio signal processing method capable of reproducing naturally connected sound, an encoding apparatus therefor, and a decoding apparatus therefor. Furthermore, one or more exemplary embodiments provide an audio signal processing method capable of enhancing audio quality, an encoding apparatus therefor, and a decoding apparatus therefor. 
         [0012]    According to an aspect of an exemplary embodiment, there is provided an audio signal processing method including: receiving an audio signal including consecutive frames; generating a first encoding parameter corresponding to a first frame among the consecutive frames and a second encoding parameter corresponding to a second frame adjacent to the first frame; and generating at least one interpolated parameter by using the first encoding parameter and the second encoding parameter. 
         [0013]    The at least one interpolated parameter may be an encoding parameter used to generate at least one interpolated frame located between a third frame decoded by using the first encoding parameter and a fourth frame decoded by using the second encoding parameter. 
         [0014]    The generating of the at least one interpolated parameter may include generating the at least one interpolated parameter by using a first predetermined value obtained by applying a first weight to the first encoding parameter and a second predetermined value obtained by applying a second weight to the second encoding parameter. 
         [0015]    The generating of the at least one interpolated parameter may further include generating the at least one interpolated parameter by using a value obtained by summing the first predetermined value obtained by multiplying the first weight and the first encoding parameter and the second predetermined value obtained by multiplying the second weight and the second encoding parameter. 
         [0016]    The first weight may be inversely proportional to the second weight. 
         [0017]    A sum of the first weight and the second weight may be 1. 
         [0018]    The method may further include: generating a bit stream corresponding to the audio signal and including the first encoding parameter, the second encoding parameter, and the at least one interpolated parameter; and transmitting the bit stream from an encoding apparatus to a decoding apparatus. 
         [0019]    The method may further include: receiving the transmitted bit stream at the decoding apparatus and de-formatting the received bit stream; and extracting the first encoding parameter, the second encoding parameter, and the at least one interpolated parameter from the de-formatted bit stream. 
         [0020]    The method may further include generating the at least one interpolated frame located between the third frame and the fourth frame by using the at least one interpolated parameter. 
         [0021]    The generating of the at least one interpolated frame may include generating n interpolated frames. 
         [0022]    The generating a first encoding parameter and a second encoding parameter may include applying an analysis window having a length L to the consecutive frames, and extracting the first encoding parameter and the second encoding parameter in a unit of frame data included in the analysis window, and generating at least one interpolated frame may include adjusting a size of a synthesis window according to the number n of the at least one interpolated parameter, and generating the n interpolated frames by using the synthesis window having the adjusted size. 
         [0023]    The encoding parameter may include at least one of an inter-channel intensity difference (IID) parameter, an inter-channel phase difference (IPD) parameter, an overall phase difference (OPD) parameter, and an inter-channel coherence (ICC) parameter. 
         [0024]    According to an aspect of another exemplary embodiment, there is provided an encoding apparatus including: an analysis filter bank which receives an audio signal including consecutive frames, and generates a first encoding parameter corresponding to a first frame among the consecutive frames and a second encoding parameter corresponding to a second frame adjacent to the first frame; an encoding unit which generates at least one interpolated parameter by using the first encoding parameter and the second encoding parameter; and a formatter which generates a bit stream including the first encoding parameter, the second encoding parameter, and the at least one interpolated parameter. 
         [0025]    According to an aspect of another exemplary embodiment, there is provided a decoding apparatus including: a de-formatter which receives a bit stream including a first encoding parameter, a second encoding parameter, and at least one interpolated parameter, and de-formats and outputs the bit stream; a decoding unit which extracts the first encoding parameter, the second encoding parameter, and the at least one interpolated parameter from the bit stream; and a synthesis filer bank which generates a first frame and a second frame by using the first encoding parameter and the second encoding parameter, and generates at least one interpolated frame located between the first frame and the second frame by using the at least one interpolated parameter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The above and other aspects will become more apparent by describing in detail exemplary embodiments with reference to the attached drawings in which: 
           [0027]      FIG. 1  is a block diagram of an encoding apparatus according to an exemplary embodiment; 
           [0028]      FIG. 2  is a flowchart illustrating an audio signal processing method according to an exemplary embodiment; 
           [0029]      FIG. 3  is a diagram for explaining the audio signal processing method of  FIG. 2  according to an exemplary embodiment; 
           [0030]      FIG. 4  is a graph for explaining weight values used in an operation of generating at least one interpolated parameter of  FIG. 2 ; 
           [0031]      FIG. 5  is a block diagram of a decoding apparatus according to an exemplary embodiment; 
           [0032]      FIG. 6  is a flowchart illustrating an audio signal processing method according to another exemplary embodiment; 
           [0033]      FIG. 7  is a diagram for explaining operations of extracting first and second encoding parameters and at least one interpolated parameter and generating first and second frames and at least one interpolated frame of  FIG. 6 ; 
           [0034]      FIGS. 8A through 8C  are diagrams for explaining interpolated parameters, interpolated frames, and an audio signal according to an exemplary embodiment; and 
           [0035]      FIGS. 9A through 9C  are diagrams for explaining interpolated parameters, interpolated frames, and an audio signal according to another exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    Below, exemplary embodiments will be described in detail with reference to accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art. The exemplary embodiments may be embodied in various forms without being limited to the exemplary embodiments set forth herein. Descriptions of well-known parts are omitted for clarity, and like reference numerals refer to like elements throughout. In this detailed description, the term “unit” denotes a hardware component and/or a software component that is executed by a hardware component such as a processor. 
         [0037]      FIG. 1  is a block diagram of an encoding apparatus  100  according to an exemplary embodiment. 
         [0038]    Referring to  FIG. 1 , the encoding apparatus  100  of the exemplary embodiment includes an analysis filter bank  120 , a formatter  125 , and an encoding unit  130 . 
         [0039]    The analysis filter bank  120  receives an audio signal including consecutive frames. The analysis filter bank  120  generates a first encoding parameter corresponding to a first frame of the consecutive frames and a second encoding parameter corresponding to a second frame adjacent to the first frame. In this regard, the second frame may be adjacent to a previous end of the first frame. For example, if the first frame is an (n+1) th  frame at a predetermined point, the second frame may be an n th  frame that is a previous frame. The second frame also may be adjacent to a subsequent end of the first frame. For example, if the first frame is an n th  frame at a predetermined point, the second frame may be the (n+1) th  frame that is a subsequent frame. 
         [0040]    The encoding parameter is used to restore a predetermined audio signal corresponding to a predetermined channel in a decoding apparatus. More specifically, the encoding parameter is used to decode frames included in a predetermined audio signal. 
         [0041]    The encoding parameter may include a multi-channel parameter that up-mixes a received and compressed audio signal and generates audio signals corresponding to multi-channels. 
         [0042]    The encoding parameter may include at least one of an inter-channel intensity difference (IID) parameter, an inter-channel phase difference (IPD) parameter, an overall phase difference (OPD) parameter, and an inter-channel coherence (ICC) parameter. 
         [0043]    The encoding unit  130  generates at least one interpolated parameter by using the first encoding parameter and the second encoding parameter. The analysis filter bank  120  may generate the at least one interpolated parameter, or a system controller (not shown) included in the encoding apparatus  100  may generate the at least one interpolated parameter. 
         [0044]    The formatter  125  generates a bit stream including the first encoding parameter and the second encoding parameter and the at least one interpolated parameter generated by the analysis filter bank  120 . More specifically, the formatter  125  may generate the bit stream in accordance with a predetermined standard, for example but not limited to, the MP 3  standard. The formatter  125  may transmit the bit stream to the decoding apparatus. 
         [0045]    The operations of the elements of the encoding apparatus  100  of the present embodiment are similar to operations of an audio signal processing method according to the present inventive concept in terms of the technical idea. Therefore, the operation of the encoding apparatus  100  of the exemplary embodiment will be described in detail with reference to  FIGS. 2 through 4  relating to the audio signal processing method according to the present inventive concept. The redundant descriptions therebetween will not be repeated here. 
         [0046]      FIG. 2  is a flowchart illustrating an audio signal processing method  200  according to an exemplary embodiment. The audio signal processing method  200  of the exemplary embodiment may be performed in an encoding apparatus according to the present inventive concept. 
         [0047]      FIG. 3  is a diagram for explaining the audio signal processing method  200  of  FIG. 2  according to an exemplary embodiment. The audio signal processing method  200  will now be described with reference to  FIGS. 1 through 3 . 
         [0048]    Referring to  FIG. 2 , the audio signal processing method  200  receives an audio signal including consecutive frames (operation  210 ). Operation  210  may be performed by the analysis filter bank  120 . 
         [0049]    In this regard, the consecutive frames may overlap by 50% and be encoded in order to prevent discontinuity between frames. More specifically, as shown in  FIG. 3 , a half of a first frame  301  and a second frame  303  subsequent to the first frame  301  overlap and are input, and encoding operations  311  and  312  are performed on the input first and second frames  301  and  303 , respectively. Referring to  FIG. 3 , the first frame  301  is an n th  frame #n frame at a predetermined point, and the second frame  303  is an (n+1) th  frame #n+1 frame subsequent to the n th  frame #n frame. 
         [0050]    A first encoding parameter  321  corresponding to the first frame  301  and a second encoding parameter  323  corresponding to the second frame  303  adjacent to the first frame  301  are generated among the consecutive frames included in the input audio signal (operation  220 ). More specifically, a predetermined encoding parameter may be generated by applying an analysis window corresponding to the length L of the first frame  301  and using frame data of the analysis window. 
         [0051]    In this regard, operation  220  may be performed by the analysis bank filter  120 . The first encoding parameter  321  and the second encoding parameter  323  may be extracted and generated during an operation of encoding the audio signal. Thus, in  FIG. 3 , the first encoding parameter  321  and the second encoding parameter  323  may be generated in operations  311  and  312  of encoding the input first and second frames  301  and  303 . 
         [0052]    At least one interpolated parameter  331  is generated by using the first encoding parameter  321  and the second encoding parameter  323  generated in operation  220  (operation  230 ).  FIG. 3  shows an example of generating the at least one interpolated parameter  331  by using the first encoding parameter  321  and the second encoding parameter  323 . As described above, operation  230  may be performed by the encoding unit  130 . As described above, operation  230  may be performed by the analysis filter bank  120  or a system controller (not shown) included in the encoding apparatus  100 . 
         [0053]    In this regard, the at least one interpolated parameter  331  is an encoding parameter used to generate at least one interpolated frame located between a third frame decoded by using the first encoding parameter  321  and a fourth frame decoded by using the second encoding parameter  323 . 
         [0054]    In operation  230 , the at least one interpolated parameter  331  may be generated by using a first predetermined value obtained by applying a first weight to the first encoding parameter  321  and a second predetermined value obtained by applying a second weight to the second encoding parameter  323 . 
         [0055]      FIG. 4  is a graph for explaining weight values used in operation  230  of  FIG. 2 . 
         [0056]    Referring to  FIG. 4 , a line  410  indicates a value of a first weight Wk 1  used to generate the interpolated parameter  331 , and a line  420  indicates a value of a second weight Wk 2  used to generate the interpolated parameter  331 . The X axis indicates a distance between frames. The Y axis indicates values of the first weight Wk 1  and the second weight Wk 2 . More specifically, if the interpolated parameter  331  is generated between a third frame decoded by using the first encoding parameter  321  and a fourth frame decoded by using the second encoding parameter  323 , the interpolated parameter  331  may be located at a point a/2 that is a middle point of the third frame and the fourth frame (not shown). 
         [0057]    The line  410  indicating the value of the first weight Wk 1  applied to the first encoding parameter  321  may be in inverse proportional to the line  420  indicating the value of the second weight Wk 2  applied to the second encoding parameter  323 . Further, a sum of the first weight Wk 1  and the second weight Wk 2  may be 1. 
         [0058]    More specifically, the interpolated parameter  331  may be defined according to Equation 1 below. 
         [0000]      Pk=Wk1*Pn+Wk2*(Pn+1)   [Equation 1]
 
         [0059]    In Equation 1, Pk denotes the interpolated parameter  331 , Pn denotes the first encoding parameter  321 , (Pn+1) denotes the second encoding parameter  323 , Wk 1  denotes the first weight applied to the first encoding parameter Pn  321 , and Wk 2  denotes the second weight applied to the second encoding parameter Pn+1  323 . 
         [0060]    Referring to Equation 1, the interpolated parameter Pk  331  may be a sum of a first predetermined value (Wk 1 *Pn) obtained by multiplying the first weight Wk 1  and the first encoding parameter Pn  321  and a second predetermined value (Wk 2 *(Pn+1)) obtained by multiplying the second weight Wk 2  and the second encoding parameter Pn+1  323 . 
         [0061]    For example, if an interpolated frame is generated between the third frame and the fourth frame, the interpolated frame may be located between the third frame and the fourth frame. Thus, the interpolated frame may be located at the point a/2 where the first weight Wk 1  and the second weight Wk 2  may have values 0.5 and 0.5, respectively. Therefore, the interpolated parameter Pk  331  may be set as a value 0.5*Pn+0.5*(Pn+1). 
         [0062]    If n interpolated frames are generated between the third frame and the fourth frame, the n interpolated frames may be disposed having the same gap between the third frame and the fourth frame. 
         [0063]    If first, second, and third interpolated frames in which n=3 are generated between the third frame and the fourth frame, for example, the first, second, and third interpolated frames Pk 1 , Pk 2 , and Pk 3  may be located at points a/4, a/2, and 3a/4, respectively. In this case, the first and second weights Wk 1  and Wk 2  used to generate the second interpolated frame Pk 2  may be 0.5 and 0.5, respectively. The first and second weights Wk 1  and Wk 2  used to generate the third interpolated frame Pk 3  may be 0.25 and 0.75, respectively. 
         [0064]    As described above, the closer to the third frame the interpolated frame, the greater the value of the first weight Wk 1  applied to the first encoding parameter Pn  321 . The closer to the fourth frame the interpolated frame, the greater the value of the second weight Wk 2  applied to the second encoding parameter Pn+1  323 . 
         [0065]      FIG. 5  is a block diagram of a decoding apparatus  500  according to an exemplary embodiment. 
         [0066]    Referring to  FIG. 5 , the decoding apparatus  500  of the exemplary embodiment includes a synthesis filter bank  560 , a de-formatter  565 , and a decoding unit  570 . The decoding apparatus  500  receives the bit stream generated and transmitted from the encoding apparatus  100  of  FIG. 1 , decodes the received bit stream, and generates audio signals corresponding to at least one channel. 
         [0067]    The de-formatter  565  receives the bit stream including first and second encoding parameters and at least one interpolated parameter from the encoding apparatus  100 , de-formats the bit stream, and outputs the bit stream. More specifically, the formatter  125  of the encoding apparatus  100  formats and outputs an encoded audio signal, and thus the de-formatter  565  converts a format of the bit stream so that the bit stream has a same format as before being formatted by the formatter  125 . 
         [0068]    The decoding unit  570  decodes the received bit stream in accordance with a predetermined standard. The decoding unit  570  extracts the first and second encoding parameters and the at least one interpolated parameter from the decoded bit stream. 
         [0069]    The synthesis filter bank  560  generates first and second frames by using the first and second encoding parameters, and generates at least one interpolated frame located between the first and second frames by using the at least one interpolated parameter. 
         [0070]    The decoding apparatus  500  may further include a frame size adjusting unit that adjusts a size of a synthesis window according to the number of interpolated parameters. The adjustment of the size of the synthesis window according to the number of interpolated parameters may be performed by the synthesis filter bank  560  or the decoding unit  570 . 
         [0071]    The operations of the elements of the decoding apparatus  500  of the exemplary embodiment are similar to operations of an audio signal processing method that will be described with reference to  FIGS. 6 and 7  below in terms of the technical idea. Therefore, the operation of the encoding apparatus  500  of the exemplary embodiment will be described in detail with reference to  FIGS. 6 and 7  relating to the audio signal processing method according to another exemplary embodiment. The redundant descriptions between  FIGS. 5 and 7  will not be repeated here. 
         [0072]      FIG. 6  is a flowchart illustrating an audio signal processing method  600  according to another exemplary embodiment. 
         [0073]    Operations  610 ,  620 , and  630  of  FIG. 6  are the similar to operations  210 ,  220 , and  230  of  FIG. 2 , respectively, and thus descriptions thereof will not be repeated here. The audio signal processing method  600  may further include at least one of operations  640 ,  650 ,  660 ,  670 , and  680 , compared to the audio signal processing method  200  of  FIG. 2 . 
         [0074]    Subsequent to operation  630 , a bit stream including the first and second encoding parameters and the at least one interpolated parameter generated by the encoding unit  130  is generated (operation  640 ). 
         [0075]    The bit stream generated in operation  640  is transmitted to the decoding apparatus  500 . Accordingly, the de-formatter  565  of the decoding apparatus  500  receives the bit stream including the first and second encoding parameters and the at least one interpolated parameter. 
         [0076]    Operations  640  and  650  may be performed by the formatter  125  of the encoding apparatus  100 . 
         [0077]    The decoding apparatus  500  receives the transmitted bit stream and de-formats the received bit stream (operation  660 ). Operation  660  may be performed by the de-formatter  565 . More specifically, in operation  660 , a format of the bit stream is converted so that the bit stream has a same format as before being formatted by the formatter  125 . 
         [0078]    Operations  670  and  680  will now be described in detail with reference to  FIG. 7 . 
         [0079]      FIG. 7  is a diagram for explaining operations  670  and  680  of  FIG. 6 . 
         [0080]    Referring to  FIG. 7 , first and second frames  701  and  703  correspond to the first and second frames  301  and  303  of  FIG. 3 , respectively. Encoding operations  711  and  712 , first and second encoding parameters  721  and  723 , and interpolated parameter  731  correspond to the encoding operations  311  and  312 , the first and second encoding parameters  321  and  323 , and the interpolated parameter  331  of  FIG. 3 , respectively. Thus, redundant descriptions between  FIGS. 3 and 7  will be omitted here. 
         [0081]    The first and second encoding parameters and the at least one interpolated parameter are extracted from the bit stream de-formatted in operation  660  (operation  670 ). More specifically, the bit stream received in the decoding apparatus  500  is decoded  751 ,  752 , and  753 , and the first and second encoding parameters and the at least one interpolated parameter may be extracted or generated. 
         [0082]    Operation  670  may be performed by the decoding unit  570 . Alternatively, operation  670  may be performed by a system controller (not shown) or the synthesis filter bank  560  included in the decoding apparatus  500 . In this regard, the at least one interpolated parameter may be n interpolated parameters. 
         [0083]    At least one interpolated frame located in a third frame  761  and a fourth frame  763  is generated by using the at least one interpolated parameter extracted in operation  670  (operation  680 ). Operation  680  may be performed by the synthesis filter bank  560 . 
         [0084]    A synthesis window may be used to generate a plurality of frames included in an original audio signal. The synthesis window defines a length of an audio frame decoded and output by the decoding apparatus  500 . 
         [0085]    In  FIG. 7 , the number n of interpolated frames located between the third frame  761  and the fourth frame  763  is 1. The size of the synthesis window may be adjusted according to the number n of the interpolated parameters or the number n of interpolated frames to be generated. More specifically, as shown in  FIG. 7 , when the number of the interpolated parameters is 1, the size of the synthesis window may be L/2. In this regard, L denotes the size of the analysis window described above. 
         [0086]    Referring to  FIG. 7 , the third frame #n frame  761  corresponding to the first frame #n frame  701  is generated by using the first encoding parameter  721 . An interpolated frame #n 1  frame  762  is generated by using the interpolated parameter  731 . The fourth frame #n+1 frame  763  corresponding to the second frame #n+1 frame  703  is generated. 
         [0087]      FIGS. 8A through 8C  are diagrams for explaining interpolated parameters, interpolated frames, and an audio signal according to an exemplary embodiment. 
         [0088]    Referring to  FIG. 8A , an interpolated parameter  812  is generated. More specifically, a first encoding parameter  811 , a second encoding parameter  813 , and the interpolated parameter  812  may correspond to the first encoding parameter  721 , the second encoding parameter  723 , and the interpolated parameter  731  of  FIG. 7 , respectively. 
         [0089]    Referring to  FIG. 8B , a third frame  821 , a fourth frame  823 , and an interpolated frame  822  are decoded corresponding to the first encoding parameter  811 , the second encoding parameter  813 , and the interpolated parameter  812  of  FIG. 8A , respectively. 
         [0090]    The third frame  821 , the fourth frame  823 , and the interpolated frame  822  correspond to the third frame #n frame  761 , the fourth frame #n+1 frame  763 , and the interpolated frame #n 1  frame  762  of  FIG. 7 , respectively. 
         [0091]    Referring to  FIG. 8C , if an interpolated frame is generated, a sound image output according to the interpolated frame changes. 
         [0092]    If an audio signal corresponding to the third frame  821  that is decoded by using the first encoding parameter  811  is output, a listener  850  perceives a sound image located at a point  851 . If an audio signal corresponding to the fourth frame  823  that is decoded by using the second encoding parameter  813  is output, the listener  850  perceives a sound image located at a point  853 . 
         [0093]    When a location of a sound image corresponding to two adjacent frames that are continuously output rapidly changes from the point  851  to the point  853  in an audio signal processing method and a decoding apparatus, a user who is a listener perceives the rapidly changing sound image and accordingly listens to unnatural sound. 
         [0094]    The interpolated parameter  812  is used to generate the interpolated frame  822 . If an audio signal corresponding to the interpolated frame  822  is output, the listener  850  perceives a sound image located at a point  852 . 
         [0095]    Therefore, the audio signal processing method, the encoding apparatus, and the decoding apparatus according to the present inventive concept can reproduce naturally connected audio signals, thereby allowing a user to perceive naturally connected sound images and enhancing quality of audio perceived by the user. 
         [0096]      FIGS. 9A through 9C  are diagrams for explaining interpolated parameters, interpolated frames, and an audio signal according to another exemplary embodiment. 
         [0097]    Referring to  FIG. 9A , three interpolated parameters  912 ,  913 , and  914  are generated. More specifically, a first encoding parameter  911  and a second encoding parameter  915  may correspond to the first encoding parameter  721  and the second encoding parameter  723  of  FIG. 7 , respectively. 
         [0098]    Weight values used to generate the three interpolated parameters  912 ,  913 , and  914  may be set according to the weight values shown in  FIG. 4 . 
         [0099]    Referring to  FIG. 9B , a third frame  921 , a fourth frame  925 , and interpolated frames  922 ,  923 , and  924  are decoded corresponding to the first encoding parameter  911 , the second encoding parameter  915 , and the interpolated parameters  912 ,  913 , and  914  of  FIG. 9A , respectively. 
         [0100]    The third frame  921  and the fourth frame  925  correspond to the third frame #n frame  761 , and the fourth frame #n+1 frame  763  of  FIG. 7 , respectively. 
         [0101]    Referring to  FIG. 9C , if three interpolated frames are generated, a sound image output according to the interpolated frames changes. 
         [0102]    If an audio signal corresponding to the third frame  921  that is decoded by using the first encoding parameter  911  is output, a listener  950  perceives a sound image located at a point  951 . 
         [0103]    If audio signals corresponding to the interpolated frames  922 ,  923 , and  924  that are decoded by using the interpolated parameters  912 ,  913 , and  914  are output, the listener  850  continuously perceives sound images located at points  952 ,  953 , and  954 . 
         [0104]    If an audio signal corresponding to the fourth frame  925  that is decoded by using the second encoding parameter  915  is output, the listener  950  perceives a sound image located at a point  955 . 
         [0105]    If the number of interpolated frames generated between two adjacent frames increases, the user can perceive more naturally sound images. 
         [0106]    The invention can also be embodied as computer readable codes on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, etc. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
         [0107]    While the present inventive concept has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present inventive as defined by the following claims.