Patent Publication Number: US-10327090-B2

Title: Distance rendering method for audio signal and apparatus for outputting audio signal using same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. § 119(e), this application claims the benefit of U.S. provisional applications Nos. 62/393,659 filed on Sep. 13, 2016 and 62/418,807 filed on Nov. 8, 2016, which are hereby incorporated by reference as if fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a distance rendering method used for audio signal output and an audio signal output apparatus using the same. 
     Discussion of the Related Art 
     Recently, with advances in information technology (IT), a variety of smart devices has been developed. Particularly, smart devices basically provide audio output having various effects. Therefore, various methods for more realistic audio output have been attempted in a virtual reality (VR) environment. Thereamong, a distance rendering method provides more realistic audio in a VR environment by adjusting sense of distance caused by the distance between a sound image and a user through a direct-to-reverberation (D/R) ratio. A conventional general distance rendering method will now be described. 
     For example, in order to reproduce, through a headphone or an earphone, an effect of localizing a sound image from an arbitrary direction in a VR space, information about the VR space and information about the direction of a sound source are needed. Generally, the information about the direction of the sound source is provided by a user. Accordingly, if a database (DB) of head-related transfer functions (HRTFs) measured in all directions is present, a sound image may be localized in a desired direction with reference to the provided direction information. Further, if a head tracker is used together with the DB, the sound image may be localized in a fixed direction regardless of movement of the head of a user. Generally, information about a space may be acquired by measuring a room impulse response (simply, “room response”) measured in the corresponding space. However, since the room response cannot be actually measured in a “VR space”, the room response may be artificially generated using a room impulse response modeling (hereinafter, simplified to “room modeling”) method. If the generated room response is filtered together with an input signal, a user may perceive a spatial sense or reverberation for the measured space. 
     A user (listener) in an arbitrary space may move and the distance between a sound image and the user differs according to a moved location. This means that reverberant sound as well as the magnitude of a sound source to which the listener listens becomes different. Accordingly, a room response characteristic varies according to movement of a user. 
       FIG. 1  illustrates a conventional normal room response characteristic. Generally, the room response characteristic is divided into a direct part  11 , an early reflection part  12 , and a late reverberation part  13  as illustrated in  FIG. 1 . The direct part  11  is associated with the magnitude of a sound source and intelligibility. The early reflection part  12  and the late reverberation part  13  are associated with a spatial sense and reverberation of a sound source. 
     A conventional distance rendering method adjusts sense of distance through signal processing by modifying a room response. Generally, the conventional distance rendering method uses a D/R ratio. The D/R ratio is expressed by Equation (1). 
     
       
         
           
             
               
                 
                   
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     In Equation (1), h(t) denotes a room response and t 1  denotes time until a response of the direct part  11  is received. As indicated by Equation (1), the D/R ratio is controlled by the ratio of energy of the direct part  11  to energy of the early reflection part  12  and the late reverberation part  13 . 
     For reference,  FIG. 2A  illustrates a room response characteristic when the distance between a user and a sound image is not changed. The room response characteristic may be indicated by distinguishing between a direct part  11   a  and an early reflection and late reverberation part  14   a , based on t 1  of Equation (1). 
     For example, if it is desired that a relative distance between the user and the sound image be short, a gain of a direct part  11   b  of the room response may be adjusted to be increased and a gain of an early reflection and late reverberation part  14   b  may be adjusted to be decreased as illustrated in  FIG. 2B . Then, a sound source sounds bigger and a reverberant sound sounds smaller. 
     On the contrary, if it is desired that a relative distance between the user and the sound image be increased, a gain of a direct part  11   c  may be adjusted to be decreased and a gain of an early reflection and late reverberation part  14   c  may be adjusted to be increased, as illustrated in  FIG. 2C . Then, the sound source sounds smaller and the reverberant sound sounds bigger. 
     However, if it is desired that the distance between the sound image and the user be very close, a gain of the direct part is remarkably increased relative to a gain of the early reflection and a gain of the late reverberation part. In addition, if a remarkably modified gain is applied to a room response, the user may not feel reverberation even though the response has been measured in a space having reverberation. That is, a spatial sense is decreased as if the response is measured in an anechoic room (or dead room) and thus a spatial characteristic varies. 
     Moreover, a correlation between left and right ears (simply, binaural correlation) according to change in distance cannot be adjusted only by adjustment of the D/R ratio. Accordingly, if the distance between the sound image and the user is longer, a gain of the sound image is decreased and the binaural correlation is also decreased. 
     Accordingly, a new method capable of maintaining a spatial characteristic even when a relative distance between the user and the sound image is changed is needed. In addition, a new method capable of maintaining a binaural correlation characteristic based on the spatial characteristic even when a relative distance between the user and the sound image is changed is needed. That is, a binaural correlation value should be changed according to change in distance in order to maintain a spatial characteristic. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a distance rendering method used for audio signal output and an audio signal output apparatus using the same that substantially obviate one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a new distance rendering method for maintaining a spatial characteristic during audio output in an arbitrary space even when a relative distance between a user and a sound image is changed. 
     Another object of the present invention is to provide a new distance rendering method for changing a correlation value so as to maintain a binaural correlation characteristic according to an initial spatial characteristic during audio output in an arbitrary space even when a relative distance between a user and a sound image is changed. 
     Another object of the present invention is to provide an audio output apparatus for providing audio output using a new distance rendering method. 
     Another object of the present invention is to provide an audio output system for providing audio output using a new distance rendering method. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an audio distance rendering method used for audio output includes receiving a decoded audio signal, checking whether a distance between a user and a sound image is changed, if the distance is changed, calculating a gain parameter g new  and a period parameter τ new , applied to room response modeling, based on the changed distance, so as to maintain a space characteristic, and generating room response modeling for maintaining the space characteristic even when the distance is changed, using the calculated period parameter τ new  and gain parameter g new . 
     In accordance with another aspect of the present invention, an audio output apparatus includes an audio decoder configured to decode an input audio stream and output the decoded audio signal, and a renderer configured to render the decoded audio signal into an audio signal suitable for a space characteristic, wherein the renderer performs a process of checking whether a distance between a user and a sound image is changed, a process of calculating, when the distance is changed, a gain parameter g new  and a period parameter τ new , applied to room response modeling, based on the changed distance, so as to maintain the space characteristic, and a process of generating room response modeling for maintaining the space characteristic even when the distance is changed, using the calculated period parameter τ new  and gain parameter g new . 
     The gain parameter g new  may be calculated by adjusting a gain of a room response by the same ratio and the period parameter τ new  may be calculated by changing a generation period of a late reverberation part among room response characteristics. 
     When the distance between the user and the sound image becomes shorter, a gain of a direct part, a gain of an early reflection part, and a gain of a late reverberation part among elements constituting the room response may be adjusted to be increased by the same ratio, and a generation period of the late reverberation part among the elements constituting the room response may be adjusted to be long, so that less late reverberation is generated in comparison with the amount of late reverberation when the distance is not changed. 
     When the distance between the user and the sound image becomes shorter, the gain parameter g new  and the period parameter τ new  may be generated to have values larger than a gain parameter g and a period parameter τ when the distance is not changed. 
     When the distance between the user and the sound image becomes longer, a gain of a direct part, a gain of an early reflection part, and a gain of a late reverberation part among elements constituting the room response may be adjusted to be decreased by the same ratio, and a generation period of the late reverberation part among the elements constituting the room response may be adjusted to be short, so that a greater amount of late reverberation is generated in comparison with the amount of late reverberation when the distance is not changed. 
     When the distance between the user and the sound image becomes longer, the gain parameter g new , and the period parameter τ new  may be generated to have values smaller than a gain parameter g and a period parameter τ when the distance is not changed. 
     In accordance with another aspect of the present invention, an audio distance rendering method used for audio output includes receiving a decoded audio signal, checking whether a distance between a user and the sound image is changed, and if the distance is changed, adjusting a binaural correlation based on the changed distance. 
     The adjusting the binaural correlation may include adjusting a correlation of a late reverberation part of a binaural room impulse response (BRIR). 
     The adjusting the binaural correlation may further include extracting the late reverberation part of the BRIR, calculating a parameter IACC Late  corresponding to an interaural cross correlation (IACC) of the extracted late reverberation part, estimating a parameter IACC Late   _   Δd  corresponding to an IACC at a changed location with reference to information about a distance variation Δd, modeling the late reverberation part of the BRIR so as to have a correlation corresponding to the estimated parameter IACC Late   _   Δd  and replacing an existing late reveration part with the modeled late reverberation part, and changing a gain of the BRIR based on the modeled late reverberation part according to change in distance. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIG. 1  illustrates a normal room response characteristic; 
         FIGS. 2A to 2C  illustrate variations in room response characteristics according to a conventional distance rendering method; 
         FIG. 3  illustrates an exemplary configuration of an audio output apparatus according to the present invention; 
         FIG. 4  illustrates a configuration of a renderer in the audio output apparatus, according to a first embodiment of the present invention; 
         FIG. 5  illustrates a detailed configuration of a renderer to which a new distance rendering method is applied according to the first embodiment of the present invention; 
         FIG. 6  illustrates an operation of a reverberator to which the new distance rendering method is applied according to the first embodiment of the present invention; 
         FIGS. 7A to 7C  illustrate room response characteristics to which the new distance rendering method according to the first embodiment of the present invention is applied; 
         FIG. 8  is a flowchart illustrating the new distance rendering method applied to output of an audio signal according to the first embodiment of the present invention; 
         FIG. 9  illustrates a configuration of a renderer in an audio output apparatus according to a second embodiment of the present invention; 
         FIG. 10  illustrates a detailed configuration of a renderer to which a new distance rendering method is applied according to the second embodiment of the present invention; 
         FIG. 11  is a view referred to for describing the new distance rendering method according to the second embodiment of the present invention; and 
         FIG. 12  is a flowchart illustrating the new distance rendering method applied to output of an audio signal according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings, and a detailed description of the same or similar elements will be omitted. The suffixes “module” and “unit” used in the description below are given or used together only in consideration of ease in preparation of the specification and do not have distinctive meanings or functions. In addition, in the following description of the embodiments disclosed herein, a detailed description of related known technologies will be omitted when it may make the subject matter of the embodiments disclosed herein rather unclear. In addition, the accompanying drawings have been made only for a better understanding of the embodiments disclosed herein and are not intended to limit technical ideas disclosed herein, and it should be understood that the accompanying drawings are intended to encompass all modifications, equivalents and substitutions within the sprit and scope of the present invention. 
       FIG. 3  illustrates an exemplary configuration of an audio output apparatus according to the present invention. 
     The audio output apparatus of the present invention includes an audio decoder  100 , a renderer  200 , a user control interface  300 , digital-to-analog (D/A) converters  401  and  402 , amplifiers  501  and  502 , and transducers  601  and  602 . 
     A bitstream input to the audio decoder  100  may be transmitted by an encoder (not shown) and may be input in the form of a compressed audio file (e.g., .mp3 or .aac). The audio decoder  100  decodes the input audio bitstream according to a coded format to output the decoded audio signal  1001 . Generally, the decoded audio signal  1001  may be pulse code modulation (PCM) data (.pcm) but the present invention is not limited thereto. The decoded audio signal  1001  is input to the renderer  200 . The renderer  200  outputs left and right signals  2001  by applying a new distance rendering method related to first and second embodiments of the present invention. The left and right output signals  2001  are reproduced through left and right transducers  601  and  602  of headphones (or earphones) via D/A converters  401  and  402  and amplifiers  501  and  502 , respectively. Hereinafter, a detailed configuration and operation of the renderer  200  to which the new distance rendering method is applied will be described in detail. 
       FIG. 4  illustrates a detailed configuration of the renderer  200  in the audio output apparatus, according to a first embodiment of the present invention. The audio renderer  200  according to the first embodiment of the present invention includes a distance information provider  204 , a room information provider  203 , a room response generator  205 , a tracking information provider  201 , an HRTF selector  202 , and a filter  206 . 
     The distance information provider  204  provides information about the distance d between a user (listener) and a sound image. The room information provider  203  provides information about a room type (e.g., a rectangular room structure, a circular room structure, a partially open room structure, etc.) and information about a room size, corresponding to an arbitrary space in which a user is located and a VR space. The tracking information provider  201  provides a localization point (θ, Φ) of the sound image. 
     The room response generator  205  receives the information (e.g., the distance information, room type information, and tracking information (θ, Φ)) provided by the distance information provider  204 , the room information provider  203 , and the tracking information provider  201  and generates a room impulse response signal according to the new distance rendering method. 
     The audio renderer  200  further includes the HRTF selector  202 . The tracking information provider  201  provides the localization point (θ, Φ) of a sound image desired to be currently output to the HRTF selector  202 . The tracking information provider  201  may be a head tracker for tracking movement of a user or the user may directly provide related information through the user control interface  300 . For example, the sound localization point (θ, Φ) provided by the tracking information provider  201  is information about an azimuth angle θ and an altitude angle Φ. The HRTF selector  202  extracts HRTF data corresponding to the sound localization point (θ, Φ) provided by the tracking information provider  201  from an HRTF (DB)  2021 . If the HRTF data corresponding to the sound localization point (θ, Φ) is not present in the HRTF DB  2021 , the HRTF selector  202  may generate new HRTF data by interpolating data present in the HRTF DB  2021 . 
     The audio renderer  200  further includes the filter  206 . The filter  206  receives the room impulse response signal generated by the room response generator  205  and the HRTF data H L  and H R  determined by the HRTF selector  202  and performs filtering using a preset filtering method to output an audio signal. 
     Particularly, new room modeling in which a period of generating a late reverberant part is adjusted is applied to the audio renderer  200  according to the first embodiment of the present invention as the new distance rendering method. Hereinafter, the audio renderer  200  and the distance rendering method according to the first embodiment of the present invention will be described in detail with reference to  FIGS. 5 to 8 . 
       FIG. 5  illustrates a detailed configuration of the renderer  200  to which the new distance rendering method is applied according to the first embodiment of the present invention. Particularly,  FIG. 5  illustrates in detail the renderer  200  focusing on a late reverberation part modeling process of a room impulse response and a distance rendering method processing process performed based on the late reverberation part modeling process. 
     The above-described HRTF selector  202  extracts HRTF data h L  and h R  corresponding to tracking information (θ, φ) of a sound image provided by the tracking information provider  201  from the HRTF DB  2021 . In addition, as described above, in a VR space environment, a user should directly model a space or a room. Therefore, the user may select preset values similar to values of a room that is desired to be made or directly input room characteristic information RT (room shape, room size, etc.), through the room information provider  203 . The distance information provider  204  provides information about a relative distance between a user and a sound image. 
     A distance determiner  2051  determines whether the location of a user is changed, from the information about the distance provided by the distance information provider  204 . That is, the distance determiner  2051  controls a switching means  2054  to select an operation according to a path “y” when it is determined that the relative location of the user is changed. Meanwhile, the distance determiner  2051  controls the switching means  2054  to select an operation according to a path “n” when it is determined that the relative location of the user is not changed. 
     First, the operation according to the path “n” through the switching means  2054  will now be described. That is, the operation is performed in the case in which a distance variation Δd out of the distance information provided by the distance information provider  204  is 0, i.e., when the relative location of the user is not changed. In this case, a switch flag of the switching means  2054  is selected as the path “n”. 
     A room response may generally enable individual modeling of an early reflection part and a late reverberation part. In  FIG. 5 , the early reflection part is modeled by an early reflection modeling unit  2052  and the late reverberation part is modeled by a late reverberation modeling unit  2057  after parameters g, c, τ, and P are set by a parameter setting unit  2053  based on the room characteristic information. 
     An early reflection part r early  modeled by the early reflection modeling unit  2052  is filtered together with the extracted HRTF data h L  and h R  and an input audio signal s by a first filter  206   a  and the first filter  206   a  generates left and right early reflection signals sr early   _   L  and sr early   _   R . 
     A late reverberation part r late  modeled by the late reverberation modeling unit  2057  is also filtered together with the input audio signal s by a second filter  206   b  and the second filter  206   b  generates a late reverberation signal sr late . The late reverberation signal sr late  signal and the early reflection signals sr early   _   L  and sr early   _   R  are added by adders  206   c  and  206   d  and then output as rendered audio signals Output L  and Output R . 
     Next, the operation according to the path “y” through the switching means  2054  will now be described. That is, the operation is performed in the case in which the distance variation Δd out of the distance information provided by the distance information provider  204  is not 0, i.e., when the relative location of the user is changed. In this case, the switch flag of the switching means  2054  is selected as the path “y”. 
     If the user moves (i.e., Δd≠0), a first gain modification unit  2055  of  FIG. 5  generates a new gain parameter g new  obtained by changing a gain parameter g in proportion to a moved distance. A gain of a room response is adjusted using the new gain parameter g new . 
     In addition, if the user moves (i.e., Δd≠0), a τ-modification unit  2056  of  FIG. 5  generates a new period parameter τ new  by changing a period parameter τ in proportion to a moved distance. As a result, the late reverberation part is modeled by a late reverberation modeling unit  2058  based on the parameters g, c, τ new , and P changed according to the room characteristic information. A gain of a modeled late reverberation part r′ late  is adjusted by a second gain modification unit  2059 . The magnitude of the gain adjusted by each of the first gain modification unit  2055  and the second gain modification unit  2059  will be described in detail with reference to  FIG. 8  and Equation (3). 
     The second filter  206   b  performs filtering on an output signal of the second gain modification unit  2059  and the input audio signal s and generates the late reverberation signal sr late . 
     The adders  206   c  and  206   d  add the output signals sr late  of the second filter  206   b  to the output signals sr early   _   L  and sr early   _   R  of the first gain modification unit  2055  and generate the rendered audio signals Output L  and Output R . 
       FIG. 6  illustrates an operation of a reverberator to which the new distance rendering method is applied according to the first embodiment of the present invention. As described above, the new distance rendering method according to the first embodiment of the present invention determines a new room modeling scheme by modifying a part of parameters applied to room modeling when the location of a user is changed in an arbitrary space (i.e., Δd≠0). Especially, the new distance rendering method generates a room response signal that maintains a spatial characteristic as a result of new room modeling. A parameter modified for new room modeling may be a reverberation generation period parameter τ used for late reverberation modeling. That is, a new parameter τ new  is applied so that a late reverberation part characteristic to which the reverberation generation period parameter τ is applied is maintained to be suitable for the spatial characteristic. In addition, the new distance rendering method generates a new gain parameter g new  which is applied to new room modeling. Particularly, the new gain parameter g new  adjusts a gain of a direct part, a gain of an early reflection part, and a gain of a late reverberation part of a room response by the same ratio in proportion to change in distance. 
     The early reflection modeling unit  2052  may model only parts from the direct part to the early reflection part of the room response and use conventional normal modeling methods. The late reverberation part of the room response is modeled using an artificial reverberator in each of the late reverberation modeling units  2057  and  2058 . The artificial reverberator has the structure of a feedback delay network (FDN) including a plurality of comb filters as illustrated in  FIG. 6 . Parameters (g(g 1 , g 2 , . . . , g P ), c(c 1 , c 2 , . . . , c P ), τ(τ 1 , τ 2 , . . . , τ P ), and P) indicated in  FIG. 6  are set by the parameter setting unit  2053  of  FIG. 5 . 
     The parameter P indicates the number of comb filters in  FIG. 6 . Although better performance is obtained as the number of comb filters is increased, since a total amount of computations is also increased, a proper number of comb filters is required according to a given environment. The parameter τ represents a total delay of the comb filters and a relationship of τ=τ 1 +τ 2 + . . . +τ P  is satisfied. In this case, τ 1 , τ 2 , . . . , τ P  may have values which are not in a multiple relationship. For example, if P=3 and τ=0.1 ms, then τ 1 , τ 2 , and τ 3  may be set such that τ 1 =0.033 ms, τ 2 =0.05 ms, and τ 3 =0.0017 ms. If the parameter τ which determines a total delay of the comb filters is applied to room response modeling, the parameter τ is used as a generation period of a specific signal part. In the present invention, the parameter τ is applied to the late reverberation modeling units  2057  and  2058  for the late reverberation part as described above and is used as a generation period of the late reverberation part. 
     The parameters g=[g 1 , g 2 , . . . , g P ] and c=[c 1 , c 2 , . . . , c P ] are values given from the user and are set to values less than 1. When the late reverberation part is modeled using the FDN structure of  FIG. 6 , optimal parameter values of a desired room response may be arbitrarily set by the user based on given information RT (room shape, room size, etc.). 
       FIGS. 7A to 7C  illustrate room response characteristics to which the new distance rendering method according to the first embodiment of the present invention is applied. If the location of a user or a sound image is changed, a room response is also changed. In a VR environment, a room response which differs according to change in location of the user (listener) may be controlled by the distance rendering method. As described above, the new distance rendering method according to the first embodiment of the present invention models a late reverberation part of the room response as illustrated in  FIG. 7B or 7C  by linking the generation period (parameter τ) of the late reverberation part with a change in relative distance, in order to perform distance rendering while maintaining a conventional spatial characteristic. 
     Referring to  FIGS. 7A to 7C , according to the first embodiment of the present invention, a gain variation value g (&gt;1) generated as the distance between a user and a sound image is shorter or longer is identically applied to the direct part and the early/late reverberation part. According to the first embodiment of the present invention, if the relative distance between the user and the sound image is short as illustrated in  FIG. 7B , the comb filter delay τ of the artificial reverberator of  FIG. 6  is set to be greater than a conventional value, so that the amount of late reverberation is reduced. According to the first embodiment of the present invention, if the relative distance between the user and the sound image is long as illustrated in  FIG. 7C , the comb filter delay τ is set to be smaller than a conventional value, so that the amount of late reverberation is further increased. 
     Referring to  FIG. 7B , although a maximum gain value of the modeled late reverberation part is greater than a gain of the conventionally modeled late reverberation part (e.g.,  FIG. 2B ), the amount of reverberation is decreased. On the other hand, referring to  FIG. 7C , although the maximum gain of the modeled late reverberation part is less than the gain of the conventionally modeled late reverberation part (e.g.,  FIG. 2C ), the amount of reverberation is increased. A D/R ratio used to apply distance rendering is a value measured by the ratio of energy. Accordingly, the modeling scheme of  FIG. 7B or 7C  leads to a result similar to the conventional method (e.g.,  FIG. 2B or 2C ) in terms of an energy ratio calculated by the D/R ratio. That is, even when the relative distance becomes short or long, a problem of excessively increasing a gain of a specific component (the direct part or late reverberation part) is solved while maintaining a similar D/R ratio. Consequently, when the first embodiment of the present invention is applied, distortion of a spatial characteristic due to the conventional excessive gain is overcome. 
       FIG. 8  is a flowchart illustrating a new distance rendering method applied to output of an audio signal according to the first embodiment of the present invention. 
     A bitstream is received (S 100 ). The bitstream is decoded and output as a decoded signal (S 101 ). It is determined through a distance tracking process (S 201 ) whether there is change in distance (S 202 ). 
     If there is change in distance, the next process (path “y”) is performed. An HRTF is extracted from an HRTF DB with reference to head tracking information (S 206 ). A new gain parameter g new  and a new period parameter τ new  are calculated by calculating the amount of change in distance (S 207 ). A new late reverberation part is modeled using the calculated period parameter τ new  (S 208 ). An early reflection part is modeled according to a conventional scheme (S 209 ). The calculated gain parameter g new  is applied to the HRTF, the modeled early reflection part, and the modeled late reverberation part (S 210 ). The HRTF, early reflection part, and late reverberation part are filtered together with the decoded signal in step S 101  (S 300 ). As a result of filtering, a rendered audio signal is output (S 400 ). 
     Meanwhile, if it is determined in step S 202  that there is no change in distance, the next process (path “n”) is performed. The HRTF is extracted from the HRTF DB with reference to the head tracking information (S 203 ). An early reverberation part is modeled (S 204 ). A late reverberation part is modeled (S 205 ). The HRTF, early reflection part, and late reverberation part are filtered together with the decoded signal in step S 101  (S 300 ). As a result of filtering, the rendered audio signal is output (S 400 ). 
     In step S 207 , a process of generating the new gain parameter g new  and the new period parameter τ new  is as follows. If a distance variation Δd is not 0, since it is determined that a user moves, a parameter τ associated with a late reverberation generation period is modified. The new parameter τ new  is calculated as indicated by Equation (2) 
     
       
         
           
             
               
                 
                   
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                   2 
                   ) 
                 
               
             
           
         
       
     
     In Equation (2), d denotes the distance (an original distance) between a user and a sound image. In consideration of an inverse square law indicating that the magnitude of a sound pressure is inversely proportional to the square of distance, the square of d is applied. Therefore, if the modified period τ new  is used as a new parameter of an artificial reverberator, since the value of τ new  becomes small as the distance between the user and the sound source becomes long (Δd&gt;0), a greater amount of reverberation is generated in a unit time. Meanwhile, since the value of τ new  is increased as the distance between the user and the sound source becomes short (Δd&lt;0), less reverberation is generated in a unit time. 
     The amount of variation in gain of a room response according to change in distance is calculated in step S 207  and the gain modification units  2055  and  2059  of  FIG. 5  and is indicated by Equation (3). 
     
       
         
           
             
               
                 
                   
                     g 
                     new 
                   
                   = 
                   
                     
                       
                         
                           d 
                           2 
                         
                         
                           d 
                           new 
                           2 
                         
                       
                       ⁢ 
                       g 
                     
                     = 
                     
                       
                         
                           d 
                           2 
                         
                         
                           
                             ( 
                             
                               d 
                               + 
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 d 
                               
                             
                             ) 
                           
                           2 
                         
                       
                       ⁢ 
                       g 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     Similar to Equation (2), in consideration of an inverse square law indicating that the magnitude of a sound pressure is inversely proportional to the square of distance, the square of d is applied. The modified gain parameter g new  is applied to the extracted HRTF responses h L  and h R  and the modeled early reflection part r early  in the gain modification unit  2055 . The modified gain parameter g new  is also applied to the late reverberation part r′ late  in the gain modification unit  2059 . That is, the modified gain parameter g new  is identically applied to all room response signals, thereby preventing gain from being excessively generated. For example, since the value of g new  is decreased as the distance between the user and the sound source becomes long (Δd&gt;0), a total gain value is decreased by the same ratio as illustrated in  FIG. 7C . Meanwhile, since the value of g new  is increased as the distance between the user and the sound source becomes short (Δd&lt;0), the total gain value is increased by the same ratio as illustrated in  FIG. 7B . 
       FIG. 9  illustrates a configuration of a renderer in an audio output apparatus according to a second embodiment of the present invention. Since the second embodiment is targeted at maintaining a binaural correlation relation even when the location of a user is changed in an arbitrary space, a binaural room impulse response (BRIR) will be described as an example of modeling. 
     Referring to  FIGS. 2A to 2C  and the D/R ratio of Equation (1), sense of distance may be changed such that if it is desired to change the distance between a user and an image sound to be short, a gain of a direct part of a room response is changed to be high and, if it is desired to change the distance between the user and the image sound to be long, the gain of the direct part of the room response is changed to be low. However, in an actual space environment, if the user is distant from the sound image, since an influence of reverberation increases, a binaural correlation decreases. Meanwhile, if the user is near to the sound image, since an influence of the reverberation decreases, the binaural correlation increases. That is, a conventional D/R ratio may adjust gain but may not adjust correlation of a response. To overcome the above problem, in accordance with the second embodiment of the present invention, modeling is performed in such a way that correlation of a late reverberation part of a measured BRIR is adjusted according to change in a relative distance. 
     In accordance with the second embodiment of the present invention, the audio renderer  200  includes a distance information provider  701 , a BRIR modifier  704 , a tracking information provider  702 , a BRIR selector  703 , and a filter  705 . 
     The distance information provider  701  provides information regarding the distance d between a user (listener) and a sound image. The tracking information provider  702  provides a localization point (θ, Φ) of the sound image to the BRIR selector  703 . The tracking information provider  702  may be a head tracker for tracking movement of the user or the user may directly provide related information through the user control interface ( 300  in  FIG. 3 ). For example, the sound localization point (θ, Φ) provided by the tracking information provider  702  is information about an azimuth angle θ and an altitude angle Φ. The BRIR selector  7032  extracts BRIR data B L  and B R  corresponding to the sound localization point (θ, Φ) provided by the tracking information provider  702  from a BRIR DB  7021 . In this case, HRTF data may be used instead of the BRIR data. 
     The BRIR modifier  704  receives information (e.g. the distance information, room type information, and BRIR data B L  and B R ) from the distance information provider  701  and the BRIR selector  703  and generates output signals B L ′ and B R ′ according to a new distance rendering method. The output signals B L ′ and B R ′ of the BRIR modifier  704  may be obtained by extracting the BRIR data B L  and B R  corresponding to the sound localization point (θ, Φ) from the BRIR DB  7021  and then modifying the extracted BRIR data B L  and B R  with reference to information about a distance so as to maintain a correlation characteristic caused by change in distance 
     The audio renderer  200  according to the second embodiment of the present invention adjusts a correction value using the new distance rendering method so as to maintain a binaural correlation characteristic. Hereinafter, a detailed configuration of the audio renderer  200  and the distance rendering method according to the second embodiment of the present invention will be described with reference to  FIGS. 10 to 12 . 
       FIG. 10  illustrates a detailed configuration of the audio renderer  200  to which the new distance rendering method is applied according to the second embodiment of the present invention. 
     Referring to  FIG. 10 , an entire process of performing distance rendering by adjusting correlation of a late reverberation part of a room response is illustrated. If direction information of a sound image in an arbitrary space is provided by a head tracker or a user through the tracking information provider  702 , the BRIR selector  703  extracts BRIR data b L  and b R  corresponding to the provided tracking information (θ, Φ) from the BRIR DB  7021 . However, if there is no BRIR DB, a BRIR may be modeled. 
     The distance information provider  701  provides information about the distance d between a user and a sound image and a distance variation Δd. A distance determiner  7041  determines whether the location of the user is changed, using the information about the distance d and the distance variation Δd provided by the distance information provider  701 . That is, if it is determined that a relative location of the user has been changed, the distance determiner  7041  controls the switching means  7042  to select an operation according to a path “y”. If it is determined that the relative location of the user has not been changed, the distance determiner  7041  controls the switching means  7042  to select an operation according to a path “n”. 
     First, the operation according to the path “n” through the switching means  7042  will now be described. That is, the operation is performed in the case in which the distance variation Δd provided by the distance information provider  7014  is 0, i.e., when the relative location of the user is not changed. In this case, a switch flag of the switching means  7042  is selected as the path “n”. The filter  705  performs filtering on the BRIR data b L  and b R  provided by the BRIR selector  703  together with an input audio signal s and outputs rendered audio signals Output L  and Output R . 
     Next, the operation according to the path “y” through the switching means  7042  will now be described. That is, the operation is performed in the case in which the distance variation Δd provided by the distance information provider  701  is not 0 (i.e., Δd≠0), i.e., when the relative location of the user is changed. In this case, the switch flag of the switching means  7042  is selected as the path “y”. 
     If the user moves (i.e., Δd≠0) in an arbitrary space, a late reverberation extraction unit  7043  extracts late reverberation parts b L,late  and b R,late  of a BRIR. Next, two processes of using interaural cross correlation (IACC) information are performed. First, an IACC at a changed location, i.e., IACC Late   _   Δd , is estimated. Second, a response of the late reverberation part is generated so as to satisfy IACC Late   _   Δd . 
     In the first process, an IACC Late  calculation unit  7044  calculates an IACC of the extracted responses b L,late  and b R,late , i.e., IACC Late . An IACC Late   _   Δd  calculation unit  7045  estimates an IACC at a changed location, i.e., IACC Late   _   Δd , with reference to the existing information about the distance d and the distance variation Δd. 
     In the second process, an adder  7043   a  adds the two extracted responses b L,late  and b R,late  to output one response b LR,late . Next, a transformer  7046  generates new responses b L ′ ,late  and b R ′ ,late  so that the response signals b L ′ ,late  and b R ′ ,late  have the same correlation with IACC Late   _   Δd  estimated in the first process. 
     Next, a BRIR modification unit  7047  outputs new BRIR responses b L ′ and b R ′ by adjusting a gain of the generated responses b L ′ ,late  and b R ′ ,late  in proportion to a distance variation of a user. Lastly, the filter  705  performs filtering on the input signal s and the BRIR signals b L ′ and b R ′ and outputs the rendered audio output signals Output L  and Output R . 
       FIG. 12  is a flowchart illustrating a new distance rendering method applied to output of an audio signal according to the second embodiment of the present invention. A bitstream is received (S 500 ). The bitstream is decoded and output as a decoded signal (S 501 ). It is determined through a distance tracking process (S 601 ) whether there is change in distance (S 602 ). If there is change in distance, the next process (path “y”) is performed. A BRIR is extracted (or modeled) from the BRIR DB with reference to head tracking information (S 604 ). A late reverberation part of the BRIR is extracted (S 605 ). An IACC of the extracted late reverberation part, i.e., IACC Late , is calculated (S 606 ). An IACC at a changed location, i.e., IACC Late   _   Δd , is estimated with reference to information about a distance variation (S 607 ). A late reverberation part of the (substantially equal) BRIR corresponding to IACC Late   _   Δd  is modeled (S 608 ). A late reverberation part of an existing BRIR is replaced with the newly modeled late reverberation part (S 609 ). A gain of the BRIR is modified with reference to the information about the distance variation (S 610 ). The modified BRIR is filtered in the decoded signal output in step S 501  (S 700 ). As a result of filtering, a rendered audio signal is output (S 800 ). 
     Meanwhile, if it is determined that there is no change in distance in step S 602 , the next process (path “n”) is performed. A BRIR is extracted (modeled) from the BRIR DB with reference to the head tracking information (S 603 ). Next, the extracted BRIR is filtered together with the decoded signal output in step S 501  (S 700 ). As a result of filtering, the rendered audio signal is output (S 800 ). 
     A process from steps S 605  to S 610  in  FIG. 12  will now be described in more detail with reference to  FIG. 10 . 
     If a user moves (Δd≠0), the late reverberation extraction unit  7043  extracts only a late reverberation part of a BRIR. There are many methods of extracting the late reverberation part of the BRIR. Generally, since components after about 50 ms to 80 ms of a response are regarded as the late reverberation part, in the present invention, only response components after about 80 ms are extracted as indicated by Equation (4). 
     
       
         
           
             
               
                 
                   
                     
                       b 
                       
                         ch 
                         , 
                         late 
                       
                     
                     ⁡ 
                     
                       ( 
                       n 
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               0 
                               , 
                             
                           
                           
                             
                               
                                 if 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 n 
                               
                               ≤ 
                               
                                 80 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 ms 
                               
                             
                           
                         
                         
                           
                             
                               
                                 
                                   b 
                                   ch 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   n 
                                   ) 
                                 
                               
                               , 
                             
                           
                           
                             
                               
                                 if 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 n 
                               
                               &gt; 
                               
                                 80 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 ms 
                               
                             
                           
                         
                       
                       , 
                       
                         ch 
                         = 
                         L 
                       
                       , 
                       R 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Next, IACC Late  is calculated using the extracted responses b L,late  and b R,late . IACC represents a correlation between two sound pressures measured at both ears and is calculated as indicated by Equation (5). 
     
       
         
           
             
               
                 
                   
                     
                       IACF 
                       ⁡ 
                       
                         ( 
                         τ 
                         ) 
                       
                     
                     = 
                     
                       
                         
                           ∫ 
                           
                             t 
                             1 
                           
                           
                             t 
                             2 
                           
                         
                         ⁢ 
                         
                           
                             
                               p 
                               L 
                             
                             ⁡ 
                             
                               ( 
                               t 
                               ) 
                             
                           
                           ⁢ 
                           
                             
                               p 
                               R 
                             
                             ⁡ 
                             
                               ( 
                               
                                 t 
                                 + 
                                 τ 
                               
                               ) 
                             
                           
                           ⁢ 
                           d 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           τ 
                         
                       
                       
                         
                           ( 
                           
                             
                               ∫ 
                               
                                 t 
                                 1 
                               
                               
                                 t 
                                 2 
                               
                             
                             ⁢ 
                             
                               
                                 
                                   p 
                                   L 
                                   2 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   t 
                                   ) 
                                 
                               
                               ⁢ 
                               dt 
                               ⁢ 
                               
                                 
                                   ∫ 
                                   
                                     t 
                                     1 
                                   
                                   
                                     t 
                                     2 
                                   
                                 
                                 ⁢ 
                                 
                                   
                                     
                                       p 
                                       R 
                                       2 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       t 
                                       ) 
                                     
                                   
                                   ⁢ 
                                   dt 
                                 
                               
                             
                           
                           ) 
                         
                         
                           1 
                           / 
                           2 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       IACC 
                       = 
                       
                         
                            
                           
                             IACF 
                             ⁡ 
                             
                               ( 
                               τ 
                               ) 
                             
                           
                            
                         
                         max 
                       
                     
                     , 
                     
                       
                         for 
                         - 
                         1 
                       
                       &lt; 
                       τ 
                       &lt; 
                       
                         
                           + 
                           1 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         ms 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     In Equation (5), p L  and p R  denote sound pressures measured at the left ear and the right ear, respectively. In the second embodiment of the present, p L  and p R  are regarded as a BRIR (b L , b R ). As two response characteristics measured at both ears become similar, the IACC approximates to 1 and, if the two response characteristics have no relation, the IACC approximates to 0. In other words, the IACC differs according to the distance between a user and a sound image. If the distance between the user and the sound image is short, the IACC is calculated as a value approximating to 1 and, if the distance between the user and the sound image is long, the IACC is calculated as a value approximating to 0. This is because, as the relative distance becomes longer, a spatial reverberation part rather than a direct part of the sound image is greatly influenced. If a gain of a direct part of a BRIR is changed to be small and therefore a D/R ratio is reduced, the user may feel as though the sound image is becoming distant. However, since IACC Late  is not changed, a sound image characteristic recognized at both ears is not changed. Therefore, a response should be changed such that the sound image characteristic may differ according to change in location of the user. The second embodiment of the present invention performs the following process in order to change a response characteristic according to change in location of the user. 
     IACC Late   _   Δd  is estimated from IACC Late  in proportion to a moved distance and is indicated by Equation (6). 
     
       
         
           
             
               
                 
                   
                     IACC 
                     
                       Late 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Δ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       d 
                     
                   
                   = 
                   
                     max 
                     ⁡ 
                     
                       ( 
                       
                         
                           
                             IACC 
                             Late 
                           
                           + 
                           
                             
                               
                                 ( 
                                 
                                   
                                     
                                       IACC 
                                       Late 
                                     
                                     - 
                                     1 
                                   
                                   
                                     d 
                                     - 
                                     0.15 
                                   
                                 
                                 ) 
                               
                               · 
                               Δ 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             d 
                           
                         
                         , 
                         0 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     Referring to  FIG. 11 , a distance from the middle of the head of a person to the front (front of the nose) is about 0.15 m and it is assumed that IACC Late  is 1 when a sound image is located at the front of the person. Therefore, if information about the location of the front of the person and IACC Late  measured at a distance d are used, IACC Late   _   Δd  at a location changed by Δd may be estimated. To generate a response of a late reverberation part satisfying IACC Late   _   Δd , the two extracted BRIR responses b L,late  and b R,late  are added to output the response b LR.late . 
     Next, in the transformer  7046 , an FFT unit  7046   a  transforms the response b LR.late  into a frequency-axis signal to be divided into a magnitude component |b LRlate | and a phase component ∠b LR.late . A random number generator  7046   b  generates a random number ∠b rand  in the range of [−π, π]. However, since the random number ∠b rand  is uncorrelated with ∠b LR.late , ∠b LR.late  is multiplied with IACC Late   _   Δd  and the multiplied result is added to ∠b rand  to generate ∠b′ rand  (i.e., ∠b′ rand =(IACC Late   _   Δd *∠b LR.late )+∠b rand ) in an adder  7046   c.  As a result, a correlation of ∠b LR.late  and ∠b′ rand  is identical to IACC Late   _   Δd . Therefore, an IFFT unit  7046   d  synthesizes |b LR.late | and ∠b LR.late  and transforms the synthesized result into a time-axis signal b L ′ ,late  (=b LR,late ). At the same time, an IFFT unit  7046   e  synthesizes |b LR.late | and ∠b′ rand  and transforms the synthesized result into a time-axis signal b R ′ ,late . Then a correlation of the two signals b L ′ ,late  and b R ′ ,late  is identical to IACC Late   _   Δd . 
     The two new response signals b L ′ ,late  and b R ′ ,late  output by the transformer  7046  are input to the BRIR modification unit  7047  and are replaced with a late reverberation part of a BRIR as indicated by Equation (7). 
     
       
         
           
             
               
                 
                   
                     
                       b 
                       ch 
                       ′ 
                     
                     ⁡ 
                     
                       ( 
                       n 
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               
                                 
                                   b 
                                   ch 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   n 
                                   ) 
                                 
                               
                               , 
                             
                           
                           
                             
                               
                                 if 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 n 
                               
                               ≤ 
                               
                                 80 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 ms 
                               
                             
                           
                         
                         
                           
                             
                               
                                 
                                   b 
                                   
                                     ch 
                                     , 
                                     late 
                                   
                                   ′ 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   n 
                                   ) 
                                 
                               
                               , 
                             
                           
                           
                             
                               
                                 if 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 n 
                               
                               &gt; 
                               
                                 80 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 ms 
                               
                             
                           
                         
                       
                       , 
                       
                         ch 
                         = 
                         L 
                       
                       , 
                       R 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     Additionally, in order to reflect characteristics of a D/R ratio in the modified BRIR, a gain of a direct part of the BRIR in proportion to Δd is changed as indicated by Equation (8). 
     
       
         
           
             
               
                 
                   
                     
                       g 
                       
                         ch 
                         , 
                         d 
                       
                       ′ 
                     
                     = 
                     
                       
                         
                           
                             d 
                             2 
                           
                           
                             
                               ( 
                               
                                 d 
                                 + 
                                 
                                   Δ 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   d 
                                 
                               
                               ) 
                             
                             2 
                           
                         
                         ⁢ 
                         
                           g 
                           
                             ch 
                             , 
                             d 
                           
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         where 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           g 
                           
                             ch 
                             , 
                             d 
                           
                         
                       
                       = 
                       
                         
                           b 
                           ch 
                         
                         ⁡ 
                         
                           ( 
                           
                             n 
                             d 
                           
                           ) 
                         
                       
                     
                   
                   , 
                   
                     
                       n 
                       d 
                     
                     = 
                     
                       
                         
                           arg 
                           ⁢ 
                           
                             
                                 
                             
                             ⁢ 
                             
                                 
                             
                           
                           ⁢ 
                           max 
                         
                         n 
                       
                       ⁢ 
                       
                         ( 
                         
                           
                             b 
                             ch 
                           
                           ⁡ 
                           
                             ( 
                             n 
                             ) 
                           
                         
                         ) 
                       
                     
                   
                   , 
                   
                     ch 
                     = 
                     L 
                   
                   , 
                   R 
                   , 
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       b 
                       ch 
                       ′ 
                     
                     ⁡ 
                     
                       ( 
                       n 
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               
                                 g 
                                 
                                   ch 
                                   , 
                                   d 
                                 
                                 ′ 
                               
                               , 
                             
                           
                           
                             
                               
                                 if 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 n 
                               
                               = 
                               
                                 n 
                                 d 
                               
                             
                           
                         
                         
                           
                             
                               
                                 
                                   b 
                                   ch 
                                   ′ 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   n 
                                   ) 
                                 
                               
                               , 
                             
                           
                           
                             elsewhere 
                           
                         
                       
                       , 
                       
                         ch 
                         = 
                         L 
                       
                       , 
                       R 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     In Equation (8), d denotes the distance between a user and a sound image and the square of d and the square of (d+Δd) are applied in consideration of an inverse square law indicating that the magnitude of sound pressure is inversely proportional to the square of the distance. g ch,d  denotes a gain value of a direct part and may be obtained by searching for a maximum value of b ch (n) of the BRIR and n d  denotes a timing at which the BRIR has a maximum value. Accordingly, finally modified responses of the BRIR modification unit  7047 , i.e., output responses b L ′ and b R ′, may be obtained by replacing the components of a late reverberation part with reference to Equations (7), (8), and (9) and modifying a gain of the direct part. 
     A distance rendering method and apparatus in accordance with an embodiment of the present invention have the following effects. 
     First, a room response characteristic can be maintained in an arbitrary space and, therefore, more realistic audio can be provided. 
     Second, since a room response characteristic can be maintained even in a VR space, a natural and realistic effect can be provided even in any virtual space by configuring a VR space characteristic. 
     Third, since a binaural correlation is also adjusted, more realistic audio can be provided during configuration of a binaural room impulse response (BRIR). 
     The present invention may be implemented as computer-readable code that can be written on a computer-readable medium in which a program is recorded. The computer-readable medium may be any type of recording device in which data that can be read by a computer system is stored. Examples of the computer-readable medium include a hard disk drive (HDD), a solid state drive (SSD), a silicon disk drive (SDD), a read only memory (ROM), a random access memory (RAM), a compact disc (CD)-ROM, a magnetic tape, a floppy disk, an optical data storage, and a carrier wave (e.g., data transmission over the Internet). The computer may include an audio decoder and a renderer. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, the present invention is intended to cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.