Patent Publication Number: US-2021176582-A1

Title: Information processing apparatus and method, and program

Description:
TECHNICAL FIELD 
     The present technology relates to an information processing apparatus, an information processing method, and a program and particularly to an information processing apparatus, an information processing method, and a program capable of reducing a processing load on a distribution side while reducing a transfer volume of information. 
     BACKGROUND ART 
     MPEG (Moving Picture Experts Group)-H encoding standards, which are standardized as conventional 3D Audio for fixed viewpoint, are established on the basis of an idea that an audio object moves within a space around an origin corresponding to a position of a listener (for example, see NPL 1). 
     Accordingly, at a fixed viewpoint, position information associated with respective audio objects as viewed from the listener located at the origin is described using polar coordinates based on angles in a horizontal direction, angles in a height direction, and distances from the listener to the respective audio objects. 
     By using the MPEG-H encoding standards described above, audio images of the audio objects can be localized at respective positions of the audio objects within the space in fixed viewpoint content. In this manner, high-presence audio reproduction is achievable. 
     CITATION LIST 
     Non Patent Literature 
     [NPL 1] 
     ISO/IEC 23008-3 Information technology—High efficiency coding and media delivery in heterogeneous environments—Part 3: 3D audio 
     SUMMARY 
     Technical Problems 
     Meanwhile, free viewpoint content is also known as content where a listener position is allowed to be located at any position within a space. At the free viewpoint, not only audio objects but also a listener can move within the space. In other words, the free viewpoint is different from the fixed viewpoint in that the listener is movable. 
     At the free viewpoint defined as above, audio reproduction is achievable similarly to the case of the fixed viewpoint by using a renderer having a polar coordinate system standardized under MPEG-H as long as position information associated with polar coordinates indicating positions of the audio objects as viewed from the listener is available. In other words, free viewpoint audio reproduction is achievable by a rendering process similar to that of the fixed viewpoint. 
     In this case, for example, audio data of the respective audio objects and position information indicating the positions of the audio objects are provided from a server to the reproduction side. Thereafter, rendering is performed on the reproduction side to achieve audio reproduction which localizes audio images at the positions of the audio objects within the space. 
     However, for achieving free viewpoint audio reproduction by using a renderer under MPEG-H, update of the positions of the audio objects as viewed from the listener and transfer of information associated with the positions of the audio objects are required every time the positions of the audio objects and the listener are changed. Accordingly, a transfer volume of information and a processing load on the content distribution side such as a server may increase. Moreover, in a case where the number of listeners connecting to the server increases, the processing load becomes heavier by a multiple of the increased number of the listeners. When the number of listeners becomes several thousands or several tens of thousands, the load may become excessive. 
     The present technology has been developed in consideration the aforementioned circumstances and achieves reduction of a processing load on a distribution side along with reduction of a transfer volume of information. 
     Solution to Problems 
     An information processing apparatus according to a first aspect of the present technology includes an acquisition unit that acquires low accuracy position information having first accuracy and indicating a position of an object within a space where a user is located and acquires additional information for obtaining position information that has second accuracy higher than the first accuracy, indicates the position of the object within the space, and corresponds to a position of the user and a position information calculation unit that obtains the position information on the basis of the low accuracy position information and the additional information. 
     An information processing method or a program according to the first aspect of the present technology includes steps of acquiring low accuracy position information that has first accuracy and indicates a position of an object within a space where a user is located, acquiring additional information for obtaining position information that has second accuracy higher than the first accuracy, indicates the position of the object within the space, and corresponds to a position of the user, and obtaining the position information on the basis of the low accuracy position information and the additional information. 
     According to the first aspect of the present technology, the low accuracy position information that has the first accuracy and indicates the position of the object within the space where the user is located is acquired. The additional information for obtaining position information that has the second accuracy higher than the first accuracy, indicates the position of the object within the space, and corresponds to the position of the user is acquired. The position information is obtained on the basis of the low accuracy position information and the additional information. 
     An information processing apparatus according to a second aspect of the present technology includes a communication unit that transmits low accuracy position information having first accuracy and indicating a position of an object within a space where a user is located and transmits additional information for obtaining position information having second accuracy higher than the first accuracy, indicating the position of the object within the space, and corresponding to a position of the user, in response to a request from a transmission destination of the low accuracy position information. 
     An information processing method or a program according to the second aspect of the present technology includes steps of transmitting low accuracy position information that has first accuracy and indicates a position of an object within a space where a user is located and transmitting additional information for obtaining position information that has second accuracy higher than the first accuracy, indicates the position of the object within the space, and corresponds to a position of the user, in response to a request from a transmission destination of the low accuracy position information. 
     According to the second aspect of the present technology, the low accuracy position information that has the first accuracy and indicates the position of the object within the space where the user is located is transmitted. The additional information for obtaining the position information that has the second accuracy higher than the first accuracy, indicates the position of the object within the space, and corresponds to the position of the user is transmitted in response to the request from the transmission destination of the low accuracy position information. 
     Advantageous Effects of Invention 
     According to the first and second aspects of the present technology, reduction of a processing load is achievable along with reduction of a transfer volume of information. 
     Note that advantageous effects to be produced are not limited to the advantageous effects described here and may be any advantageous effects described in the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram depicting a configuration example of a content reproduction system. 
         FIG. 2  is a diagram explaining a processing sequence of the content reproduction system. 
         FIG. 3  is a diagram depicting a configuration example of the content reproduction system. 
         FIG. 4  is a diagram depicting a configuration example of a server. 
         FIG. 5  is a diagram depicting a configuration example of a client. 
         FIG. 6  is a diagram explaining a perceptive limit angle. 
         FIG. 7  is a flowchart explaining an encoding process and a file storing process. 
         FIG. 8  is a diagram presenting a syntax example of a highest accuracy position encoded data file. 
         FIG. 9  is a flowchart explaining a position information acquiring process and a position information transmitting process. 
         FIG. 10  is a diagram presenting a syntax example of header information. 
         FIG. 11  is a diagram presenting a syntax example of a bit stream containing low accuracy quantized position information. 
         FIG. 12  is a diagram explaining an encoding example of normalized position information. 
         FIG. 13  is a flowchart explaining an additional bit information acquiring process and an additional bit information transmitting process. 
         FIG. 14  is a diagram presenting a syntax example of a transmission request of additional bit information. 
         FIG. 15  is a diagram presenting a syntax example of difference data. 
         FIG. 16  is a diagram depicting a configuration example of a computer. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     An embodiment to which the present technology is applied will hereinafter be described with reference to the drawings. 
     First Embodiment 
     &lt;Configuration Example of Content Reproduction System&gt; 
     The present technology switches levels of quantized accuracy of position information indicating a position of an object according to a distance between a listener and the object, to reduce a processing load on a content distribution side such as a server while reducing a transfer volume of information. 
     Note that described below is an example of a case where rendering of audio data of an audio object is performed on the content reproduction side on the basis of information indicating a position of the audio object as viewed from a listener, more specifically, a case where free viewpoint audio reproduction is implemented by using a renderer under MPEG-H. However, the present technology is also applicable to a case where a content video containing an object as an object of imaging is reproduced on the basis of information indicating a position of the object as viewed from a listener, for example. 
     Note that, hereinafter, an audio object will simply be referred to as an object. 
     For example, in a case where free viewpoint audio reproduction is performed by using a renderer under MPEG-H, audio reproduction may be achieved by using a content reproduction system depicted in  FIG. 1 . 
     The content reproduction system depicted in  FIG. 1  includes a listener position acquisition apparatus  11 , a polar coordinate position information encoder  12 , a server  13 , a client  14 , and an MPEG-H renderer  15 . 
     According to this content reproduction system, a user U 11  on the server side, such as a content creator, inputs object position information indicating positions of respective objects within a space to the polar coordinate position information encoder  12  for each of the objects in the space. Note that the object position information may indicate either absolute coordinates or polar coordinates. 
     In addition, a user who views and listens to reproduced content, i.e., a listener U 12  listening to sound of the content, is located on the client  14  side. The listener position acquisition apparatus  11  acquires listener position information indicating a position of the listener U 12  within the space. 
     For example, the listener position acquisition apparatus  11  includes a measuring device which measures the position of the listener U 12  within the space, such as a GPS (Global Positioning System) and a gyro sensor, an input apparatus which acquires virtual position information associated with the listener U 12  within a virtual space, or the like, and outputs listener position information indicating the position of the listener U 12 . 
     The listener position information here is absolute coordinate information indicating an absolute position of the listener U 12  within the space and expressed by coordinates of a three-dimensional orthogonal coordinate system, i.e., an xyz coordinate system (x coordinate, y coordinate, and z coordinate). Information expressed by coordinates of the xyz coordinate system and indicating an absolute position within the space is hereinafter also referred to as absolute coordinates. 
     The listener position information output from the listener position acquisition apparatus  11  is received by the polar coordinate position information encoder  12  via the client  14  and the server  13 . 
     The polar coordinate position information encoder  12  generates polar coordinates indicating the position of the object as viewed from the listener U 12  within the space as polar coordinate position information, on the basis of the listener position information received from the listener position acquisition apparatus  11  and the object position information input from the user U 11 . 
     Thereafter, the polar coordinate position information encoder  12  encodes the polar coordinate position information obtained for each object and transmits the encoded polar coordinate position information to the client  14  via the server  13 . 
     The client  14  receives the polar coordinate position information from the polar coordinate position information encoder  12 , decodes the polar coordinate position information by using a polar coordinate position information decoder  21  provided on the client  14 , and supplies the polar coordinate position information thus obtained to the MPEG-H renderer  15 . 
     The MPEG-H renderer  15  receives supply of the polar coordinate position information for each object from the client  14  and also receives supply of audio data of each object from the server  13 . The MPEG-H renderer  15  is a renderer which has a polar coordinate system standardized under MPEG-H. 
     The MPEG-H renderer  15  performs rendering on the basis of the audio data and the polar coordinate position information associated with the respective objects, generates reproduction audio data where audio images of the objects are localized at respective positions within the space, and outputs the generated reproduction audio data to a reproduction system such as a speaker. 
     In a case where N objects exist within the space, for example, a processing sequence presented in  FIG. 2  is performed by the content reproduction system. 
     According to the example presented in  FIG. 2 , the client  14  first requests the server  13  to issue a notification regarding the number of objects present within the space, i.e., an object number, as indicated by an arrow A 11 . 
     In this case, the server  13  issues a notification regarding the object number to the client  14  in response to the request from the client  14  as indicated by an arrow A 12 . 
     Moreover, when the client  14  receives the listener position information from the listener position acquisition apparatus  11 , the client  14  transmits the acquired listener position information to the polar coordinate position information encoder  12  via the server  13  as indicated by an arrow A 13 . 
     When the polar coordinate position information encoder  12  receives the listener position information, the polar coordinate position information encoder  12  calculates a position of a 0th object as viewed from the listener U 12 , on the basis of the listener position information and object position information associated with the 0th object, and encodes polar coordinate position information indicating a calculation result thus obtained. In other words, the polar coordinate position information is encoded into encoded data in a transferable format. 
     Thereafter, the polar coordinate position information encoder  12  transmits the encoded polar coordinate position information obtained for the 0th object, i.e., the encoded data of the polar coordinate position information, to the client  14  via the server  13  as indicated by an arrow A 14 . 
     On the client  14  side, the encoded data of the received polar coordinate position information associated with the 0th object is decoded by the polar coordinate position information decoder  21 . 
     Similarly, the polar coordinate position information encoder  12  generates encoded data of polar coordinate position information obtained for a 1st object and transmits the encoded data of the polar coordinate position information associated with the 1st object to the client  14  via the server  13  as indicted by an arrow A 15 . In addition, on the client  14  side, the polar coordinate position information decoder  21  decodes the encoded data of the received polar coordinate position information associated with the 1st object. 
     Thereafter, generation and transmission of encoded data of polar coordinate position information, and decoding of encoded data of polar coordinate position information are sequentially performed for objects up to an (N−1)th object in following processing. 
     Polar coordinate position information is obtained for each of the N objects from the 0th object to the (N−1)th object by the above processing. Thereafter, rendering is performed by the MPEG-H renderer  15  on the basis of the polar coordinate position information and the object data associated with the respective objects. 
     By reproducing sound on the basis of reproduction audio data obtained by the rendering process, audio images of the objects can be localized at correct positions as viewed from the listener U 12 . 
     For reproducing free viewpoint content, for example, polar coordinate position information expressed by polar coordinates and indicating the positions of the objects as viewed from the listener U 12  is needed as input to the MPEG-H renderer  15 , to perform rendering using the MPEG-H renderer  15 . 
     According to the content reproduction system depicted in  FIG. 1 , the MPEG-H renderer  15  for fixed viewpoint is also available for free viewpoint without any change. Moreover, generation and transmission of polar coordinate position information in real time by the polar coordinate position information encoder  12  produce such an advantageous effect that polar coordinate position information need not be retained by the server  13 . 
     However, at the free viewpoint, not only the objects but also the listener U 12  moves within the space. Accordingly, update and transfer of polar coordinate position information are required every time either any of the objects or the listener moves. 
     Particularly in the content reproduction system depicted in  FIG. 1 , update (encoding) of polar coordinate position information associated with all objects is performed in real time for all of the listeners U 12  in a case where plural listeners U 12  are present, i.e., in a case where plural clients  14  are connected to the server  13 . In this case, a processing load of the polar coordinate position information encoder  12  on the content distribution side increases, and therefore, it becomes difficult to supply necessary polar coordinate position information associated with the objects to the client  14  by reproduction time, in some cases. 
     To solve this problem, it is possible to supply object position information indicating the positions of the objects expressed by absolute coordinates within the space to the client  14  from the server  13  and calculate polar coordinate position information on the client  14  side. 
     However, absolute coordinates are not originally dependent on the position of the listener U 12 . In this case, highly accurate expression is required, and therefore, transmission of the object position information to the client  14  is not desirable in view of a transfer volume. In other words, in the case of transfer of the object position information indicating absolute coordinates, the transfer volume of information (object position information) becomes larger than that volume in a case of transfer of polar coordinate position information indicating polar coordinates. 
     According to the present technology, therefore, information indicating low accuracy object positions and having a small information volume is temporarily transmitted to the client side, and then, information indicating a difference between the low accuracy information and high accuracy information is additionally transmitted as necessary to obtain sufficiently accurate information indicating the object positions. In this manner, not only reduction of a transfer volume of information but also reduction of a processing load on the content distribution side such as a polar coordinate position information encoder and a server is achievable. 
     For example, the content reproduction system to which the present technology described above is applied is configured as depicted in  FIG. 3 . Note that parts in  FIG. 3  identical to corresponding parts in  FIG. 1  are given identical reference signs. Description of these parts is not repeated where appropriate. 
     The content reproduction system depicted in  FIG. 3  includes an absolute coordinate position information encoder  51 , a server  52 , a listener position acquisition apparatus  53 , a client  54 , and an MPEG-H renderer  55 . According to this content reproduction system, the client  54  calculates polar coordinate position information expressed by polar coordinates and indicating positions of objects as viewed from the listener U 12 . 
     More specifically, on the content distribution side, the user U 11  inputs normalized position information indicating the positions of the respective objects within the space and others to the absolute coordinate position information encoder  51 . 
     This normalized position information is normalized absolute coordinate information expressed by coordinates of a three-dimensional orthogonal coordinate system, i.e., an xyz coordinate system, and indicating absolute positions of the objects within the space. 
     The absolute coordinate position information encoder  51  encodes normalized position information and the like input from the user U 11  and transmits a highest accuracy position encoded data file thus obtained to the server  52 . Further, the server  52  is an information processing apparatus including a recording unit  61 . The highest accuracy position encoded data file received from the absolute coordinate position information encoder  51  is recorded in the recording unit  61 . 
     The highest accuracy position encoded data file here contains highest accuracy quantized position information obtained by quantizing normalized position information with highest accuracy for each of the objects, i.e., obtained by quantizing the normalized position information with a small quantized step width. 
     Quantized accuracy for obtaining highest accuracy quantized position information from normalized position information is hereinafter also referred to as highest accuracy, while a position indicated by the highest accuracy quantized position information is also referred to as a highest accuracy absolute position. 
     As described in detail below, quantized position information obtained by quantizing normalized position information with quantized accuracy lower than highest accuracy can be acquired by extracting a part of the highest accuracy quantized position information. 
     The quantized position information obtained by quantizing normalized position information with quantized accuracy lower than highest accuracy is hereinafter also referred to as low accuracy quantized position information. Low accuracy quantized position information with lowest quantized accuracy in the low accuracy quantized position information is also particularly referred to as lowest accuracy quantized position information. Moreover, a position indicated by the low accuracy quantized position information is hereinafter also referred to as a low accuracy absolute position, while a position indicated by the lowest accuracy quantized position information is also referred to as a lowest accuracy absolute position. 
     Furthermore, an absolute position of an object in a case of no necessity of particular distinction between a highest accuracy absolute position and a low accuracy absolute position is hereinafter also simply referred to as an absolute position of an object. Quantized position information associated with an object in a case of no particular necessity of distinction between highest accuracy quantized position information and low accuracy quantized position information is also simply referred to as quantized position information associated with an object. 
     The low accuracy quantized position information is absolute coordinate information indicating a position of an object with lower accuracy than that of highest accuracy quantized position information. The low accuracy quantized position information has a smaller volume of information, i.e., a smaller bit number, than that of the highest accuracy quantized position information, and thus achieves reduction of a transfer volume of information. 
     In addition, on the client  54  side, listener position information indicating the position of the listener U 12  is acquired by the listener position acquisition apparatus  53  corresponding to the listener position acquisition apparatus  11  depicted in  FIG. 1  and is supplied to the client  54 . For example, the listener position acquisition apparatus  53  includes a measuring device such as a GPS and a gyro sensor, an input apparatus which acquires virtual position information associated with the listener U 12  within a virtual space, and the like. 
     The client  54  is an information processing apparatus which includes an absolute coordinate position information decoder  71  and a coordinate transformation unit  72 , and acquires lowest accuracy quantized position information from the server  52 . Note that described below will be an example where the client  54  acquires lowest accuracy quantized position information from the server  52 . However, low accuracy quantized position information with any level of quantized accuracy other than the lowest accuracy may be acquired as long as the quantized accuracy is lower than the highest accuracy. 
     The absolute coordinate position information decoder  71  decodes the lowest accuracy quantized position information acquired from the server  52  and determines whether a position of an object indicated by the lowest accuracy quantized position information has sufficient accuracy, on the basis of the listener position information. 
     At this time, the client  54  acquires additional bit information for obtaining quantized position information with sufficient accuracy from the server  52  for the object determined as not having sufficient accuracy. The additional bit information is difference information between quantized position information with sufficient accuracy and the lowest accuracy quantized position information. Quantized position information with sufficient accuracy can be obtained by adding the additional bit information to the lowest accuracy quantized position information. Note that the quantized position information with sufficient accuracy coincides with the highest accuracy quantized position information in some cases. 
     When quantized position information with sufficient accuracy is obtained for each of the objects, the coordinate transformation unit  72  transforms the respective pieces of the quantized position information into polar coordinates indicating relative positions of the respective objects within the space as viewed from the listener U 12  and designates the polar coordinates as polar coordinate position information. 
     The coordinate transformation unit  72  supplies the polar coordinate position information associated with the respective objects to the MPEG-H renderer  55 . The MPEG-H renderer  55  performs rendering on the basis of the supplied polar coordinate position information and audio data that is associated with the respective objects and is acquired from the server  52 . 
     Thereafter, the MPEG-H renderer  55  outputs, to the reproduction system such as a speaker, reproduction audio data obtained by rendering, as data where audio images of the objects are localized at respective positions within the space, to allow the reproduction system to reproduce sound. Note that the MPEG-H renderer  55  is a renderer which has a polar coordinate system standardized by MPEG-H, similarly to the MPEG-H renderer  15  of  FIG. 1 . 
     According to the content reproduction system configured as described above, information indicating positions of objects and transmitted and received to and from the server  52  and the client  54  is lowest accuracy quantized position information indicating absolute coordinates. Accordingly, offered are such advantageous effects that the position of the listener U 12  within the space need not be considered and that lowest accuracy quantized position information associated with only a moving object is required to be encoded and transferred to the client  54 . 
     &lt;Configuration Example of Server&gt; 
     Described next will be a more detailed configuration example of the server  52  and the client  54  depicted in  FIG. 3 . The configuration example of the server  52  will first be described. 
     For example, the server  52  is configured as depicted in  FIG. 4 . Note that parts in  FIG. 4  identical to corresponding parts in  FIG. 3  are given identical reference signs. Description of these parts is not repeated where appropriate. 
     The server  52  depicted in  FIG. 4  includes a communication unit  101 , the control unit  102 , and the recording unit  61 . 
     The communication unit  101  transmits various types of information supplied from the control unit  102  to the client  54  and also receives various types of information transmitted from the absolute coordinate position information encoder  51  and the client  54 , to supply the received information to the control unit  102 . 
     The control unit  102  controls overall operations of the server  52 . The control unit  102  includes a communication control unit  111  and a transmission information generation unit  112 . 
     The communication control unit  111  controls the communication unit  101  to control communication performed by the communication unit  101  with the absolute coordinate position information encoder  51  and the client  54 . The transmission information generation unit  112  generates various types of information to be transmitted to the client  54 , by using information recorded in the recording unit  61 , such as the highest accuracy position encoded data file, as necessary. 
     &lt;Configuration Example of Client&gt; 
     In addition, for example, the client  54  is configured as depicted in  FIG. 5 . Note that parts in  FIG. 5  identical to corresponding parts in  FIG. 3  are given identical reference signs. Description of these parts is not repeated where appropriate. 
     The client  54  depicted in  FIG. 5  includes a communication unit  141 , a control unit  142 , and an output unit  143 . 
     The communication unit  141  transmits various types of information supplied from the control unit  142  to the server  52  and also receives various types of information transmitted from the server  52 , to supply the received information to the control unit  142 . 
     The control unit  142  controls overall operations of the client  54 . The control unit  142  includes a communication control unit  151 , the absolute coordinate position information decoder  71 , and the coordinate transformation unit  72 . 
     The communication control unit  151  controls the communication unit  141  to control communication performed by the communication unit  141  with the server  52 . For example, the communication control unit  151  controls the communication unit  141  to function as an acquisition unit for acquiring lowest accuracy quantized position information and additional bit information from the server  52 . 
     The absolute coordinate position information decoder  71  calculates information indicating absolute positions of objects on the basis of the lowest accuracy quantized position information and the additional bit information, to function as a position information calculation unit which decodes encoded normalized position information. 
     The output unit  143  outputs, to the MPEG-H renderer  55 , polar coordinate position information associated with the respective objects and obtained by coordinate transformation performed by the coordinate transformation unit  72 . 
     &lt;Encoding of Normalized Position Information&gt; 
     Described subsequently will be encoding (quantization) of normalized position information for each object. 
     For example, suppose that a space corresponding to a content target, i.e., a space where the listener U 12  corresponding to a user and an object are present, is a cubic space and that the listener U 12  is located at a center position within the space at a certain time as depicted in  FIG. 6 . Note that parts in  FIG. 6  identical to corresponding parts in  FIG. 3  are given identical reference signs. Description of these parts is not repeated where appropriate. 
       FIG. 6  is a figure presenting a region R 11  inside a quadrangular external shape in a three-dimensional space where the listener U 12  and the object are present, as a view overlooked in a direction of a z-axis from a positive side to a negative side in an xyz coordinate system. A center position of the three-dimensional space corresponds to an origin O of the xyz coordinate system. In addition, the listener U 12  is in a state located at the position of the origin O here. 
     It is further assumed that half the length of one side of a cube corresponding to the space expressed by the region R 11 , i.e., an actual length from the origin O to an end of the cube, is an absolute distance absoluteDistance. It is assumed here that the length of the absolute distance absoluteDistance is expressed in meters (m) or the like, for example, and that information indicating the absolute distance absoluteDistance is hereinafter also referred to as absolute distance information absoluteDistance. 
     According to human auditory sensation, it is known that an angle in a horizontal direction within a certain right and left range with respect to a front object is recognized as an angle identical to a front angle. This angle is called a perceptive limit angle θ. It is assumed here that the perceptive limit angle θ is an angle of 1.5 degrees. 
     Accordingly, assuming that the perceptive limit angle θ is an angle formed by a line L 11  and a line L 12 , for example, the listener U 12  positioned at the origin O perceives sounds of audio images located at any positions as if these sounds come from the same direction in a case where the audio images are localized at any positions between a point PT 11  and a point PT 12 . Accordingly, in this case, a distance between the point PT 11  and the point PT 12  in normalized position information associated with an object located between the point PT 11  and the point PT 12  is quantized as a quantized step width, and a quantized representative value obtained at such time is designated as a value indicating a position PtQ. In this manner, a bit number of quantized position information can be reduced without giving a sense of disagreement of the audio image position. 
     In addition, a tolerance of the listener U 12  in the horizontal direction with respect to a sound coming direction is the perceptive limit angle θ as angle information. Accordingly, an absolute width of the tolerance becomes larger in a case of a long distance between the listener U 12  and the object than in a case of a short distance therebetween even within the same range of 0.75 degrees to the left and right for each in both cases. 
     According to the present technology, a transfer volume of information can be reduced without giving a sense of a perceptive difference from an original audio image direction by changing quantized accuracy of quantized position information, i.e., a quantized step width, according to a distance between the listener U 12  and an object, by using the human perceptive limit angle θ. 
     More specifically, an object number nObj, the absolute distance information absoluteDistance, minimum distance information, normalized position information for each object, and the perceptive limit angle θ are input from the user U 11  to the absolute coordinate position information encoder  51 . 
     The object number nObj here is the number of objects present within a space. It is assumed below that a space corresponding to a content target has a cubic shape and that a center position of the cube corresponds to the origin O of the xyz coordinate system. 
     The minimum distance information is information indicating a minimum distance MinDist as an allowable minimum distance between the listener U 12  and each of the objects. 
     For example, the minimum distance MinDist is expressed in meters (m) similarly to the absolute distance absoluteDistance. For example, the minimum distance MinDist described above is determined such that the listener U 12  and each of the objects do not overlap each other, in consideration of a head size of the listener U 12 . Needless to say, an audio image of each of the objects may be localized at the position of the listener U 12  by setting the minimum distance MinDist=0. It is assumed below that minimum distance information indicating the minimum distance MinDist is also referred to as minimum distance information MinDist. 
     Moreover, normalized position information associated with each of the objects is information which includes Px(i), Py(i), and Pz(i) corresponding to an x coordinate, y coordinate, and a z coordinate, respectively and indicating an absolute position of an object in the xyz coordinate system. In each of the coordinates, i (provided, 0≤i&lt;nObj) is an index for identifying the object. 
     Further, for example, it is assumed that the perceptive limit angle θ is a predetermined angle, i.e., an angle of 1.5 degrees, and that the perceptive limit angle θ thus determined is also known on the client  54  side. 
     When the user U 11  inputs respective items of information, the absolute coordinate position information encoder  51  encodes the respective input items of information as necessary to generate a highest accuracy position encoded data file as output encoded information. For example, the highest accuracy position encoded data file contains the object number nObj, the absolute distance information absoluteDistance, the highest accuracy quantized position information, and an exponent part index exp_index_high. 
     For example, each of the object number nObj and the absolute distance information absoluteDistance is a non-compressed value here. In addition, the highest accuracy quantized position information is information including Qpx_high(i), Qpy_high(i), and Qpz_high(i) corresponding to mantissa parts of respective coordinates of an x coordinate, a y coordinate, and a z coordinate indicating a highest accuracy absolute position in the xyz coordinate system, respectively and sign_x(i), sign_y(i), and sign_z(i) corresponding to sign bit information indicating a positive or negative sign of the respective coordinates. 
     Note that each of the mantissa parts of the highest accuracy absolute position and i (provided, 0≤i&lt;nObj) in the sign bit information is an index for identifying an object. In addition, each sign bit information has a non-compressed value. The sign bit information having a value of 0 indicates that the coordinate has a positive value, while the sign bit information having a value of 1 indicates that the coordinate has a negative value. 
     The exponent part index exp_index_high is an index of a value of ½ raised to the power of an exponent, i.e., an index of an exponent part of ½ raised to the power of the exponent in a case of the minimum distance MinDist, i.e., in a case of highest quantized accuracy. For example, the exponent part index exp_index_high has a compressed value. 
     Specifically, the exponent part index exp_index_high at the minimum distance MinDist is obtained by calculating the following Equation (1) on the basis of the minimum distance MinDist. 
       [Math. 1] 
       exp_index_high= INT (max({ n |(½) n &lt;MinDist}))  (1)
 
     Note that INT( ) in Equation (1) indicates an INT function which outputs an integer part of an argument. 
     Moreover, mantissa parts Qpx_high(i), Qpy_high(i), and Qpz_high(i) of highest accuracy quantized position information of an ith object can be obtained by calculating the following Equation (2) on the basis of an x coordinate Px(i), a y coordinate Py(i), and a z coordinate Pz(i) of normalized position information, the exponent part index exp_index_high, and the perceptive limit angle θ. 
       [Math. 2] 
         Qpx _high( i )=| Px ( i )+(½)step_high|/step_high
 
         Qpy _high( i )=| Py ( i )+(½)step_high|/step_high
 
         Qpz _high( i )=| Pz ( i )+(½)step_high|/step_high  (2)
 
     In Equation (2), step_high indicates a quantized step width corresponding to the exponent part index exp_index_high and is calculated by the following Equation (3). In Equation (3), sqrt( ) indicates a square root. 
       [Math. 3] 
       step_high=2×tan(θ/2)×absoluteDistance/sqrt(3)×(½) exP     _     index     _     high    (3)
 
     Note that the value of the exponent part index exp_index_high is decreased in increments of one to obtain the value of the exponent part index exp_index of low accuracy quantized position information corresponding to each of quantized accuracy. Quantized accuracy lowers as the value of the exponent part index exp_index decreases. Accordingly, the value of the exponent part index exp_index of lowest accuracy quantized position information becomes 0. 
     An index of an exponent part of ½ raised to the power of the exponent with predetermined quantized accuracy including the exponent part index exp_index_high is hereinafter also simply referred to as an exponent part index exp_index, in a case where no particular distinction is needed between respective levels of quantized accuracy. 
     According to the present technology, as described above, the quantized step width with highest accuracy is a value of ½ raised to the power of an exponent, more specifically, a value obtained by multiplying a value of ½ raised to the power of an exponent by a constant 2 tan (θ/2)/sqrt(3) determined by the perceptive limit angle θ. The exponent of the value of ½ raised to the power of exponent at this time corresponds to the exponent part index exp_index_high. In this manner, a mantissa part of low accuracy quantized position information can easily be obtained only by extracting a part of a mantissa part of highest accuracy quantized position information. 
     In addition, the absolute coordinate position information encoder  51  encodes a sign bit of normalized position information in the following manner. 
     Specifically, the value of the sign bit information sign_x(i) of the x coordinate is set to 0 when the value of the x coordinate Px(i) is 0 or larger. The value of the sign bit information sign_x(i) of the x coordinate is set to 1 when the value of the x coordinate Px(i) is smaller than 0. 
     Similarly, the value of the sign bit information sign_y(i) of the y coordinate is set to 0 when the value of the y coordinate Py(i) is 0 or larger. The value of the sign bit information sign_y(i) of the y coordinate is set to 1 when the value of the y coordinate Py(i) is smaller than. Further, the value of the sign bit information sign_z(i) of the z coordinate is set to 0 when the value of the z coordinate Pz(i) is 0 or larger. The value of the sign bit information sign_z(i) of the z coordinate is set to 1 when the value of the z coordinate Pz(i) is smaller than 0. 
     On the other hand, decoding of highest accuracy quantized position information and low accuracy quantized position information is performed in the following manner on the client  54  side. 
     Specifically, during decoding, the following Equation (4) is calculated on the basis of the perceptive limit angle θ known beforehand, the absolute distance information absoluteDistance received from the server  52 , and an exponent part index exp_index_sel finally decided, to obtain a quantized step width step_dec. 
       [Math. 4] 
       step_dec=2×tan(θ/2)×absoluteDistance;sqrt(3)×(½) exp     _     index     _     sel    (4)
 
     The exponent part index exp_index_sel corresponds to the exponent part index exp_index. 
     If quantized position information to be decoded is highest accuracy quantized position information, for example, the value of the exponent part index exp_index_sel is set to the same value as the value of the exponent part index exp_index_high. In addition, if quantized position information to be decoded is lowest accuracy quantized position information, the value of the exponent part index exp_index_sel is set to 0. 
     Further, decoding of the sign bit information sign_x(i), sign_y(i), and sign_z(i) is also performed. 
     Specifically, if the value of the sign bit information sign_x(i) is 0, a value of sign bit information sign_x_val(i) indicating the sign of the x coordinate of normalized position information obtained by decoding is set to 1. If the value of the sign bit information sign_x(i) is 1, the value of the sign bit information sign_x_val(i) indicating the sign of the x coordinate of the normalized position information obtained by decoding is set to −1. 
     Similarly, if the value of the sign bit information sign_y(i) is 0, a value of sign bit information sign_y_val(i) indicating the sign of the y coordinate of normalized position information obtained by decoding is set to 1. If the value of the sign bit information sign_y(i) is 1, the value of the sign bit information sign_y_val(i) indicating the sign of the y coordinate of the normalized position information obtained by decoding is set to −1. 
     If the value of the sign bit information sign_z(i) is 0, a value of sign bit information sign_z_val(i) indicating the sign of the z coordinate of normalized position information obtained by decoding is set to 1. If the value of the sign bit information sign_z(i) is 1, the value of the sign bit information sign_z_val(i) indicating the sign of the z coordinate of the normalized position information obtained by decoding is set to −1. 
     When the quantized step width step_dec and the sign bit information sign_x_val(i), sign_y_val(i), and sign_z_val(i) subjected to decoding are obtained, the following Equation (5) is calculated on the basis of these items of information, the absolute distance information absoluteDistance received from the server  52 , and the mantissa parts of the quantized position information finally decided, to obtain final decoded normalized position information. The decoded normalized position information is absolute coordinate information obtained by decoding encoded normalized position information. 
       [Math. 5] 
         Dpx ( i )=sign_ x _ val ( i )× Qpx _ sel ( i )×step_ dec /absoluteDistance
 
         Dpy ( i )=sign_ y _ val ( i )× Qpy _ sel ( i )×step_ dec /absoluteDistance
 
         Dpz ( i )=sign_ z _ val ( i )× Qpz _ sel ( i )×step_ dec /absoluteDistance   (5)
 
     Note that Dpx(i), Dpy(i), and Dpz(i) in Equation (5) are an x coordinate, a y coordinate, and a z coordinate obtained by decoding an x coordinate Px(i), a y coordinate Py(i), and a z coordinate Pz(i) of normalized position information associated with an encoded ith object. Moreover, position information including the x coordinate Dpx(i), the y coordinate Dpy(i), and the z coordinate Dpz(i) is designated as decoded normalized position information indicating an absolute position of the object in the xyz coordinate system and obtained by decoding. 
     Furthermore, Qpx_sel(i), Qpy_sel(i), and Qpz_sel(i) in Equation (5) are mantissa parts of the x coordinate, the y coordinate, and the z coordinate of the quantized position information associated with the ith object and finally decided. For example, in a case where the quantized position information associated with the object and finally decided is highest accuracy quantized position information, the mantissa parts Qpx_sel(i), Qpy_sel(i), and Qpz_sel(i) become the mantissa parts Qpx_high(i), Qpy_high(i), and Qpz_high(i), respectively. 
     &lt;Description of Encoding Process and File Storing Process&gt; 
     Described next will be a specific process performed by the content reproduction system. 
     An encoding process performed by the absolute coordinate position information encoder  51  and a file storing process performed by the server  52  will first be described with reference to a flowchart of  FIG. 7 . 
     With a start of the encoding process, the absolute coordinate position information encoder  51  in step S 11  acquires an object number nObj, absolute distance information absoluteDistance, minimum distance information MinDist, normalized position information for each object, and a perceptive limit angle θ, each input from the user U 11 . 
     In step S 12 , the absolute coordinate position information encoder  51  calculates Equation (1) to calculate an exponent part index exp_index_high when a distance between the listener U 12  and an object becomes the minimum distance MinDist. 
     In step S 13 , the absolute coordinate position information encoder  51  calculates Equation (2) for each object on the basis of normalized position information, an exponent part index exp_index_high, the absolute distance information absoluteDistance, and the perceptive limit angle θ, to calculate mantissa parts Qpx_high(i), Qpy_high(i), and Qpz_high(i) of highest accuracy quantized position information. 
     In step S 14 , the absolute coordinate position information encoder  51  encodes sign bits of normalized position information for each object to obtain sign bit information sign_x(i), sign_y(i), and sign_z(i). 
     The normalized position information associated with each object is encoded (quantized) with highest accuracy by obtaining the mantissa parts and the sign bit information corresponding to the highest accuracy quantized position information by the above-described processing. 
     In step S 15 , the absolute coordinate position information encoder  51  generates a highest accuracy position encoded data file containing highest accuracy quantized position information for each object. 
     In this manner, a highest accuracy position encoded data file in a format depicted in  FIG. 8  is generated, for example. Specifically,  FIG. 8  is a diagram presenting an example of syntax of the highest accuracy position encoded data file. 
     In this example, the absolute distance information absoluteDistance is disposed at the head of the highest accuracy position encoded data file, and the exponent part index exp_index_high is disposed after the absolute distance information absoluteDistance. Moreover, information indicating the object number nObj expressed by a character “Num_of_Object” is disposed subsequently to the exponent part index exp_index_high. 
     Further, the number of sign bit information sign_x(i), sign_y(i), and sign_z(i) and mantissa parts Qpx_high(i), Qpy_high(i), and Qpz_high(i) of the highest accuracy quantized position information indicated by the object number nObj are disposed for each object after the information indicating the object number nObj. 
     Note that ceil( ) indicating the bit number of the mantissa part of the highest accuracy quantized position information in the example of  FIG. 8  represents a ceiling function which outputs a minimum integer value equal to or larger than an argument. 
     When the highest accuracy position encoded data file containing the absolute distance information absoluteDistance, the exponent part index exp_index_high, the object number nObj, the sign bit information associated with the highest accuracy quantized position information for each object, and the mantissa part of the highest accuracy quantized position information for each object is obtained in this manner, the process subsequently proceeds to step S 16  of  FIG. 7 . 
     In step S 16 , the absolute coordinate position information encoder  51  transmits the generated highest accuracy position encoded data file to the server  52  by wireless or wired communication or the like. Thereafter, the encoding process ends. 
     Note that the server  52  transmits a storage completion notification indicating that the highest accuracy position encoded data file has been stored correctly in the server  52  as described below when this storage is correctly completed. Accordingly, the absolute coordinate position information encoder  51  receives the transmitted storage completion notification and displays this notification in an appropriate manner. 
     Moreover, in response to transmission of the highest accuracy position encoded data file, the server  52  starts a file storing process. 
     Specifically, the communication unit  101  of the server  52  in step S 31  receives the highest accuracy position encoded data file transmitted from the absolute coordinate position information encoder  51 , under the control by the communication control unit  111 , and supplies the received highest accuracy position encoded data file to the control unit  102 . 
     In step S 32 , the control unit  102  supplies the highest accuracy position encoded data file supplied from the communication unit  101  to the recording unit  61  and causes the recording unit  61  to store (record) the highest accuracy position encoded data file. In this manner, the highest accuracy position encoded data file is stored (recorded) in the recording unit  61 . 
     Subsequently, the communication control unit  111  controls the communication unit  101  to transmit a storage completion notification indicating that the highest accuracy position encoded data file has been stored correctly to the absolute coordinate position information encoder  51 . Thereafter, the file storing process ends. 
     In the manner described above, the absolute coordinate position information encoder  51  encodes normalized position information associated with each object with highest accuracy and transmits a highest accuracy position encoded data file containing the highest accuracy quantized position information thus obtained to the server  52 . In addition, the server  52  stores the highest accuracy position encoded data file received from the absolute coordinate position information encoder  51 . 
     As a result, the server  52  is capable of generating quantized position information with any level of quantized accuracy from highest accuracy quantized position information in response to a request from the client  54  and transmitting the generated quantized position information to the client  54 . 
     In this manner, more reduction of a processing load on the content distribution side, such as the server  52  and the absolute coordinate position information encoder  51 , is achievable along with more reduction of a transfer volume of information, by obtaining polar coordinate position information for each object on the client  54  side, than in a case where the highest accuracy quantized position information is transferred to the client  54  without any change. 
     &lt;Description of Position Information Acquiring Process and Position Information Transmitting Process&gt; 
     After a highest accuracy position encoded data file is stored in the server  52 , the client  54  is allowed to receive, from the server  52 , supply of quantized position information associated with content for each object. Described below will be a process performed by the client  54  when acquiring quantized position information from the server  52 . Specifically, a position information acquiring process performed by the client  54  and a position information transmitting process performed by the server  52  will hereinafter be described with reference to a flowchart of  FIG. 9 . 
     When the client  54  starts the position information acquiring process, the communication unit  141  in step S 61  transmits an object number transmission request to the server  52  via wireless or wired communication or the like, under the control by the communication control unit  151 . 
     The object number transmission request here is information which requests transmission of object number notification information indicating the number of objects constituting content, i.e., the number of objects present within the space. 
     In response to transmission of the object number transmission request, the server  52  starts the position information transmitting process. Specifically, the communication unit  101  in step S 81  receives the object number transmission request transmitted from the client  54 , under the control by the communication control unit  111 , and supplies the received request to the control unit  102 . 
     Subsequently, the transmission information generation unit  112  generates object number notification information indicating an object number nObj with reference to a highest accuracy position encoded data file recorded in the recording unit  61 . The communication control unit  111  supplies the generated object number notification information to the communication unit  101 . 
     In step S 82 , the communication unit  101  transmits, to the client  54 , the object number notification information supplied from the communication control unit  111 , under the control by the communication control unit  111 . 
     On the other hand, the communication unit  141  of the client  54  in step S 62  receives the object number notification information transmitted from the server  52 , under the control by the communication control unit  151 , and supplies the received information to the control unit  142 . 
     In this manner, the client  54  is capable of recognizing the object number nObj of the content and making preparation or the like for processes to be performed in a following stage according to the object number nObj. 
     Note that the object number notification information may be a frame or the like containing header information in a format (syntax) presented in  FIG. 10 , for example. 
     According to the example of  FIG. 10 , the header information contains absolute distance information absoluteDistance and information indicating an object number nObj expressed by a character “Num_of_Object.” Note that the header information depicted in  FIG. 10  may be added to all signals to be transmitted from the server  52  to the client  54 , transmitted to the client  54  at an appropriate timing such as the time of initiation, or regularly transmitted to the client  54 . 
     When the object number nObj is specified, the communication control unit  151  generates a transmission request for requesting transmission of lowest accuracy quantized position information to the server  52  and supplies the generated request to the communication unit  141 . 
     While described here is the example where low accuracy quantized position information initially acquired by the client  54  from the server  52  is lowest accuracy quantized position information, the low accuracy quantized position information may be low accuracy quantized position information with any level of quantized accuracy as long as the quantized accuracy is lower than the highest accuracy. 
     In step S 63 , the communication unit  141  transmits, to the server  52 , the transmission request supplied from the communication control unit  151  and requesting transmission of the lowest accuracy quantized position information, under the control by the communication control unit  151 . 
     Subsequently, the communication unit  101  of the server  52  in step S 83  receives the lowest accuracy quantized position information transmission request transmitted from the client  54  and supplies the received request to the control unit  102 , under the control by the communication control unit  111 . 
     In step S 84 , the transmission information generation unit  112  generates mantissa parts of the lowest accuracy quantized position information with reference to the highest accuracy position encoded data file recorded in the recording unit  61 , in response to the transmission request supplied from the communication unit  101 . 
     Specifically, for example, the transmission information generation unit  112  extracts mantissa parts Qpx_high(i), Qpy_high(i), and Qpz_high(i) of highest accuracy quantized position information contained in the highest accuracy position encoded data file for each object. 
     Moreover, the transmission information generation unit  112  shifts the mantissa parts Qpx_high(i), Qpy_high(i), and Qpz_high(i) by a difference between an exponent part index exp_index_high and a lowest accuracy exponent part index exp_index=0 with lowest quantized accuracy and designates the shifted mantissa parts as Qpx_low(i), Qpy_low(i), and Qpz_low(i) which are mantissa parts of respective coordinates of an x coordinate, a y coordinate, and a z coordinate representing a lowest accuracy absolute position. 
     In other words, the mantissa parts of the lowest accuracy quantized position information can be obtained by extracting information corresponding to a bit number of the lowest accuracy exponent part index exp_index from an MSB (Most Significant Bit) side (highest order bit side) of the mantissa part of the highest accuracy quantized position information. 
     If the value of the exponent part index exp_index_high is 9, for example, information obtained by eliminating information corresponding to low-order 9 bits of the mantissa part Qpx_high(i) by a shift process for the mantissa part Qpx_high(i) is designated as the mantissa part Qpx_low(i) of the x coordinate of the lowest accuracy absolute position. 
     In addition, the transmission information generation unit  112  designates sign bit information sign_x(i), sign_y(i), and sign_z(i) of highest accuracy quantized position information contained in the highest accuracy position encoded data file, as sign bit information included in the lowest accuracy quantized position information without change. No change is needed because the sign bit is identical regardless of levels of quantized accuracy. 
     In step S 85 , the transmission information generation unit  112  generates lowest accuracy quantized position information which contains the mantissa parts Qpx_low(i), Qpy_low(i), and Qpz_low(i) obtained by processing in step S 84  and the sign bit information sign_x(i), sign_y(i), and sign_z(i). 
     In this manner, lowest accuracy quantized position information presented in  FIG. 11  is obtained, for example. In more detail,  FIG. 11  presents an example of syntax of a bit stream containing lowest accuracy quantized position information for each object. 
     According to this example, sign bit information sign_x(i), sign_y(i), and sign_z(i) of lowest accuracy quantized position information and mantissa parts Qpx_low(i), Qpy_low(i), and Qpz_low(i) of respective coordinates of lowest accuracy quantized position information are stored in a bit stream for each of the number of objects indicated by an object number nObj. 
     When the lowest accuracy quantized position information is obtained in this manner, the communication control unit  111  supplies the lowest accuracy quantized position information for each of the objects to the communication unit  101 . 
     In step S 86 , the communication unit  101  transmits, to the client  54 , the lowest accuracy quantized position information supplied from the communication control unit  111  for each of the objects, under the control by the communication control unit  111 . Thereafter, the position information transmitting process ends. 
       FIG. 12  presents here a specific example of encoding of a coordinate of one axis included in normalized position information associated with a certain object. 
     In  FIG. 12 , a perceptive limit angle θ is set to an angle of 1.5 degrees, while a tolerance angle defined by the perceptive limit angle θ is an angle of 0.75 degrees. In addition, an absolute distance absoluteDistance has a length of 30 m, while a coordinate of normalized position information is set to 0.1. 
     The example of  FIG. 12  presents values of binary numbers, i.e., binary values, of mantissa parts corresponding to respective levels of quantized accuracy for the coordinate value 0.1, and others. 
     More specifically, “exponent of ½” indicates an exponent part index exp_index. Quantized accuracy increases as the value of the exponent part index exp_index increases. 
     Particularly here, a value of an exponent part index exp_index_high with highest quantized accuracy is “9,” while a value of an exponent part index exp_index with lowest quantized accuracy corresponding to lowest quantized accuracy is “0.” 
     In addition, “distance between listener and object” indicates a distance between the listener U 12  and the object when two positions spaced away from each other by a quantized step width with quantized accuracy corresponding to the exponent part index exp_index are located at positions spaced away from each other by the perceptive limit angle θ as viewed from the listener U 12 . 
     Indicated by “quantized step width” is a quantized step width corresponding to the exponent part index exp_index. 
     Represented by “real number quantized value” is a real value when the coordinate value “0.1” of normalized position information is quantized using the quantized step width corresponding to the exponent part index exp_index. 
     In addition, indicated by “quantized bit number” is a bit number of a mantissa part of quantized normalized position information. Indicated by “binary” is a binary value (value of binary number) of the mantissa part of the quantized normalized position information, and indicated by “integer quantized value” is a value (integer value) of the mantissa part. Accordingly, the value indicated by “integer quantized value” is the value of the mantissa part of the quantized normalized position information, and a binary value of this value is the value indicated by “binary.” 
     Particularly here, as for the exponent part index exp_index having the value of 9, an integer value of the value indicated by “real number quantized value” is designated as an integer quantized value of the mantissa part of the quantized normalized position information. 
     On the other hand, as for the exponent part indexes exp_index having values of 8 to 0, each mantissa part of these indexes is obtained by extracting a part of the binary value of the mantissa part of the exponent part index exp_index having the value of 9. 
     For example, a value obtained by extracting high-order seven bits of the binary value of the mantissa part of the exponent part index exp_index having the value of 9 becomes the binary value of the mantissa part of the exponent part index exp_index having the value of 0. 
     Note that “0000” existing on the MSB side is omitted here from the part of the binary value of the mantissa part for easy understanding of the figure. 
     Moreover, “Position after decoding” indicates a coordinate value of normalized position information obtained by decoding on the basis of the mantissa part of the quantized normalized position information, i.e., the value indicated by “binary.” 
     According to this example, the coordinate value of the quantized (encoded) normalized position information is “0.1.” In this case, ideally, the coordinate value of the decoded normalized position information becomes “0.1.” However, here, quantized accuracy decreases as the exponent part index exp_index decreases. Therefore, an error of the coordinate value after decoding also increases as quantized accuracy decreases. 
     At the time of encoding (quantization) of normalized position information, the quantized bit number is determined for the exponent part index exp_index, and the mantissa part of the quantized bit number, i.e., the binary value of the quantized value of the coordinate value, is obtained. 
     According to comparisons between the mantissa parts of the respective exponent part indexes exp_index, it is understood that the quantized bit number increases as the value of the exponent part index exp_index increases and that a value is added to the mantissa part in a direction toward the LSB (Least Significant Bit), i.e., toward the lowest-order bit. 
     This means that the quantized accuracy of the mantissa part increases as the exponent part index exp_index increases. In addition, if only information with high quantized accuracy, i.e., the mantissa part of the highest accuracy quantized position information, is retained, the mantissa part of the low accuracy quantized position information can be obtained only by eliminating information on the LSB side of the mantissa part without a necessity of new calculation of quantization. 
     The quantized step width step corresponding to the exponent part index exp_index here is expressed by the following Equation (6). 
       [Math. 6] 
       step=2×tan(θ/2)/sqrt(3)×(½) exp     _index     (6).
 
     In addition, the quantized bit number of the mantissa part corresponding to the exponent part index exp_index can be obtained by calculating ceil(log 2(1/step+1)) using the quantized step width step. Note that ceil( ) is a ceiling function. 
     Accordingly, in a case where the value of the exponent part index exp_index is “0,” for example, the quantized bit number becomes 7. 
     Suppose here that the value of the exponent part index exp_index_high is “9,” for example. In this case, a difference between the exponent part index with highest accuracy exp_index_high=9 and the exponent part index exp_index with lowest accuracy=0 becomes 9. 
     Accordingly, the mantissa part of the coordinate of the lowest accuracy quantized position information becomes a 7-bit value “0000110” obtained by eliminating low-order bits of the mantissa part “0000110100111011” of the coordinate of the highest accuracy quantized position information by 9 bits corresponding to the difference between the exponent part indexes. 
     In other words, in a case where the exponent part index exp_index with lowest accuracy is 0, the quantized bit number becomes 7. Accordingly, the mantissa part of the coordinate of the lowest accuracy quantized position information is obtained by extracting high-order 7 bits of the mantissa part of the coordinate of the highest accuracy quantized position information. 
     Returning to the description referring to the flowchart of  FIG. 9 , the client  54  performs processing in step S 64  when the lowest accuracy quantized position information is transmitted from the server  52 . 
     In step S 64 , the communication unit  141  receives the lowest accuracy quantized position information transmitted from the server  52 , under the control by the communication control unit  151 , and supplies the received information to the control unit  142 . The communication control unit  151  therefore acquires the lowest accuracy quantized position information. 
     In response to reception of the lowest accuracy quantized position information, the absolute coordinate position information decoder  71  selects the number of the respective objects indicated by the object number nObj one by one as a processing target object and calculates lowest accuracy absolute position of these objects. 
     More specifically, in step S 65 , the absolute coordinate position information decoder  71  calculates a quantized step width by performing calculation similar to the calculation of Equation (4), on the basis of the perceptive limit angle θ already known and the absolute distance information absoluteDistance contained in the header information included in the frame or the like received from the server  52 . The value of exponent part index exp_index with lowest accuracy here is 0. Accordingly, the quantized step width is calculated by substituting 0 for the value of the exponent part index exp_index_sel in Equation (4). 
     In step S 66 , the absolute coordinate position information decoder  71  decodes the sign bit information sign_x(i), sign_y(i), and sign_z(i) included in the lowest accuracy quantized position information received in step S 64  for the processing target object. In this manner, respective pieces of decoded sign bit information sign_x_val(i), sign_y_val(i), and sign_z_val(i) are obtained. 
     In step S 67 , the absolute coordinate position information decoder  71  calculates a lowest accuracy absolute position of the processing target object on the basis of the quantized step width obtained in step S 65 , the sign bit information sign_x_val(i), sign_y_val(i), and sign_z_val(i) obtained in step S 66 , and the mantissa parts Qpx_low(i), Qpy_low(i), and Qpz_low(i) of the lowest accuracy quantized position information received in step S 64 . 
     In other words, the absolute coordinate position information decoder  71  performs calculation similar to the calculation of Equation (5) described above to obtain decoded lowest accuracy normalized position information including x coordinate Dtx(i), y coordinate Dty(i), and z coordinate Dtz(i) indicating the decoded lowest accuracy absolute position. 
     Specifically, in Equation (5), the quantized step width obtained in step S 65  is substituted for the quantized step width step_dec, and the mantissa parts Qpx_low(i), Qpy_low(i), and Qpz_low(i) are substituted for Qpx_sel(i), Qpy_sel(i), and Qpz_sel(i). In addition, the absolute distance information absoluteDistance received from the server  52  is used. In this manner, the x coordinate Dtx(i), the y coordinate Dty(i), and the z coordinate Dtz(i) corresponding to the x coordinate Dpx(i), the y coordinate Dpy(i), and the z coordinate Dpz(i) are obtained. 
     The decoded lowest accuracy normalized position information including the x coordinate Dtx(i), the y coordinate Dty(i), and the z coordinate Dtz(i) thus obtained is temporary decoded normalized position information. The processing from step S 65  to step S 67  described above corresponds to a process for decoding the lowest accuracy quantized position information. 
     In step S 68 , the absolute coordinate position information decoder  71  determines whether or not all of the objects have been processed as processing target objects. 
     In a case of determination that not all of the objects have been processed in step S 68 , the process returns to step S 66  to repeat the processing described above. In this case, an object not processed as a processing target is selected as the next processing target object, and decoded lowest accuracy normalized position information associated with this object is obtained. 
     On the other hand, in a case of determination that all of the objects have been processed in step S 68 , the position information acquiring process ends. 
     In the manner described above, the client  54  receives lowest accuracy quantized position information from the server  52 , performs the decoding process, and obtains decoded lowest accuracy normalized position information. In addition, the server  52  generates lowest accuracy quantized position information in response to a request from the client  54  and transmits the generated information to the client  54 . 
     In this manner, a transfer volume of information transmitted and received between the server  52  and the client  54  can be reduced more than in a case where highest accuracy quantized position information is transmitted and received. 
     Note that described here has been the example where lowest accuracy quantized position information to be transferred (transmitted) to the client  54  is generated on the basis of highest accuracy quantized position information which is the only information recorded in the server  52  beforehand. However, quantized position information at respective levels of quantized accuracy may be retained in the server  52  beforehand to read out quantized position information with requested quantized accuracy and transmit the read-out information to the client  54 . 
     &lt;Description of Additional Bit Information Acquiring Process and Additional Bit Information Transmitting Process&gt; 
     Meanwhile, when the position information acquiring process described with reference to  FIG. 9  is performed, decoded lowest accuracy normalized position information is obtained for each object. 
     Whether or not the lowest accuracy quantized position information, i.e., the decoded lowest accuracy normalized position information, has sufficient accuracy as quantized position information indicating an absolute position of an object within a space can be specified on the basis of a distance between the listener U 12  and a position indicated by the normalized position information. 
     The quantized position information with sufficient accuracy here refers to information indicating a state where an angle formed by a direction of a position defined by normalized position information as viewed from the listener U 12  and a direction of a position defined by quantized position information as viewed from the listener U 12  becomes θ/2 or smaller. In other words, the position indicated by the quantized position information as viewed from the listener U 12  is located at a position within a range of the perceptive limit angle θ around a center corresponding to the position indicated by the normalized position information. 
     The decoded lowest accuracy normalized position information indicates a not exact but approximate position of the object within the space. Accordingly, an approximate distance between the listener U 12  and the object within the space can be obtained by using the decoded lowest accuracy normalized position information. 
     Accordingly, the client  54  can specify whether or not lowest accuracy quantized position information has sufficient quantized accuracy and quantized position information with sufficient quantized accuracy for each object, on the basis of listener position information with high accuracy measured by GPS or the like and the decoded lowest accuracy normalized position information. 
     In a case where the lowest accuracy quantized position information does not have sufficient quantized accuracy, the client  54  acquires additional bit information from the server  52  to obtain decoded normalized position information with sufficient accuracy. Processes performed by the client  54  and the server  52  in such a case will be described below. Specifically, an additional bit information acquiring process performed by the client  54  and an additional bit information transmitting process performed by the server  52  will be described below with reference to a flowchart of  FIG. 13 . 
     When the client  54  starts the additional bit information acquiring process, the absolute coordinate position information decoder  71  in step S 121  calculates a distance ObjectDistance between the listener U 12  and the object for each of the objects. 
     More specifically, a Euclidean distance between the listener U 12  and each object within the space is calculated as the distance ObjectDistance on the basis of the listener position information supplied from the listener position acquisition apparatus  53  and the decoded lowest accuracy normalized position information. 
     In step S 122 , the absolute coordinate position information decoder  71  compares a distance “distance” determined for the exponent part index exp_index and the distance ObjectDistance while changing the value of the exponent part index exp_index from 0 to a larger value. 
     More specifically, for example, the absolute coordinate position information decoder  71  calculates the following Equation (7) on the basis of the exponent part index exp_index and the absolute distance information absoluteDistance, to calculate the distance “distance” corresponding to the exponent part index exp_index. 
       [Math. 7] 
       distance=2× qrt (3)×alsoluteDistance×(½) exp     _index     (7).
 
     Thereafter, the absolute coordinate position information decoder  71  compares the obtained distance “distance” and the distance ObjectDistance and determines whether or not the distance “distance” is equal to or shorter than the distance ObjectDistance. 
     The absolute coordinate position information decoder  71  specifies the smallest exponent part index exp_index at which the distance “distance” becomes the distance ObjectDistance or shorter while increasing the value of the exponent part index exp_index in increments of one until the distance “distance” becomes equal to or shorter than the distance ObjectDistance. 
     Note that the smallest exponent part index exp_index at which the distance “distance” becomes the distance ObjectDistance or shorter is hereinafter also referred to as an exponent part index exp_index_cover. 
     The exponent part index exp_index_cover is an exponent part index exp_index having the smallest value in the exponent part indexes exp_index of quantized position information with sufficient accuracy described above. 
     When the exponent part index exp_index_cover is specified for each object, the process proceeds to step S 123 . 
     In step S 123 , the absolute coordinate position information decoder  71  compares the exponent part index exp_index_cover with the exponent part index exp_index of the lowest accuracy quantized position information for each object, to examine objects with insufficient quantized accuracy. 
     The exponent part index exp_index_cover here is an exponent part index exp_index with minimum necessary quantized accuracy. Accordingly, an object corresponding to the exponent part index exp_index indicated by the lowest accuracy quantized position information and smaller than the exponent part index exp_index_cover is considered as an object with insufficient quantized accuracy. 
     Particularly here, the value of the exponent part index exp_index of the lowest accuracy quantized position information is 0. Accordingly, an object corresponding to the exponent part index exp_index_cover having a value of 1 or larger is considered as an object with insufficient accuracy and requiring additional bit information. 
     By this examining process, an object with insufficient quantized accuracy and requiring additional bit information is specified, and necessary quantized accuracy is determined (specified) from plural levels of quantized accuracy determined beforehand for the specified object. The necessary quantized accuracy referred to here is quantized accuracy (quantized step width) corresponding to the exponent part index exp_index_cover. 
     In step S 124 , the absolute coordinate position information decoder  71  designates decoded lowest accuracy normalized position information obtained for lowest accuracy quantized position information indicating an exponent part index exp_index equal to or larger than the exponent part index exp_index_cover, as final decoded normalized position information. 
     In other words, decoded lowest accuracy normalized position information with sufficient quantized accuracy has been obtained for the object corresponding to the exponent part index exp_index equal to or larger than the exponent part index exp_index_cover. Accordingly, the x coordinate Dtx(i), the y coordinate Dty(i), and the z coordinate Dtz(i) of the decoded lowest accuracy normalized position information are designated as the x coordinate Dpx(i), the y coordinate Dpy(i), and the z coordinate Dpz(i) of the decoded normalized position information without any change. 
     In step S 125 , the communication unit  141  transmits a transmission request for additional bit information for the object specified as the object corresponding to the exponent part index exp_index smaller than the exponent part index exp_index_cover, i.e., the object requiring additional bit information. 
     For example, the absolute coordinate position information decoder  71  generates a transmission request for additional bit information containing the number of objects requiring transmission of additional bit information, an object index resend_object_index(j), and an exponent part index resend_exe_index(j). 
     The object index resend_object_index(j) here is an index i for identifying the object requiring transmission of the additional bit information, i.e., the object corresponding to the exponent part index exp_index smaller than the exponent part index exp_index_cover. 
     The exponent part index resend_exp_index(j) is an exponent part index exp_index corresponding to quantized accuracy finally required for the object indicated by the index resend_object_index(j). In this case, the value of the exponent part index exp_index_cover is used as the value of the exponent part index resend_exp_index(j) without any change. 
     In this manner, a transmission request in a format (syntax) presented in  FIG. 14 , for example, is obtained. 
     According to this example, information indicating the number of objects requiring transmission of additional bit information and expressed by a character “num_of_resend_objects” is disposed at the head of the transmission request. 
     Moreover, the number of the object indexes resend_object_index(j) and the exponent part indexes resend_exp_index(j) indicated by num_of_resend_objects are disposed after the information indicating the number of objects. 
     Returning to the description of  FIG. 13 , the communication control unit  151  supplies the transmission request generated in such manner for requesting transmission of additional bit information to the communication unit  141  and causes the communication unit  141  to transmit the transmission request to the server  52 . 
     In response to transmission of the transmission request for additional bit information, the server  52  starts an additional bit information transmitting process. 
     Specifically, the communication unit  101  in step S 161  receives the transmission request for additional bit information transmitted from the client  54 , under the control by the communication control unit  111 , and supplies the received request to the control unit  102 . 
     In step S 162 , the transmission information generation unit  112  generates additional bit information associated with the object for which transmission of the additional bit information is requested, in response to the transmission request supplied from the communication unit  101 , i.e., in response to a request from the client  54  corresponding to a transmission destination of lowest accuracy quantized position information. 
     Specifically, for example, the transmission information generation unit  112  extracts mantissa parts Qpx_high(i), Qpy_high(i), and Qpz_high(i) of highest accuracy quantized position information contained in the highest accuracy position encoded data file, for the object indicated by the index resend_object_index(j). 
     Moreover, the transmission information generation unit  112  shifts the mantissa parts Qpx_high(i), Qpy_high(i), and Qpz_high(i) by a difference between the exponent part index exp_index_high and the exponent part index resend_exp_index(j). 
     In this manner, bits corresponding to the difference between the exponent part index exp_index_high on the low-order bit side of each of the mantissa parts Qpx_high(i), Qpy_high(i), and Qpz_high(i) and the exponent part index resend_exp_index(j) are eliminated to obtain the mantissa parts of the quantized position information associated with the exponent part index resend_exp_index(j). 
     The transmission information generation unit  112  eliminates the bits corresponding to the bit number of the mantissa parts of the lowest accuracy quantized position information on the high-order bit side from the obtained mantissa parts of the quantized position information indicating the exponent part index resend_exp_index(j) and designates the remaining parts as additional bit information. 
     The additional bit information includes additional bit information Qpx_diff(j), Qpy_diff(j), and Qpz_diff(j) corresponding to difference information between the mantissa parts of the respective coordinates of the x coordinate, the y coordinate, and the z coordinate of the quantized position information indicating the exponent part index resend_exp_index(j) and the corresponding mantissa parts of the lowest accuracy quantized position information. 
     For example, the additional bit information Qpx_diff(j) is a difference between the mantissa part of the x coordinate of the quantized position information indicating the exponent part index resend_exp_index(j) and the mantissa part Qpx_low(i) of the x coordinate of the lowest accuracy quantized position information. 
     Suppose that the value of the exponent part index resend_exp_index(j) is 7 in the example presented in  FIG. 12 , for example. 
     In this case, the exponent part index exp_index_high of highest accuracy quantized position information is 9. Accordingly, a difference between this value of 9 and the exponent part index resend_exp_index(j)=7 becomes 2. 
     In addition, by eliminating the low-order 2 bits from the mantissa part “0000110100111011” of the highest accuracy quantized position information, a mantissa part “00001101001110” of the low accuracy quantized position information indicating the exponent part index resend_exp_index(j)=7 is obtained. 
     In addition, the bit number of the mantissa part of the lowest accuracy quantized position information is 7. Accordingly, additional bit information “1001110” is obtained by eliminating the high-order 7 bits from the mantissa part “00001101001110.” The client  54  side adds the additional bit information “1001110” thus obtained to the low-order bit side of mantissa part “0000110” of the lowest accuracy quantized position information. In this manner, a mantissa part “00001101001110” of the low accuracy quantized position information indicating the exponent index resend_exp_index(j)=7 finally required is obtained. 
     When the additional bit information is obtained by the above processing for the object indicated by each of the indexes resend_object_index(j), the transmission information generation unit  112  generates difference data containing the respective pieces of additional bit information. 
     In this manner, difference data in a format (syntax) presented in  FIG. 15  is obtained, for example. According to this example, the difference data contains the number of additional bit information Qpx_diff(j), Qpy_diff(j), and Qpz_diff(j) indicated by num_of_resend_objects described above. 
     Note that the bit number of each piece of the additional bit information in  FIG. 15  is the bit number corresponding to the number of resend_exp_index(j). 
     Returning to the description of  FIG. 13 , the communication control unit  111  supplies the difference data containing the additional bit information to the communication unit  101  to control transmission to the client  54 . 
     In step S 163 , the communication unit  101  transmits, to the client  54 , the difference data containing the additional bit information and supplied from the communication control unit  111 , under the control by the communication control unit  111 . Thereafter, the additional bit information transmitting process ends. 
     Moreover, in response to transmission of the difference data, the client  54  performs processing of step S 126 . 
     In step S 126 , the communication unit  141  receives the difference data transmitted from the server  52 , under the control by the communication control unit  151 , and supplies the difference data to the control unit  142 . Accordingly, the communication control unit  151  acquires the difference data containing the additional bit information. 
     In step S 127 , the absolute coordinate position information decoder  71  calculates Equation (4) using the value of the exponent part index resend_exp_index(j) as an exponent part index exp_index_sel, for each of the objects indicated by the indexes resend_object_index(j), to calculate a quantized step width step_dec. 
     In step S 127 , the quantized step width step_dec is calculated for each object determined to have insufficient quantized accuracy in step S 123 , i.e., each of the objects indicated by indexes resend_object_index(j). 
     In step S 128 , the absolute coordinate position information decoder  71  generates a mantissa part of quantized position information indicating the exponent part index resend_exp_index(j) on the basis of the difference data supplied from the communication unit  141 , for each of the objects indicated by the indexes resend_object_index(j). 
     Specifically, the absolute coordinate position information decoder  71  adds additional bit information Qpx_diff(j), Qpy_diff(j), and Qpz_diff(j) contained in the difference data to the low-order bit side of the mantissa parts Qpx_low(i), Qpy_low(i), and Qpz_low(i) of the lowest accuracy quantized position information. 
     In this manner, the mantissa parts of the respective coordinates of the quantized position information indicating the exponent part index resend_exp_index(j) are obtained and designated as mantissa parts Qpx_sel(i), Qpy_sel(i), and Qpz_sel(i) finally decided. 
     In step S 129 , the absolute coordinate position information decoder  71  calculates decoded normalized position information associated with each object indicated by the respective indexes resend_object_index(j). 
     More specifically, Equation (5) is calculated on the basis of the quantized step width step_dec obtained in step S 127 , the absolute distance information absoluteDistance, the sign bit information subjected to decoding obtained in step S 66  of  FIG. 9 , and the mantissa parts obtained in step S 128  and finally decided, to calculate decoded normalized position information. 
     The processing from step S 127  to step S 129  described above is a process for decoding the quantized position information obtained from the lowest accuracy quantized position information and the additional bit information. Moreover, the decoded normalized position information is obtained by the above processing for all of the objects indicated by the object number nObj. 
     In step S 130 , the coordinate transformation unit  72  calculates polar coordinate position information indicating the position of the object as viewed from the listener U 12  within the space, on the basis of the decoded normalized position information and the listener position information supplied from the listener position acquisition apparatus  53 , for each of the objects. 
     Thereafter, the coordinate transformation unit  72  supplies the obtained polar coordinate position information to the output unit  143 . The output unit  143  outputs the respective pieces of polar coordinate position information to the MPEG-H renderer  55 . When the output unit  143  completes output of the polar coordinate position information for all of the objects to the MPEG-H renderer  55 , the additional bit information acquiring process ends. 
     After the end of the additional bit information acquiring process, the MPEG-H renderer  55  performs rendering. Specifically, the MPEG-H renderer  55  performs rendering on the basis of audio data for each of the objects acquired from the server  52  or the like and the polar coordinate position information supplied from the output unit  143 , generates reproduction audio data where audio images of the objects are localized at respective positions within the space, and outputs the generated reproduction audio data to the reproduction system such as a speaker. 
     In the manner described above, the client  54  acquires (receives) additional bit information from the server  52  and calculates decoded normalized position information with sufficient accuracy for objects with insufficient quantized accuracy. Moreover, the server  52  generates additional bit information in response to a request from the client  54  and transmits the generated additional bit information to the client  54 . 
     In this manner, the client  54  is capable of obtaining decoded normalized position information with sufficient accuracy by an information transfer volume smaller than that volume in a case where highest accuracy quantized position information is acquired from the server  52  at the beginning. 
     Moreover, the process for obtaining necessary quantized accuracy and the process for calculating polar coordinate position information are all performed by the client  54 . Accordingly, reduction of the processing load is achievable on the content distribution side such as the server  52  and the absolute coordinate position information encoder  51 . Particularly, this processing load reduction effect increases as the number of the clients  54  connected to the server  52  increases. 
     Note that the polar coordinate position information on the client  54  side changes at the time of reproduction of content every time any of the positions of the objects and the listener U 12  within the space changes. 
     Accordingly, the client  54  updates the polar coordinate position information when the listener position information associated with the listener U 12  changes, for example. 
     However, in a case where the listener U 12  moves in a direction away from the object which is stationary within the space, update of decoded normalized position information is not particularly required for this object. This update is not required because a necessary level of accuracy further decreases in a state where the distance between the object and the listener U 12  increases, in addition to the stationary state of the object. In other words, the update is not required because decoded normalized position information with sufficient accuracy has already been provided. 
     In such a case, for example, the communication control unit  151  of the client  54  causes the server  52  to transmit a transmission request by controlling the communication unit  141  to request transmission of lowest accuracy quantized position information containing indexes i of only an object having moved and an object located at a shorter distance than before from the listener U 12 . Thereafter, the communication unit  141  receives, from the server  52 , only the lowest accuracy quantized position information associated with the objects corresponding to the indexes i in step S 64  of  FIG. 9 . The client  54  performs subsequent processing to update the polar coordinate position information. 
     In addition, necessary quantized accuracy for the object stationary and located at a shorter distance than before from the listener U 12  can be specified on the basis of the decoded normalized position information obtained in the foregoing processing and new listener position information associated with the listener U 12 . 
     Accordingly, in this case, decoded normalized position information with sufficient accuracy can be obtained without the necessity of acquiring new lowest accuracy quantized position information, by performing the additional bit information acquiring process in  FIG. 13  on the client  54  side, for the object which is stationary and located at a shorter distance than before from the listener U 12 . 
     As described above, according to the present technology, information indicating a position of an object can be transferred while a one-sided processing load on a content distribution side is avoided in free-viewpoint 3D audio. Moreover, appropriate quantized accuracy is specified according to a distance between the listener U 12  and an object and the human perceptive limit angle θ. Accordingly, transfer of quantized position information producing a difference from an original audio image direction not exceeding a perceptive limit is achievable along with reduction of a transfer volume. 
     &lt;Configuration Example of Computer&gt; 
     Meanwhile, a series of processes described above may be executed either by hardware or by software. In a case where the series of processes is executed by software, a program constituting the software is installed in a computer. Examples of the computer here include a computer incorporated in dedicated hardware and a computer capable of executing various functions under various programs installed in the computer, such as a general-purpose personal computer. 
       FIG. 16  is a block diagram depicting a configuration example of hardware of a computer executing the series of processes described above under the program. 
     In the computer, a CPU (Central Processing Unit)  501 , a ROM (Read Only Memory)  502 , and a RAM (Random Access Memory)  503  are connected to each other via a bus  504 . 
     An input/output interface  505  is further connected to the bus  504 . An input unit  506 , an output unit  507 , a recording unit  508 , a communication unit  509 , and a drive  510  are connected to the input/output interface  505 . 
     The input unit  506  includes a keyboard, a mouse, a microphone, an imaging element, and the like. The output unit  507  includes a display, a speaker, and the like. The recording unit  508  includes a hard disk, a non-volatile memory, and the like. The communication unit  509  includes a network interface and the like. The drive  510  drives a removable recording medium  511  such as a magnetic disk, an optical disk, a magneto-optical disk, and a semiconductor memory. 
     According to the computer configured as above, the CPU  501  loads the program recorded in the recording unit  508  into the RAM  503  via the input/output interface  505  and the bus  504  and executes the loaded program to perform the series of processes described above, for example. 
     The program to be executed by the computer (CPU  501 ) is allowed to be recorded in the removable recording medium  511 , such as a package medium, and provided in this form. Alternatively, the program is allowed to be provided via a wired or wireless transfer medium, such as a local area network, the Internet, and digital satellite broadcasting. 
     According to the computer, the program is allowed to be installed in the recording unit  508  via the input/output interface  505  from the removable recording medium  511  attached to the drive  510 . Alternatively, the program is allowed to be received by the communication unit  509  via a wired or wireless transfer medium and installed in the recording unit  508 . Instead, the program is allowed to be installed in the ROM  502  or the recording unit  508  beforehand. 
     Note that the program to be executed by the computer may be a program where processes are performed in time series in an order described in the present description or may be a program where processes are performed in parallel or at a necessary timing such as at an occasion of a call. 
     Further, embodiments of the present technology are not limited to the embodiment described above and may be modified in various manners without departing from the scope of the subject matters of the present technology. 
     For example, the present technology is allowed to have a configuration of cloud computing where one function is shared and processed by plural apparatuses in cooperation with each other via a network. 
     Moreover, the respective steps described in the above flowcharts are allowed to be executed by one apparatus or shared and executed by plural apparatuses. 
     Furthermore, in a case where one step contains plural processes, the plural processes contained in the one step are allowed to be executed by one apparatus or shared and executed by plural apparatuses. 
     In addition, the present technology may also have the following configurations. 
     (1) 
     An information processing apparatus including: 
     an acquisition unit that acquires low accuracy position information having first accuracy and indicating a position of an object within a space where a user is located and acquires additional information for obtaining position information that has second accuracy higher than the first accuracy, indicates the position of the object within the space, and corresponds to a position of the user; and 
     a position information calculation unit that obtains the position information on the basis of the low accuracy position information and the additional information. 
     (2) 
     The information processing apparatus according to (1), in which 
     the position information calculation unit specifies the object that requires the additional information, on the basis of user position information indicating the position of the user and the low accuracy position information, and 
     the acquisition unit acquires the additional information associated with the object included in one or a plurality of the objects and specified by the position information calculation unit. 
     (3) 
     The information processing apparatus according to (2), in which 
     the position information calculation unit determines the second accuracy of the position information from plural levels of accuracy on the basis of the user position information and the low accuracy position information, for each of the objects requiring the additional information. 
     (4) 
     The information processing apparatus according to (2) or (3), in which 
     each of the low accuracy position information and the position information includes information that indicates an absolute coordinate of the position of the object within the space, and 
     the user position information includes information that indicates an absolute coordinate of the position of the user within the space. 
     (5) 
     The information processing apparatus according to (4), further including: 
     a transformation unit that transforms the position information into polar coordinate information that indicates a relative position of the object as viewed from the user, on the basis of the position information and the user position information. 
     (6) 
     The information processing apparatus according to any one of (1) to (5), in which 
     the additional information includes information that indicates a difference between the position information and the low accuracy position information. 
     (7) 
     The information processing apparatus according to any one of (1) to (6), in which 
     the object includes an audio object. 
     (8) 
     An information processing method performed by an information processing apparatus, including: 
     acquiring low accuracy position information that has first accuracy and indicates a position of an object within a space where a user is located; 
     acquiring additional information for obtaining position information that has second accuracy higher than the first accuracy, indicates the position of the object within the space, and corresponds to a position of the user; and 
     obtaining the position information on the basis of the low accuracy position information and the additional information. 
     (9) 
     A program under which a computer executes a process including steps of: 
     acquiring low accuracy position information that has first accuracy and indicates a position of an object within a space where a user is located; 
     acquiring additional information for obtaining position information that has second accuracy higher than the first accuracy, indicates the position of the object within the space, and corresponds to a position of the user; and 
     obtaining the position information on the basis of the low accuracy position information and the additional information. 
     (10) 
     An information processing apparatus including: 
     a communication unit that transmits low accuracy position information having first accuracy and indicating a position of an object within a space where a user is located, and transmits additional information for obtaining position information having second accuracy higher than the first accuracy, indicating the position of the object within the space, and corresponding to a position of the user, in response to a request from a transmission destination of the low accuracy position information. 
     (11) 
     The information processing apparatus according to (10), in which 
     each of the low accuracy position information and the position information includes information that indicates an absolute coordinate of the position of the object within the space. 
     (12) 
     The information processing apparatus according to (10) or (11), in which 
     the additional information includes information that indicates a difference between the position information and the low accuracy position information. 
     (13) 
     The information processing apparatus according to (12), further including: 
     a recording unit that records highest accuracy position information obtained by quantizing information indicating the position of the object with a quantized step width having highest accuracy; and 
     a transmission information generation unit that generates the low accuracy position information or the additional information by extracting a part of the highest accuracy position information. 
     (14) 
     The information processing apparatus according to (13), in which 
     the quantized step width is set to a value obtained by multiplying a value of ½ raised to the power of an exponent by a constant. 
     (15) 
     The information processing apparatus according to any one of (10) to (14), in which 
     the object includes an audio object. 
     (16) 
     An information processing method performed by an information processing apparatus, including: 
     transmitting low accuracy position information that has first accuracy and indicates a position of an object within a space where a user is located; and 
     transmitting additional information for obtaining position information that has second accuracy higher than the first accuracy, indicates the position of the object within the space, and corresponds to a position of the user, in response to a request from a transmission destination of the low accuracy position information. 
     (17) 
     A program under which a computer executes a process including steps of: 
     transmitting low accuracy position information that has first accuracy and indicates a position of an object within a space where a user is located; and 
     transmitting additional information for obtaining position information that has second accuracy higher than the first accuracy, indicates the position of the object within the space, and corresponds to a position of the user, in response to a request from a transmission destination of the low accuracy position information. 
     REFERENCE SIGNS LIST 
       52  Server,  54  Client,  61  Recording unit,  71  Absolute coordinate position information decoder,  72  Coordinate transformation unit,  101  Communication unit,  102  Control unit,  141  Communication unit,  142  Control unit