Patent Publication Number: US-2022232338-A1

Title: Information processing apparatus, information processing method, and program

Description:
TECHNICAL FIELD 
     The present disclosure relates to an information processing apparatus, an information processing method, and a program. 
     BACKGROUND ART 
     In accordance with improvement of an acoustic reproduction technology in recent years, there have been proposed a variety of technologies which reproduce sound fields. For example, in the below-mentioned Non-Patent Document 1, a technology relating to vector base amplitude panning (VBAP) is described. The VBAP is a method in which when a virtual sound source (virtual sound image) is reproduced by three loudspeakers in proximity to one another, gains are determined such that a direction of a synthetic vector obtained by weighting and adding three directional vectors spanning from a listening position toward the loudspeakers by gains imparted to the loudspeakers matches a direction of the virtual sound source. Besides this, there have been proposed technologies and the like which are referred to as wavefront synthesis and higher order ambisonics (HOA). 
     CITATION LIST 
     Patent Document 
     Non-Patent Document 1: Ville Pulkki, “Virtual Sound Source Positioning Using Vector Base Amplitude Panning”, Journal of the Audio Engineering Society vol. 45, Issue 6, pp. 456-466 (1997) 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, the technology described in Non-Patent Document 1 or the like presupposes that the loudspeakers which reproduce sound are fixed onto a surface of the ground or the like. Accordingly, a system in which a sound field is formed by using loudspeakers which are not fixed to the surface of the ground or the like has a problem in that these technologies cannot be applied to the system as they are. 
     One of objects of the present disclosure is to provide an information processing apparatus, an information processing method, and a program, each of which is applicable to the system which forms the sound field by using the loudspeakers which are not fixed to the surface of the ground or the like. 
     Solutions to Problems 
     The present disclosure is, for example, an information processing apparatus including 
     an audio signal generation unit which generates an audio signal reproduced from a loudspeaker on the basis of position information of each of a plurality of unmanned aerial vehicles, each of the unmanned aerial vehicles having the loudspeaker. 
     In addition, the present disclosure is, for example, an information processing method including 
     generating, by an audio signal generation unit, an audio signal reproduced from a loudspeaker on the basis of position information of each of a plurality of unmanned aerial vehicles, each of the unmanned aerial vehicles having the loudspeaker. 
     In addition, the present disclosure is, for example, a program which causes a computer to execute an information processing method including 
     generating, by an audio signal generation unit, an audio signal reproduced from a loudspeaker on the basis of position information of each of a plurality of unmanned aerial vehicles, each of the unmanned aerial vehicles having the loudspeaker. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration example of a reproduction system according to an embodiment. 
         FIG. 2  is a block diagram illustrating a configuration example of each of a UAV and a master device according to the embodiment. 
         FIG. 3  is a diagram which is referenced when one example of processing performed by an audio signal generation unit according to the embodiment is described. 
         FIG. 4  is a diagram which is referenced when one example of processing performed by the audio signal generation unit according to the embodiment is described. 
         FIG. 5  a diagram schematically illustrating one example of a reproduced sound field. 
         FIG. 6  is a diagram which is referenced when one example of a GUI according to the embodiment is described. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, with reference to the accompanying drawings, an embodiment and the like of the present disclosure will be described. Note that the description will be given in the following order.
     &lt;Problem to be Considered&gt;   &lt;Embodiment&gt;   &lt;Modified Example&gt;   

     The below-described embodiment and the like are favorable specific examples of the present disclosure and contents of the present disclosure are not limited to the embodiment and the like. 
     Problem to be Considered 
     In order to facilitate understanding of the present disclosure, first, a problem which should be considered in the embodiment of the present disclosure is described. In the embodiment of the present disclosure, the description will be given by citing a system, as an example, in which a plurality of unmanned flying objects (hereinafter, appropriately referred to as unmanned aerial vehicles (UAVs) is used and audio signals are reproduced from the UAVs, thereby forming a desired sound field. In this system, there is a case where when sound is reproduced by performance or the like by using the plurality of UAVs, it is desired that a sound field is reproduced in accordance with movement of the UAVs. At this time, there is a case where it is preferable that an incoming direction of the sound is from midair where the UAVs are present. However, for example, since positions where loudspeakers can be installed are limited, it is often the case that a desired sense of localization is hardly obtained. For this problem, although it is considered that the loudspeakers are mounted on the UAVs themselves to reproduce the sound, in this case, since it is difficult to obtain accurate positions of the loudspeakers and the positions thereof temporally change, even if the above-mentioned technology is simply applied, it is highly likely that the desired sound field cannot be obtained. Therefore, in the present embodiment, for example, on the basis of position information of the UAVs which change in real time, audio signals assigned from the loudspeakers which the UAVs have are reproduced, thereby realizing the desired sound field, Hereinafter, the present embodiment will be described in detail. 
     Embodiment 
     [Configuration Example of Reproduction System] 
       FIG. 1  is a diagram illustrating a configuration example of a reproduction system (reproduction system  1 ) according to an embodiment of the present disclosure. The reproduction system  1  has, for example, a plurality of UAVs and a master device  20  as one example of an information processing apparatus. The UAVs fly autonomously or in accordance with user control. 
     In  FIG. 1 , three UAVs (UAVs  10 A,  10 B and  10 C) are illustrated. A number of the UAVs in the reproduction system  1  is not limited to three and can be appropriately set, and the number of the UAVs can vary in real time. Note that in a case where it is not required to discern the individual UAVs, the UAVs are collectively called a UAV  10 . 
     The master device  20  is, for example, a personal computer or a smartphone. The master device  20  generates audio signals reproduced from the UAV  10 . Then, the master device  20  supplies the generated audio signals to the UAV  10 . The master device  20  supplies the audio signals to the UAV  10 , for example, by using wireless communication. 
     In an example illustrated in  FIG. 1 , the master device  20  generates the audio signals reproduced from the UAV  10 A and supplies the generated audio signals to the UAV  10 A. In addition, the master device  20  generates audio signals reproduced from the UAV  10 B and supplies the generated audio signals to the UAV  10 B. In addition, the master device  20  generates audio signals reproduced from the UAV  10 C and supplies the generated audio signals to the UAV  10 C. Each UAV reproduces the audio signals supplied from the master device  20  from a loudspeaker which each UAV itself has. The audio signals are reproduced from the UAV  10 , thereby reproducing a desired sound field for a listener LM. 
     [Configuration Example of UAV and Master Device] 
     (Configuration Example of UAV) 
       FIG. 2  is a block diagram illustrating a configuration example of the UAV  10  and the master device  20 . The UAV  10  has, for example, a control unit  101 , an information input unit  102 , a communication unit  103 , and an output unit  104 . 
     The control unit  101  is constituted of a central processing unit (CPU) or the like and comprehensively controls the whole UAV  10 . The UAV  10  has a read only memory (ROM) in which a program executed by the control unit  101  is stored, a random access memory (RAM) used as a work memory upon executing the program, and the like (illustration of these is omitted). 
     The information input unit  102  is an interface to which various kinds of information are inputted from sensors (not illustrated) which the UAV  10  has. As specific examples of the information inputted to the information input unit  102 , motor control information  102   a  for driving a motor, propeller control information  102   b  for controlling a propeller speed of the UAV  10 , and airframe angle information  102   c  which indicates an angle of an airframe of the UAV  10  are cited. 
     In addition, as the information inputted to the information input unit  102 , UAV position information  102   d  which is position information of the UAV  10  is cited. As the sensors for acquiring the UAV position information, stereo vision, a distance sensor, an atmospheric pressure sensor, image information captured by a camera, a global positioning system (GPS), distance measurement by inaudible sound, and a combination of these, and the like are cited. These sensors are used and the heretofore known method is employed, thereby acquiring the position information of the UAV  10  to be inputted to the information input unit  102 . 
     The communication unit  103  is configured to communicate with devices which are present on the surface of the ground and a network, other UAVs, and the like in accordance with control performed by the control unit  101 . Although the communication may be performed in a wired manner, in the present embodiment, wireless communication is supposed. As the wireless communication, a local area network (LAN), Bluetooth (registered trademark), Wi-Fi (registered trademark), a wireless USB (WUSB), or the like is cited. Via the above-mentioned communication unit  103 , the above-described UAV position information is transmitted from the UAV  10  to the master device  20 . In addition, via the above-mentioned communication unit  103 , the audio signals transmitted from the master device  20  are received by the UAV  10 . 
     The output unit  104  is a loudspeaker which outputs the audio signals. The output unit  104  may include an amplifier or the like which amplifies the audio signals. For example, the control unit  101  subjects the audio signals received by the communication unit  103  to predetermined processing (decompression processing or the like) and thereafter, the processed audio signals are reproduced from the output unit  104 . Note that for the output unit  104 , an appropriate configuration such as a single loudspeaker and a loudspeaker array having radial arrangement can be adopted. Note that in the below description, there may be a case where a loudspeaker which the UAV  10 A has is referred to as a loudspeaker  104 A, a loudspeaker which the UAV  10 B has is referred to as a loudspeaker  104 B, a loudspeaker which the UAV  10 C has is referred to as a loudspeaker  104 C, and a loudspeaker which the UAV  10 D has is referred to as a loudspeaker  104 D. 
     Note that the UAV  10  may have a configuration which is different from the above-described configuration. For example, the UAV  10  may have a microphone or the like, which measures sound on the surface of the ground. 
     (Configuration Example of Master Device) 
     The master device  20  has, for example, a control unit  201 , a communication unit  202 , a loudspeaker  203 , and a display  204 . The control unit  201  has an audio signal generation unit  201 A as a function thereof. 
     The control unit  201  is constituted of a CPU or the like and comprehensively controls the whole master device  20 . The audio signal generation unit  201 A which the control unit  201  has generates audio signals corresponding to each of the UAVs. 
     The communication unit  202  is configured to communicate with the UAV  10 . Via the above-mentioned communication unit  202 , the audio signals generated by the audio signal generation unit  201 A are transmitted from the master device  20  to the UAV  10 . 
     The loudspeaker 203 outputs audio signals processed by the UAV  10  and appropriate audio signals. In addition, the display  204  displays various pieces of information. 
     The master device  20  may have a configuration which is different from the above-described configuration. For example, although in the above-described example, the UAV  10  acquires the position information (UAV position information) thereof, the UAV position information may be acquired by the master device  20 . Then, the master device  20  may have various kinds of sensors for acquiring the UAV position information. Note that the acquisition of the UAV position information includes observation of a position of each of the UAVs or estimation of the UAV position thereof based on a result of the observation. 
     [Example of Processing of Master Device] 
     Subsequently, an example of processing performed by the master device  20 , specifically, an example of processing performed by the audio signal generation unit  201 A which the master device  20  has will be described. On the basis of the position information of each of the plurality of UAVs  10 , the audio signal generation unit  201 A generates audio signals reproduced from the output unit  104  which each of the UAVs  10  has. 
     (First Processing Example) 
     The audio signal generation unit  201 A determines driving signals of the loudspeakers for reproducing the desired sound field by utilizing the acquired UAV position information. The present example is an example in which as a sound field reproduction method, VBAP is applied. 
     For simplification, it is assumed that each of the UAVs (UAV  10 A,  10 B, and  10 C) has one loudspeaker. Note that even in a case where each of the UAVs includes a plurality of loudspeakers, when a distance between the loudspeakers is sufficiently close, as compared with other loudspeakers of the other UAV  10 , the loudspeakers may be treated as a single loudspeaker and driving thereof may be conducted by the same signal. In order to perform the processing according to the present example, the UAV  10 A to  10 C among the plurality of UAVs  10  which are present in a space are selected. As the three UAVs selected to perform the processing according to the present example, any three UAVs can be selected. In the present example, three UAVs (UAV  10 A,  10 B, and  10 C) which are close to a position of a virtual sound source VS which is desired to be reproduced are selected. 
     As illustrated in  FIG. 3 , in a case where a unit vector p which faces toward the virtual sound source VS is defined as 
       p∈R 3 , and
 
     unit vectors which surround the unit vector p and face toward the three loudspeakers are defined as 
       l 1 , l 2 , l 3  ∈R 3 ,
 
     the three loudspeakers are selected in such a way that the unit vector p is included within a solid angle surrounded by l 1 , l 2 , and l 3 . In the example illustrated in  FIG. 3 , the loudspeakers  104 A to  104 C which the UAV  10 A to  10 C respectively have are selected. In the present example, l 1 , l 2 , and l 3  and L (described later) based on these correspond to pieces of position information of the UAV  10 A,  10 B, and  10 C. Note that a subscript numeral 1(first) corresponds to the UAV  10 A, a subscript numeral 2 (second) corresponds to the UAV  10 B, and a subscript numeral 3 (third) corresponds to the UAV  10 C. In addition, in a case where subscript or superscript numeral “123” is described, the subscript or superscript numeral indicates values of gains or the like obtained on the basis of the UAVs  10 A to  10 C. In addition, it is indicated that the later-described subscript numeral 4 (fourth) corresponds to the later-described UAV  10 D. Also as to other formulas described below, representation based on the similar prescription is made. 
     Next, the unit vector p can be represented in a linear combination of l 1 , l 2 , and l 3  as follows. 
     
       
         
           
             
               p 
               T 
             
             = 
             
               gL 
               123 
             
           
         
       
     
     However, 
     
       
         
           
             g 
             = 
             
               ( 
               
                 
                   g 
                   1 
                 
                 , 
                 
                   g 
                   2 
                 
                 , 
                 
                   g 
                   3 
                 
               
               ) 
             
           
         
       
     
     represents each loudspeaker gain, and 
     
       
         
           
             
                 
             
             ⁢ 
             
               L 
               = 
               
                 
                   
                     
                       ( 
                       
                         ? 
                       
                       ) 
                     
                     T 
                   
                   . 
                   
                     
 
                   
                   ⁢ 
                   
                     ? 
                   
                 
                 ⁢ 
                 
                   indicates text missing or illegible when filed 
                 
               
             
           
         
       
     
     In the above formula, T represents a matrix or transposition of a vector. 
     The loudspeaker gain g can be obtained by using an inverse matrix from the following formula 1. 
     
       
         
           
             
               
                 
                   g 
                   = 
                   
                     
                       p 
                       T 
                     
                     ⁢ 
                     
                       L 
                       123 
                       
                         - 
                         1 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Although in order for L 123  to have the inverse matrix, it is required for l 1 , l 2 , and l 3  to be linearly independent, because in the present example, it is supposed that the three loudspeakers are not located on one linear line, the inverse matrix of L 123  is invariably present. By normalizing the loudspeaker gain g, a gain of each of the loudspeakers can be obtained. The audio signal generation unit  201 A performs calculation of the obtained loudspeaker gain of each of the loudspeakers for audio signals of the source. Then, the master device  20  transmits the audio signals after the calculation via the communication unit  202  to the UAV  10  having the corresponding loudspeaker. 
     Note that although it is supposed that in the VBAP, distances from a listening position (position where the listener LM is present) to the loudspeakers are equal, even in a case where the distances are not equal, by adding delay to each of the driving signals, the similar effect can be obtained in a quasi manner. A delay time can be obtained from Δl i /c, where a difference between each of the distances and a distance of the loudspeaker which is most distant from the listener LM is Δl i , but c represents sonic speed. However, c represents sonic speed. 
     Incidentally, since the UAV  10  is floating in midair, it is difficult to completely obtain an accurate position of the UAV  10 . Furthermore, in a case where the UAV  10  moves, it is considered that accuracy at which the position of the UAV  10  is estimated is worsened in accordance with speed of the movement. Specifically, the higher the speed of the movement of the UAV  10  is, the larger a movement distance from a current time to a next time is and the larger an error in estimation of the position is. In a case where the error in the estimation of the position is large, even when the reproduction is performed by using the loudspeaker driving signals obtained by supposing ideal positions, the sound field cannot be correctly reproduced. 
     Accordingly, it is desirable that certainty of the position information of the UAV  10  be attained by the audio signal generation unit  201 A of the master device  20 , that is, processing in accordance with the error in the estimation of the position be performed by the audio signal generation unit  201 A thereof. Specifically, it is desirable that driving signals of the loudspeakers in consideration of the error in the estimation of the position be set. For example, it is desirable that filters for obtaining the driving signals of the loudspeakers be regularized and are weighted in accordance with a magnitude of the error in the estimation of the position. Specifically, it is desirable that a weight which contributes to generation of the audio signals of the UAV  10  remaining still among the UAVs  10  which are equally distant from a target sound source be made larger than those of the UAVs  10  which are moving at high speed (UAV  10  whose error in the estimation of the position is large) since the error in the estimation of the position of the UAV  10  remaining still is small. Hereinafter, the processing in consideration of the error in the estimation of the position in the present example will be described. 
     For example, as illustrated in  FIG. 4 , it is supposed that for a reason that the UAV  10 C is moving or other reason, the error in the estimation of the position of loudspeaker  104 C is large. In this case, when panning is performed by using the loudspeakers  104 A,  104 B, and  104 C, a position of a sound image is deviated or moved. Therefore, by using a loudspeaker  104 D (loudspeaker which a UAV  10 D flying in the vicinity of UAV  10 C has) which is close to the loudspeaker  104 C and has an error in the estimation of the position, which allows the virtual sound source VS to be within the solid angle, L 124  is calculated and a normalized gain g 124  is obtained. By using the loudspeakers  104 A,  104 B,  104 C, and  104 D, a sound field can be finally reproduced. Each of the driving signals can be represented as a linear sum of g 123  and g 124 . Specifically, it can be expressed by the following formula. 
     
       
         
           
             g 
             = 
             
               
                 [ 
                 
                   
                     g 
                     1 
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     g 
                     2 
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     g 
                     3 
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     g 
                     4 
                   
                 
                 ] 
               
               = 
               
                 
                   λ 
                   ⁡ 
                   
                     [ 
                     
                       
                         g 
                         1 
                         123 
                       
                       ⁢ 
                       
                         g 
                         2 
                         123 
                       
                       ⁢ 
                       
                         g 
                         3 
                         123 
                       
                       ⁢ 
                       0 
                     
                     ] 
                   
                 
                 + 
                 
                   
                     ( 
                     
                       1 
                       - 
                       λ 
                     
                     ) 
                   
                   ⁡ 
                   
                     [ 
                     
                       
                         g 
                         1 
                         124 
                       
                       ⁢ 
                       
                         g 
                         2 
                         124 
                       
                       ⁢ 
                       
                         g 
                         4 
                         124 
                       
                     
                     ] 
                   
                 
               
             
           
         
       
     
     Here, λ can be defined as a function of the error in the estimation of the position on the basis of a previously conducted experiment or the like. For example, λ can be set to one when an error in the estimation of the position Δr is a certain threshold value Δr min  or less and to zero when the error in the estimation of the position Δr is Δr max  or less. 
     Note that in a case where all of the positions of the UAVs  10  associated with the reproduction of the virtual sound source similarly include the errors, several combinations of the UAVs which allow the virtual sound source VS to be included in the solid angle are determined and an average thereof is taken, thereby allowing averagely correct direction information to be presented. 
     (Second Processing Example) 
     The audio signal generation unit  201 A determines driving signals of loudspeakers which reproduce a desired sound field by utilizing acquired UAV position information. The present example is an example in which as the sound field reproduction method, HOA is applied. 
     When a mode domain coefficient of the desired sound field is defined as follows 
       a n   m (ω),
 
     a reproduction signal D 1 (ω) of the l-th loudspeaker which reproduces the desired sound field can be represented by the following formula 2. 
     
       
         
           
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         D 
                         ⁢ 
                         
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                         ⁢ 
                         
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                             ⁢ 
                             
                                 
                             
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                               ⁢ 
                               
                                 
                                   
                                     a 
                                     n 
                                     m 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     ω 
                                     ) 
                                   
                                 
                                 
                                   G 
                                   ⁢ 
                                   
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                               ⁢ 
                               
                                 
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                                   m 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
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                                       ⁢ 
                                       
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                                       ⁢ 
                                       
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                         indicates text missing or illegible when filed 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     However, each of (r 1 , θ 1 , ϕ 1 ) in Formula 2 indicates a distance from the origin to the l-th loudspeaker (The speaker may be referred to as a loudspeaker l.), an elevation angle, and an azimuth angle, which correspond to the position information in the second processing example. 
     In addition, 
       Y n   m    
     represents spherical harmonics, and m and n are HOA orders. 
     In addition, 
       G n   m    
     is an HOA coefficient of a transfer function of a loudspeaker, and in a case where the loudspeaker is a point sound source, the HOA coefficient can be represented by the following formula. 
     
       
         
           
             
                 
             
             ⁢ 
             
               
                 
                   G 
                   n 
                   m 
                 
                 ⁡ 
                 
                   ( 
                   
                     
                       r 
                       ⁢ 
                       
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               = 
               
                 
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                         2 
                         ) 
                       
                     
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                 ⁢ 
                 
                   
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                     ) 
                   
                 
               
             
           
         
       
       
         
           
             
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             ⁢ 
             
               indicates text missing or illegible when filed 
             
           
         
       
     
     However, 
       h n   (2)    
     is a ball Hankel function of the second kind. 
     Also in the present example, processing in consideration of an error in estimation of a position can be performed. There may be a case where the processing described below is referred to as a mode matching since the processing is to match modes of HOA. 
     In the later-described multi-point control (an example in which a plurality of control points is present), a sound field excluding the control points is not considered, and there is a problem in that it is required to determine arrangement of optimum control points. On the other hand, in a method of the mode matching, by performing conversion to a mode region and aborting an expansion coefficient at an appropriate order, a range with one control point as a center can be averagely controlled. 
     A desired sound field is defined as p(r) and a transfer function G(r|r l ) from the loudspeaker l to a point r within a control region is expanded by a prescribed function shown below. 
     
       
         
           
             
               
                 φ 
                 n 
                 m 
               
               ⁡ 
               
                 ( 
                 r 
                 ) 
               
             
             = 
             
               
                 
                   j 
                   n 
                 
                 ⁡ 
                 
                   ( 
                   kr 
                   ) 
                 
               
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                   Y 
                   n 
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                 ⁡ 
                 
                   ( 
                   
                     θ 
                     , 
                     ψ 
                   
                   ) 
                 
               
             
           
         
       
     
     The desired sound field p(r) and the transfer function G(r|r l ) can be represented by using expansion coefficients 
       b n   m , c n,l   m    
     as 
     
       
         
           
             
                 
             
             ⁢ 
             
               
                 G 
                 ⁡ 
                 
                   ( 
                   
                     r 
                     | 
                     
                       r 
                       ⁢ 
                       
                         ? 
                       
                     
                   
                   ) 
                 
               
               = 
               
                 
                   ∑ 
                   
                     n 
                     = 
                     0 
                   
                 
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                         m 
                         = 
                         
                           - 
                           n 
                         
                       
                       n 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       c 
                       ⁢ 
                       
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                       ⁢ 
                       
                         
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                           n 
                           m 
                         
                         ⁡ 
                         
                           ( 
                           r 
                           ) 
                         
                       
                     
                   
                 
               
             
           
         
       
       
         
           
             
                 
             
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                       ⁢ 
                       
                         b 
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               ⁢ 
               
                 
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                   indicates text missing or illegible when filed 
                 
               
             
           
         
       
     
     respectively. 
     Here, when the expansion is aborted at the Nth order, relationship between a reproduced sound field in a mode region and a driving signal of the loudspeaker can be represented as follows 
     Cd=b (b represents a desired sound field in the mode region), 
     but 
     
       
         
           
             
               C 
               = 
               
                 [ 
                 
                   
                     
                       
                         c 
                         
                           0 
                           , 
                           1 
                         
                         0 
                       
                     
                     
                       ⋯ 
                     
                     
                       
                         c 
                         
                           0 
                           , 
                           L 
                         
                         0 
                       
                     
                   
                   
                     
                       ⋮ 
                     
                     
                       ⋱ 
                     
                     
                       ⋮ 
                     
                   
                   
                     
                       
                         c 
                         
                           N 
                           , 
                           1 
                         
                         N 
                       
                     
                     
                       ⋯ 
                     
                     
                       
                         c 
                         
                           N 
                           , 
                           L 
                         
                         N 
                       
                     
                   
                 
                 ] 
               
             
             , 
             
               b 
               = 
               
                 
                   [ 
                   
                     
                       
                         
                           b 
                           0 
                           0 
                         
                       
                     
                     
                       
                         ⋮ 
                       
                     
                     
                       
                         
                           b 
                           N 
                           N 
                         
                       
                     
                   
                   ] 
                 
                 . 
               
             
           
         
       
     
     A pseudo inverse matrix of C is obtained, thereby allowing the driving signal of the loudspeaker corresponding to each of the UAVs to be obtained. However, as described above, in a case where the error in the estimation of the position of the loudspeaker which the l-th UAV has is large, it is anticipated that an error in sound field reproduction by a driving signal d l  of the l-th loudspeaker is large. Therefore, it is desirable that contribution made by d l  be decreased. In order to decrease the contribution of d l , a regularization term (regularization component) is added to the driving signal as shown below. 
     
       
         
           
             
               d 
               ^ 
             
             = 
             
               
                 arg 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   
                     min 
                     d 
                   
                   ⁢ 
                   
                     
                        
                       
                         b 
                         - 
                         Cd 
                       
                        
                     
                     2 
                   
                 
               
               + 
               
                 λ 
                 ⁢ 
                 
                   
                      
                     Ad 
                      
                   
                   2 
                 
               
             
           
         
       
     
     Here, λ is a parameter which determines strength of regularization, and A represents a diagonal matrix which has a weight a l , which determines relative strength of the regularization for the loudspeaker l, as a diagonal component. 
     A solution of this optimization problem is obtained as shown below. 
     
       
         
           
             
               d 
               ^ 
             
             = 
             
               
                 
                   ( 
                   
                     
                       
                         C 
                         R 
                       
                       ⁢ 
                       C 
                     
                     + 
                     
                       λ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       A 
                     
                   
                   ) 
                 
                 
                   - 
                   1 
                 
               
               ⁢ 
               
                 C 
                 H 
               
               ⁢ 
               b 
             
           
         
       
     
     As described above, the audio signal generation unit  201 A can generate the audio signals in consideration of the error in the estimation of the position. 
     Note that for example, by performing the above-described first and second processing examples, it is made possible to reproduce various sound fields (sound images). 
     (Third Processing Example) 
     The present example is an example in which sound field reproduction is performed by multi-point control in which driving signals of loudspeakers at a plurality of control points are obtained. The control points are previously set positions. In addition, a transfer function from a position of a loudspeaker up to the control points can be obtained by previous measurement or by assumption of a free space and approximation by using a green function. 
     When sound pressure at a control point i is defined as p i , a transfer function from a loudspeaker l to the control point i, which is position information in the present example, is defined as G il , and a loudspeaker driving signal of the loudspeaker l is defined as d l , and the following is defined, 
     
       
         
           
             
                 
             
             ⁢ 
             
               
                 P 
                 = 
                 
                   
                     [ 
                     
                       
                         p 
                         ⁢ 
                         
                           ? 
                         
                       
                       , 
                       … 
                       ⁢ 
                       
                           
                       
                       , 
                       
                         p 
                         ⁢ 
                         
                           ? 
                         
                       
                     
                     ] 
                   
                   ⁢ 
                   
                     ? 
                   
                 
               
               , 
               
                 
 
               
               ⁢ 
               
                   
               
               ⁢ 
               
                 D 
                 = 
                 
                   
                     [ 
                     
                       
                         d 
                         ⁢ 
                         
                           ? 
                         
                       
                       , 
                       … 
                       ⁢ 
                       
                           
                       
                       , 
                       
                         d 
                         ⁢ 
                         
                           ? 
                         
                       
                     
                     ] 
                   
                   T 
                 
               
               , 
               
                 
 
               
               ⁢ 
               
                   
               
               ⁢ 
               
                 G 
                 = 
                 
                   [ 
                   
                     G 
                     ⁢ 
                     
                       ? 
                     
                   
                   ] 
                 
               
             
           
         
       
       
         
           
             
               ? 
             
             ⁢ 
             
               indicates text missing or illegible when filed 
             
           
         
       
     
     and when a loudspeaker driving signal to obtain an optimum sound field in the meaning of least squares is defined as follows, 
       {circumflex over (d)} 
     the loudspeaker driving signal can be obtained as 
     
       
         
           
             
               d 
               ^ 
             
             = 
             
               arg 
               ⁢ 
               
                 
                   min 
                   d 
                 
                 ⁢ 
                 
                   
                     
                        
                       
                         P 
                         - 
                         Gd 
                       
                        
                     
                     2 
                   
                   . 
                 
               
             
           
         
       
     
     In the present example, processing in consideration of an error in estimation of a position may be performed. 
     For example, in a case where an error in estimation of a position of a loudspeaker which the l-th UAV among a plurality of UAVs has is large, since it is anticipated that an error in sound field reproduction is increased due to a driving signal d l  of the l-th loudspeaker, it is desirable that contribution of the driving signal d l  of the loudspeaker be decreased. Therefore, as shown below, a regularization term is added to the driving signal. 
     
       
         
           
             
               d 
               ^ 
             
             = 
             
               
                 arg 
                 ⁢ 
                 
                   
                     min 
                     d 
                   
                   ⁢ 
                   
                     
                        
                       
                         P 
                         - 
                         Gd 
                       
                        
                     
                     2 
                   
                 
               
               + 
               
                 λ 
                 ⁢ 
                 
                   
                      
                     Ad 
                      
                   
                   2 
                 
               
             
           
         
       
     
     Here, λ is a parameter which determines strength of regularization, and A represents a diagonal matrix which has a weight a l , which determines relative strength of the regularization for the loudspeaker l, as a diagonal component. For example, in a case where an error in estimation of a position of a third UAV  10 C is large, a value of a component of the UAV  10 C in A is made large, thereby allowing contribution of a driving signal of the UAV  10 C to be decreased. 
     A solution of this optimization problem is obtained as shown below. 
     
       
         
           
             
               d 
               ^ 
             
             = 
             
               
                 
                   ( 
                   
                     
                       
                         G 
                         H 
                       
                       ⁢ 
                       G 
                     
                     + 
                     
                       λ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       A 
                     
                   
                   ) 
                 
                 
                   - 
                   1 
                 
               
               ⁢ 
               GP 
             
           
         
       
     
     The above-described processing is performed by the audio signal generation unit  201 A, thereby generating the audio signals reproduced by the UAVs. 
     (Fourth Processing Example) 
     A fourth processing example is an example in which sound field reproduction is performed by spherical harmonics expansion in which a region where the sound field reproduction is performed is designated. In the above-described mode matching, it is expected that one point is designated as the control point and an order is determined in the mode region for control, thereby smoothly reproducing the periphery of the control point, and a control region is not directly designated. In contrast to this, in the present example, a region V is explicitly controlled, thereby obtaining driving signals of loudspeakers of UAVs. 
     When a desired sound field is defined as p(r) (note that r is a three-dimensional vector), a transfer function from a loudspeaker l up to a point r within a control region, which is position information in the present example, is defined as G(r|r l ), g(r)=[G(r|r 1 ), G(r|r 2 ) . . . G(r|r L )] T  is defined, and a driving signal of the loudspeaker to obtain an optimum sound field within the region V is defined as follows, 
       {circumflex over (d)} 
     a loudspeaker driving signal can be obtained as d(ω) which minimizes a loss function J shown below. 
     
       
         
           
             J 
             = 
             
               
                 ∫ 
                 
                   r 
                   ∈ 
                   V 
                 
               
               ⁢ 
               
                 
                   
                      
                     
                       
                         p 
                         ⁡ 
                         
                           ( 
                           r 
                           ) 
                         
                       
                       - 
                       
                         
                           g 
                           ⁡ 
                           
                             ( 
                             r 
                             ) 
                           
                         
                         ⁢ 
                         d 
                       
                     
                      
                   
                   2 
                 
                 ⁢ 
                 dr 
               
             
           
         
       
     
     Since the above-described formula is shown by a space region, conversion is made from the space region to a mode region, and an order of the spherical harmonics function is aborted at the Nth order, the loss function J can be thereby approximated to 
     
       
         
           
             
               J 
               ≈ 
               
                 
                   
                     ( 
                     
                       Cd 
                       - 
                       b 
                     
                     ) 
                   
                   H 
                 
                 ⁢ 
                 
                   W 
                   ⁡ 
                   
                     ( 
                     
                       Cd 
                       - 
                       b 
                     
                     ) 
                   
                 
               
             
             , 
           
         
       
     
     but 
     
       
         
           
             
                 
             
             ⁢ 
             
               C 
               = 
               
                 [ 
                 
                   
                     
                       
                         c 
                         
                           0 
                           , 
                           1 
                         
                         0 
                       
                     
                     
                       ⋯ 
                     
                     
                       
                         c 
                         
                           0 
                           , 
                           L 
                         
                         0 
                       
                     
                   
                   
                     
                       ⋮ 
                     
                     
                       ⋱ 
                     
                     
                       ⋮ 
                     
                   
                   
                     
                       
                         c 
                         
                           N 
                           , 
                           1 
                         
                         N 
                       
                     
                     
                       ⋯ 
                     
                     
                       
                         c 
                         
                           N 
                           , 
                           L 
                         
                         N 
                       
                     
                   
                 
                 ] 
               
             
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               W 
               = 
               
                 [ 
                 
                   
                     
                       
                         w 
                         
                           00 
                           , 
                           00 
                         
                       
                     
                     
                       ⋯ 
                     
                     
                       
                         w 
                         
                           00 
                           , 
                           NN 
                         
                       
                     
                   
                   
                     
                       ⋮ 
                     
                     
                       ⋱ 
                     
                     
                       ⋮ 
                     
                   
                   
                     
                       
                         w 
                         
                           NN 
                           , 
                           00 
                         
                       
                     
                     
                       ⋯ 
                     
                     
                       
                         w 
                         
                           NN 
                           , 
                           NNL 
                         
                       
                     
                   
                 
                 ] 
               
             
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               
                 w 
                 ⁢ 
                 
                   ? 
                 
               
               = 
               
                 
                   ∫ 
                   
                     r 
                     ∈ 
                     V 
                   
                 
                 ⁢ 
                 
                   
                     ? 
                   
                   ⁢ 
                   
                     ( 
                     r 
                     ) 
                   
                   ⁢ 
                   
                     
                       φ 
                       
                         
                           n 
                           ′ 
                         
                         ⁢ 
                         
                           m 
                           ′ 
                         
                       
                     
                     ⁡ 
                     
                       ( 
                       r 
                       ) 
                     
                   
                   ⁢ 
                   dr 
                 
               
             
           
         
       
       
         
           
             
               ? 
             
             ⁢ 
             
               indicates text missing or illegible when filed 
             
           
         
       
     
     Here, ϕ n  is a basis function which can be represented by the following formula. 
     
       
         
           
             
               
                 φ 
                 nm 
               
               ⁡ 
               
                 ( 
                 r 
                 ) 
               
             
             = 
             
               
                 
                   j 
                   n 
                 
                 ⁡ 
                 
                   ( 
                   kr 
                   ) 
                 
               
               ⁢ 
               
                 
                   Y 
                   n 
                   m 
                 
                 ⁡ 
                 
                   ( 
                   
                     θ 
                     , 
                     ψ 
                   
                   ) 
                 
               
             
           
         
       
     
     In the above formula, j n  (kr) is a spherical Bessel function, Y n   m  is spherical harmonics, and c ml  and b l  are expansion coefficients of G(r|rl) and p(r) by a prescribed function ϕ n . 
     In the present example, processing in consideration of an error in estimation of a position may be performed. 
     In a case where an error in estimation of a position of the l-th loudspeaker is large, since it is anticipated that an error in sound field reproduction due to a driving signal d l  of the loudspeaker l, it is desirable that contribution of the driving signal d l  be decreased. Therefore, as shown in the following formula 3, a regularization term is added to a loudspeaker driving signal. 
     
       
         
           
             
               
                 
                   J 
                   ≈ 
                   
                     
                       
                         
                           ( 
                           
                             Cd 
                             - 
                             b 
                           
                           ) 
                         
                         H 
                       
                       ⁢ 
                       
                         W 
                         ⁡ 
                         
                           ( 
                           
                             Cd 
                             - 
                             b 
                           
                           ) 
                         
                       
                     
                     + 
                     
                       λ 
                       ⁢ 
                       
                         
                            
                           Ad 
                            
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     In the formula 3, A is a diagonal matrix which has a weight a l , which determines strength of regularization for the loudspeaker l, as a diagonal component. Large regularization can be imposed on the loudspeaker l whose error in the estimation of the position is large. An optimum solution in the formula 3 is obtained as shown below. 
     
       
         
           
             
               d 
               ^ 
             
             = 
             
               
                 
                   ( 
                   
                     
                       
                         C 
                         H 
                       
                       ⁢ 
                       WC 
                     
                     + 
                     
                       λ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       A 
                     
                   
                   ) 
                 
                 
                   - 
                   1 
                 
               
               ⁢ 
               
                 C 
                 H 
               
               ⁢ 
               
                   
               
               ⁢ 
               Wb 
             
           
         
       
     
     In a mode region, minimization of an error within a certain region V q  can be approximated in the formula 3 as shown below. 
     
       
         
           
             
               d 
               ^ 
             
             = 
             
               
                 arg 
                 ⁢ 
                 
                   
                     min 
                     d 
                   
                   ⁢ 
                   
                     
                       ∑ 
                       
                         q 
                         = 
                         1 
                       
                       Q 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         ∫ 
                         
                           r 
                           ∈ 
                           
                             V 
                             q 
                           
                         
                       
                       ⁢ 
                       
                         
                            
                           
                             p 
                             - 
                             
                               
                                 g 
                                 ⁡ 
                                 
                                   ( 
                                   r 
                                   ) 
                                 
                               
                               ⁢ 
                               d 
                             
                           
                            
                         
                         2 
                       
                     
                   
                 
               
               + 
               
                 λ 
                 ⁢ 
                 
                   
                      
                     Ad 
                      
                   
                   2 
                 
               
             
           
         
       
     
     The above-described processing is performed by the audio signal generation unit  201 A, thereby generating the audio signals reproduced by the UAVs. 
     [Example of Reproduced Sound Field] 
     As one example of a designing method of a reproduced sound field, it is considered that irrespective of movement of an UAV  10 , sound field reproduction is performed. For example, as schematically illustrated in  FIG. 5 , while three UAVs (UAV  10 A to  10 C) move around a listener LM, a localization position of a virtual sound source VS can be fixed in a predetermined position in a space. This sound field reproduction can be realized by fixing a coordinate system in the above-described formula 1 and formula 2 in the space and calculating loudspeaker driving signals of the UAVs while position information of the UAVs is updated. Specifically, the loudspeaker driving signals are obtained while values of L described in the first processing example and (r l , θ l , ϕ l ) described in the second processing example are updated, thereby allowing a sound field according to the present example to be reproduced. By the sound field reproduction according to the present example, for example, in a case where evacuation guidance is conducted by sound by using the UAVs  10 , while the UAVs  10  are changing positions in order to avoid obstacles and flying, a sound field where sound is invariably reproduced from an appropriate arrival direction (for example, a direction of an emergency exit) can be realized. 
     As other example of the designing method of the reproduced sound field, by setting the coordinate system in the above-described formula 1 and formula 2 in such a way as to be in conjunction with a position and a direction of a specific UAV, it is made possible to move the position of the virtual sound source VS in accordance with movement of the above-mentioned specific UAV. For example, by fixing the coordinate system to a certain UAV and moving and rotating the UAV group which includes the above-mentioned specific UAV without deforming formation of the UAV group, the virtual sound source VS can also be parallelly moved and rotated in accordance with the movement of the UAV group. 
     [Sound Field Designing Tool] 
     According to the present disclosure, for example, a tool for designing a sound field for creators is provided. This tool is, for example, a tool which performs displaying of limitation of a sound field which can be designed and accuracy in accordance with moving speeds of the UAVs  10 . 
     For example, considered is a situation where a creator previously designs the movement of the UAV group as in a case where the UAV group which includes the plurality of UAVs is used for a show or other case. In a case where the sound field reproduction is performed by the plurality of UAVs, a creator also designs the sound field by using the tool. When the creator makes this designing, as illustrated in  FIG. 6 , on a sound field designing tool with which the virtual sound source VS is located on a graphical user interface (GUI), reproduction accuracy of the virtual sound source VS can be presented to a user in accordance with arrangement of the UAVs. In an example illustrated in  FIG. 6 , a listener LM is displayed in a substantially center. In addition, on the GUI illustrated in  FIG. 6 , information that a predetermined space region AA and space region AC are regions, in each of which reproduction accuracy is high, since the movement of the UAV group is small; information that other space region AB is a region in which reproduction accuracy is low since the movement of the UAV group is large and the plurality of UAVs is densely present; and information that other space region AD is a region in which a reproduction region is narrow since the UAVs are only sparsely present can be visually presented to a user. In addition, on the basis of the accuracy of the above-described sound field reproduction, locating the virtual sound source VS may be forbidden on the tool. For example, it may be arranged on the GUI that the virtual sound source VS cannot be located in a place where the accuracy of the sound field reproduction is low (for example, the space region AD). Thus, mismatching between the sound field on the tool which a creator designs and the sound field actually reproduced by using the UAVs can be prevented. 
     [Relocation and Increase/Decrease in Number of UAVs] 
     In the embodiment of the present disclosure, the UAVs may be relocated and a number of UAVs may be increased or decreased. The positions of the UAVs  10  are relocated so as to optimize the reproduced sound field (as a more specific example, wavefronts to realize the desired sound field). 
     Considered is a situation where previous arrangement of optimum UAVs  10  and designing of a reproduced sound field cannot be made as in case where wavefronts reproduced are dynamically determined in accordance with surrounding circumstances or other case. As the above-mentioned situation, supposed is a situation where in accordance with a position of a listener who moves, the position of the reproduced sound field is changed by the UAVs  10 ; a situation where in accordance with a number of persons to whom a dynamically changing reproduced sound field is desired to be delivered, a range of the reproduced sound field is changed; a situation where in accordance with gesture or movement of a person, the reproduced sound field such as the position of the virtual sound source is changed; or other situation. In a case where in the above-described situation, it is determined by the master device  20  that in order to reproduce the desired sound field at sufficient accuracy, a number of UAVs  10  is small, a UAV  10  or UAVs  10  may be added by control performed by the master device  20  or the UAVs  10  may be relocated in optimum positions to reproduce the desired sound field. For example, the control is made so as to increase density of UAVs  10  in a virtual sound source direction. In order to obtain the arrangement of the UAVs  10 , for example, the technology described in “S. Koyama, et al., “Joint source and sensor placement for sound field control based on empirical interpolation method”, Proc. IEEE ICASSP, 2018.E” can be applied. 
     Modified Example 
     Hereinbefore, although the embodiment of the present disclosure is described, the present disclosure is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present disclosure. 
     The master device in the above-described embodiment may be a device which remotely controls the UAVs. In addition, one or a plurality of UVAs among the plurality of UAVs may function as the master device, that is, the information processing apparatus. In other words, one or the plurality of UAVs among the plurality of UAVs may have the audio signal generation unit or audio signal generation units and audio signals generated by the audio signal generation unit or audio signal generation units may also be transmitted to the other UAVs. In addition, the master device  20  may be a server device on a cloud or the like. 
     The above-described calculation in each of the processing examples is one example, the processing in each of the processing examples may be realized other calculation. In addition, the processing in each of the above-described processing examples may be independently performed or may be performed together with other processing. In addition, the configuration of each of the UAVs is also one example, and the heretofore known configuration may be added to the configuration of each of the UAVs in the embodiment. In addition, the number of the UAVs can be appropriately changed. 
     The present disclosure can also be realized by an apparatus, a method, a program, a system, and the like. For example, a program which performs the function described in the above-described embodiment can be downloaded, and an apparatus which does not have the function described therein downloads and install the program, thereby making it possible to perform the control described in the embodiment on the apparatus. The present disclosure can also be realized by a server which distributes the program described above. In addition, the matters described in the embodiment and the modified example can be appropriately combined. In addition, contents of the present disclosure are not limitedly interpreted by the effect exemplified in the present description. 
     The present disclosure can also adopt the below-described configuration.
     (1)   

     An information processing apparatus including 
     an audio signal generation unit which generates an audio signal reproduced from a loudspeaker on the basis of position information of each of a plurality of unmanned aerial vehicles, each of the unmanned aerial vehicles having the loudspeaker.
     (2)   

     The information processing apparatus according to (1), in which 
     the audio signal generated by the audio signal generation unit is an audio signal which forms a sound field.
     (3)   

     The information processing apparatus according to (2), in which 
     the audio signal generation unit generates the audio signal by VBAP.
     (4)   

     The information processing apparatus according to (2) or (3), in which 
     the audio signal generation unit generates the audio signal by wavefront synthesis.
     (5)   

     The information processing apparatus according to any one of (2) to (4), in which 
     the sound field is a sound field which is fixed in a space.
     (6)   

     The information processing apparatus according to any one of (2) to (4), in which 
     the sound field is a sound field which changes in conjunction with movement of a predetermined unmanned aerial vehicle.
     (7)   

     The information processing apparatus according to any one of (1) to (6), in which 
     the audio signal generation unit performs processing in accordance with certainty of position information of the predetermined unmanned aerial vehicle.
     (8)   

     The information processing apparatus according to (7), in which 
     by weighting and adding a first loudspeaker gain and a second loudspeaker gain, the first loudspeaker gain calculated on the basis of position information of a plurality of unmanned aerial vehicles which include the predetermined unmanned aerial vehicle, the second loudspeaker gain calculated on the basis of position information of a plurality of unmanned aerial vehicles which do not include the predetermined unmanned aerial vehicle, the audio signal generation unit calculates a third loudspeaker gain and generates the audio signal by using the third loudspeaker gain.
     (9)   

     The information processing apparatus according to (7), in which 
     by adding, to the audio signal, a regularization component in accordance with the certainty of the position information, the audio signal generation unit generates the audio signal reproduced from the loudspeaker.
     (10)   

     The information processing apparatus according to any one of (7) to (9), in which 
     the certainty of the position information is determined in accordance with a moving speed of the predetermined unmanned aerial vehicle.
     (11)   

     The information processing apparatus according to any one of (1) to (10), in which 
     the information processing apparatus is any one of the plurality of unmanned aerial vehicles.
     (12)   

     The information processing apparatus according to any one of (1) to (10), in which 
     the information processing apparatus is an apparatus which is different from the plurality of unmanned aerial vehicles.
     (13)   

     An information processing method including 
     generating, by an audio signal generation unit, an audio signal reproduced from a loudspeaker on the basis of position information of each of a plurality of unmanned aerial vehicles, each of the unmanned aerial vehicles having the loudspeaker.
     (14)   

     A program which causes a computer to execute an information processing method including 
     generating, by an audio signal generation unit, an audio signal reproduced from a loudspeaker on the basis of position information of each of a plurality of unmanned aerial vehicles, each of the unmanned aerial vehicles having the loudspeaker. 
     REFERENCE SIGNS LIST 
     
         
           1  Reproduction system 
           10 A to  10 D UAV 
           20  Master device 
           201 A Audio signal generation unit