Patent Publication Number: US-2021185174-A1

Title: Call terminal, call system, control method of call terminal, and non-transitory recording medium

Description:
TECHNICAL FIELD 
     The present invention relates to a call terminal, a call system, and a control method of a call terminal, in which a call is performed with multiple people. The present invention also relates to a call program for causing a computer to operate as the call terminal, and a recording medium recording such a call program. 
     The present application claims priority to Japanese Patent Application No. 2018-141663 filed in Japan on 27 July, 2018, of which contents are incorporated herein by reference. 
     BACKGROUND ART 
     In recent years, as information terminals as typified by smartphones have become widespread, it is commonplace for each individual to acquire various pieces of information and perform communication via the Internet. As such an information terminal, not only the smartphone, but also a smart television capable of receiving information on the Internet via an interface of the television, a smart speaker capable of receiving such information via voices, and the like have been developed, which are appropriately used depending on their purposes and applications. 
     One example of the communication means using the information terminal is a call. A call, which is communication performed in a conversational style mainly using voices, is capable of implementing natural communication, and is frequently used in the modern life as well. In other words, the information terminal described above is used as a call terminal as well. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP H11-68977 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, conventionally, a general call made by a call terminal mainly assumes a one-to-one call. A one-to-many or many-to-many call as used in a teleconference system or the like presupposes a dedicated system. For example, a multi-person call system described in PTL 1 presupposes a dedicated call server apparatus. 
     A main object of one aspect of the present invention is to provide a call terminal capable of appropriately implementing a call by a large number of people, and techniques pertaining to the call terminal. 
     Solution to Problem 
     A call terminal according to one aspect of the present invention includes: a reception unit configured to receive voice signals of one or more call partners; a localization position determination unit configured to determine localization positions corresponding to respective voice signals received in the reception unit in a manner of not overlapping with each other; and a voice output unit configured to output voices corresponding to voice signals in a manner that the voices are localized at the localization positions determined by the localization position determination unit. 
     A call system according to one aspect of the present invention is a call system including: a call terminal; and a call server, wherein the call terminal receives voice signals of one or more call partners, the call system comprises a localization position determination unit configured to determine localization positions corresponding to respective voice signals received by the call terminal in a manner of not overlapping with each other, and the call terminal outputs voices corresponding to the received voice signals in a manner that the voices are localized at the localization positions determined by the localization position determination unit. 
     A control method of a call terminal according to one aspect of the present invention includes: a reception step of receiving voice signals of one or more call partners; a localization position determination step of determining localization positions corresponding to respective voice signals received in the reception step in a manner of not overlapping with each other; and a voice output step of outputting voices corresponding to voice signals in a manner that the voices are localized at the localization positions determined by the localization position determination step. 
     Advantageous Effects of Invention 
     According to one aspect of the present invention, a call by a large number of people can be appropriately implemented by using a call terminal. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a principal configuration of a call terminal according to a first embodiment. 
         FIG. 2  is a diagram illustrating examples of a localizable range according to the first embodiment. 
         FIG. 3  is a diagram illustrating examples of localization positions of voices according to the first embodiment. 
         FIG. 4  is a diagram illustrating examples of localization positions of voices according to the first embodiment. 
         FIG. 5  is a diagram illustrating examples of localization positions of voices according to the first embodiment. 
         FIG. 6  is a diagram illustrating examples of localization positions of voices according to the first embodiment. 
         FIG. 7  is a flowchart illustrating an example of a procedure of control processing of the call terminal according to the first embodiment. 
         FIG. 8  is a block diagram illustrating a principal configuration of a call terminal according to a second embodiment. 
         FIG. 9  is a diagram illustrating examples of a localizable range according to the second embodiment. 
         FIG. 10  is a flowchart illustrating an example of a procedure of control processing of the call terminal according to the second embodiment. 
         FIG. 11  is a block diagram illustrating a principal configuration of a call system according to a third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Each embodiment of the present invention will be described below in detail. Note that, unless otherwise specifically noted, the configuration described in these embodiments is not to limit the scope of the present invention only to the configuration. 
     First Embodiment 
     A call terminal  1  and a control method of the call terminal  1  according to a first embodiment will be described below with reference to  FIGS. 1 to 7 . 
     Call Terminal  1   
       FIG. 1  is a block diagram illustrating a principal configuration of the call terminal  1  according to the first embodiment. As illustrated in  FIG. 1 , the call terminal  1  includes a call participant count acquisition unit  101 , a voice signal acquisition unit (reception unit)  102 , a control unit  103 , a voice signal reproduction unit (voice output unit)  104 , and a storage unit  105 . 
     Note that the call terminal  1  is configured to be capable of implementing a call by a large number of people (at least three people). The call terminal  1  can be appropriately used for a teleconference system, a call system using a VR space, or the like as well. People who participate in a call made by a large number of people are hereinafter referred to as call participants. Among the call participants, a person who operates the call terminal  1  is hereinafter referred to as a user, and people other than the user are hereinafter referred to as call partners. 
     Call Participant Count Acquisition Unit  101   
     The call participant count acquisition unit  101  acquires the number of call partners who are calling the user from the outside of the call terminal  1 . In the present embodiment, the number of call partners refers to the number of call participants among the call participants who participate in the call, except for the user himself/herself. For example, in a case where there is a one-to-one call being performed with a certain user, the number of call partners is one, whereas in a case where there is a call being performed with three people being involved, the number of call partners is two. Note that the call participant count acquisition unit  101  may calculate the number of call partners by acquiring the number of call participants who participate in the call and then subtracting 1 from the acquired number. 
     Note that the call participant count acquisition unit  101  may not be included in the call terminals of all of the call participants. For example, the call terminal  1  of the user may serve as a main terminal, and only the call terminal  1  of the user may include the call participant count acquisition unit  101 . In this case, information of the call participant count acquired by the call participant count acquisition unit  101  in the call terminal  1  of the user may be configured to be transmitted to the call terminals of other call participants (call partners). With this configuration, the call participant count can be efficiently acquired while reducing the processing amount of the entire system. Instead of the call terminal of each call participant, a server (not illustrated) may include the call participant count acquisition unit. In this case, information of the call participant count acquired by the call participant count acquisition unit of the server may be configured to be transmitted to the call terminal of each call participant. With this configuration as well, the call participant count can be efficiently acquired while reducing the processing amount of the entire system. 
     Voice Signal Acquisition Unit  102   
     The voice signal acquisition unit  102  acquires a voice signal of each of one or more call partners. Specifically, the voice signal acquisition unit  102  acquires as many voice signals as the number of the call participant count acquired by the call participant count acquisition unit  101  from the outside of the call terminal  1 . In the present embodiment, the voice signal is a voice signal corresponding to the voice of the call partner(s) with which the user performs a call, and preferably is a voice signal in a monaural format. The voice signal acquisition unit  102  may be configured to acquire the voice signal that is compressed with some compression method. In this case, the voice signal acquisition unit  102  decodes the acquired voice signal with an appropriate decoding method. The voice signal acquisition unit  102  may be configured to acquire the voice signal in a format other than the monaural format, that is, the voice signal having two or more channels. In this case, the voice signal acquisition unit  102  may be configured to downmix the acquired multi-channel voice signal into a monaural signal. 
     Control Unit  103   
     The control unit  103  controls the call participant count acquisition unit  101 , the voice signal acquisition unit  102 , the voice signal reproduction unit  104 , and the storage unit  105 , and inputs and outputs data to and from each of these units. The control unit  103  is, for example, implemented by a central processing unit (CPU) executing a program stored in a prescribed memory. Further, the control unit  103  includes a localization position determination unit  106  and a voice signal processing unit  107 . 
     Localization Position Determination Unit  106   
     The localization position determination unit  106  determines the localization positions corresponding to the respective voice signals acquired in the voice signal acquisition unit  102  so that the localization positions do not overlap with each other. The localization positions corresponding to the voice signals refer to the localization positions of the voices corresponding to the respective voice signals in output voices. The localization position determination unit  106  determines each of the localization positions so that the localization positions of the respective voices of one or more call partners do not overlap with each other in output voices output from the call terminal  1 . In this manner, the call terminal  1  can output the voices originating from each of the call partners so that the user can easily hear and distinguish the voices. The details of the determination method of the localization position of the voice by the localization position determination unit  106  will be described later. 
     Voice Signal Processing Unit  107   
     The voice signal processing unit  107  configures (generates) voices to be reproduced from the voice signal reproduction unit  104 , based on the voice signals of each of the call partners obtained from the voice signal acquisition unit  102  and the localization positions corresponding to the respective voice signals obtained from the localization position determination unit  106 . 
     Here, the voices configured by the voice signal processing unit  107  are voices able to have the user perceive a sense of localization that is based on the localization positions determined by the localization position determination unit  106 . The method of implementing the sense of localization varies depending upon the configuration of the voice signal reproduction unit  104 . For example, in a case where the voice signal reproduction unit  104  is a pair of headphones or earphones, the voice signal processing unit  107  configures a binaural voice signal that is implemented by using the head-related transfer function (HRTF). In this manner, the voice signal processing unit  107  has the user (listener) perceive the sense of localization. In contrast, in a case where the voice signal reproduction unit  104  is a stereo speaker, the voice signal processing unit  107  may have the user (listener) perceive the sense of localization by configuring a transaural voice signal using the head-related transfer function described above. Further, the voice signal processing unit  107  may configure the voice signal by using sound pressure panning such as vector base amplitude panning (VBAP). 
     Voice Signal Reproduction Unit  104   
     The voice signal reproduction unit (voice output unit)  104  outputs voices so that the voices corresponding to the respective voice signals are localized at the localization positions determined by the localization position determination unit  106 . As an example, the voice signal reproduction unit  104  reproduces each voice signal that has been subjected to sound effect processing by the control unit  103  through the speaker, the headphones, the earphones, or the like that is connected to the voice signal reproduction unit  104 . In this manner, the voice signal reproduction unit  104  can output the voices and have the user (listener) hear the voices. Further, the voice signal reproduction unit  104  outputs the voices of each of the call partners so that the voices are localized at the localization positions determined by the localization position determination unit  106 . In this manner, the voices originating from each of the call partners can be output so that the user can easily hear and distinguish the voices. 
     Storage Unit  105   
     The storage unit  105  includes a secondary storage apparatus for storing prescribed data used by the control unit  103 . The storage unit  105  is, for example, implemented as a magnetic disk, an optical disc, or a flash memory. Specifically, the storage unit  105  is implemented as a hard disk drive (HDD), a solid state drive (SSD), a Blu-Ray (trade name) (BD Disc), or the like. The control unit  103  can read data from the storage unit  105  and record data into the storage unit  105  as necessary. 
     Determination of Localization Position by Localization Position Determination Unit  106   
     Next, the determination method of the localization position by the localization position determination unit  106  will be described below in detail with reference to  FIGS. 2 to 6 . 
     Configuration of Localizable Range 
     The localization position determination unit  106  may configure a localizable range, which is a range in which each voice can be localized, before determining the localization positions of the voices corresponding to voice signals. In this manner, the localization position of each voice can be more appropriately determined. Note that the localization position determination unit  106  may determine the localization position of each voice without configuring the localizable range. The configuration method of the localizable range by the localization position determination unit  106  will be described below with reference to  FIG. 2 .  FIG. 2  is a diagram illustrating examples of the localizable range according to the first embodiment. 
     Configuration Example 1 of Localizable Range 
     In one aspect, for example, as illustrated in (A) of  FIG. 2 , the localization position determination unit  106  may configure a localizable range  202   a , which is defined between a localizable range start position  2030  and a localizable range end position  204  within a circle about a user  201  (around the user  201 ). In this case, the localization position determination unit  106  determines the localization position (for example, the localization position  205 ) of each voice in the localizable range  202   a.    
     In one aspect, for example, the call terminal  1  may include a range input unit  108  (not illustrated), such as a keyboard or a touch panel, that receives input of the localizable range from the user  201 , and the localization position determination unit  106  may configure the range input into the range input unit  108  as the localizable range. For example, the range input unit  108  is configured to receive input of the localizable range start position  203  and the localizable range end position  204 , and the localization position determination unit  106  configures the range defined between the localizable range start position  203  and the localizable range end position  204  as the localizable range  202   a.    
     In this manner, in a case where the number of call partners is small, for example, the range to which attention should be paid during a call can be reduced by limiting the localizable range  202   a , whereas in a case where the number of call partners is large, for example, the voices originating from each of the call partners can be made to be more easily heard and distinguished by widening the localizable range  202   a.    
     Note that the radius of the circle about the user  201  being used for defining the localizable range is not specifically limited, and may be set to any distance. For example, the localization position determination unit  106  may determine the radius of the circle by receiving the distance from the user  201  to the localization position of the voice via any command input unit  109  (not illustrated), such as a keyboard or a touch panel, from the user  201 . 
     Configuration Example 2 of Localizable Range 
     The user  201  may input the localizable range start position  203  and the localizable range end position  204  to be the same. The user  201  may omit the input of the localizable range. In such cases, as illustrated in (B) of  FIG. 2 , the localization position determination unit  106  may configure the localizable range to be a localizable range  202   b , which corresponds to the whole circle about the user  201 . In this case, the localization position determination unit  106  determines the localization position (for example, the localization position  206 ) of each voice in the localizable range  202   b.    
     Configuration Example 3 of Localizable Range 
     The above example describes a case in which the localizable range is a continuous range. However, the localizable range need not necessarily be such a continuous range. For example, as illustrated in (C) of  FIG. 2 , the localization position determination unit  106  may configure a plurality of non-continuous localizable ranges  202   c  and  202   d  as the localizable range. 
     Configuration Example 4 of Localizable Range 
     In one aspect, the call terminal  1  may include a detection unit  110  (not illustrated) that detects ambient sound of the call terminal  1 , and the localization position determination unit  106  may determine the localization positions corresponding to voice signals so as to avoid the generation source of the sound detected by the detection unit  110 . 
     For example, in a case where the detection unit  110  detects sound such as television sound from the front side of the user  201 , as illustrated in (C) of  FIG. 2 , the localization position determination unit  106  configures the non-continuous localizable ranges  202   c  and  202   d  except for the front side of the user  201  as the localizable range, and determines localization positions  207  to  209  of each voice in the localizable ranges  202   c  and  202   d . In this manner, the localization position determination unit  106  can determine the localization positions corresponding to the voice signals so as to avoid the generation source of the sound detected by the detection unit  110 . 
     In this manner, for example, even in a case where sound such as television sound is generated from a certain direction, the voices originating from the call partners can be arranged to be heard from a direction different from the generation source of the sound. In this manner, the user  201  can be made to more easily hear and distinguish the voices originating from each of the call partners. Note that, as long as the configuration of determining the localization position of each voice so as to avoid the generation source of sound is adopted, the configuration is not limited to the configuration of configuring the localizable range so as to avoid the generation source of sound. The localization position determination unit  106  may be configured to determine the localization position of each voice so as to avoid the generation source of sound in a freely configured localizable range. 
     Configuration Example 5 of Localizable Range 
     In one aspect, the localization position determination unit  106  may configure the localizable range, based on the range in which the voice signal reproduction unit  104  can actually localize the output voice. Specifically, the localization position determination unit  106  may configure the localizable range, based on the position of the voice signal reproduction unit  104  or the position of the voice signal reproduction unit  104  and a voice signal configuration method of the voice signal processing unit  107 . 
     For example, as illustrated in (D) of  FIG. 2 , it is assumed that the voice signal reproduction unit  104  is stereo speakers  210  and  211 , and the voice signal configuration method of the voice signal processing unit  107  is VBAP. In this case, the range in which the voice signal reproduction unit  104  can localize the output voice is a range between the stereo speaker  210  and the stereo speaker  211 . In this case, the localization position determination unit  106  may determine a line connecting the user  201  and the stereo speaker  210  as the localizable range start position  203 , and configure a line connecting the user  201  and the stereo speaker  211  as the localizable range end position  204 . 
     As illustrated in (E) of  FIG. 2 , in a case where the voice signal reproduction unit  104  is 5.1-ch multi-channel speakers  212  to  214  disposed adjacently to each other on the circle about the user  201 , and the voice signal configuration method of the voice signal processing unit  107  is VBAP, the voice signal reproduction unit  104  can localize the output voice at omnidirectional positions as seen from the user  201 . In this case, the localization position determination unit  106  may configure, for example, the localizable range  202   b  illustrated in (B) of  FIG. 2  as the localizable range. 
     Configuration Example 6 of Localizable Range 
     In the above example, the localization position determination unit  106  configures the localizable range in advance. However, the present embodiment is not limited to this. In the present embodiment, the localization position determination unit  106  may configure or change (reconfigure) the localizable range during a call. 
     For example, during a call, the call terminal  1  may receive a change command of the localization position from the user  201  via the command input unit  109 , and the localization position determination unit  106  may change the localization positions corresponding to the voice signals, based on the change command. In this manner, for example, during a call, in a case where it is difficult to hear the voices originating from each of the call partners due to a reason such as that the range of the localization position is excessively wide or is excessively narrow, by changing the configuration of the localizable range, the localization positions of the voices originating from each of the call partners can be changed to the positions that allow the voices to be more easily heard and distinguished. 
     Configuration Example 7 of Localizable Range 
     In the above example, the localization position determination unit  106  configures at least a part of the range in the circle about the user  201  as the localizable range. However, the present embodiment is not limited to this. In the present embodiment, the localization position determination unit  106  can determine any range as the localizable range. In one aspect, the localization position determination unit  106  may configure at least a part of the range on a semicircle about the user  201  as the localizable range. In this case, the localization position determination unit  106  can determine the above of the user  201  as the localization position of the voice. Further, in one aspect, the localization position determination unit  106  may configure a range on the circumference of the circle about the user  201  as the localizable range, and determine the localization position of each voice on the circumference. Further, in one aspect, the localizable range may have a shape other than a circle. 
     Determination of Localization Position 
     Next, the determination method of the localization position of the output voice originating from the call partner will be described with reference to  FIGS. 3 to 6 . 
     Determination Example 1 of Localization Position 
     An example of the determination method of the localization position of the voice (output voice originating from each call partner) corresponding to the voice signal of each call partner by the localization position determination unit  106  will be described with reference to  FIG. 3 . Note that, in the following description, it is assumed that the localization position determination unit  106  configures the localizable range  202   a.    
     In a case where the number of call partners is one, as illustrated in (A) of  FIG. 3 , the localization position determination unit  106  determines a localization position  301  which is determined in advance in the localizable range  202   a  as the localization position of the voice originating from the call partner. Note that, although the localization position  301  is a position in front of the user  201 , this is not restrictive. The localization position determination unit  106  may determine another position, or the localization position may be determined based on a command of the user  201  via the command input unit  109 . 
     In a case where the number of call partners is two or more, the localization position determination unit  106  determines the localization positions of the voices originating from each of the call partners so that the localization positions of the voices do not overlap with each other. Specifically, the localization position determination unit  106  determines the localization positions of the voices originating from each of the call partners at positions different from each other in the localizable range  202   a , and preferably determines the localization positions of the voices originating from each of the call partners so that the directions in which the voices originating from each of the call partners arrive the user  201  do not overlap with each other. For example, as illustrated in (B) of  FIG. 3 , the localization position determination unit  106  may determine localization positions  302  and  303  of the voices originating from each of the call partners at both the ends of the localizable range  202   a.    
     In one aspect, the localization positions corresponding to each voice signal may be determined so that the intervals between the adjacent localization positions are uniform in the localizable range  202   a . For example, as illustrated in (C) of  FIG. 3 , the localization position determination unit  106  determines the localization positions so that the intervals between two adjacent localization positions are uniform in the localizable range  202   a  of the voices. Specifically, the localization position determination unit  106  determines the localization positions of the voices originating from five call partners at the positions to equally divide the localizable range  202   a  of the voices into four parts. In this manner, the voices originating from each of the call partners can be more easily heard and distinguished. 
     As described above, in a case where the localization position determination unit  106  determines the localization positions of the voices originating from each of the call partners, based on the number of call partners, the voices of each of the call partners can be output so that the user  201  can more easily hear and distinguish the voices, depending on the number of call partners. 
     Determination Example 2 of Localization Position 
     Another example of the determination method of the localization position of the voice (output voice originating from each call partner) corresponding to the voice signal of the call partner by the localization position determination unit  106  will be described with reference to  FIG. 4 . Note that, in the following description, it is assumed that the localization position determination unit  106  configures the localizable range  202   b.    
     In a case where the number of call partners is one, as illustrated in (A) of  FIG. 4 , the localization position determination unit  106  determines a localization position  401  which is determined in advance and is a position in front of the user  201  in the localizable range  202   b , for example, as the localization position. Note that the position of the localization position  401  is not limited to this. 
     In a case where the number of call partners is two or more, the localization position determination unit  106  determines the localization positions of the voices originating from each of the call partners so that the localization positions of the voices do not overlap with each other. Specifically, the localization position determination unit  106  determines the localization positions of the voices originating from each of the call partners at positions different from each other in the localizable range  202   b , and preferably determines the localization positions of the voices originating from each of the call partners so that the directions in which the voices originating from each of the call partners arrive the user  201  do not overlap with each other. 
     In one aspect, the localization positions corresponding to each voice signal may be determined so that the intervals between the adjacent localization positions are uniform in the localizable range  202   b.    
     For example, as illustrated in (B) and (C) of  FIG. 4 , the localization position determination unit  106  determines the localization positions so that the intervals between two adjacent localization positions are uniform in the localizable range  202   b  of the voices. For example, in a case where the number of call partners is two, as illustrated in (B) of  FIG. 4 , the localization position determination unit  106  determines the localization positions of the voices originating from the two call partners at the positions to equally divide the localizable range  202   b  of the voices into two parts. For example, in a case where the number of call partners is five, as illustrated in (C) of  FIG. 4 , the localization position determination unit  106  determines the localization positions of the voices originating from the five call partners at the positions to equally divide the localizable range  202   b  of the voices into five parts. In this manner, the voices originating from each of the call partners can be more easily heard and distinguished. 
     In a case where equally dividing the localizable range  202   b  into parts, the localization position determination unit  106  can equally divide the localizable range  202   b  in any manner of equal division. For example, in a case where the call participant count is two and the localization position determination unit  106  determines the positions to equally divide the localizable range  202   b  into two parts as the localization positions of the voices originating from each of the call partners, the localization position determination unit  106  may determine localization positions  409  and  410  illustrated in (D) of  FIG. 4  instead of localization positions  402  and  403  illustrated in (B) of  FIG. 4 . In a case where the call participant count is five and the localization position determination unit  106  determines the positions to equally divide the localizable range  202   b  of the voices into five parts as the localization positions of the voices originating from each of the call partners, the localization position determination unit  106  may determine localization positions  411  to  415  illustrated in (E) of  FIG. 4  instead of localization positions  404  to  408  illustrated in (C) of  FIG. 4 . 
     Determination Example 3 of Localization Position 
     Another example of the determination method of the localization position of the voice (output voice originating from each call partner) corresponding to the voice signal of the call partner by the localization position determination unit  106  will be described with reference to  FIG. 5 . Note that, in the following description, it is assumed that the localization position determination unit  106  configures the localizable ranges  202   c  and  202   d.    
     In a case where the number of call partners is one, the localization position determination unit  106  determines the localization position which is determined in advance in any of the localizable ranges  202   c  and  202   d  as the localization position of the voice originating from the call partner. For example, as illustrated in (A) of  FIG. 5 , the localization position determination unit  106  may determine a localization position  501  which is determined in advance in the localizable range  202   c  as the localization position of the voice originating from the call partner. 
     In a case where the number of call partners is two or more, the localization position determination unit  106  determines the localization positions of the voices originating from each of the call partners so that the localization positions of the voices do not overlap with each other. In this case, the localization position determination unit  106  determines the localization positions so that the localization positions are distributed in both the localizable range  202   c  and the localizable range  202   d.    
     For example, in a case where the number of call partners is two, as illustrated in (B) of  FIG. 5 , the localization position determination unit  106  determines one localization position in each of the localizable ranges  202   c  and  202   d  (the localization position  502  in the localizable range  202   c  and the localization position  503  in the localizable range  202   d ). 
     Further, for example, in a case where the number of call partners is three, as illustrated in (C) of  FIG. 5 , the localization position determination unit  106  may determine two localization positions ( 504  and  505 ) in the localizable range  202   c  and determine one localization position ( 506 ) in the localizable range  202   d . As illustrated in (D) of  FIG. 5 , the localization position determination unit  106  may determine one localization position ( 507 ) in the localizable range  202   c  and determine two localization positions ( 508  and  509 ) in the localizable range  202   d.    
     Further, for example, in a case where the number of call partners is five, the localization position determination unit  106  determines the localization positions so that the intervals between the adjacent localization positions of the voices of the call participants are uniform in each of the localizable ranges  202   c  and  202   d . In this case, for example, as illustrated in (E) of  FIG. 5 , the localization position determination unit  106  may determine four localization positions  510  to  513  in the localizable range  202   c  and determine one localization position  514  in the localizable range  202   d . As illustrated in (F) of  FIG. 5 , the localization position determination unit  106  may determine three localization positions  515  to  517  in the localizable range  202   c  and determine two localization positions  518  and  519  in the localizable range  202   d.    
     In this case, as illustrated in (E) and (F) of  FIG. 5 , it is preferable that the localization position determination unit  106  determine each of the localization positions so that the intervals between the adjacent localization positions of the voices of the call participants are uniform in at least one of the localizable ranges  202   c  and  202   d  of the voices. 
     In this manner, by determining the localization positions so that the intervals between the adjacent localization positions of the voices of the call participants are uniform in at least one of the localizable ranges  202   d  and  202   d  in a case where the call participant count is three or more, the voices of each of the call participants can be easily localized at the positions where the user  201  can easily hear and distinguish the voices. 
     Determination Example 4 of Localization Position 
     The localization position determination unit  106  may change the localization position of the voice originating from the call partner during a call. In this manner, even in a case where it is difficult for the user  201  to hear and distinguish the voices localized at the localization positions of the voices determined in advance, the user  201  can cause the localization position determination unit  106  to change the localization positions of the voices originating from each of the call partners afterwards by inputting a change command via the command input unit  109 , for example. As a result, the localization positions of the voices originating from each of the call partners can be determined at appropriate positions where the user  201  can more easily hear and distinguish the voices. 
     Determination Example 5 of Localization Position 
     In a case where the change command via the command input unit  109  is a rotation command of the localization positions, the localization position determination unit  106  may rotate the localization positions of the voices originating from each of the call partners about the user  201  (listener of each voice), based on the rotation command. 
     For example, it is assumed that the number of call partners is two, and the localization position determination unit  106  determines the localizable range to be the localizable range  202   b . In this case, based on the command of the user  201 , the localization position determination unit  106  may perform rotation from the localization positions  402  and  403  illustrated in (B) of  FIG. 4  to the localization positions  409  and  410  illustrated in (D) of  FIG. 4  about the user  201  (listener of each voice). Then, the localization position determination unit  106  may determine the localization positions of the voices originating from each of the call partners at the localization positions  409  and  410  after the rotation. 
     Further, for example, it is assumed that the number of call partners is five, and the localization position determination unit  106  determines the localizable range to be the localizable range  202   b . In this case, based on the command of the user  201 , the localization position determination unit  106  may rotate the localization positions  404  to  408  of the voices originating from each of the call partners illustrated in (C) of  FIG. 5  to the localization positions  411  to  415  illustrated in (E) of  FIG. 5  about the user  201  (listener of each voice). Then, the localization position determination unit  106  may determine the localization positions of the voices originating from each of the call partners at the localization positions  411  to  415  after the rotation. 
     In this manner, for example, even in a case where it is difficult to hear and distinguish the voices originating from each of the call partners heard from the localization positions of the voices determined in advance during a call with the call partners, the localization positions of the voices originating from the call partners can be changed to the positions where the user  201  can more easily hear and distinguish the voices originating from each of the call participants. 
     Determination Example 6 of Localization Position 
     In the above example, in a case where the number of call partners is a prescribed number or more, the localization position determination unit  106  determines each of the localization positions in the localizable range so that the intervals between the adjacent localization positions are uniform. Note that the localization position determination unit  106  need not determine each of the localization positions so that the intervals between the adjacent localization positions are uniform. 
     With reference to  FIG. 6 , an example of the determination method of the localization position of the voice of the call participant by the localization position determination unit  106  will be described below.  FIG. 6  is a diagram illustrating an example of the localization position of the voice according to the first embodiment. 
     For example, in a case where the number of call partners is five, the localization position determination unit  106  may equally divide the localizable range  202   b  into five parts as illustrated in (A) of  FIG. 6 , or may not equally divide the localizable range  202   b  into five parts as illustrated in (B) of  FIG. 6 . In particular, in a case where the localizable range  202   b  is divided into a front region  601  and a rear region  602  by a boundary line  603 , the user  201  may perceive the voices from the rear less clearly than the voices from the front. In this case, as illustrated in (B) of  FIG. 6 , the localization position determination unit  106  can output each voice to the user more appropriately by determining the interval between localization positions  607  and  608  in the rear region  602  to be wider than each of the intervals between adjacent ones of localization positions  604  to  606  in the front region  601 . 
     The localization position determination unit  106  may determine each of the localization positions so that the localization positions of the voices originating from each of the call partners are separated away from each other at least by a prescribed angle or more as seen from the user  201 . Although the prescribed angle is not particularly limited, the prescribed angle may be set to 1 degree, 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, or the like, as appropriate. In this manner as well, the localization positions can be determined in a range where the user  201  can easily hear the voices of the call partners. 
     Control Processing of Call Terminal  1   
     Next, with reference to  FIG. 7 , the procedure of the control processing of the call terminal  1  (control method of the call terminal) according to the present embodiment will be described.  FIG. 7  is a flowchart illustrating an example of the procedure of the control processing of the call terminal  1  according to the first embodiment. 
     In Step S 101 , the call participant count acquisition unit  101  acquires the number of call partners from the outside of the call terminal  1 . Further, the voice signal acquisition unit  102  acquires (receives) the voice signals of each of one or more call partners (reception step, voice signal acquisition step). Subsequently, the processing proceeds to Step S 102 . 
     In Step S 102 , the localization position determination unit  106  determines whether the number of call partners acquired by the call participant count acquisition unit  101  is larger than one. In a case where the number of call partners is larger than one (YES in Step S 102 ), the processing proceeds to Step S 103 . In a case where the number of call partners is one (NO in Step S 102 ), the processing proceeds to Step S 104 . 
     In Step S 103 , the localization position determination unit  106  determines the localization positions corresponding to the respective voice signals acquired in the voice signal acquisition step so as not to overlap with each other (localization position determination step). In this case, preferably, the localization position determination unit  106  determines the localization positions so that the intervals between the adjacent localization positions of the voices of the call participants are uniform. Subsequently, the processing proceeds to Step S 105 . 
     In Step S 104 , the localization position determination unit  106  determines the localization positions of output voices originating from the call partners at the positions determined in advance (localization position determination step). Subsequently, the processing proceeds to Step S 105 . 
     In Step S 105 , the voice signal processing unit  107  generates the output voices so that the voices corresponding to the voice signals of each of the call partners are localized at the localization positions determined in the localization position determination step, and causes the voice signal reproduction unit  104  to output the generated output voices (voice output step). 
     Through the processing described above, a call by a large number of people can be appropriately implemented by using the call terminal  1 . 
     Second Embodiment 
     The call terminal  10  according to the second embodiment will be described below with reference to  FIGS. 8 to 10 . Note that, for the sake of convenience of description, members having the same functions as the members described in the first embodiment are denoted by the same reference signs, and the description thereof will be omitted. 
     Call Terminal  10   
       FIG. 8  is a block diagram illustrating a principal configuration of the call terminal  10  according to the second embodiment. 
     As illustrated in  FIG. 8 , the call terminal  10  includes a control unit  1030  instead of the control unit  103  of the call terminal  1  according to the first embodiment. Except for this configuration, the call terminal  10  has the same configuration as the call terminal  1  according to the first embodiment. 
     Control Unit  1030   
     As illustrated in  FIG. 8 , the control unit  1030  includes a localization position determination unit  1060  instead of the localization position determination unit  106  according to the first embodiment. Except for this configuration, the control unit  1030  has the same configuration as the control unit  103  according to the first embodiment. 
     Localization Position Determination Unit  1060   
     The localization position determination unit  1060  determines the localization positions corresponding to the voice signals of each of the call partners, based on the number of call partners obtained from the call participant count acquisition unit  101 . 
     In one aspect, the localization position determination unit  1060  determines the localizable range such that the localizable range is increased as the number of call partners is increased. For example, localizable ranges determined in advance may be stored in the storage unit  105  depending on the number of call partners, and the localization position determination unit  1060  may determine a localizable range by reading a localizable range according to the number of call partners from the storage unit  105 . 
     By determining the localizable range such that the localizable range is increased as the number of call partners is increased, in a case where the number of call partners is small, the localizable range is reduced, and thus the range to which attention should be paid during a call can be reduced to the minimum necessary, whereas in a case where the number of call partners is large, the localizable range is increased, and thus each of the localization positions can be disposed so that a large number of voices can be heard and distinguished. 
     Then, the localization position determination unit  1060  determines the localization positions corresponding to the respective voice signals so that the intervals between the adjacent localization positions are uniform and the intervals are the largest in the determined localizable range. In this manner, the localization position determination unit  1060  can determine appropriate localization positions according to the number of call partners obtained from the call participant count acquisition unit  101 . 
     Note that the present embodiment is not limited to this. The localization position determination unit  1060  may determine the localization positions so that the intervals between the localization positions are smaller as the number of call partners is larger. In this manner as well, the localization position determination unit  1060  can determine appropriate localization positions according to the number of call partners obtained from the call participant count acquisition unit  101 . 
     An example of the determination method of the localizable range and the localization position by the localization position determination unit  1060  will be described below with reference to  FIG. 9 .  FIG. 9  is a diagram illustrating examples of the localizable range according to the second embodiment. 
     In a case where the number of call partners is one, as illustrated in (A) of  FIG. 9 , the localization position determination unit  1060  determines the localizable range to be a localizable range  902   a  being a straight line in front of the user  201 . Further, the localization position determination unit  1060  determines the localization position of the voice originating from the call partner at a localization position  901  that is uniquely determined based on the localizable range  902   a.    
     In a case where the number of call partners is two, as illustrated in (B) of  FIG. 9 , the localization position determination unit  1060  determines the localizable range to be a localizable range  902   b  corresponding to a case in which the call participant count is two. Further, the localization position determination unit  1060  determines localization positions  903  and  904  of the voices originating from each of the call partners so that the intervals between the adjacent localization positions are uniform in the localizable range  902   b.    
     In a case where the call participant count is five, as illustrated in (C) of  FIG. 9 , the localization position determination unit  1060  determines the localizable range to be a localizable range  902   c  corresponding to a case in which the call participant count is five. Further, the localization position determination unit  1060  determines each of the localization positions of the voices originating from each of the call partners at localization positions  905  to  909  at which the localizable range  902   c  is equally divided into four parts so that the intervals between the adjacent localization positions are uniform in the localizable range  902   c.    
     Note that, in the present embodiment as well, the localization position determination unit  1060  may change the localizable range and the localization position during a call. In this manner, for example, even in a case where it is difficult to hear and distinguish the voices originating from each of the call partners heard from the localization positions in the localizable range determined in advance during a call with the call partners, the localization positions of the voices originating from the call partners can be changed to positions where the user  201  can more easily hear and distinguish the voices. 
     Control Processing of Call Terminal  10   
     Next, with reference to  FIG. 10 , the procedure of the control processing of the call terminal  10  (control method of the call terminal) according to the present embodiment will be described.  FIG. 10  is a flowchart illustrating an example of the procedure of the control processing of the call terminal  10  according to the second embodiment. 
     In Step S 201 , the call participant count acquisition unit  101  acquires the number of call partners from the outside of the call terminal  1 . Further, the voice signal acquisition unit  102  acquires (receives) the voice signals of each of one or more call partners (reception step, voice signal acquisition step). 
     In Step S 202 , the localization position determination unit  1060  determines the localizable range of the voices, based on the call participant count acquired from the call participant count acquisition unit  101 . 
     In Step S 203 , the localization position determination unit  1060  determines the localization positions corresponding to the respective voice signals acquired in the voice signal acquisition step so as not to overlap with each other. Further, the localization position determination unit  1060  determines each of the localization positions so that the intervals between the adjacent localization positions in the determined localizable range are uniform (localization position determination step). 
     In Step S 204 , the voice signal reproduction unit  104  outputs the voices corresponding to the respective voice signals so that the voices are localized at the localization positions determined in the localization position determination step of Step S 203 , and ends the processing (voice output step). 
     Third Embodiment 
     The function of the call terminal  1  according to the first embodiment may be implemented by a call system  100  according to a third embodiment. 
     The call system  100  according to the third embodiment will be described below with reference to  FIG. 11 . Note that, for the sake of convenience of description, members having the same functions as the members described in the embodiments described above are denoted by the same reference signs, and the description thereof will be omitted. 
     Call System  100   
       FIG. 1  is a block diagram illustrating a principal configuration of the call system  100  according to the third embodiment. The call system  100  includes a call terminal  200  and a call server  300 . The call server  300  includes the localization position determination unit  106 . 
     In this manner, in the call system  100 , the call terminal  200  includes a control unit  10300  not including the localization position determination unit  106  instead of the control unit  103  including the localization position determination unit  106  in the call terminal  1  according to the first embodiment, and the call system  100  further includes the call server  300  including the localization position determination unit  106 . 
     In the call system  100 , the call terminal  200  receives the voice signals of each of one or more call partners, and the call system  100  includes the localization position determination unit  106  that determines the localization positions corresponding to the respective voice signals received by the call terminal  200  so as not to overlap with each other, and the call terminal  200  outputs the voices corresponding to the received voice signals so that the voices are localized at the localization positions determined by the localization position determination unit  106 . 
     More specifically, as illustrated in  FIG. 11 , in the call system  100 , the call participant count acquisition unit  101  of the call terminal  200  acquires the number of call partners, and the voice signal acquisition unit  102  acquires the voice signals of each of the call partners. The localization position determination unit  106  of the call server  300  determines the localization positions corresponding to the respective voice signals acquired in the voice signal acquisition unit  102  of the call terminal  200  so as not to overlap with each other. The voice signal processing unit  107  of the call terminal  200  configures (generates) the voices to be reproduced from the voice signal reproduction unit  104 , based on the voice signals of each of the call partners obtained from the voice signal acquisition unit  102  of the call terminal  200  and the localization positions corresponding to the respective voice signals obtained from the localization position determination unit  106  of the call server  300 . The voice signal reproduction unit  104  of the call terminal  200  outputs the voices corresponding to the respective voice signals so that the voices are localized at the localization positions determined by the localization position determination unit  106  of the call server  300 . 
     In this manner, the call system  100  functions in a manner similar to the call terminal  1  according to the first embodiment as a whole. According to the call system  100 , with the call server  300  performing the processing of the localization position determination unit  106 , the processing amount of the call terminal  200  can be reduced. 
     Note that the above example describes a case in which, in the call system  100 , the call server  300  includes the localization position determination unit  106  instead of the call terminal  200 . However, the present embodiment is not limited to this. In the present embodiment, it is only necessary that the call terminal  200  include at least the voice signal reproduction unit  104 , and the call server  300  may include other members instead of the call terminal  200 . For example, the call server  300  may include the storage unit  105 , the localization position determination unit  106 , and the control unit  10300 , that is, the storage unit  105  and the control unit  103  of  FIG. 1 , instead of the call terminal  200 , and the call server  300  may further include the call participant count acquisition unit  101  and the voice signal acquisition unit  102  in addition to the control unit  103  and the storage unit  105  instead of the call terminal  200 . In this case as well, the call system  100  can function in a manner similar to the call terminal  1  according to the first embodiment as a whole while reducing the processing amount of the call terminal  200 . 
     Implementation Example by Software 
     Control blocks of the call terminal  1  or  10  (in particular, the localization position determination unit  106  or  1060  and the voice signal reproduction unit  104 ) may be implemented by logic circuits (hardware) formed in integrated circuits (IC chips) and the like, or may be implemented by software. 
     In the latter case, the call terminal  1  or  10  is provided with a computer that executes commands of a call program, which is software for implementing each function. The stated computer includes at least one processor (control apparatus), for example, and includes at least one computer-readable recording medium having stored the call program therein. In the computer, the processor reads out the call program from the recording medium and executes the call program, thereby accomplishing the object of the present embodiment. For example, a Central Processing Unit (CPU) may be used as the processor. As the recording medium, a “non-transitory tangible medium” such as a tape, a disk, a card, a semiconductor memory, and a programmable logic circuit may be used in addition to a Read Only Memory (ROM). A Random Access Memory (RAM) on which the call program is loaded, or the like may be further provided. The call program may be supplied to the computer via any transmission medium (communication network, broadcast wave, or the like) capable of transmitting the call program. Note that an aspect of the present invention may be implemented in a form of data signal embedded in a carrier wave, which is embodied by electronic transmission of the call program.