In general, a communication conference system is configured such that audio of conference participants is collected by a plurality of microphones, and is mixed and then transmitted. On the reception side, the audio is reproduced from all of loudspeakers at an equal level of sound volume and phase. In the case of such a communication conference system, the audio data is reproduced with a same sound image regardless of who is speaking among the conference participants. As a result, it is difficult on the reception side to identify who spoke.
Moreover, on the reception side, since the sound volume of a loudspeaker is fixed, the sound volume from the loudspeaker significantly fluctuates when there is a plurality of conference participants on the transmission side, due to differences in the audio sound volume of the respective participants and in the distance between microphones and the participants.
Based on such circumstances, there has been proposed a voice telephone conference device that determines a speaker and the position of the speaker based on the temporal waveform and the frequency spectrum of a microphone input signal (for example, refer to Patent Document 1).                Patent Document 1: Japanese Unexamined Patent Application, First Publication (JP-A) No. H09-261351        
The voice telephone conference device disclosed in Patent Document 1 determines a speaker and the position of the speaker based on the temporal waveform and the frequency spectrum of a microphone input signal, and transmits position information along with audio data. The reception side controls the sound volume of each loudspeaker based on the received position information. Moreover, there is provided a switch for switching to select audio data with a highest input level among the respective microphones, and the reception side is set so that the audio is emitted from the loudspeaker that corresponds to the microphone that collected the audio.
However, a sound field with a high level of presence (for example, a feel of depth) can not be realized by only controlling the sound volumes of the respective loudspeaker (stereo loudspeaker units) based on the position information.
Furthermore, each of the microphones is provided with the switch for switching to select audio data with a highest input level among the respective microphones. However, there is an issue in that when a plurality of speakers start speaking simultaneously, this switching needs to be performed in a short period of time, and accurate audio data cannot be transmitted as a result.