A few days later, I heard voices from the upper room in my hotel. They called my name in the same way, but I could tell all of them correctly who they were.
It looked like they gathered some voices to confirm that I had an ability to identify who they were. I thought it was recorded as it was actually not calling my name, but speaking my name as asked to do so, meaning there were no emotions of their sound.
There was another purpose for this plot that they tried to disguise an identity of the spies. I had actually recognized many spies until then due to their voice so that they added other voices to degrade the original spy identity just to a collaborator.
Their mistake was that I had a better recognition of the voice than they assumed as I could even tell whether it was recorded or not. They thought I just used an information of the voice to uncover an identity of the spy, which was so wrong that their disguise was basically failed.
Eventually, they understood I could recognize the voice correctly even for the friends in the past, but on the other hand, I realized one important fact due to their trial that the conversation on the other day was not conducted by the same type of voices from the upper room. It was definitely not a directional speaker but there was a methodology to deliver a voice to the brain directly from the outside.
I also considered a possibility of the ultrasonic wave, but it was concluded improbable as I heard a human voice. I have no clue whether the ultrasonic wave can deliver a thought to another human being, but we should accept its sound at the deep end of our cochlear if that is the case. The human being recognizes its sound according to the frequency that the low frequency is received at the front end of our cochlear and the high is at the back end.
This structure implies that the ultrasonic sound should be received as a high pitch in any way, which cannot be perceived as a human voice. It is basically impossible to hear the sound out of the audible range, though, even if hearable, it cannot be a voice of someone else.
This analysis suggested that there was a way to deliver the voice by other than sound, but I had no idea what it was at that time. All I could get was that there was an unknown methodology to send a voice directly to the brain from a distance.