Has a device been invented that can lower a person's voice by various decibels (as in the loudness of their voices)? This would be to enable silent communication as in whispering at a much lower rate people can hear. Or how would it work? I see some potential dangers in that technology but it also I think it would have some interesting applications I am not thinking of. (what I mean to answer with this question is a simple method for muting people's voices or enabling quiet interactions of people not using their voices).
For example, there are some sounds that humans cannot hear than other species and animals make and humans cannot hear them yet animals can. What if we had a reverse situation where humans cannot hear other humans? I have the articles below I found, for others to help give me their opinions. It's not telepathy but rather hearing people talking silently without being heard with conventional technology and people and still receiving messages from people talking.
Thanks for any answers offered in your replies and for your time.
An addendum I have added to this post: The reason of this post is to ask a question to see if I can write a story based on silent communication. The science is an idea on eavesdropping and muting people's voices. It would help create justice to eavesdrop in some cases in my conviction and silencing human voices can be problematic when used for the wrong reasons.
I know little of hard science and yet would feel a little bit intimidated to try to discuss it here with all of you here. I appreciate all the research and effort given in these below posts. I like asking questions to scientists who are generous enough to help me in the community and anyone who can help I plan to try something similar to: Low Notes on a High Level by J. B. Priestley. In the story he invents a device that can mute human beings. By lowering the sound of their own voices. It is very much appreciated all of what I have learned from others. (I had to modify the question as well as it was unclear). I want to try a modern spin on the tale.
Thanks for your patience.