Euler already has that one

don't forget you'll have to modulate the two channels if you are going in through the RF connection

Masking systems have been used for years in courtrooms and banks to keep people from hearing things they shouldn't. When the lawyers approach the bench, they turn on the system and it allows them to have a private conversation while the jury can't here it. Masking systems are also used in conjunction with paging/background music systems, and if it was installed properly, you don't even realize that you are listening to filtered white noise. No fancy "sensors" or crazy DSP (ok,just a little DSP).