Espionage and Spying: Is it really that easy to blur out a conversation so it won't get picked up by… by Tony Garcia
Answer by Tony Garcia:
What you have described is sound masking, which is the addition of natural or artificial sound (such as white noise or pink noise) into an environment to cover up unwanted sound by using auditory masking. This is in contrast to the technique of active noise control. Sound masking reduces or eliminates awareness of pre-existing sounds in a given area and can, for example, make a work environment more comfortable, while creating speech privacy so workers can better concentrate and be more productive. Sound masking can also be used in the outdoors to restore a more natural ambient environment.
White noise has the abililty to defeat the intelligibility of the spoken word within the surrounding perimeter (rather than simply create a pleasant sound environment). It is more appropriate because energy is evenly distributed and the higher frequency components (and thus the intelligibility) of the spoken word are more greatly impacted by the energy level created by a white noise system. This is more likely the method you are referring to.