Signal masking in Gaussian channels

We consider the problem of modifying the noise properties of a channel in order to make the source as indecipherable as possible given the output. Applications include jamming communications, maintaining confidentiality near spoken conversations and masking noise pollution. We present results as to how this can be done efficiently, assuming that we have a Gaussian channel and a constraint on the power of the noise. We go on to consider the case in which there is a positive signal which we want to remain coherent, as well as a negative signal which we wish to confound. We also discuss the application of the theory to acoustic signals, where we consider aspects of the human auditory system.