Correct if I am wrong on two points. 1) The cd standard 44.1KHz was chosen because it supports the limit of AUDIBLE frequencies that the human ear can hear. So the watermark either has to be greater than 22.1KHz, or less than 20Hz. In the case that it's greater than 22.1KHz, the signal will definately not be reproduced correctly, and will result in folded frequencies within the audible hearing range, creating distortion. In the case that it's lower than 20Hz, it may very well create high currents through the amp and speakers, destroying your equipment faster. 2) MP3 and most lossy compression formats throw away "unheard" information, and only approximates the audible frequencies anyway. In this case, to be preserved the watermark must be within the audible frequencies Furthermore the amplitude has to be quite large, otherwise the approximaion will most likely discard the small ripple signal as noise. Congratulations guys for once again creating an unusable audio protection scheme. I still can't believe they pay you for that, and where can I sign up for your job. :g I have a job that is measured in both volume of output and timeliness.