Directed attack

To mount this attack, one needs a partial understanding of the watermarking scheme. The idea is to apply a transformation of a similar kind as the one used for marking. For example, if it is known that the marking process is only modifying the phase of the signal, one can try to apply all-pass filters or similar transformations. This is not in theory extremely different from the previous attack, but in practice, the transformations performed are less likely to degrade the song (because they change only part of it), and are also more likely to remove the mark (because they modify the same parameters).

Naturally, the better one understands the scheme, the highest are his chances of success. The problems with this attack are that (a) one cannot be sure the attack will work against every song, (b) one cannot be sure the final audio quality will be good enough for every song. Consequently, this attack cannot really be automated.