A system and method of retrieving a watermark in a watermarked signal are disclosed. The watermarked signal comprises odd and even overlapped blocks where the watermark is contained in the even blocks. The method comprises, for each k-th even block, subtracting the two adjacent odd blocks from the k-th even block of the watermarked signal to retrieve {overscore (s)}*.sub.k(n), transforming {overscore (s)}*.sub.k(n) into the frequency domain to generate {overscore (S)}.sub.k(f), calculating a phase of {overscore (S)}.sub.k(f) as {overscore (.phi.)}(f) and a phase of S.sub.k(f) as .phi.(f), calculating the difference .PSI.(f) between {overscore (.phi.)}(f) and .phi.(f), unwrapping .PSI.(f) to obtain the phase modulation {tilde over (.PHI.)}.sub.k(f), and using a Viterbi search to retrieve the watermark embedded in {tilde over (.PHI.)}.sub.k(f).