Patent ID: 7451318

Claim:
A method of retrieving a watermark in a watermarked signal, the watermarked signal comprising odd- and even-overlapped blocks where the watermark is contained in the even blocks, the method comprising, for each k-th block: subtracting the odd-numbered blocks from the k-th block of the watermarked signal to generate s * k (n); applying an FFT to s * k (n) to generate a phase S k (ƒ); calculating a phase of S k (ƒ) as φ (ƒ) and a phase of an original signal S k (ƒ) as φ(ƒ); calculating the difference Ψ(ƒ) between φ (ƒ) and φ(ƒ); and retrieving the watermark embedded in Ψ(ƒ), wherein if, during a phase-modulation stage of generating the watermarked signal, the result of adding the phase modulation to the phase of the original signal has an absolute value greater than π, then the method further comprises unwrapping Ψ(ƒ) to obtain the correct phase modulation {tilde over (Φ)} k (ƒ), wherein the unwrapping only occurs when φ(ƒ)>π/2 and Ψ(ƒ) is greater than a dynamic range of a phase modulation; and retrieving watermark embedded in {tilde over (Φ)} k (ƒ) using a Viterbi Search.