Audio watermarks are often made signal-dependant to keep them imperceptible. A blind watermark detector, which does not have access to the original unwatermarked signal, seems handicapped, because an approximate watermark has to be re-derived from the watermarked signal. Referring to the exact watermark known scenario as a semi-blind detector, some reduction in performance is anticipated in blind detection over that of semi-blind detection. The present work is an experimental investigation into this issue, explored around a typical correlation-based audio watermark detection scheme. It is found, surprisingly, that the statistical performance of the blind detector is better than that of the semi-blind detector. It is found that the rederived watermark is better correlated to the host signal and hence leads to better detection performance. It is confirmed that this happens only if the embedded watermark is the same as the examined watermark.
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