This paper presents an improved method for asynchronous embedding and recovery of sub-audible watermarks in speech signals. The watermark, a sequence of DTMF tones, was added to speech without knowledge of its time-varying characteristics. Watermark recovery began by implementing a synchronized zero-phase inverse filtering operation to decorrelate the speech during its voiced segments. The final step was to apply the sign correlation technique, which resulted in performance advantages over linear correlation detection. Our simulations include the effects of finite word length in the correlator.
Bibliographic reference. Morris, Robert / Johnson, Ralph / Goncharoff, Vladimir / DiVita, Joseph (2009): "Watermark recovery from speech using inverse filtering and sign correlation", In INTERSPEECH-2009, 1311-1314.