On a Synchronization Method for Audio Watermarks Robust Against Aerial Transmission Using Embedded Random Synchronization Pattern
We evaluated the effect of synchronization on audio watermarks. Synchronization signal was generated by using an M-sequence for the phase, and shaping its magnitude relative to the host signal spectrum. Synchronization at the detector was achieved by calculating a cross-correlation function with the same M-sequence, and detecting the peak in the correlation. The synchronization signal was added to a spread-spectrum watermarked audio signal. This signal was then transmitted over analog channels, by simply connecting the D/A output to the A/D input using a cable, and also playing out the analog signal through a loudspeaker and recording this signal using a microphone. The addition of the synchronization signal enabled the detection of the watermark through analog channels at acceptable accuracy. The synchronization rate was also shown to strongly influence the watermark bit error rate (BER).
KeywordsAudio watermark frame synchronization M-sequence Cross-correlation aerial transmission
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