Robust audio watermarking using a chirp based technique

In this study, we propose a new spread spectrum audio watermarking algorithm that embeds linear chirps as watermark messages. Different chirp rates, i.e., slopes on the time-frequency (TF) plane, represent watermark messages such that each slope corresponds to a different message. We extract the watermark message using a line detection algorithm based on the Hough-Radon transform (HRT). The HRT detects the directional elements that satisfy a parametric constraint in the image of a TF plane. The proposed method not only detects the presence of watermark, but also extracts the embedded watermark bits and ensures the message is received correctly. The results show that the HRT detects the embedded watermark message even after common signal processing operations such as MPEG audio coding, resampling, lowpass filtering and amplitude re-scaling.