In conventional echo watermarking methods, the robustness of watermarks could be improved by increasing the amplitudes of the echo signals, also known as the decay rates, but at the expense of sacrificing audio quality. The objective of this work is to achieve a better audio quality and preserve the robustness of the watermarks. Along with the proposed analysis-by-synthesis approach, there are two other considerations used to adjust the appropriate decay rates of each audio signal segment. One is the characteristics of the audio signals after watermarking, and the other being the accuracy of the watermarks that are decoded and recovered after MP3 attacks on the watermarked audio signals. Looking at the average decay rates and the signal-to-noise ratios, the proposed method exhibits better audio quality than those of the conventional method. Furthermore, the experimental results show that the recovery accuracy rates of watermarks from the watermarked audio signals after attacks are much higher than those of the conventional method.
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