| Summary: | 碩士 === 國立臺灣大學 === 資訊工程學研究所 === 104 === Audio watermark is a technology used for DRM (Digital Rights Management) in earlier days. Now, with the increase of popularity and improvement of computation of smartphones and tablets, we can transmit information via audio watermark. The advantage of audio watermark is that it only requires a speaker and a microphone.
In this paper, we implement audio watermark system by using MCLT (Modulated Complex Lapped Transform), and embed data by modifying the phase of the MCLT coefficients because of the imperceptibility of human auditory to modified phase. As a result, we can hardly distinguish the transformed signal from the original audio signal. The MCLT does not produce blocking artifacts so we can get better audio quality.
Audio watermark is very sensitive to any acoustic interferences, and even the microphone’s directions will make impact on accuracy. There are two main problems in audio watermark using MCLT. First, some audio signal’s energy is too weak to extract data. Second, the coefficients of MCLT will rotate under some acoustic interferences, and this will lead to data extraction error. For the first problem, we mix the specific frequency band of white noise signal to the audio signal, and increase the energy of weak parts. For the second problem, we use K-means clustering as a solution, and we also try to alter the initial center of K-means clustering to improve the result.
In our experiments, the mixing of white noise signals, distances, angles, microphone’s directions, music genre and segment size are independent variables, and we tried many possible combinations to simulate the practical situations. We recorded many audio signals and decoded the result using the proposed system. As a result, we obtain a greater improvement of accuracy by adding white noise signal energy to the audio signal.
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