## 1 Introduction  
Over the last couple of years, High Efficiency Advanced Audio Coding (HE-AAC) [1; 2; 3] has become one of the most important enabling technologies for state-of-the-art multimedia systems. It delivers compact disc (CD) quality stereo at 48 kbps and 5.1 channel surround sound at 128 kbps. This efficiency level is the optimal choice for current internet content delivery. At the same time, it has basically realized novel applications in mobile digital broadcasting and mobile markets. It also enhances audio services while enhancing video services, such as digital television. Without reducing the quality of the audio signal, more bits can be distributed to video signal by coupling HE-AAC with MPEG-4 video.  
Though HE-AAC is popular in the field of multimedia systems, as far as we know, there is no audio watermarking related scientific paper that have developed a watermarking algorithm for HE-AAC or have evaluated performance under it. Therefore, the objective of this study was to design an audio watermarking algorithm to maximize the robustness against low-bit rate HE-AAC compression. This paper is an expansion of our previously published conference paper [4]. We illustrate this algorithm in more detail through more experiments and visualization. The parameters of the proposed algorithm are optimized by thorough experiments, and its performance on multi-channel audio is also added. Moreover, synchronization design is discussed.  
The rapid growth of computer multimedia technology as well as the broad utilization of the internet have promoted the distribution as well as transmission of digital multimedia content. Digitalwatermarking [5] refers to the procedure of embedding data into digital multimedia content such as audio, video, and image. It was initially utilized for security-related purposes like copyright protection and source tracking, but nowadays it is dedicated to various non-security-oriented applications [6], such as broadcast monitoring and automatic content recognition.  
An audio watermarking method must comply with the following requirements [7]. (1) Imperceptibility: The perception of the original audio signal is similar to that of the watermarked audio signal. (2) Security: Watermarks can only be detected by authorized personnel. (3) Payload: It is a number of bits in which audio can be inserted in a unit of time. The watermarking data payload needs to be greater than 20 bps (bit/second). (4) Robustness: This means that the watermark should be resistant to common malicious attacks as well as signal processing. However, there is no algorithm that can meet all the demands mentioned above. The goal of the watermarking algorithm is to achieve an appropriate trade-off between requirements. Security-oriented applications may require high robustness and security, because it is more likely to receive malicious attacks. By contrast, non-security-oriented applications may require high payload and a certain degree of robustness against one or two specific attacks that are known in advance.  
The organization of the rest of the thesis is as follows. In the next part, we give a simple instruct of HE-AAC and audio watermarking algorithms. In the third part, we introduce the audio watermarking algorithm in detail. Experimental results are discussed in Section 4, and these evaluate the function of the algorithm in the data payload, robustness under compression attack, and imperceptibility aspects. Finally, Section 5 summarizes and analyzes the future direction of development.