Principles of Psychoacoustics

Abstract

Book Motivations and Objectives Motivated by the booming of the digital media applications, plenty of research has been conducted to investigate the methods of audio watermarking for copyrights protection. However, clear and easy to follow information about the audio watermarking subject are still not widely available and scattered among many publications. Currently, it is hard to find an easy pathway to develop research in this field. One main reason to this difficulty is that most of the works are bounded by IP or patent constraints. On the implementation side it is still hard to find or write the implementation programs for the known audio watermarking techniques to see how the algorithms work. This book is introduced to establish a shortcut to get into this interesting field with minimal efforts. The commonly known techniques are well explained and supplemented with MATLAB codes to get a clear idea about how each technique performs. In addition, the reader can reproduce the functional figures of the book with provided MATLAB scripts written specifically for this purpose. From the robustness and security perspectives, the commonly used audio watermarking techniques have limitations on the resistance to various attacks (especially desynchronization attacks) and/or security against unauthorized detection. Thus, in this book we develop new robust and secure audio watermark algorithm; it is well explained and implemented in MATLAB environment. This algorithm can embed unperceivable, robust, blind, and secure watermarks into digital audio files for the purpose of copyrights protection. In the developed algorithm, additional requirements such as data payload and computational complexity are also taken into account and detailed. Apart from the improvement of audio watermarking algorithms, another landmark of this book is the exploration of benchmarking approaches to evaluate different algorithms in a fair and objective manner. For the application in copyrights protection, audio watermarking schemes are mainly evaluated in terms of imperceptibility, robustness, and security. In particular, the extent of imperceptibility is graded by perceptual quality assessment, which mostly involves a laborious process of subjective judgment. To facilitate the implementation of automatic perceptual measurement, we explore a new method for reliably predicting the perceptual quality of the watermarked audio signals. A comprehensive evaluation technique is illustrated to let the readers know how to pinpoint the strengths and weaknesses of each technique. The evaluation techniques are supported with tested MATLAB codes. Furthermore to what we have just stated that this book extensively illustrates several commonly used audio watermarking algorithms for copyrights protection along with the improvement of benchmarking approaches, we may pinpoint the following new contributions of the current book: We introduce a spread spectrum based audio watermarking algorithm for copyrights protection, which involves Psychoacoustic Model 1, multiple scrambling, adaptive synchronization, frequency alignment, and coded-image watermark. In comparison with other existing audio watermarking schemes [1–10], the proposed scheme achieves a better compromise between imperceptibility, robustness, and data payload. We design a performance evaluation which consists of perceptual quality assessment, robustness test, security analysis, estimations of data payload, and computational complexity. The presented performance evaluation can serve as one comprehensive benchmarking of audio watermarking algorithms. We portray objective quality measures adopted in speech processing for perceptual quality evaluation of audio watermarking. Compared to traditional perception modelling, objective quality measures provide a faster and more efficient method of evaluating the watermarked audio signals relative to host audio signals. We analyze methods for implementing psychoacoustic models in the MPEG standard, with the goal of achieving inaudible watermarks at a lower computational cost. With the same level of minimum masking threshold, Psychoacoustic Model 1 requires less computation time than Psychoacoustic Model 2. We identify the imperceptibility, robustness, and security characteristics of audio watermarking algorithms and further use them as attacks in the process of multiple watermarking. We propose the use of variable frame length to make the investigated cepstrum domain watermarking, wavelet domain watermarking, and echo hiding robust against time-scale modification.