Analysis of digital audio compression and digital rights management techniques

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Title: Analysis of digital audio compression and digital rights management techniques
Author: Majewicz, Eric
Abstract: This paper starts with an initial discussion on digital audio principles, which is important to understanding advanced digital audio concepts such as compression. The process by which an analog waveform is converted into its digital equivalent is done in three steps: sampling, quantization, and coding. Sampling and quantization take the analog signal, which is a continuous voltage varying with time, and divides it into discrete intervals. Coding is the process by which this information is represented as a series of digital words. A discussion is also presented on the major uncompressed digital audio format for PC, the WAVE file format. The main focus of this paper is on lossless and lossy compression techniques and their applications. Lossless compression techniques such as Huffman Coding, Arithmetic Coding, and Dictionary-based Coding remove redundancies in the content and code the information as efficiently as possible. These techniques are rarely used alone because of the small compression ratios that they provide as compared to lossy techniques. Lossy compression takes advantage of the fact that the human ear does not perceive all frequencies equally. Instead, critical bands in the ear divide up the frequency spectrum and perceive these bands with different fidelity. Lossy compression techniques that use these principles are discussed, which include subband coding, the psychoacoustic model, and stereo redundancy coding. Applications of these techniques are often referred to as perceptual audio coders, which provide high compression ratios with little loss in audio quality. This paper looks at the following audio coders: MPEG-1 Layer 1,2 and 3, MPEG 2/4 (AAC), Dolby AC-3, and Sony ATRAC. These standards were chosen for evaluation because each of them has an important industry application. MPEG-1 Layer 3, also known as MP3, has been the format used on the internet for transferring and storing music. More recently, AAC has been used for online music services such as Apple iTunes, which is an attractive option because it provides protection of the content as well as compression. Dolby AC-3 is the standard that is used currently used in HDTV, and the ATRAC format is used by Sony’s popular MiniDisc device. This paper concludes with a discussion on Digital Rights Management, which is addressed by many new compression formats. The spread of illegal file sharing across the internet has prompted a strong response from the music industry for formats and standards that can provide both compression and content protection. This paper will look at some of the common techniques that are used for digital rights management such as cryptographic-based protection, digital licensing, and digital watermarking. The applications of these techniques will be discussed by looking at standards such as the Secure Digital Music Initiative (SDMI) and MPEG-4 Intellectual Property Management Protection (IPMP). These standards will be analyzed based on their technologies and the effectiveness in providing sufficient protection.
Description: An independent study report prepared for Dr. Chance M. Glenn Sr., Department of Electrical, Computer, and Telecommunications Engineering Technology, Rochester Institute of Technology.
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Date: 2004

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