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U. Glaeser

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Adam Dabrowski<br />

Poznan University<br />

Tomasz Marciniak<br />

Poznan University<br />

27.1 Introduction<br />

© 2002 by CRC Press LLC<br />

27<br />

Audio Signal Processing<br />

27.1 Introduction<br />

27.2 Elements of Technical Acoustics<br />

27.3 Parametric Modeling of Audio Signals<br />

27.4 Psychoacoustics and Auditory Perception<br />

27.5 Principles of Audio Coding<br />

27.6 Digital Audio Signal Processing Systems<br />

27.7 Audio Processing Basics<br />

DFT and Related Transformations • FIR Filters<br />

• IIR Filters • Filter Banks • Sampling Rate Conversion<br />

27.8 Lossless Audio Coding<br />

Pulse Code Modulation • Entropy Coding Using<br />

Huffman Method<br />

27.9 Transparent Audio Coding<br />

27.10 Audio Coding Standards<br />

MUSICAM and MPEG Standards • Dolby AC-3<br />

Standard • Adaptive Transform Acoustic Coding<br />

ATRAC Standard<br />

Information and communication systems play bigger and bigger role in our modern society—the so-called<br />

information society. Sound (audio and speech) is one of the most important signals in these systems and<br />

the growing need for audio and speech processing (transmission, storing, etc.) generates new scientific<br />

problems (e.g., formulates new questions about data acquisition, compression, and coding), stimulates<br />

new technologies and techniques, as well as creates new areas of science and technology in informatics,<br />

communications, artificial intelligence, psychoacoustics, etc.<br />

Applications of digital audio processing systems are in audio production, storage, distribution, exchange,<br />

broadcasting, transmission, Internet services, etc. Modern multimedia coding standards (e.g., moving<br />

picture expert group (MPEG) standards: MPEG-4, MPEG-7, and MPEG-21) [3,18–20,34,36] cover the<br />

whole range of audio signals starting from high fidelity audio, through the regular quality of audio and<br />

speech, down to relatively low quality mobile-access and synthetic speech and audio.<br />

In order to evaluate various audio coding systems it is necessary to qualify the audio quality they offer.<br />

Generally, three main parameters are used to describe the quality of audio: bandwidth, fidelity, and spatial<br />

realism.<br />

For high-fidelity (wideband) audio a bandwidth of at least 20 kHz is needed. The acoustic signals with<br />

higher frequencies are not audible by human beings. Compact disc (CD)—the today’s most popular<br />

standard for digital audio representation—offers a bandwidth of 20–20,000 Hz. Traditional (analog)<br />

radio covers the bandwidth of up to 15 kHz for frequency modulation (FM) and up to 4.5 kHz only for

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