Introduction to Digital Audio

This chapter describes the most important and prevailing technologies and algorithms of audio coding and standards activities. The three papers on audio coding present excellent overviews on the state of the art in speech and audio coding, its brief history, current research directions, and standards activities. The paper on psychoacoustics foundations includes audio perception, masking, and perceptual coding, and a paper on immersive audio systems, which have wide applications in virtual reality systems and the Internet. New algorithms and standards for audio coding are being developed quickly to meet the growing needs of diverse applications. As the research focus moves toward rates of 2.4 Kbps and below, waveform coding with the best CELP algorithms will face difficulties in meeting the ever higher quality objectives. Consequently, interest in vocoder studies is resurging as researchers focus on lower bit rates. On the other hand, wideband audio coding activities have been dominated by the work developed for the MPEG/Audio standards. The chapter also presents a novel desktop audio system with integrated listener-tracking capability that circumvents several of the technological limitations faced by today's digital audio workstations.