6 - Audio data compression

Abstract

This chapter discusses the importance of audio data compression. In analog systems, noise reduction systems have been vigorously used to enhance the dynamic range of noisy transmission systems such as the analogue tape. All of these analogue systems rely on a method called “compansion,” which refers to the dynamic range deliberately reduced (compressed) in the recording stage processing and recovered (expanded) in the playback electronics. There are some systems where this compansion acts over the entire frequency range. Usually, the digital systems chosen to work for digital television have carried the principle of sub-band working to a degree of sophistication in analog implementations. The chapter explains that audio data- rate reductions may be made because real audio signals do not change instantly from very large to very small values. The chapter also describes that wide-band compansion systems view the phenomenon of masking simply, whereby relying on the fact that program material will mask system noise. One of the leading players in audio data compression should be Dolby, along with the company's unrivalled track record in noise reduction systems for analog magnetic tape.