Digital audio delivery to the consumer

Dolby Digital is a system for coding up to 5.1 channels of audio into a low bit rate data stream intended to deliver audio to the consumer. High quali ty is obtained with compression ratios approaching 12:1 for multichannel au dio programs. The high-compression ratio is achieved by methods that do not increase decoder memory and, thus, cost. The methods employed include tran smission of a high-frequency resolution spectral envelope and a novel forwa rd/backward adaptive bit allocation algorithm. In order to satisfy practica l requirements of an emissions coder, the syntax includes a number of featu res useful to broadcasters and consumers: loudness uniformity between progr ams; dynamic range control; and broadcaster control of downmix coefficients . Optimum application of the system involves the creation and delivery of m etadata describing dialogue loudness and intended dynamic range.