User Guide

268 Appendix B, AC-3 Encoding
What is Dolby Digital Audio?
Dolby Digital offers five full-range audio channels, commonly referred to as 3/2, with three
front channels (left, center, and right) and two surround channels. A sixth low frequency
effects (LFE or subwoofer) channel is also provided, giving rise to the term 5.1 channels.
Delivering six channels of digital audio in a format similar to that of audio CDs (44.1 kHz,
16-bit uncompressed audio) would yield data too large to store or transmit economically.
Dolby’s AC-3 Encoder provides compression algorithms that deliver multi-channel audio at
lower data rates with a minimum of sound degradation. The AC-3 Encoder uses a method of
compression (often referred to as perceptual coding) that removes audio data where
frequencies are less perceptible to human hearing, and for frequencies that contain limited
signal strengths. In addition, individual channels are compared so that only their differences
is retained, with the redundant audio information being discarded.
The DVD Specification supports Dolby Digital files within the following parameters:
Dolby listening environment
DVD-compliant Dolby Digital parameters
Bit Rate
192–448 kbps
Frequency
48 kHz
Encoding Mode
1/0, 2/0, 3/0, 2/1, 3/1, 2/2, 3/2 (1+1 is not DVD-compliant)
Ls
Rs
LFE
LR
C
Screen