DVD Demystified

DVD Comparison
373
determines the dynamic range (approximately 6 decibels per bit), but it
also has benefits for noise shaping and other digital signal-processing
techniques that can take advantage of the extra bits of precision.
CD audio uses two channels: left and right stereo. At lower sample rates
and bit rates, DVD PCM can have up to eight channels. Dolby Digital uses
5.1 channels: left, right, center, left-rear, right-rear, and subwoofer. MPEG-
2 optionally can add left-center and right-center channels.
Both of DVD-Video’s surround-sound formats are compressed from 16-,
18-, or 20-bit 48-kHz sources. Psychoacoustic processing is used to remove
imperceptible sounds and redundant information. Occasional compression
artifacts may be heard, but the resulting surround-sound experience is similar
to that of a theater—assuming the DVD player is hooked up to a sufficiently
good home sound system.
A few CDs are available with DTS surround sound. These CDs are not
playable on regular CD players. DVD offers DTS as an option, and with its
larger capacity, DVD can contain standard PCM audio, a Dolby Digital version
for those with Dolby Digital decoders, and a DTS version for those with
DTS decoders.
Capacity. By squeezing the tracks tightly together, an audio CD can be
made to hold as much as 84 minutes of audio rather than the specified 72
or 74 minutes. DVD, even at its highest level of uncompressed stereo sound
quality on a single-layer disc, holds over two hours of audio. Using all 5.1
channels of Dolby Digital audio, a single-sided, single-layer DVD can play
for over 27 hours. And using only two channels of Dolby Digital, more than
54 hours fit on a single layer, and a mind-boggling 197 hours can be packed
onto a double-sided, dual-layer disc.
Video. It may seem strange to list video as an advantage of DVD over
audio CD, but there have been many attempts to add video to music CDs,
including CDV, CDG, and Enhanced CD (see the sections on laserdisc and
other CD formats in this chapter for details).
Given the achievements of MTV, the success of music performance
videos, and the amount of existing music video footage with no retail channel,
it is expected that DVD-Video’s combination of high-quality video with
the convenience and audio quality of CD will tap a larger market of music
listeners who are interested in the visual aspects of the performance. DVD
music video also will appeal to the karaoke market, especially with its multilingual
subtitle capabilities.