DVD Demystified

DVD at Home
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should be turned on for environments where the dialogue cannot be clearly
heard, such as when everyone else in the house has gone to bed and the volume
is down low.
Dolby Digital also has a feature called dialog normalization, which is
designed to match the volume level from various sources. Each encoded
audio source includes information about the relative volume level. Dialog
normalization automatically adjusts the playback volume so that the overall
level of dialog remains constant. It makes no other changes to the audio,
including dynamic range; it is equivalent to manually turning the volume
control up or down when a new program is too soft or too loud. Usually, only
one setting exists in a program; that is, the volume control does not change
in the middle. Dialog normalization is especially useful with a digital television
source, to handle variations in volume when changing channels. It is
less useful for DVDs, unless they have many separate programs on them.
DTS is not used on most DVD discs. SDDS is not used on any discs. They
are optional multichannel surround formats that are allowed in the DVD
format but not directly supported by most players. Each requires the appropriate
decoder in the receiver or a separate audio processor.
Connecting Digital Audio Two different standards govern the digital
audio connection interface: coaxial and optical. The arguments are many
and varied as to which one is better, but since they are both digital signal
transports, good-quality cables and connectors will deliver the exact
same data. Some players have only one type of connector, although many
have both.
Coaxial digital audio connections use the IEC-958 II standard, also
known as S/PDIF (Sony/Philips Digital Interface Format). Most players
use RCA phono connectors, but some use BNC connectors. Use a 75-ohm
cable to connect the player to the audio system. Multichannel connectors
are usually labeled “Dolby Digital” or “AC-3.” PCM audio connectors usually
are labeled “PCM,” “digital audio,” “digital coax,” “optical digital,” or so
on. Dual-purpose connectors may be labeled “PCM/AC-3,” “PCM/Dolby Digital,”
or something similar. Make sure you use a quality cable; a cheap RCA
patch cable may degrade the digital signal to the point that it does not
work.
Optical digital audio connections use the EIAJ CP-340 standard, also
known as Toslink. Connect an optical cable between the player and the
audio receiver or audio processor. The connectors are labeled “Toslink,”
“PCM/AC-3,” “optical,” “digital,” “digital audio,” or the like.
If the connection (either coaxial or optical) is made to a multichannel
audio system, select Dolby Digital/AC-3 (or DTS or MPEG multichannel)