Chapter 1

DVD Technical Details 105
sound may only use the left and right channels for surround or plain stereo.
Even movies with old monophonic soundtracks may use Dolby Digital, with
only one or two channels. Some players can optionally downmix to nonsurround
stereo. If surround audio is important to you, you will hear significantly
better results from multichannel discs if you have a Dolby Digital
system.
The new Dolby Digital Surround EX (DD-EX) format, which adds a rear
center channel, is compatible with DVD discs and players, as well as with
existing Dolby Digital decoders. The new DTS Digital Surround ES (DTS-ES)
format, which likewise adds a rear center channel, works with existing DTS
decoders and with DTS-compatible DVD players. However, for full use of
either new format, you need a new decoder to extract the rear center channel,
which is phase matrixed into the two standard rear channels in the
same way Dolby Surround is matrixed into standard stereo channels. Without
a new decoder, you’ll get the same 5.1-channel audio you get now.
Because the additional rear channel isn’t a full-bandwidth discrete channel,
it’s appropriate to call the new formats “5.2-channel” digital surround. There
is also DTS-ES Discrete, which adds a full-bandwidth discrete rear center
channel in an extension stream that is used by DTS-ES Discrete decoders
but ignored by older DTS decoders. DTS-ES decoders include DTS Neo:6,
which is not an encoding format but a matrix decoding process that provides
5 or 6 channels.
The Dolby Digital downmix process does not usually include the LFE
channel and may compress the dynamic range in order to improve dialog
audibility and keep the sound from becoming muddy on average home
audio systems. This can result in reduced sound quality on high-end audio
systems. The downmix is auditioned when the disc is prepared, and if the
result is not acceptable, the audio may be tweaked or a separate left or
right Dolby Surround track may be added. Experience has shown that
minor tweaking is sometimes required to make the dialog more audible
within the limited dynamic range of a home stereo system. Some disc producers
include a separately mixed stereo track rather than fiddle with the
surround mix.
The Dolby Digital dynamic range compression (DRC) feature, often called
midnight mode, reduces the difference between loud and soft sounds so
that you can turn the volume down to avoid disturbing others yet still hear
the detail of quiet passages. Some players have the option to turn off DRC.
Dolby Digital also includes a feature called dialog normalization (DN),
which should more accurately be called volume standardization. DN is
designed to keep the sound level the same when switching between different
sources. This will become more important as additional Dolby Digital
sources (digital satellite and DTV) become common. Each Dolby Digital
track contains loudness information so that the receiver can automatically