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Multi-Channel Music & Cinema Systems
Theory and Design
Lexicon
Dolby Digital and DTS
possible to make sound which comes from speakers at the sides of the
listeners appear to come from behind the listener by applying a notch filter
which has the frequency characteristic of the notches in natural hearing
which occur at about 150 degrees. This process is possible because sound
which arrives from the side is remarkably free of notches in natural hearing.
We can add an appropriate notch without having to remove one which is
inappropriate.
Engaging the 5 Speaker Enhance setting inserts these notches when sound
pans from the fronts to the sides and then to the rear. The result is that sound
moving around the listener appears to move smoothly from the front to the
side, and then behind the listener. This occurs even if the side/rear speakers
are at 90 degrees relative to the front. (However the ideal position for these
speakers is at about 120 degrees from the front.)
Although films have not yet been deliberately mixed to take advantage of
the capabilities of the new decoding, the improvement on standard films
can be dramatic. The improvement in spaciousness with music and ambi-
ence is obvious. On films with aggressive sound effects the combination of
surround steering and localization can convince listeners they are listening
to a true discrete surround mix.
Discrete digital formats such as Dolby Digital and DTS provide six discrete
channels of information. Five channels: Left, Center, Right, Left Surround
and Right Surround are full-range (3Hz to 20,000Hz). The sixth channel is
called the Low Frequency Effects (LFE) channel. It can contain additional
bass to emphasize the impact of scenes such as explosions or crashes.
Because the LFE channel has a limited frequency response, it is often
referred to as the “.1” channel. When added to the five full-range channels,
these surround formats are commonly referred to as having “5.1” channels.
As all channels are discrete digital tracks, channel separation and dynamic
range are greatly improved over analog surround sound. One advantage is
a dramatic improvement in localization of dialog. In addition, full-range
surround effects can be independently directed to left surround or right
surround speakers for a heightened sense of realism. Another benefit is
increased dynamic range, which allows subtle audio cues to be more easily
heard while giving loud effects, such as explosions, life-like impact.
The LFE channel delivers deep bass information for special effects and
music soundtracks, but is not always used. Recordings made without the
LFE channel are referred to as "5.0" soundtracks.
5 Speaker Enhance simulates 7 channels
of surround in 5-speaker setups.
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