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Comparison with conventional Dolby
Pro Logic
Dolby Pro Logic features analog matrix processing which means that
the S signals become mixed in with both the L and R signals, which
gives rise to crosstalk
(sound
interference)
between
adjacent
channels.
The human ear can hear sound in the high range up to 20 kHz
(high-range threshold frequency). However, with Dolby Pro Logic, it
was possible to record surround sound only up to 7 kHz in order to
compensate for the crosstalk between the channels.
In contrast, Dolby Digital (AC-3) features a 5-plus-1-channel format
for the reproduction channels in which an extra channel (which
handles the sound of the deep-bass effect in the low frequency range
below 120 Hz) is recorded discretely in addition to the 3 channels (L,
C and R) at the front and 2 channels (LS and RS) at the back. As a
result, there is no crosstalk between the channels, and the sound field
can be controlled to match the viewing and listening space. Further-
more, the high-frequency reproduction range of the 5 channels ex-
tends up to 20 kHz which is the same as for CDs, making for clearer
sound reproduction with enhanced expressiveness.
Dolby Digital (AC-3) program format display
However, Dolby Digital (AC-3) signal has the channel formats of 1
channel to 5-plus-1 channels and not all signals are recorded in the
5-plus-1 channel format.
The configuration of the speakers through which the sound is output
differs in accordance with the type of signal format used with Dolby
Digital (AC-3) input, and the corresponding Dolby Digital (AC-3)
program format indicator lights to announce the configuration.
When the sound has been input using PCM signals*, the AC-3 indica-
tor goes off.
'This refers to the recording format of signals (44.1 kHz, linear
16 bits) used for a music CD.
Differences between Dolby Digital (AC-3) and Dolby Pro
Logic
Dolby Digital
System comparison
L, R, C, S (SW is
recommended)
1 channel to
5-plus-1 channels
No. of reproduced
sound channels
5-plus-1 channels
Reproduced sound
channel configuration
L, R, C, LS, RS, SW
Digital discrete
processing,
AC-3 encoding
and decoding
Analog matrix
processing,
Dolby Surround
Audio processing
High-range reproduction
threshold of surround
channels
@4-2-4 matrix
e5-plus-
1 channels,
system
separate
è Differential
eHigh dynamic
components
range
including
eSuperior
reverse phase
localization,
between L and
phase
R for surround
characteristics,
signals
sound field
eL+R signals
inor atures
reproduction
added together
for center
channels
eNo separate
channel for
subwoofer;
sound taken
out from front
channels using
low-pass filters.
SW (subwoofer)
è Encoding (encoding of original signals)
® Decoding (restoration of cade to original signals)
Oper
a
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