User guide

DSP presets
39
❍ The time synchronisation between loudspeakers is adjusted to
compensate for the fact that the speakers in a home system
tend to be a lot closer to the listener than in a movie theatre.
THX can also be used with Pro Logic, or the 5.1 Movie DSP
presets; see THX Cinema, page 40, and Dolby Digital THX, DTS
THX, and MPEG THX, page 47.
PLII Movie and PLII THX preset
parameters
Parameter Options What it changes
Steered All Steered Rear, Which of the four surround
Steered Side, channels are generated by
Steered All steering.
R Delay 10ms to 25ms The delay of the rears.
S Delay 10ms to 25ms The delay of the sides.
Pro Logic Off, On On selects the original
Pro Logic decoding.
Pro Logic
Dolby Surround is an encoding system based on a phase-
amplitude matrix whose output can be decoded by a very
simple passive matrix. Such a decoder gives quite a poor
separation.
The Pro Logic system uses psychoacoustically optimised
directional enhancement to increase the separation in both
left–right and front–back directions. It does this by continuously
calculating the position and degree of the currently dominant
sound. This sound is then steered to a greater or lesser extent to
that position in the arriving sound. This technique is very
successful for cinema and other dramatic programmes.
Further refinements in the Pro Logic decoder include the filtering
and delay of the rear surround signal to reduce any tendency for
the surround signals to divert attention or become dominant.
The Pro Logic decoder also uses a modified digital Dolby noise-
reduction process in the surround signal. Since Dolby Surround
material is encoded with this in mind the noise-reduction is
permanently operating in this mode.