Meridian Audio 568 - Manual (Page 45)

DSP presets
38
Logic DSP presets
The digital surround processor provides four DSP presets
specifically designed for reproducing stereo film soundtracks.
Three of these presets, Pro Logic, THX Cinema, and TV Logic,
are designed for Dolby Surround encoded material. Most films,
and many TV programmes and series, are encoded using Dolby
Surround, and it is increasingly being used to encode music.
The 568 Digital Surround Processor follows the Meridian
philosophy of performing all the signal processing digitally, and
the Dolby Surround decoding operates purely in a digital mode.
This gives it a far higher performance and a better subjective
sound than other analogue-based decoders.
The remaining Logic preset, Mono, is designed for films with
mono soundtracks.
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.