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THX post-processing
THX recommend that the surround back
loudspeakers are placed quite close together,
facing towards the listener, although during
the setup of the AV32R ‘Dual Processor’ you
will be asked whether the surround back
speakers are close together or apart (for
details see page 60), and signal levels sent
to the back speakers will be adjusted
accordingly to achieve consistent results.
introduction of back channels
A significant recent development has been the addition of the
surround back channel, which first appeared in cinema soundtracks
in 1999. THX have been at the forefront of this development,
working closely with Dolby Laboratories to produce THX Surround
EX. THX Surround EX encodes an additional channel within the left
and right surround channel signals, which is extracted by a Dolby 3
decoder. DTS-ES discrete takes this process a step further, with a
discretely encoded 6th channel.
replay of 5.1 through 7.1 speakers
THX boundar y gain compensation
The addition of the surround back channel has prompted a rethink on the
processing front, with a view to making best use of the extra loudspeakers
with 5.1 material. THX Surround EX processing can be applied to any 5.1
source material to generate a signal for the back channel. This works well
for much 5.1 material, but gives poor results if the surround content of the
5.1 material is mono as this results in all of the surround information being
directed to the back speakers and none to the surrounds. To prevent this,
and improve results with all 5.1 source material, THX Cinema is replaced
by
THX Ultra2
, which employs THX Advanced Speaker Array processing to
optimise the surround experience.
There have also been enhancements to bass management, with a new
optional ‘Boundary Compensation’ mode added to achieve better bass
integration when the listening positions are close to the back wall. Such
positioning results in low frequencies being boosted (by a process called
‘Boundary Gain’, in which the reflected sound from the wall adds to the
direct sound from the speaker increasing its level). Boundary Compensation
provides additional low frequency filtering on all channels to achieve a
more natural low frequency balance, for details see page 61.
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