Sony G90 - Manual (Page 29)

process takes about eight minutes, can be per-
formed with the AVP installed in your system,
and doesn’t erase your set-up and configuration
settings.
New software can add capabilities such as
DTS or MPEG decoding (by changing the DSP
code), refine the user interface (by updating
the operating system), or configure the unit to
accept formats not available when the product
was designed (by changing the input-receiver software).
The AV P ’s Proceed input receiver (the chip that receives,
identifies, and decodes the incoming bitstream) is custom
made, which allows the AVP to work with future formats
whose interface protocols have not yet been established.
Updating software in this way reduces the likelihood of
needing expensive hardware changes.
Another method of heading off controller obsoles-
cence is “modular” construction. A modular
controller is built like a PC, with a mother-
board and smaller circuitboards that fit into
slots on the motherboard. If a new technology
comes along or better digital-to-analog con-
verters become available, as examples, you
simply swap out a circuitboard to bring your
controller up to date. Some controllers com-
bine the ability to update software with modular
construction for the ultimate in upgrade flexibility.
Bass Management
An important controller function performed by the DSP
chips is bass management, the subsystem that lets you
selectively direct bass information in the soundtrack to the
main loudspeakers or to the subwoofer. Bass management
allows a controller to work correctly with a wide variety of
S ome controllers are “THX Certi-
f i e d ,” meaning they incorporate
Lucasfilm signal processing – a
technology that Lucasfilm believes better
translates film soundtracks created for
theater playback into the home. THX-cer-
tified controllers must also meet a set of
technical performance criteria established
by Lucasfilm. If the product corr e c t l y
implements the THX technologies and
meets the performance criteria, the unit
can be branded “THX Certified.” The man-
u fa c turer then pays a license fee to
Lucasfilm on every unit sold.
The goal of Home THX is to re-create
as closely as possible in a home-theater
system the sound that the mixing engi-
neers heard on the film-dubbing stage.
THX-certified controllers employ fo u r
processes that Lucasfilm has found to
i m p r ove the home-theater ex p e r i e n c e :
surround decorrelation, timbre matching,
re-equalization, and the subwo o fe r
crossover. Let’s look at each of these.
S u rround decorr e l a t i o n m a kes the
monaural surround signal slightly different
in the left and right surround channels by
varying the time and/or phase of those
signals. This technique prevents the “in
the head” localization of surround signals,
and “smears” the surround signal so that
we feel a greater sense of envelopment
in the film soundtrack. With the advent of
5.1-channel formats with separate left and
right surround channels, THX surround
d e c o rrelation has ta ken a new tw i s t ,
called “adaptive de-correlation.” Adaptive
de-correlation turns off the de-correlation
circuit when the two surround channels
carry different information, but smoothly
turns it on when the surround channels
are identical. Most 5.1 soundtracks still
have mono surrounds most of the time,
so this is a useful feature. (See the side-
bar to the Denon AVR-5700 review in
Issue 25 for more on surround decorrela-
tion.)
Timbre matching makes it possible
for sounds arriving from the sides to have
the same perceived timbre as sounds
arriving from the front. This makes pans
(movements of sounds) from front to rear
more realistic, because the perceive d
timbre doesn’t change with movement.
You can easily demonstrate for yo u r s e l f
h ow perceived timbre changes with direc-
tion: Snap your fingers in front of your fa c e ,
and again to the side of your head. Th e
sound is “sharper” to the side. THX timbre
m a t ching compensates for this diffe r e n c e
with signal processing in the controller.
Re - e q u a l i z a t i o n is a treble cut applied
on play b a ck to make soundtracks mixe d
for movie theaters sound natural when
p l ayed in the home. Mixers intentionally
m a ke soundtracks bright for several rea-
sons. Theaters are usually full of absorbent
seats, drapes, and people, all of which roll
o ff high frequencies to a greater degree
than midrange and bass frequencies. In
addition, the long distance between the
audience and loudspeakers tends to selec-
t i vely attenuate treble. Consequently, the
s o u n d t r a ck has a natural tonal balance in
the theater, but exc e s s i ve brightness on a
home-theater system. The answer is to
e q u a l i ze the soundtrack during play b a ck so
it sounds correct in the home.
But how much treble cut is correct?
And what should the equalization curve
look like? To find out the correct THX re-
equalization curve, THX’s inventor, Tomlin-
son Holman (THX stands for Tom Hol-
man’s eXperiment), asked a series of top-
level film-sound mixers to listen to their
films on a home-theater system. Th e
mixer had an equalizer in front of him, and
was asked to adjust the equalizer until the
soundtrack sounded “right” on the home-
theater system. Holman averaged the
equalization curves created by the mixing
engineers (which were remarkably close)
to generate the patented THX re-equaliza-
tion curve.
To save money, some budget con-
trollers license only the re-equalization
part of THX processing, not the entire sig-
nal-processing suite. Other controllers
not licensed by Lucasfilm may employ a
selectable treble cut, often carrying a
name such as “Cinema EQ.”
F i n a l l y, the THX s u b wo o fer crossove r
s ta n d a r d i zes the crossover ch a r a c t e r i s t i c s
( c u t - o ff frequency and slopes) that split the
frequency spectrum into bass for the sub-
wo o fer and midrange/treble frequencies
for the main speakers. The THX crossove r
frequency is 80 Hz, with fourth-order low-
pass and second-order high-pass slopes.
The subwo o fe r-out jack on a T H X - c e r t i f i e d
controller thus carries a precisely defined
signal. When decoding 5.1- channel Dolby
D i g i tal or DTS (so-called THX 5.1 mode),
the subwo o fer output carries the Low Fr e-
quency Effects (LFE) channel, plus the
bass from any number of the other five
channels. When decoding Dolby Surr o u n d ,
the THX subwo o fer output is a mix of the
front three ch a n n e l s’ bass below 80 Hz,
assuming that the front speakers are small
satellite ty p e s .
You may have recently seen the desig-
nations “THX Select” and THX Ultra”
replace plain old THX. THX Select products
h ave relaxed performance standards, and
are designed to allow products suitable fo r
smaller rooms to benefit from THX pro-
c e s s i n g. The more rigorous Ultra perfo r-
mance level corresponds to what used to
be simply called “THX” and is built on the
assumption that the room invo l ved may be
3 , 000 cubic feet or larger. R H
THX-Certified Controllers