Specifications
Group delay (0.5 to 4.2 MHz)
Chroma Gain
Chroma Delay
Differential Gain
Differential Phase
Noise
Video Conversion
Harmonic Distortion and Noise
Difference-Frequency Distortion
Dynamic Range
Digital Data Sampling Rate Support
Input Mode Control and User Interface
Design
Input Mode Switching
Automatic Detection of Data Types
Output Modes and Post Processing
Equalization and Tone Controls
Signal Headroom
Bass Management
Filter Characteristics
LFE Channel Level Scaling
Loudspeaker Position Time Synchronization
Auto Calibration
Auto Setup
Output Levels
Dialogue Normalization
Myth: "THX's De-Correlation was made
obsolete by the discreet surrounds of Dolby
Digital."
Reality: For Dolby Digital and other 5.1
the WHOLE system is assured, without any "matching"
effort required by you, the end user. THX controllers
are a perfect match for THX amplifiers, end of story.
You can think of this in terms of dynamic range
windows: when they all line up, you get maximum
performance all the way through.
The second, somewhat distinct aspect of certification
of a THX Controller is the inclusion and implementation
of various design features, including the THX
Post-Processes. Here we are starting to get into what I
was previously saying about THX addressing the realities
of home theater.
All THX Controllers include one or more THX modes
which are NOT surround sound decoding schemes or
codecs. When engaged, the THX modes apply a set of
processes or filters to the soundtrack AFTER it has been
Pro Logic, Dolby Digital, or DTS decoded.
The most basic THX mode is called simply "THX
Cinema". This mode includes:
Re-Eq, or ReEqualization. Ironically this is the best
known, and the single most misunderstood element of a
THX processor. Remember we said that Tom Holman
found sound tracks sounded different in the home-style
rooms? One of the reasons was that they were coming
across as too bright, which is a fancy way of saying there is too much treble. Why? The equipment was
excellent, high fidelity stuff. The "culprit" if you will, was the room itself. Lacking the extensive
acoustical treatments of professional sound and production rooms, high frequency energy is bounced
around and sustained. At elevated playback levels (at or close to reference) it gets subjectively worse
and you start to squint. Here is the very first example of what THX does to address the realities of the
consumer market: THX knew that no one would be talked into turning their family's living room into a
sound studio. Instead, Re-Eq simply applies a rational, mild roll-off of the high frequencies. It's that
simple.
Everything you have read about movie sound tracks themselves having too much high frequency energy,
including what THX's own marketing department has put out there, is inaccurate. The treble is not
exaggerated by the sound artist to overcome the perforated screens at the theater (the theater does its
own EQ to address that). The tracks do not have too much treble because movie theaters are aligned to
something called the X-Curve. We have an entire article on the
history of cinema sound system curves
which discusses the relevance of the X-Curve, and why it has absolutely nothing to do with why sound
tracks sound too bright in a home. Please feel free to digest it when you are done here.
Another quick sidebar: For many years, my living room was my home theater. As a reviewer, I had the
privilege of playing with some very nice amps, preamps, and more speakers than I care to remember, but
regardless of the caliber of equipment, movies just sounded harsh without a THX controller and Re-Eq. As soon
as I created a serious screening room complete with extensive acoustical treatments, I found Re-Eq necessary
only at the absolute loudest output levels. Go figure. This is why our Secrets SSP Benchmark specifications
require that THX controllers offer the option of turning Re-Eq off independently.
Adaptive De-Correlation / De-Correlation. The THX
Home Theater program was launched in 1991 at a time
when Dolby Pro Logic, the consumer equivalent of
Dolby Stereo, was the only thing going in surround
sound. While virtually all surround sound configurations
used two surround speakers, Pro Logic decoding yields
only one surround channel, meaning both speakers get