Pioneer VSX-21TXH User Guide

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The THX technologies are explained below. See 
www.thx.com for more detailed information.

THX is an exclusive set of standards and technologies established by 
THX Ltd. THX grew from George Lucas’ personal desire to make your 
experience of the film soundtrack, in both movie theatres and in your 
home theatre, as faithful as possible to what the director intended. 
Movie soundtracks are mixed in special movie theatres called 
dubbing stages and are designed to be played back in movie theatres 
with similar equipment and conditions. This same soundtrack is then 
transferred directly onto Laserdisc, VHS tape, DVD, etc., and is not 
changed for playback in a small home theatre environment. THX 
engineers developed patented technologies to accurately translate 
the sound from the movie theatre environment into the home, 
correcting the tonal and spatial errors that occur. On this product, 
when the THX indicator is on, THX features are automatically added 
in Cinema modes (e.g. THX Cinema, THX Surround EX).

The tonal balance of a film soundtrack will be excessively bright and 
harsh when played back over audio equipment in the home because 
film soundtracks were designed to be played back in large movie 
theaters using very different professional equipment. Re-Equalization 
restores the correct tonal balance for watching a movie soundtrack in 
a small home environment.

The human ear changes our perception of a sound depending on the 
direction from which the sound is coming. In a movie theatre, there is 
an array of surround speakers so that the surround information is all 
around you. In a home theatre, you use only two speakers located to the 
side of your head. The Timbre Matching feature filters the information 
going to the surround speakers so that they more closely match the 
tonal characteristics of the sound coming from the front speakers. This 
ensures seamless panning between the front and surround speakers.

In a movie theatre, a large number of surround speakers help create 
an enveloping surround sound experience, but in a home theatre 
there are usually only two speakers. This can make the surround 

speakers sound like headphones that lack spaciousness and 
envelopment. The surround sounds will also collapse into the closest 
speaker as you move away from the middle seating position. Adaptive 
Decorrelation slightly changes one surround channel’s time and 
phase relationship with respect to the other surround channel. This 
expands the listening position and creates—with only two speakers— 
the same spacious surround experience as in a movie theatre. 

ASA is a proprietary THX technology which processes the sound fed 
to 2 side and 2 back surround speakers to provide the optimal 
surround sound experience. When you set up your home theater 
system using all eight speaker outputs (Left, Center, Right, Surround 
Right, Surround Back Right, Surround Back Left, Surround Left and 
Subwoofer) placing the two Surround Back speakers close together 
facing the front of the room will provide the largest sweet spot. If for 
practical reasons you have to place the Surround Back speakers 
apart, you will need to go THX Audio Set-up screen and choose the 
setting that most closely corresponds to the speaker spacing, which 
will re-optimize the surround sound-field.
ASA is used in three new modes; THX Select2 CINEMA, THX Select2 
MUSIC and THX Select2 GAMES.

Depending on the listener’s and the subwoofer’s position, the listener 
may experience an excessive bass effect. This feature compensates 
for excessive bass resulting from a boundary gain effect. This feature 
is designed to operate when used with a subwoofer certified to THX 
Select2™ specifications. 

THX Loudness Plus is a new volume control technology featured in 
THX Ultra2 Plus™ and THX Select2 Plus™ Certified amplifiers. With 
THX Loudness Plus, home theater audiences can now experience the 
rich details in a surround mix at any volume level. A consequence of 
turning the volume below Reference Level is that certain sound 
elements can be lost or perceived differently by the listener. THX 
Loudness Plus compensates for the tonal and spatial shifts that occur 
when the volume is reduced by intelligently adjusting ambient 
surround channel levels and frequency response. This enables users 
to experience the true impact of soundtracks regardless of the volume 
setting. THX Loudness Plus is automatically applied when listening in 
any THX listening mode. The new THX Cinema, THX Music, and THX 
Games modes are tailored to apply the proper THX Loudness Plus 
settings for each type of content.

Before any home theatre component can be THX Select2 Plus 
certified, it must incorporate all the features above and also pass a 
rigorous series of quality and performance tests. Only then can a 
product feature the THX Select2 Plus logo, which is your guarantee 
that the Home Theatre products you purchase will give you superb 
performance for many years to come. THX Select2 Plus requirements 
cover every aspect of the product including pre-amplifier and power 
amplifier performance and operation, and hundreds of other 
parameters in both the digital and analog domain.

THX Surround EX - Dolby Digital Surround EX is a joint development 
of Dolby Laboratories and the THX Ltd. In a movie theater, film 
soundtracks that have been encoded with Dolby Digital Surround EX 
technology are able to reproduce an extra channel which has been 
added during the mixing of the program. This channel, called 
Surround Back, places sounds behind the listener in addition to the 
currently available front left, front center, front right, surround right, 
surround left and subwoofer channels. This additional channel 
provides the opportunity for more detailed imaging behind the 
listener and brings more depth, spacious ambience and sound 
localization than ever before. Movies that were created using the 
Dolby Digital Surround EX technology, when released into the home 

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