Bryston SP 1 Series Instructions Manual page 25

The SP1, contains special processing designed by THX to
correct those errors and restore the appropriate tonal and
spatial balance to a movie soundtrack, so that you can hear
what the film's producer/director intended.
This processing includes:
1. An Electronic Crossover
Electronic Crossovers allow the use of the more typical
residentially sized smaller main speakers by sending the bass
signals to a separate subwoofer.
With Dolby Pro Logic sources, only the main front channels
pass through the crossover. For Dolby Digital or DTS sources,
all channels pass through the crossover.
2. Re-Equalization
This processing is designed to correct the excess high
frequency content or brightness of movie soundtracks.
This excess brightness occurs because as noted above motion
pictures are mixed in spaces representing the size and
acoustics of movie Theatres which incorporate a special
international standard called the "X-Curve".This frequency
response curve is used because there is a natural high
frequency rolloff (loss) when sound sources are some distance
from the listener.This is the case with the speakers in a
commercial cinema.
When the speakers are much closer, such as in a home
cinema, the soundtrack will be excessively bright.
The THX processing uses a special Re-Equalization Curve,
designed for home environments, to restore the correct tonal
balance of a movie soundtrack.
3.Timbre Matching
In a commercial Theatre, the multiple loudspeakers used are in
front [ the LCR speakers], and all around you [the surround
speakers located along the sides, and behind you].The many
surround speakers are carefully equalized to match the front
channels.
The THX Timbre Matching processing corrects the surround
tonal balance to match the front channels so you hear one
continuous soundfield.
Additionally for the majority of residential systems, the system
must also correct for the fact that only two surround speakers
are used.
The THX processing help to insure that there is always smooth
sound movement from front to the surrounds.This helps to
place you, the listener, inside the movie experience.
4. Adaptive Decorrelation
Additionally the THX processing system is designed to deal
with the fact that in Dolby Pro Logic mode (the system used
on the vast majority of videotape versions of movies) the
surround channels are monophonic.
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