What is THX?
The THX system is not a recording technology and it does not specify a sound recording format: all sound formats, whether digital (Dolby Digital, SDDS) or analog (Dolby Stereo, Ultra-Stereo), can be "shown in THX." THX is mainly a quality assurance system.
THX-certified theatres provide a high-quality, predictable playback environment to ensure that any film soundtrack mixed in THX will sound as near as possible to the intentions of the mixing engineer. THX, as a company, also provide certified theatres with a special crossover circuit as part of the standard.
Certification of an auditorium entails specific acoustic and other technical requirements; architectural requirements include a floating floor, baffled and acoustically-treated walls, non-parallel walls (to reduce standing waves), a perforated screen (to allow centre channel continuity), and NC30 rating for background noise ("ensures noise from air conditioning units and projection equipment does not mask the subtle effects in a movie's soundtrack.")
The following are proprietary processing that is applied in order to obtain a THX-like environment at home.
Your ears hear different tonal qualities in sounds coming from different directions. Timbre Matching restores the frequency balance between your front and surround speakers, ensuring seamless and smooth panning between the front to back of the room.
Many movie soundtracks are mixed in studios for playback in large cinema auditoriums with an array of speakers. When played on home systems, they may appear abrasive and edgy. Re-EQ establishes a more accurate tonal balance when enjoying movies in your home.
Adaptive Decorrelation changes one surround channel's time and phase relationship with respect to the other surround channel, expanding the listening position and creating the same spacious audio experience at home as in a movie theatre. And since too many speakers are being set too close to the wall (especially subwoofers), in order to get rid of the boominess due to boundary gain of any given room, THX applies Boundary Gain. Compensation (BGC)
Sitting near a wall may result in distorted bass response. BGC corrects the way low frequency sound is perceived when seated near a wall. This results in a more true and accurate bass response.
THX Loudness Plus
THX Loudness Plus is a new volume control technology featured in THX Ultra2 Plus and THX Select2 Plus-certified receivers, pre-amps and amplifiers. With THX Loudness Plus, home theatre audiences can now experience the rich details of surround sound at any volume level.
THX Loudness Plus employs two technologies to make it work: THX Multi-channel Spectral Balancing adjusts frequency response to counter the perceptual loss of low and high frequency sound in all channels. It begins with a flat response at Reference Level, and continually adjusts the response as the user selects lower listening levels. The equalization is applied to all channels in a multi-channel listening environment.
THX Dynamic Ambience Preservation surround channel processing preserves the spatial detail that is lost when listening below Reference Level. It automatically shapes the output on surround channels to maintain the perceived balance in the original mix.
THX Certifications in Home Theatre Environment
Depending on the size of your room, THX has a solution for every consumers' needs.
THX's Ultra2 certification is given for home theatre components said to be good enough for a large home cinema of 3,000 cubic feet or more.
THX's Select2 certification is given for home theatre components said to be good enough for medium-sized rooms, up to 2,000 cubic feet in size, with a 10-12 feet viewing distance from the screen.
I/S Plus Systems
THX's I/S Plus Systems include an AV Receiver + Speaker Bundle and are certified to fill a small home theatre or dorm where the viewing distance from the screen is 6-8 feet.
THX-certified multimedia products are designed and engineered for PC gaming and multimedia on the desktop.
THX-certified video displays (plasma and LCD flat panels and projectors) include a THX mode that allows users to see a program or movie as the creator intended.
The latest addition, is the THX Compact System certification. Until now, smaller, more compact speaker systems have been about convenience and form factor rather than performance. Times are changing, and recent advances in technology and design have challenged this precedent. Today, it's quite possible for smaller speaker systems to deliver excellent sound experiences.
Stay tuned for Part 2 next week to learn more about THX.