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THX FAQs thread

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This is an area we get questions on every now and then, so I might as well put a collection of links I found useful in finding out more about THX.


Here goes:




THX is the trade name of a high-fidelity sound reproduction system for movie theaters, screening rooms, home theaters, computer speakers, gaming consoles, and car audio systems. THX was developed by Tomlinson Holman at George Lucas's company Lucasfilm in 1982 to ensure that the soundtrack for the third Star Wars film, Return of the Jedi, would be accurately reproduced in the best venues.


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 SR, Ultra-Stereo), can be "shown in THX." THX is mainly a quality assurance system. THX-certified theaters 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 also provides certified theaters with a special crossover circuit whose use is 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, no parallel walls (to reduce standing waves), a perforated screen (to allow center channel continuity), and NC30 rating for background noise.





"What is the difference between "THX Select" and "THX Ultra"?


For receivers and loudspeakers, the THX Select certification is for components that are certified to perform in a mid-sized home theater environment of up to 2,000 cubic feet.  The volume of a room, expressed in cubic feet, is computed by multiplying the length by the width by the height of the room.  (For example, a room that is 18 feet wide by 14 feet wide by 9 feet high, has a volume of 18 x 14 x 9 = 2,268 cubic feet.)  The more stringent THX Ultra certification (which is equivalent to the original, plain THX certification) is given to components that meet the THX performance standards for larger home theater environments (up to 3,000 cubic feet).  Theoretically, if you have a home theater environment that is 2,000 cubic feet or less, THX Select receivers and loudspeakers should deliver about the same presentation standards as the higher-end THX Ultra components. "

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Each THX certified disc comes with this:




THX Optimizer

For the best possible playback, each THX Certified DVD features THX Optimizer, an easy-to-use on-screen calibration tool for home theater systems. THX Optimizer helps you fine-tune your audio and video settings through a series of test signals. These test signals allow you to match the reference levels used during the DVD mastering process – giving you the exact sound and picture presentation that the filmmaker wanted you to experience.


THX Optimizer offers a quick and easy solution on how to set color, tint, contrast and sharpness, as well as check speaker assignments, phase and crossovers on your surround sound system.


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Not a standard by itself, THX Home Cinema aims at delivering cinema-quality picture and sound to the home.


"THX Home Cinema is able to achieve this through a double front approach:


It defines precise specifications for hardware, e.g. THX certified main front channel speakers have to meet very specific design goals in terms of their horizontal and vertical radiation patterns.


It also makes use of proprietary technologies and processes that form an integral part of the whole system. "


Major aspects of the THX Home Cinema certification program include:

Re-equalization to compensate for the differing tonal balances that are appropriate in home theaters versus movie theaters, thus reducing the normally higher treble associated with the latter.


Timber matching to complement the tonal qualities of the front and rear speakers to create a more uniform surround soundstage.


Decorrelation of the surround channels in Dolby Pro Logic surround systems. The scope is to introduce minor diversity to the mono-surround channel serving the two rear speakers in this surround format, thus leading to a more diffused feel. This helps avoid the collapse of the centered rear soundfield produced by this monaural signal to the speaker closest to the listener. The latest THX Home Cinema certified receivers include adaptive decorrelation that automatically switches off the related circuitry when not required e.g. in Dolby Digital.


Bass management based on a precise crossover cut-off point at exactly 80Hz, and a defined sub-woofer ‘sloop’ driver response. While THX recommends using a sub-woofer and setting all other speakers to 'small' to be able to place the subwoofer at the best sounding position in the room, at the same time, it also supports other options, including that of mixing the bass information from the left and right channels with the sub woofer channel.


Amplifier Specs that are much tougher than on non-THX certified gear; these include the ability to drive low impedance (3.2Ohms) speakers while still producing a volume level of 105dB.


A THX reference level (of 75dB) that aims at reproducing the same level, at which the movie was mixed in the studio.


THX Optimizer or Optimode for DVD movie releases. This places a set of test patterns on the disc to enable the home theater enthusiast to tweak the video display to the same settings as used during the production stage.


THX Select and THX Select2 Certified Products


THX Home Cinema certified products within the Select/Select2 categories are designed to deliver optimal quality audio and video presentations in small to medium sized home theater rooms.


More specifically, these are designed for a viewing distance of approximately 10 feet / 3 meters from the display to the listening position, and an overall room volume of circa 2,000 cu. ft.


THX Select2 specifically addresses receivers, incorporating new features and improved noise floor performance. Based on the same values and principles of THX Ultra2, THX Select2 Certified Receivers deliver higher quality to smaller home theater environments.


THX Select addresses the performance of speakers and DVD players. THX Select Certified Products complement the presentation of the THX Select2 category.


THX Ultra and THX Ultra2 Certified Products


The THX Home Cinema 'Ultra' and 'Ultra2' certifications are designed to ensure that certified products within these categories deliver top quality audio and video presentations in large home theater rooms.


More specifically, these are geared for a viewing distance of approximately 13 feet / 4 meters from the display to the listening position, and an overall room volume of around 3,000 cu. ft. room.


THX Ultra2 is considered as the benchmark for home theater products in that it offers uncompromised playback of multi-channel movies, music and games. The Ultra2 incorporates new features such as EX auto-detection and switching, high-bandwidth video switching, adaptive side-surround decorrelation, and boundary gain compensation. In addition, it also includes more power requirements for premium home theater receivers, pre-amplifiers, power amplifiers and speakers, to ensure the optimal distribution of a wide enough soundstage across the whole viewing area in the larger dedicated home theater room.


THX Ultra brings high-end performance to interconnects, equalizers, projection screens and DVD players, thus complementing the THX Ultra2 category. Unlike THX Ultra2 Certified Products, which are dependent on the room size, THX Ultra Certified Products are not.



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THX Certified Multimedia


The THX certification for multimedia products aims at delivering cinema-quality picture and sound to the desktop by ensuring that multimedia products comply with the THX rigorous standards.


While computer speakers and systems have the potential to deliver high quality pictures and sound, compatibility problems, non-standard set-ups and even complicated user controls may limit a potentially 'great' immersive experience.


For this purpose, THX have created performance standards specific to the challenges associated with Multimedia systems. The THX Multimedia certification program requires stringent specifications for the display, sound system, audio/video processing and even user controls. When you purchase computer systems or components carrying the THX logo, you are assured that special effects, graphics, and robust audio intended by film producers, musicians, and game developers, are accurately reproduced on your desktop.


In other words, the THX Certified Multimedia stamp is a guarantee that your computer setup is capable of delivering the highest possible fidelity for your MP3s, CDs, DVDs, games, and other digital audio sources, through cinema-quality audio and visual experience.


This also means that, as with other THX product certifications, THX Certified Multimedia is also associated with the viewing distance requisite; in this case, certified Multimedia products are designed for an optimum viewing distance of approximately 28 inches / 0.7 meters.


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Q: Everyone is familiar with the buzz phrase "THX Certified" but we want to bring this mystery down to an easy-to-digest level. Can we talk about first, the different levels of THX certification, and then speak as specific as possible about what types of criteria are involved in achieving such certifications?



A: [glow=red,2,300]THX Select is a more affordable version of THX Certification.[/glow] It is designed to play at reference levels in rooms of approximately 2,000 cubic feet,. THX Ultra2 is a 7.1-speaker extension of the original Ultra spec. Ultra2 is designed to work well with multi-channel music and movie presentations playing up to reference levels in rooms of 3,000 cubic feet or larger. Each certification requires components to produce high volume levels, to play at a low level of distortion, and to disperse sound in specific ways, as well as to have extremely low noise and behave in a stable and predictable way.


We have worked with most of our licensees for many years and on numerous products. When working on a product from a company accustomed to our requirements, we typically invest 40-60 hours in testing and correspondence before issuing certification. When working with a new licensee, we often invest 120-200+ hours per product before granting certification. What all this means is that the product performs and performs well. A $500 THX Certified receiver will have a very high level of performance, while a $4,500 THX Certified receiver will have even higher level of performance and will include whatever additional features the manufacturer chooses.






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