THX

THX is a trade name of a high-fidelity sound reproduction standard for movie theaters, screening rooms, home theaters, computer speakers, gaming consoles, and car audio systems.
THX stands for Tomlinson Holman's eXperiment and is a throwback to George Lucas' first feature film, THX 1138. THX was developed by Tomlinson Holman at George Lucas's company, Lucasfilm, in 1983 to ensure that the soundtrack for the third Star Wars film, Return of the Jedi, would be accurately reproduced in the best venues. The distinctive crescendo used in the THX trailers, created by Holman's coworker James A. Moorer, is known as the "Deep Note".
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 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.