The THX system is not a recording technology, and it does not specify a sound recording format; all digital (Dolby Digital, SDDS) and all analog sound formats (Dolby SR, Ultra-Stereo) can be "shown in THX." THX is mainly a quality assurance system. If a producer has his or her film mixed in THX, it merely means that when the film is shown in theaters, the soundtrack will sound exactly as it did when it was mixed, provided that the theaters in question are THX-certified theaters. THX also provides certified theaters with special equipment (a special crossover) required for compliance with the standard. Theaters become certified by meeting certain acoustic and technical requirements.
There is a small controversy over the origin of the name THX. The rumor for many years has been that the name comes from Lucas's early film, THX-1138. The THX web site [1] does not substantiate this theory, nor give any other reason in its press materials for the name.
A more plausible explanation may be that the name is an acronym for Tomlinson Holman EXperiment. Tomlinson Holman is a sound technician and professor, and was the original inventor of the THX system. He left Lucasfilm in the early 1990s, but the name, a striking and immediately recognizable trademark, along with the THX "Wow" trailer, have stuck. It has been claimed that Lucas said in an interview that the X stood for "crossover." This is logical, since the core of the THX system is the THX crossover, a special filter designed to improve bass management.
THX Limited, the company that licenses THX and the associated technology, is based in San Rafael, California.
The distinctive sound used in the THX "Wow" trailer, which precedes any film that has been certified with the THX program, is copyrighted, and those who have sampled the sound have been met with lawsuits.