THX Is a Quality Standard Not a Format Sound in Film
Lucas wanted theaters to play Star Wars the way he mixed it
THX originated from a specific frustration. George Lucas mixed Return of the Jedi (1983) at Sprocket Systems (later Skywalker Sound) in a carefully calibrated environment, then discovered that most theaters reproducing the film sounded nothing like his mixing stage. Lucas had a blunt view of where sound ranked:
"The sound and music are 50% of the entertainment in a movie." — George Lucas
Tomlinson Holman, Lucasfilm's technical director, designed a set of specifications for theater construction and equipment that would ensure predictable, reference-quality playback. Holman saw the existing theater speaker standard as the bottleneck:
"THX was kind of a no brainer because looking at the whole chain the Voice of the Theater which had 80% market share was the most limiting stage to range, response, and uniformity of coverage." — Tomlinson Holman, Sound Magazine
The program launched in 1983 as THX — named after Holman (Tomlinson Holman's eXperiment) and referencing Lucas's first feature, THX 1138. Theaters that met the specifications earned THX certification and could display the THX logo. The origin of the name was more prosaic than the film reference:
"The guy who hired me, Jim Kessler, thought it up. His first thought was that this was Tom Holman's crossover, abbreviated XVR... He dropped the VR and stuck together TH and X, then realized that also applied to George's first movie, so it was perfectly appropriate." — Tomlinson Holman, SVC Online
Lucasfilm's resources gave Holman the freedom to design for the ideal rather than the feasible:
"We really got to say what ought to be rather than what's the best we can do with what is." — Tomlinson Holman, Sound Magazine
THX certifies the room and the equipment, not the content
This is the single most important thing to understand about THX, and the point most commonly confused in home-theater discussion. THX is not a sound format. It does not encode or decode audio. It does not compete with Dolby or DTS. A THX-certified theater can play Dolby Stereo, Dolby Digital, DTS, or any other format — THX certifies that the playback environment meets a defined standard of quality, regardless of the source format.
The THX specification covers: minimum amplifier power per channel, speaker placement and dispersion patterns, background noise levels (NC-30 or below), reverberation time, sight lines to ensure no acoustic obstructions, and calibration of the playback chain to a reference curve. A theater that meets these specs will reproduce the mixers' intent more faithfully than one that doesn't.
THX certification expanded to home equipment in the 1990s
Holman saw home theater as the next battlefield:
"About 1987, after seven years at Lucasfilm, I went to the Consumer Electronics Show and saw how badly home theater was being done, so I felt I had a role to play there, too." — Tomlinson Holman, SVC Online
In 1992, Lucasfilm extended the THX certification program to home-theater equipment — receivers, amplifiers, speakers, and processors. THX-certified home equipment met specifications designed to reproduce theatrical mixes accurately in smaller rooms. The home certification included requirements for amplifier output, speaker design, room-correction processing, and a "re-equalization" curve that compensated for the fact that film soundtracks were mixed for large rooms with different acoustic properties than living rooms.
THX-certified home equipment was typically more expensive than non-certified alternatives, and the certification fee was passed through to consumers. Whether the THX premium was worth paying became one of the perennial debates of the home-theater hobbyist community.
The THX logo before a film is a system test, not a production credit
The "THX Deep Note" trailer — the crescendo of sound that plays before films in THX-certified theaters — is a system check. It verifies that the theater's audio system is calibrated and functioning correctly. It is not part of the film, not a production credit, and not an indication that the film was "mixed in THX." Any film can play in a THX-certified theater. The trailer just confirms the room is ready.
The Deep Note itself, composed by Lucasfilm engineer James A. Moorer in 1983, became one of the most recognized audio logos in cinema. Its cultural impact far exceeded its technical purpose.
For physical media collectors, THX certification on a disc meant quality control
Starting in the late 1990s, THX also certified individual home video releases — laserdiscs, DVDs, and later Blu-rays. A THX-certified disc had undergone a quality-control review by THX engineers who verified the transfer quality, audio calibration, and compression. The certification didn't change the content — it was a stamp of approval that the disc met THX's quality bar for home release.
THX-certified discs were generally reliable indicators of above-average transfer quality, especially in the early DVD era when mastering standards varied enormously between studios. The certification became less meaningful as mastering quality improved industry-wide through the Blu-ray era.