THX started as a certification program guaranteeing that audio products such as speakers and receivers would work well together, achieving high volumes with consistent quality. It has since expanded to include video products (displays, projectors, screens, DVRs) and even accessories such as cables. THX certification typically co-exists with Dolby and DTS surround standards. However, THX began moving into standard-setting territory by co-developing Surround EX (a.k.a. Dolby Digital EX), which added back-surround speakers to the then-standard 5.1-channel array. More recently THX developed technologies that compete directly with Dolby and DTS, such as THX Loudness Plus, which competes with Dolby Volume.

Following are the THX certification programs for home theater and multimedia use:

THX Ultra2: For home theater systems in larger rooms, the original THX Ultra, the current Ultra2, and the new Ultra2 Plus work for viewing distances of more than 12 feet and rooms of more than 3000 cubic feet in volume. Ultra2 Plus includes THX Loudness Plus (see below).

THX Select: For home theater systems in smaller rooms, the original THX Select, the current Select2, and the new Select2 Plus work for viewing distances of 10 to 12 feet and room up to 2000 cubic feet in volume. Select2 Plus includes THX Loudness Plus.

THX Integrated System: THX certification for "home theater in a box" systems is designed for viewing distances of six to eight feet.

THX Multimedia: This slimmed-down version of THX is suitable for desktop computing and gaming applications with a viewing distance of two feet, four inches.

Here are some of the main benefits of THX certification:

Re-EQ: Movie soundtracks mixed for large theaters may be abrasive in a home theater system. Re-EQ establishes a less edgy and more accurate tonal balance for home listening.

Timbre Matching: Our ears hear different tonal qualities in sounds coming from different directions. Timbre matching restores the frequency balance between front and surround speakers.

Boundary Gain Compensation: Sitting near a wall may result in bloated bass response. The boundary gain compensation filters and corrects the bass.

Decorrelation: In early surround soundtracks with a single mono rear channel, this feature adjusts the relationship between the two (or more) rear speakers to prevent the soundfield from collapsing to one side. Adaptive decorrelation senses discrete and mono surround information, decorrelating only the mono content.

THX also licenses these technologies, some of which are included in some of the certification programs above:

THX Loudness Plus: Programming mixed at the THX reference level may contain dynamic swings too extreme for home listening. Loudness Plus adjusts the tonal and spatial balances for lower-volume listening, enabling you to catch every word, and you won’t have to flinch at too-loud effects. It is incorporated into the THX Select2 Plus and THX Ultra2 Plus certification programs.

THX Media Director: This set of automatic controls helps the viewer enjoy programming as it was meant to be seen and heard without having to access adjustments in user menus. For instance, it will correct the shape of pictures, and select the right listening modes for surround soundtracks. To work, it must be supported by both hardware and software.
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