Introduction| Mono| Dolby Stereo| Dolby Surround|
Dolby Pro-Logic| Dolby Pro-Logic II| Dolby Digital|
Dolby Digital Surround-EX| DTS| DTS-ES| THX| Sony SDDS|

THX

The THX sound system is not a sound format in the same way as Dolby Digital or Dolby Stereo. THX is a set of requirements forming a specification that can be applied to hardware, software and even some theatres. Developed by Lucasfilm, the specification is designed to ensure that a THX presentation remains as close to the director's original cut - they way he or she intended. For example, a movie would be mastered in the studio for theatrical release using THX approved equipment. It would be presented in a theatre with a THX approved auditoria through a THX sound system. The movis would be re-mastered onto DVD using THX hardware, and for the best results should be used in a home cinema featuring THX approved processors, amplifiers and speakers. By ensuring that the equipment used in every part of the mastering process conforms to the THX specification, the original quality and appearance of the movie release is maintained. Home cinema THX equipment is badged as either THX Ultra or THX Select. Ultra is the top-of-the-range hardware intended for large rooms, while Select is a more forgiving standard intended for the more common small living room environments. Lucasfilm has released a third version of the THX specification called THX Ultra2. This system provides a specification for hardware and software that uses the latest Dolby Digital Surround-EX and dts-ES 6.1 channel soundtracks. Ultra2 adds guidelines for the use of additional rear surround speakers on the back wall behind the audience.