What is the difference between these two modes? Some web refs say that they are the same. The THX site says
So should The Phantom Menace be played in THX or Dolby EX modes (eg, on a Yamaha 2400)?THX Surround EX has its roots in the Dolby Digital-Surround EX technology developed jointly by Lucasfilm THX and Dolby Laboratories. Gary Rydstrom, the Academy Award-winning Director of Creative Operations at Skywalker Sound, wanted more creative flexibility on soundtracks, including the ability to position sounds directly behind the audience. As a result, Dolby Digital-Surround EX allows sound mixers to encircle the audience with 360-degree pans and more realistic fly-over and ambient sound effects. First heard in George Lucas Star Wars: Episode I-The Phantom Menace, Dolby Digital-Surround EX is likely to become the audio standard for major studio blockbusters. The new technology is backward-compatible, with the ability to play any Digital 5.1 source in both the theatre and home versions.
THX Surround EX is the home version of this latest advance in hyper-realistic sound technology. Available exclusively in THX-licensed Ultra and Select Series products, THX Surround EX decodes a back surround signal from the left and right surround channels on specially encoded DVD movie releases. Unlike products offering "6.1" channel decoding schemes, only select THX Certified components adhere to superior performance specifications through the following features.
Redirects bass energy in the Surround back channels to the subwoofer, ensuring optimum bass performance.
Requires Re-Equalization of the Surround back channels to match characteristics of the front and left/right surround channels.
Synchronizes the Surround Back Left and Surround Back Right speakers in time and position relative to the listener, providing a seamless surround sound experience.
Preserves the original sound perspective in soundtracks from older films with mono surround channels by automatically re-directing the surround signal to both Surround Left and Surround Right rather than to the Surround back speakers only.
Maintains the same technical standards for Surround back channels as for Left and Right channel surround, eliminating compromise in channel separation, noise, headroom, bandwidth and decoding accuracy.