Dolby Digital-Surround EX v THX Surround EX


Standard Member
What is the difference between these two modes? Some web refs say that they are the same. The THX site says

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.

So should The Phantom Menace be played in THX or Dolby EX modes (eg, on a Yamaha 2400)?


Prominent Member
Technically, Dolby EX is a superior mode as it uses ProLogic II to extrapolate the rear centre. THX Surround EX uses good old Pro Logic to do the same. Of course using DD-EX you don't get the other benefits of THX. It's really your call.



Standard Member
Originally posted by russraff
the other benefits of THX

Thanks. Helpful to have such a straighforward explanation!

Supplementary: Will these other benefits not already been applied to DVDs (unless they have a separate THX setting such as T2)?

Rolo Tomasi

Established Member
In short, no. THX is a post-decoding process.There is lots of info on THX processing so I won't repeat it all again. Try searches for THX on this forum and the net.

I find that THX reduces the treble too much for my liking unless the sound level is relatively high. Somebody compared it to throwing a blanket over each speaker which, at moderate volumes, I would agree with. At the end of the day it comes down to personal preference.

In any event, a number of DD EX titles also have a DTS ES option which some people would always select anyway. I hope this doesn't start another DD/DTS war!


Standard Member
Originally posted by Rolo Tomasi
In any event, a number of DD EX titles also have a DTS ES option which some people would always select anyway. I hope this doesn't start another DD/DTS war!

OK, so all the re-equalisation and bass/treble limiting has not been pre-applied.

Why can TX processing not be applied to DTS-ES in the same way that it can be applied to Dolby Digital EX? (In fact I think that my receiver can apply THX to most decoders from Dolby Pro Logic up.)

Rolo Tomasi

Established Member
THX processing can be applied to DTS-ES.

Some early receivers only had THX Surround EX to decode a DD EX encoded DVD. THX had an exclusive licence to decode this format. When the licence expired, THX Surround EX was no longer the only way of decoding and pure DD EX decoders officially appeared. If a receiver has DD EX and THX Surround EX then you have a choice of whether to engage the THX processing or not.

The latest video from AVForums

⭐ Philips OLED+908 TV preview + Avid Accent amplifier reviews + Hi-Fi & AV News
Subscribe to our YouTube channel
Support AVForums with Patreon
Top Bottom