I agree totally that THX has been a major driving force for raising the performance bar, but I'd like to add a couple things to illustrate my original point.

Regarding the theater compensation for the "X" curve, etc. - all DVDs are now re-EQ'd in a mastering suite using speakers much more typical of a home setup. They remove the "mixed in" brightness of an original film sound mix as part of creating the DVD master. While this was not true of laserdiscs and earlier DVDs, it is standard practice now, along with a rebalancing of the channels and to some extent dynamic range compression. In some instances, the film's original mixing engineers bring some small (usually Genelec) speakers into the original dubbing theater, position them around the console, and create a DVD mix at the conclusion of the film's theatrical mix. This is one feature of THX that release format technology is catching up with and eliminating the need for.

Decorrelation is another THX technology that was once vital to any surround system. However now that the presentation norm is DVD, and the surrounds are always mixed in discrete stereo, decorrelation is not really needed. I have never experienced a single instance in a film's mixing where the engineer intentionally mixed a purely mono signal into both the left and right side surrounds - at the least, stereo reverb is added and usually the mono signal is time-shifted on one side to simulate stereo. If decorrelation is added to a true stereo signal in the surrounds, the imaging is destroyed. An argument could be made for it's use in the rear surrounds in a 7.1 system, but then again part of the usefulness of rear surrounds is to allow precise placement for behind-the-listener effects. Decorrelation used on these channels tends to muddy up that rear imaging and meld it into the side surrounds too much, thus loosing the effect intended by the mixing engineers.

The controlled directivity aspect is one technology that is immune to delivery format advances. This is a technology that I rarely see used on home speakers, outside of THX equipment - probably because of cost. The absolute best way to achieve controlled directivity is by the use of horns, and my good 'ol Altec Lansing A-7-500 speakers were one of the original models used for establishing the amount and nature of the "ideal" controlled dispersion. Horns have been used in movie theaters for dispersion control for decades - the Altec multi-cellular horns are a prime example of this. The later "constant directivity" horns refined the frequency-dispersion performance so that there was better high frequency dispersion.

Personally, I never agreed with electronic timbre matching in any home component (as opposed to timbre matched speakers all around). During the creation and mixing of sound effects and music, these signals are created without the use of any timbre matching scheme - they are intended to be listened to in this way. It doesn't make sense to me to add a layer of equalization which essentially second guesses the intention of the film's mixers and sound designers. Timbre matching (again, I'm talking about the electronic variety, not timbre matched speakers) seems to me to be a solution in search of a problem.

[This message has been edited by soundhound (edited June 06, 2004).]