Adaptive Decorrelation (THX technology)

[Tron]

Hmmm...

So, the receiver or decoder you have doesn't comply with all of the THX technologies to be considered "THX Ultra" compliant (nor did the manufacturer pay the royalty to be "THX Ultra certified").

This post begs the question: is it possible to apply a few mods (in this case non-permanent) to your HT system to enjoy some of these technological innovations?

Here's one idea:

First off, here's a clip from one of Denon's manuals explaining Adaptive Decorrelation (which, according to the manual, is a patented THX technology)...

Adaptive DecorrelationTM

In a movie theater, a large number of surround speakers help create an enveloping surround sound experience, while in a home theater there

are usually only two speakers. This can make the surround speakers sound like headphones that lack spaciousness and envelopment. The

surround sounds will also collapse into the closest speaker as you move away from the middle seating position. Adaptive Decorrelation slightly

changes one surround channels time and phase relationship with respect to the other surround channel. This expands the listening position

and createswith only two speakersthe same spacious surround experience as in a movie theater.

So, even though the phase difference is only "slight" with the THX technology, would switching the positive and negative leads of one of the surround speakers have the same effect? What would the drawbacks be?

[Tron]

Hmmm...

What if the receiver has the ability to delay the left and right surrounds seperately? Delay one side a step or two more than the other and you have "Adaptive Decorrelation...?"

[VideoGUY]

eh, its one of those things that i don't really buy into. do you think you will hear a difference. at least i doubt it. and don't really buy into the TXH certification. from what i have read, its mearly a very "rough" set of standards set by lucas. if a reviever meets those standards then its gets slapped with the logo, which the company then pays royalties for....as you already know. but i believe its very possible to get a reciever w/o the stamp and it could technically sound "better" than the thx certified. BUT this is my opinion and have never AB tested. but it is what i believe....just my .02. but i would doubt you would even hear a difference. rack up some more $$$ for Denon for a new catch phrase. i give 'em credit. decorrelation is a pretty good word.....lol!!! oh, and its adaptive. sorry for the sarcasm....but it really makes me laugh.

[Marvel]

Reversing one channel's speaker leads will put the two channels 180 degress out of phase. Any material that was to be heard right in the middle would be out of phase left/right, and would drop in level by quite a few db. This would be most noticeable if you were stting equidistant from the two speakers. If you were off center a tiny bit, the phase relationships would be different.

An old trick used in recording a large vocal group was to feed two speakers a mono signal, but reverse the polarity to one of the speakers. Have them facing each other in the studio. The single microphone would then be placed in the null point between the two speakers. People who weren't dead center could hear well enough to sing along with the tracks being played back, and have almost no level from the speaker playback. Saved the price of a bunch of headphones.

Marvel

This message has been edited by Marvel on 11-02-2001 at 04:36 PM

[WMcD]

I doubt reversing phase in one speaker is going to mimic the overall effect of the more sophisticated de correlation. Futher, discrete surround channels in the recording have made it unnecessary.

The problem was that in analog Dolby, the surround channel (Left minus Right) shared a lot of the same information as the front channels of Left and Right, also the center, which is Left plus Right. So the overall problem was to fool the brain to think what was in the surround speakers was not also a source of what was in the mains. Specifically, dialog leaking into the surrounds shouldn't be heard as having equal merit as dialog in the mains.

The first line of defense was to delay of 10 milliseconds to the Left minus Right in the surround. Essentially, if two sounds are heard, but one is delayed, the one arriving earlier is considered the true source. In other words, the delayed source is considered a distant echo. This makes sense in that the delayed Left minus Right surround is supposed to be just that. (The non delayed dialog in front is the true source. Hamilton Ford was not speaking from the back.)

The problem may have been that this delay wasn't quite enough. There was still a lot of corelation, which is to say, similarity. Further, the two mono surround speakers did not come close to recreating a surround sound field which should have been multiple sources.

The decorrelation circuits introduced more ambiguity, which I think was more varied delay and frequency response variations.

Of course with discrete surround channels in Dolby Digital, we don't need the processing to create artificial sound fields. The surround mix is in the discrete channels.

Gil

[Tron]

Well,

Gil effectively pointed out that there really isn't any need for this particular THX technology.

There definitely isn't any need for it today since we have Dolby Prologic II and DTS Neo:6 for stereo sources.

Thanks to all that replied.

This message has been edited by Tron on 11-06-2001 at 10:02 AM