Is it really 7.1 without THX?

Dan Belina · 06-09-2004, 10:43 AM

I was looking at a number of receivers with 7.1 (example Yamaha HTR-5760)

Then a buddy of mine said that its not really 7.1 unless it has THX processing. Something about how it is only 5.1 and the rear surrounds play same sound as front surrounds..is this true?

On that note the HTR-5790 THX Select Processing, but I have also seen products with THX Ultra2. Is one preferred over the other?

Stephen Hopkins · 06-09-2004, 11:04 AM

It's really not 7.1... ever. There are no discrete 7.1 sources out there... none. So no matter what decoding method you use it's still going to be deriving the back channels from either one back channel if given a 6.1 source (DD-EX & DTS-ES)or from the side channels if given a 5.1 source (DD and DTS).

What your friend was saying is still mainly true because before recently THX Ultra2 processing was the only way to get stereo back surrounds. Logic7 also does this (and debatably better) but is only available on HK and Lexicon products.

With the recent addition PLIIx there are many more receivers capable of playing stereo back surround information (while it's still matrixed, or derived from the other surrounds, it's not just playing the same information). Both Yamaha receivers you are looking at have PLIIx.

That said if you have the funds to move up to the 5790 I would do so, but not because of THX Certification. The 5790 has full YPAO including automatic room equalization. The 5760 only automatically sets up speaker size and speaker level.

Hope this helps

Chris Cash · 06-09-2004, 03:43 PM

DTS EX and THX Ultra 2 is the same thing. The only difference is paying for the THX licensing. And he is correct. There is no discrete 7 channel receiver yet. There doesn't need to be. There is no 7 channel format. The way a 7 channel receiver works is the two back center channel are mono. Meaning your getting the same information with two rear centers as one. Having two just gives you a larger sound stage. These speakers are only used for effects anyway. They are most noticeable during scenes with rain and things that envelope you in the atmosphere of the movie.

~C.C.~

Ned · 06-09-2004, 04:20 PM

Actually, Roger Dressler (Dolby guy), said that THX Ultra 2 is mono in the rears even with 2 back surrounds. So Logic 7 and DPLiix are the only "7.1" matrices.

Stephen Hopkins · 06-09-2004, 06:01 PM

Chris,

Dolby Digital EX and THX-EX are essentially the same thing. Everything else you said is right on the money.

Ned,

I was under the impression that Ultra2 post-processing offered some decorelation of the back surrounds but I most definitely could be wrong.

**HTF Ads**

Shane Martin · 06-09-2004, 06:07 PM

DTS ES discrete is discrete in the rears. Adding 1 more speaker back there doesn't make a big difference though unless you have a huge space to fill.

Stephen Hopkins · 06-09-2004, 06:16 PM

Adding a second rear surround can help eliminate a common phenomenon where sounds directly behind you are perceived by the ear to be coming from directly in front of you. The same sound coming from 2 sources to either side of you let the brain interpolate that the sound is directly behind you and triggers the sense of the sound being directly behind you properly.

Drew_W · 06-09-2004, 06:51 PM

Quote:

Dolby Digital EX and THX-EX are essentially the same thing.

Quote:

DTS EX and THX Ultra 2 is the same thing.

Neither is correct. DTS and DD are surround sound formats. THX is not...it is a post-processing algorithm whose goal is to tame soundtracks that would otherwise sound overly bright in small size home theatres, because of the way and the purpose for which they were originally conceived (for large movie houses).

THX to my knowledge does not process 5/6 channel into 7. You rely on DPLIIx, Logic 7, or something similar to that to simulate the extra channels. THX then plays around with the signal before it hits the amplifiers.

Stephen Hopkins · 06-09-2004, 07:09 PM

Drew,

Not quite true. THX RE-EQ (or re-equalization) is a post processing algorithm use to tame theatrical soundtracks which would sound overly bright in a home theater environment (even though almost ALL dvd tracks are re-equalized anyway before DVD release).

THX-EX is indeed a matrixing technology used for deriving a rear surround from Dolby Digital 5.1 material and for matrixing the information intentionally matrix encoded in Dolby Digital EX tracks. It was developed jointly by Dolby and THX and original marketed as THX-EX and later as just Dolby Digital EX once the technology trickled down into lower end receivers that did not carry THX certification (and higher end receivers that didn't rely on THX certification's marketing ability).

Dan Belina · 06-09-2004, 07:57 PM

Thanks for the input. I was curious, because I am interested in the Yamaha HTR-5790, but I live in an apartment and my living room is sized such that 6.1 would probably be more feasible than 7.1

I like the features of that receiver, but I don't really need 7 channels, and from what you guys have said I dont really need THX.

Is there a comparable 6.1 receiver with or without THX? (With the features that the 5790 has over the 5760)