Is it really 7.1 without THX?

Discussion in 'AV Receivers' started by Dan Belina, Jun 9, 2004.

  1. Dan Belina

    Dan Belina Agent

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    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?
     
  2. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    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 [​IMG]
     
  3. Chris Cash

    Chris Cash Stunt Coordinator

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    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.~
     
  4. Ned

    Ned Supporting Actor

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    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.
     
  5. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    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.
     
  6. Shane Martin

    Shane Martin Producer

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    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.
     
  7. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    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.
     
  8. Drew_W

    Drew_W Screenwriter

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    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.
     
  9. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    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).
     
  10. Dan Belina

    Dan Belina Agent

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    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)
     
  11. David Judah

    David Judah Screenwriter

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    Besides RE-EQ, you also get timbre matching and adaptive decorrelation with THX post-processing(some gear also adds a sub limiter and a boundary compensation circuit). Ultra 2 was developed to be used with 7.1 speaker systems, although as accurately mentioned, it's only 6.1 channels.

    DJ
     
  12. Aaron Gilbert

    Aaron Gilbert Second Unit

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    As David mentioned, some THX gear adds a subwoofer limiter, in the case of my Kenwood, called Bass Peak Level Manager. For this alone, I think it's worth getting THX. However, I've also found that I like what the Re-EQ does in my system, as well as the THX EX adding the surround back channel to all my 5.1 soundtracks (or 6.1 soundtracks that don't detect properly). As has been mentioned, I use two speakers for the surround back, though they are mono.

    Thumbs up for THX [Select] in my system!


    Aaron Gilbert
     
  13. ChrisWiggles

    ChrisWiggles Producer

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    *******************************************
    Ack, there is so much misinformation in this thread I don't even know where to begin! [​IMG]
    ****************************************
    Star over, lets begin from the beginning, and maybe clear somet things up:

    First, as covered, there are no discrete 7.1 formats.
    THX is not a sound format, but a standard of quality, that comes along with features and processing methods, etc. The usefulness of THX is something that can be heavily debated, and the various forms it takes is confusing certainly.

    The actual sound formats we are dealing with are DD and DTS, which I don't want to thoroughly explain, but DD EX and DTS ES matrix are "6.1" formats that are expanded from discrete 5.1 tracks. They use the same technology, and DD EX is the exact same thing as THX Surround EX, except as implemented in the home in non-THX receivers. DTS-ES matrix utilizes the same thing, and if I recall correctly they pay royalties to DD/THX, who implemented their EX processing jointly.

    THX EX and DD EX are not exactly sound formats in particular, but an encode/decode method, a processing method really. IT can be implemented on any 5.1 disc manually as well, not only "EX" labeled discs.

    DTS-ES discrete carries that 6th channel discretely.

    THX Ultra 2 comes with it extra processing beyond plain EX, which creates on rear back, and Ultra 2 creates stereo rears, since dolby, THX, DTS, etc all recommend using a 7.1 speakers setup, so why not make those non-mono. Ultra 2 is one way to get a "7.1" soundfield, and other propriatary methods are very prevalent in higher end receivers as mentioned.


    So, hopefully it is clear that first: there is no discrete 7.1 format. We are usually dealing with 5.1 that is expanded to 6, or perhaps 7 channels. You do not need THX certification to do this, though as part of the Ultra 2 certification, you will have the ability for "7.1" channel playback.

    When referring to 7.1, etc we are usually talking about the numbers of speakers in the playback system. This gets confusing, because this may or may not be the number of matrixed channels (and it is NOT the number of discrete channels.) So let me give you a for instance: my receiver is strictly 6.1 capable (DD EX, DTS ES matrix, and DTS ES discrete). I can put in a 5.1 DVD, and manually apply DD EX processing to create "6.1" which is matrixed. I have two surround backs in a 7.1 setup as recommended because of the reversal problem with 6.1 setups. So the end result is that I have a 7.1 speakers setup playing "6.1" from 5.1 discrete channels. I hope maybe I'm making some sense. Read through all that and if you're still confused please ask and hopefully I and others can clear up more of the confusion.
     
  14. Drew_W

    Drew_W Screenwriter

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    I must have missed this THX-EX revolution, since I've never even heard of it, only DD-EX, which it seems is what it evolved into.

    Are there any receivers now that have THX-EX?



    As Chris pointed out, this is not true, and it is the precise reason behind THX post-processing. And in my theatre using Athena speakers and a Pioneer Elite receiver (THX Select), it makes a huge difference in taming the overall sound.

    I'm surprised noone has brought up the issue of is 7.1 really necessary.
     
  15. ChrisWiggles

    ChrisWiggles Producer

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    As I mentioned, they are completely identical. But since relatively few receivers are THX certified, you see the DD-EX labeled version instead (but they are the same). THX certified 6.1 receivers will carry the THX-EX logo, along with the other benefits that THX carries with it (which is debatable, I am one who does not believe that THX is really worth much, but that has been argued to death in the past, I don't really want to take this thread down in flames, so run searches and read elsewhere pls)

    Yes, you can find THX receivers that have THX-EX:

    You can look here: http://www.thx.com/mod/products/productFind.html

    edit: wording to not make it sound like all THX receivers had THX-EX capability, which they do not. Some do, others are only 5.1.
     
  16. Ned

    Ned Supporting Actor

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    RE: 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.

    Could you provide the post link? I don't think he would have said that, perhaps you misinterpreted.


    He said it in a thread on AVS forum regarding DPLIIx. Search in the amps/receivers section for posts by him. My recollection is accurate though.
     
  17. ChrisWiggles

    ChrisWiggles Producer

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    I just searched all his posts on that forum, and I could find no such statement. Please link it, because I am positive you misinterpreted what he said, as clearly Ultra 2 goes to a 7-channel implementation, similar, but different to PLIIx. The only post that said something about PLIIx and Ultra 2 was this one:

    http://www.avsforum.com/avs-vb/showt...ra#post3739709

    Roger said:
    Which you may have misinterpreted.
     
  18. Roger Dressler

    Roger Dressler Stunt Coordinator

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    Here is what was reported in Twice about Ultra2, 9/3/2001:

    >>•If the soundtrack delivers a stereo surround signal, the devices must feed the stereo signal to the left-right dipole surrounds as usual, switch off decorrelation, and feed a portion of the stereo signal to the back surrounds. Signal processing is used to widen the back-surround stage. >•If the 5.1-soundtrack delivers mono to the surround channels, the devices must feed the mono signal to the left-right dipole surrounds and to the two back surrounds, and the devices must turn on side-surround decorrelation. The result is that predominantly ambient information is delivered by the side surrounds and direction information emanates from the back surrounds.
     

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