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How do they generate the sound for the 7.1 or 6.1 surround sound?

Discussion in 'Beginners, General Questions' started by WaterEC, Apr 17, 2007.

  1. WaterEC

    WaterEC Active Member

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    I'm thinking of upgrading my 5.1 to 7.1, but I'm still not quite sure how they generate the sound for the 2 extra speakers (surround left and surround right), since all DVDs are just encoded in 5.1 only as far as I know. Do they just mix the front left with rear left to generate the surround left, front right with rear right to generate surround right?

    Also, where should I put the two extra speakers? I have seen quite different layouts, let me draw it below:

    Layout 1:
    FL TV FR

    SL SR

    RL Viewer RR


    Layout 2:
    FL TV FR


    SL RL Viewer RR SR


    Looks to me layout1 makes more sense, because in layout2 the 4 speakers are almost in the same plane. But without knowing how they generate the 2 extra speaker sound in the first place, I can't really make a good judgement.

    BTW, will HD DVD or Blu-ray have true 7.1 effect?

    Lots of questions in this thread, thanks in advance!
     
  2. bassman99floyd

    bassman99floyd Well-Known Member

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    7.1 is encoded on DVD's, and it will have the symbol THX on the box. Movies that are in THX will use the 6th & 7th channel's. HD-DVD and Blu-Ray are also encoded in THX. If you're playing a DVD that was recorded in 5.1, the 6th & 7th channel's will not be used.

    The following site has a diagram, but not a great one.
    http://www.dolby.com/consumer/technology/dolby_ex.html

    What I didn't like about this site, is it's showing the rear speakers to the right/left sides of the couch. Space provided, you should have them at least a foot back on the left/right side. When you watch a movie that is only 5.1, those speakers become the rear speakers so they should be behind you.

    Good Luck!
     
  3. chuckg

    chuckg Well-Known Member

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    The extra two channels are the rears, not surrounds.

    5.1 looks like this:

    .....FR.....C.....FL.....
    ..............tv.........
    ...........................
    ............you.........
    ..........................
    SL......................SR


    Then you add two more channels for 7.1:


    .....FR.....C.....FL.....
    ..............tv.........
    ...........................
    ............you.........
    ..........................
    SL......................SR
    ...........................
    ...........................
    .....BL..........BR.....

    The channels are
    Front Left, Center, Front right
    Surround Left, Surround Right
    Back Left, Back Right.

    If the disc is encoded with 6.1, then the back left and back right will carry the same sound.
     
  4. WaterEC

    WaterEC Active Member

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    Thanks to both of you. Now it starts to make some sense to me. HTF is a great place to visit, I can always get my questions answered in a very satisfactory way, you guys are much much better and a lot more knowledgable than BestBuy and CC sales persons. Thanks again!
     
  5. Jeff Gatie

    Jeff Gatie Well-Known Member

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    Wow, I don't know where to start. [​IMG]

    THX is a theater, software and hardware certification created by George Lucas that specifies standards for THX labeled theaters, films, DVD's and HT hardware. It has absolutely, positively, certifiably nothing at all to do with 7/6.1 sound, except when the THX specs are applied to a 6.1 soundtrack.

    I think what you mean to say is EX, as in DD-EX, which is Dolby's version of 6.1 sound (since the rear surrounds in these various audio schemes are mono, they are actually 6.1, not 7.1. The 7th channel just puts out the same sound as the 6th in the case ot 7.1). DTS also has DTS-ES and DTS-ES Discrete. In the case of DD-EX and DTS-ES, the rear channel is matrixed from the two side surround channels, similar to the surrounds in Dolby Pro-Logic. In DTS-ES Discrete, the rear channel is actually discrete, as opposed to matixed. For the HD versions of such, you'll have to ask someone else. I'm not up to speed with those.
     
  6. Mark-P

    Mark-P Well-Known Member

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    Make that similar to the center channel in Dolby Pro-Logic.
     
  7. bassman99floyd

    bassman99floyd Well-Known Member

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    I was making generalizations as to how to easily recognize a movie recorded in 7.1. Isn't it safe to say ALL movies recorded in 7.1 on a standard DVD will have the THX logo on the box???
    I was using the term THX to stand for 7.1 format.
     
  8. Jeff Gatie

    Jeff Gatie Well-Known Member

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    THX has nothing to do with the 6.1 format. Not all films with a THX logo are 6.1 and not all 6.1 are THX. THX is simply a specification to which some films/filmmakers adhere (and pay George Lucas to have them certified). Same thing with THX hardware and theaters. The easiest way to recognize a 6.1 DVD is to look for a DD-EX or DTS-ES logo. Looking for the THX logo means nothing.
     
  9. bassman99floyd

    bassman99floyd Well-Known Member

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    Jeff, did I once ever mention 6.1? Not once is the answer since, I can't hear you right now. I see that you have all the technical jargon down. Congrats to you!

    My point, that you feel you must debate, is to easily recognize a movie that is in 7.1, look for the THX logo.

    Am I wrong here Jeff?? Do you see my point now??
     
  10. Michael Reuben

    Michael Reuben Well-Known Member

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    I'm afraid you are.

    M.
     
  11. bassman99floyd

    bassman99floyd Well-Known Member

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    Live and Learn...

    Sorry about the giant font above. I couldn't figure out how to edit it, and bring it back to normal size.

    I'm VERY happy how my 7.1 HT sounds.

    Live and Learn...
     
  12. WaterEC

    WaterEC Active Member

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    Right, live and learn. Every time I visit HTF, I learn something new. I consider myself to have above average knowledge regarding home theater system, among my friends and colleagues, but still a complete novice here at HTF. Good thing is that every time when I ask a question here, no matter how naive it is, there are always people willing to help without sneering at me. Thanks again guys.

    Now I'm hesitant to do the upgrade, since most DVDs are still 5.1 encoded, not too many 6.1, and none true 7.1. I'm thinking of upgrade my home theater in a few more years, together with DVD to HD-DVD or Blu-ray upgrade. Hopefully, in 5 years or less, the price of HD-DVD or Blu-ray player will come down to today's DVD player's price, and the format war shall settle...
     
  13. Jeff Gatie

    Jeff Gatie Well-Known Member

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    Thanks for clarifying my explanation Michael. Glad to see the original poster learned what he wanted (if not anyone else - but hey, we tried). [​IMG]
     
  14. Kevin Stewart

    Kevin Stewart Well-Known Member

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    Bottom line:

    If you have a 7.1 set-up and a receiver capable of ProLogic IIx, the sound will be much better than a 5.1 set up.

    When I go back and forth on my receiver (from 5.1 to 7.1 IIx) the sound difference is VERY noticeable.
     
  15. WaterEC

    WaterEC Active Member

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    Thanks for the information about the comparison between 5.1 and 7.1, that's what I thought too, even though the 7.1 is not real. Now the thing is to convince my wife to let me spend the money.
     
  16. Jeff Gatie

    Jeff Gatie Well-Known Member

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    It's not that the "7.1" is not real, it's just that the 2 rear surrounds are not stereo, they are mono, so calling the audio format or a DVD "7.1" is incorrect. The difference between a 5.1 and 7/6.1 HT setup is real and noticable, especially with DVD's that are mastered for DD-EX or DTS-ES.
     
  17. WaterEC

    WaterEC Active Member

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    Thanks Jeff, I understand. What I mean by not real is that they are not truly discrete 7.1, just as you and Michael had explained. Now I'm really thinking of upgrade to 7.1 first within a few months, then upgrade to HD-DVD/Blu-ray in a few more years.
     
  18. Jeff Gatie

    Jeff Gatie Well-Known Member

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    I had a 7.1 setup at my last home, space considerations have my current setup only 5.1. There was a definite advantage in a larger room. Make sure you demo the scene from Gladiator when Maximus enters the arena for his first battle. There's a guy just inside the entrance swinging a spiked ball on a chain and the DTS-ES effect is amazing. It's like the ball is being swung around your head.
     
  19. WaterEC

    WaterEC Active Member

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    Thanks Jeff for the specific tip. Actually I just watched Gladiator a second time a few weeks ago (I first watched it in theaters in 2000), and my wife was already complaining about the loud sound...
     
  20. leafswillwin

    leafswillwin Well-Known Member

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    just wondering if my dvd player outputs audio through digital coaxial, will my receiver be able to decode dts es and others or is that only possible through toslink?

    thanks
     

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