What is Dolby Digital EX?

Discussion in 'Archived Threads 2001-2004' started by John_Berger, Jul 24, 2002.

  1. John_Berger

    John_Berger Cinematographer

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    Before I get targeted, I *did* do a dearch for Dolby Digital EX and the results were 152 pages of different threads, the vast majority of which dealt with movies,not hardware. Needless to say, ah weren't gonna be a-lookin' through all uh those threads!
    What is Dolby Digital EX and how does it differ from "standard" Dolby Digital? Is this sort of like THX and non-THX where the only difference (supposedly) is sound quality but there are no technical differences?
    Everyone seems to be psyched about LOTR coming out in DD EX. So, what in blazes is it? [​IMG]
     
  2. Vince Maskeeper

    Vince Maskeeper Producer

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    EX is a 6.1 format which adds a rear center channel to the standard 5.1 configuration. It's been in exiatsnace for about 4 years and has been available in Home Theater equipment for about the last 2-3.
    http://www.hometheaterforum.com/htfo...082#post513082
    Scroll to the bottom of the post "So what the heck is 6.1?"
    http://www.geocities.com/Heartland/P...urroundex.html
    http://www.avrocks.com/faq_arq.asp#q9
    http://www.dolby.com/tech/m.ot.0006....erFAQ.html#q11
    http://www.dolby.com/ht/co_br_0110_L...rsGuideEX.html
    http://www.dvdanswerman.com/movies/exandes.html
    http://www.hometheaterforum.com/htfo...threadid=10663
     
  3. John_Berger

    John_Berger Cinematographer

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    Ah. I see. So, it adds a faux rear-center channel by mixing the same audio in the rear-left and rear-right channels with the unique rear-left and rear-right audio.

    Okay ... but why does this requires compatible hardware? That really makes to sense to me.

    I'm no audio expert, but it seems to me that by putting the same sound in both rear-left and rear-right speakers equally with whatever unique sounds are there would accomplish the same thing. This is no different that what has been done with music since stereo sound came out in the 1960s -- focus the singer in the center by making his/her voice equal in volume on both left and right but give instrumentation unique volume in each speaker to bring forth the stereo sound.

    It sounds like this is exactly what is being done with the rear channels. So, why the need for a Dolby EX decoder as opposed to a "standard" DD 5.1 decoder?
     
  4. Vince Maskeeper

    Vince Maskeeper Producer

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    John,

    First off it isn't quite that simple. The rear center in EX works exactly as the front center in Pro Logic. It isn't simply sending an equal amount of L/R to the center- rather it is a bit more complex.

    First off, summing L/R to center would result in a 3db boost, so that must be adjusted for. Secondly, they only extract a center image from what is actually sent to both speakers equally- once a sound is panned more than about 15% off center, it is faded out of the center and into the appropriate side channel.

    The need for new hardware is pretty obvious. Even if it only did what you suggested above, at the minimum an extra channel of amplifier and processing to route the Sr/Sl material to this new channel would be necessary (there would be no way with just a 5.1 receiver to sum and amplify a 6th channel regardless).

    So the extra hardware not only does the processing of the material to "extract" a center (which is, again, a bit more complex than simply summing L/R)-- but then obviously must offer any processing (bass management, cinema re-eq, channel level compensation, etc) and then offer amplification, or at the very least a preamp send in order to route this 6th channel to an external amp.

    Technically speaking, however- you can perform a "home brew" EX setup, which many have done. You can use an old Pro Logic processor, route the preamp Sl/Sr from your main receiver, into the prologic processor (say into the VCR input) and trun on the prologic processing. You will then extract a center from the rear signal, and use the ProLogic receiver to drive the rear 3 channels...

    -Vince
     
  5. Wayne Clark

    Wayne Clark Agent

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    time lag, already answered. wayne
     
  6. Michael Reuben

    Michael Reuben Studio Mogul

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    Vince has covered the technical points with his usual thoroughness, but let me add one thing. DD Surround EX was initially developed for theatrical exhibition. In large auditoriums, it isn't possible to focus a stereo image (at least, not for most of the audience) with the same precision that can be achieved in a home theater setup. The rear center channel was created to fill a "gap" in the soundfield that sound designers felt was limiting their ability to create -- for the entire audience -- realistic transitions from left to right rear and from rear to front.
    These considerations are less critical in the home environment, where it's often possible to fill in that same gap by careful placement of left and right rear speakers. Of course, much depends on the accoustics and layout of each individual HT.
    M.
     
  7. John_Berger

    John_Berger Cinematographer

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    Well, okay. Linking it in with Dolby ProLogic makes a bit more sense. I will admit that I see the benefit to having a front center channel as opposed to just left and right, so I can't really criticize doing the same thing in the rear speaker configuration.
    At least if it is ProLogic for the rear, I shouldn't lose too much of the effect to really care about only having two speakers. (I can say this with a clean conscience because I've never heard 6.1. [​IMG] ) Besides, I don't have room behind me for a rear center speaker anyway.
    But as usual my question was answered and in the kind of detail that I like. Thanks, all!
     

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