TRUTH in the multichannel world

Discussion in 'Archived Threads 2001-2004' started by RichardMA, Apr 25, 2002.

  1. RichardMA

    RichardMA Second Unit

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    Never mind 7.1, there is only ONE 6.1 format: DTS 6.1 DISCRETE.

    All the other modes are 6.1 channel with the rear centre channel being a matrix derived from the left and right surrounds. None of the other centre-surround channels have the discreteness of a true digitally-encoded channel.

    Now, as far as 7.1 channels are concerned, if splitting signals is all that is needed to "create" a new channel (and it flies in the FACE of the wonderful, discrete digital DD and DTS 5.1 we've now

    got and even the matrixed channels that are appearing) then why not have 4 speakers in the rear, and why not split the

    side surrounds into 2 each for 11.1 channels! The sky's the limit when all you are doing is adding speakers.

    Right now, the most "channels" you can have would be playing a Yamaha receiver, in DTS-ES discrete mode, overlayering it with Yamaha's own "upper front channels" for a total of 6 discrete channels, 2 matrixed

    and one subwoofer channel, for a total of 8.1 channels. I'm sure there are other companies working on even more elaborate systems.

    So, what you have here is three types of "channel making;"

    True discrete digital channels with wide separation and isolation such as DD 5.1 and DTS 5.1 and 6.1, Digital and "matrix" channel mixes such as DD 6.1 and DTS 6.1 non-discrete, and finally simply splitting

    outputs to add more speakers for a multi-speaker monophonic effect.

    Which has been done in theaters for years.

    The last thing is the possibility of the deriving of marginally discrete "information" channels by interposing things like a Circle Surround decoders between discrete digital channels. This was reported in Wide Screen Review magazine where the tester claimed to have heard

    isolated channel information between the normal 5.1 digital channels we now have with DD and DTS. I am not sure of the writer's claims, he seemed to think it was possible to derive SDDS (Sony's 8.1 digital discrete theatrical process) channel information from DVDs. Kind of wild.

    (Side issue: If we could have Sony's SDDS decoding at home, I would be in heaven simply because their theatrical digital is better than anyone else's) but it's worth messing around with since it's cheap. You can even fool around with old Pro-Logic receivers, feeding them two outputs (L-R surrounds) from a digital receiver and letting them output a kind of "center rear" channel effect by outputting from the Pro-Logic receiver's L-R surround and centre outputs. However, to preserve the discreteness of the digital channels, it would be advisible to simply use a splitter on the outputs, running one line to the Pro-Logic processor's inputs and one line to the normal surround power amps.

    The thing that separates "true" channels from fake ones are directionality and discreteness. If any matrix form of 6.1 (DD 6.1, DTS 6.1 non-discrete, etc) can actually do something like a pan across the rear three speakers, then it is directional. If the left surround and center image the sound, then the center and right surround do,

    then the centre channel is NOT directional because it did not really assist the panning of the sound. It merely functioned as a "fleshing out" apparatus designed to assist the L-R surrounds with their narrow dispersion, much like dipole or bi-pole speakers already do.

    THX used this "Hafler-esk" technique with Pro-Logic to achieve a crude and directionless "stereo effect" with Pro-Logic's monophonic surrounds way back when. They still use it to differentiate (slightly) your discrete

    L-R surrounds in new processors when "THX processing" is added to regular digital sound. It's a good thing humans cannot always link what's happening on screen with what sound is coming out of the speakers of THX's method would be very confusing.

    Secondly, channel separation with digital channels is WIDE. On the order of 80db or better. A matrixed channel is likely to have separation no better than 50db from the channels is was derived from. In this case, the

    centre surround is deriving the information it has from the L-R surrounds, with digital channels, the information is entirely "owned" by the each channel. The result is that matrix channels have the "bleed" we hear with Pro-Logic channels. Basically, information "leaks" into it from the

    other channels. The only time discrete digital channels have information in them that is in other digital channels is when the engineer encodes it into them.

    Do matrixed channels contain directional or discrete information?

    Maybe. My advise is to find out for yourself. Get ready to tweak your ears and CONCENTRATE like Hell.

    What all this means is that to get the best sonic quality out of these channels, you will have to experiment diligently with your system, adjusting

    levels, etc, to achieve the best result.

    Also, check out Dolby's website for a really good explaination for Dolby Digital EX and Pro-Logic II.
     
  2. Tim Hoover

    Tim Hoover Screenwriter

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    I agree with your points, Richard. I'll even go one step further and say that I believe that referring to DD-EX and matrixed DTS-ES as 6.1 is false advertising. The "6.1" implies that there are six discrete channels and an LFE track. You don't hear matrixed Pro-Logic referred to being 4.0 do you?
     
  3. Kevin C Brown

    Kevin C Brown Producer

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    But DD EX and DTS-ES do genuinely support a 6.1 speaker setup. (And 7.1 with mono rears.)
    Same-o for CES by Outlaw and xS by Rotel.
    And, DD EX and DTS-ES are both also backwards compatible to 5.1 setups.
    And Logic 7 and THX Ultra2 do genuinely support a 7.1 speaker setup.
    I personally think it's important to consider the source "discreteness" as well as what type(s) of speaker systems are supported. That considers both sides of the equations... [​IMG]
    Dolby Surround Stereo is only 2.0, but if you only focussed on the 2 discrete channels of the source, you'd be missing out on what the benefits could be with DPL II decoding on a 5.1 system...
     
  4. Harold_C

    Harold_C Stunt Coordinator

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  5. Philip Hamm

    Philip Hamm Lead Actor

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    What a long post. I couldn't read it all.

    This is why I'm absolutely in no hurry whatsoever to upgrade my 5.1 system. I'm not a fan of DSPs and matrixing when it's not really needed (like with DPL). After going for years with matrixed ProLogic to the fantastic discrete 5.1 systems we came up with, I personally see any 6.1 or 7.1 system as a step backwards.

    Plus my room won't really accomodate 6.1.

    -Phil Hamm
     
  6. RichardMA

    RichardMA Second Unit

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    A friend of mine basically says in his opinion, matrixed

    channels are a backward step (back to Pro-Logic quality)

    so he's content to wait for true digital, discrete

    multi-channel setups beyond 5.1 (6.1 for the one DTS mode)

    before changing up to new gear. In a way, I agree since

    it's been a long time since I've played VHS tapes except

    as a television recording source so matrixed sound has

    little appeal. Personally, I just want to experiment

    but my core listening will still be 5.1
     
  7. Kevin C Brown

    Kevin C Brown Producer

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    I can see where the opinions on this thread lie... [​IMG]
    But you're all missing the following point: consider a 5.1 system with 2 surround channels. Now consider a DD EX or DTS-ES (matrix) soundtrack with a center rear channel encoded into the 2 surround channels. Now, with a 5.1 system, you will effectively get "imaging" of that rear center channel in the correct place if you are exactly equi-distant from both of the surround speakers.
    But if you are anywhere from that exact center position, the image of that virtual rear center channel is "pulled" to the speaker that you are closer too. *That's* what a 6.1/7.1 speaker setup prevents. It keeps the imaging of that rear channel fixed in space because there is/are speaker(s) there actually outputting that info.
    I have had both in my system. I much prefer the current 6.1 setup I have to 5.1. Better imaging throughout the entire room. And, that center rear channel fills in a gap in the soundstage that you don't even know exists until it's gone...
     
  8. Harold_C

    Harold_C Stunt Coordinator

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    Kevin,

    I think you've summed up both the benefit and the disadvantage quite nicely.

    On certain soundtracks, having rock solid dead center imaging in the surround channels will be a decided plus -- a soundtrack where the intent is to place a particular sound rock solid dead center and draw your attention to it.

    However, there are probably soundtracks where this would be a decided negative. I'm thinking of surround effects intended to create ambience effects -- such as rainstorms, jungle atmospherics, underwater ambience. Here, the surround channels are being used for a much more diffuse non-localized effect and having the soundfield localized to a single speaker may not be ideal.

    Net gain? Probably really depends on the room. In my case, I'm almost always very close to equidistant between the two surround channels due to their height relative to the seating positions. I doubt that a center back channel would do much for me. However, I can certainly think of room configurations where it would be a plus.
     

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