Dolby Digital 5.1 output to 6.1 or 7.1 setup: What happens?

Discussion in 'AV Receivers' started by Dave Hahn, Jan 6, 2005.

  1. Dave Hahn

    Dave Hahn Second Unit

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    What happens when you play a dvd, (or a HDTV television signal), encoded with DD 5.1, over a 6.1 or 7.1 system? Do you get anything from the rear(s)?

    I assume :b that one of two things happen: a receiver extrapolates the 5.1 information and spreads it to all speakers in the system, be it 6.1 or 7.1, or, only signals that contain information for the rear,(or rears), will output to the speakers.

    I know that in Dolby Pro II, (or any of the other proprietary systems), sound is spread to all speakers no matter what the original signal may be. I guess I'm asking what happens in Dolby Digital?
     
  2. FeisalK

    FeisalK Screenwriter

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  3. Kevin C Brown

    Kevin C Brown Producer

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    Depends on your receiver. [​IMG] Should be in the manual. For 7.1, a lot of receivers simply copy the surrounds info to the rears. For 6.1, it might combine both surrounds into one mono signal. Some however, might simply play the DVD back as DD 5.1, and then you'd get nothing in the extra speaker or two. The receiver manual should say what happens. Worst comes to worst, play a DVD and stick your ear up to the extra speaker ot two, at least to make sure you're getting *something* there.
     
  4. MikeGee

    MikeGee Second Unit

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    If they are running either 6.1 or 7.1 and the rears are just basically receiving the same info as the front or side speakers its not true 6.1/7.1 then no?
    I know some receivers say 7.1 but don't give you a discrete 7.1 sound or even 6.1 sound. the rears are just mono'd
     
  5. Kevin C Brown

    Kevin C Brown Producer

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    It depends. [​IMG]

    You need to understand what the source of the recording is, vs what the physical setup for playback is, and what (if any) processing is going on in between.

    First, there is no such thing as "true" 7.1. And there is only 1 version of "true" 6.1: discrete DTS-ES.

    5.1 includes Dolby Digital, Dolby Digital EX, DTS, and matrix DTS-ES. (The rear channel of DD EX and matrix DTS-ES is matrixed into the discrete surround channels. They are all 5.1 sources, even though both DD EX and DTS-ES matrix are designed to be played back on 6.1 or 7.1 systems.)

    DPL IIx on a 7.1. system with a 5.1 Dolby Digital soundtrack gives you 7.1 channels of output. The unique rears are synthesized from the info in the surrounds.

    But if you have a 7.1 system, and you play back a Dolby Digital movie with the "Dolby Digital" setting on a receiver, you could get 5.1 channel output or 7.1 channel output, depending on how the receiver manufacturer chose to implement Dolby Digital playback on a 7.1 system.
     
  6. Dave Hahn

    Dave Hahn Second Unit

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    Thanks for the explanation Kevin.


    I've been plodding through the user's guide for my Denon 2805, as you suggested in your first post, to see what they have to say about this. From what I have come to understand, when I play a 5.1 DD signal the rear or rear(s) receive matrixed information from the Denon, unless I'm in DTS-ES.

    I've yet to hook up my rear speaker as I need to order another one as well as Omnipoint mounts. When I do, I'll let you know exactly what happens.
     
  7. Kevin C Brown

    Kevin C Brown Producer

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    Now I understand! [​IMG] Denon manuals are not known for their understandability. You might want to check out what they say about Widescreen mode. I believe that it copies the surrounds to the rears. Others have said that it does more, but that might be the mode you want for Dolby Digital and DTS soundtracks.
     
  8. Brian L

    Brian L Cinematographer

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    FWIW, my AVR (NAD 762) allows me to leave my DD EX in automatic, meaning I will only get a signal to the center back with content flagged as DD EX.

    Or, I can set it to "always on" which means that it will create a center back from the SR and SL, whether or not the film was correctly encoded as such.

    Thats handy, since certain early DD EX films (the 1st Harry Potter IIRC for example) were not flagged correctly, so you HAD to be able to manually invoke DD EX for that film.

    As far as Dolby, all thats really happening with the back is more or less simple PL II processing of a center from the SR and SL. And if its a 7.1 system, as someone said previously, both center back signals are the same.

    Now, I think I read that PLIIx is much more elaborate, and may be able to create distinct surround signals to all four back/surround channels.

    And I have NFI what happens in the DTS world, although I think it too uses matrix encoding like Dolby (would that be DTS EX?), but they have a a true discrete back capability (DTS ES?) for certain films (the exteded cut of LoTR tRotK) for example.

    BGL
     
  9. Kevin C Brown

    Kevin C Brown Producer

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    It's "DTS-ES Matrix" or "DTS-ES Discrete". The matrix version does something similar to DD EX: creates the rear info from matrixed info in the surround channels.

    Be careful though: I have had some 5.1 DD and DTS soundtracks where the soundfield collapses in the back of the room when I've tried EX or ES decoding with them (i.e., older soundtracks with a lot of common info between the surround channels). I believe the best approach is to use a sound field specifically meant for 6.1/7.1 playback of DD or DTS soundtracks.

    But it never hurts to experiment either. [​IMG]
     
  10. Dave_vega

    Dave_vega Stunt Coordinator

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    i know on my panasonic rx50 i can set 6.1 decoding for 5.1 material, etc..and it does just about a good of a job as DD EX, but a true discrete 6.1 dts-es from a movie such as gladiator is a whole new world in that rear channel..good to have the option though, because nearly everything is 5.1 or 6.1 matrix..
     

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