Dolby 5.1 played on pro Logic receiver

Discussion in 'AV Receivers' started by ashley__cooper, Sep 14, 2003.

  1. ashley__cooper

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    Having some problems setting up my new new(ish) HT system. I have an 11 year old Denon receiver w/ Dolby Pro Logic for surround, some older Polk Audio speakers in the center and 2 front positions, and just bought 2 Polk FXi 30's for the rear.
    But I'm having 2 problems:
    1- The rear speakers have a staticy sound, which doesn't make any sense as they are brand new.
    2- I just made a Dobly Digital 5.1 version of my first short film. It's a silent film in the tradition of Charlie Chaplin et al. and I added the sound of a projector to only the rear channels to give it more of a theater feel. But the projector sound also plays in the front and the levels don't seem quite right.

    Is this a problem of playing Dolby 5.1 on a Pro Logic only receiver, or should I look elsewhere to find the problem?
    Thanks ahead of time for any advice or help!
     
  2. Chuck Kent

    Chuck Kent Supporting Actor

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    ashley: First, the speakers. Do both speakers have the static? Have you double checked your speaker wiring? Have you tried substituting one of the other speakers temporarily to see if the static continues? If you swap speakers and it continues, try doing the processor reset (normally detailed in the back of the manual.) The reset sets everything (tuner stations and all) back to factory defaults.

    I've owned Denons for many years and did have an AVR-2500 that had a static problem in the rear channels that I never could cure at home (I ended up swapping it for a good one at the dealer. This is the only Denon problem I've ever had, BTW.)

    Let us know what you find out.


    As for the DVD, I'm not a DVD authoring expert. But I do know that if you mixed the DVD in 5.1 and are now playing it as DPL, AND, you only placed sound only in the rears, you could indeed have sound anomalies. In 5.1, each channel is separate. including the rears. But in DPL, you only have 2 signals, left and right. The front, center and the 2 rear sounds are extracted. (Center is made from L+R and the mono rears are from the difference of the 2 front channels, L-R.) So if your mix is rear signals only, you're attempting to force the DPL decoder to extract a signal for the rears and play nothing from the primary front left and right channels. Well, as I said, I'm no expert. But I don't see how this is possible without having troubles. The level oddities you are hearing is the decoder struggling to do it's best at this extremely difficult situation.

    Bottom line is that unless you run your DVD through a true 5.1 setup, it probably won't sound right...
     
  3. Doug_B

    Doug_B Screenwriter

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    I don't know if this is the case for all DPL receivers, but my guess is that your receiver does not have a digital audio input (otherwise it would be more than a DPL receiver methinks; please verify). If so, you would have your audio from the DVD player to the receiver via 2 channel (L/R) analog. All DVD players should automatically downmix a DD 5.1 source to the 2 ch analog outs (note that players do not do this with DTS signals), which means that any info in the discrete surrounds (and center ch) would be collapsed into these 2 channels. Then when your DPL receiver processes the analog input, it will create center and surround channels per standard DPL algorithms. Makes sense that you'd hear the projector in more than the surround channels and at "awkward" volume levels.

    Doug
     
  4. ashley__cooper

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    Thanks for the help, yall. I've been trying to isolate the problem and here's what I've got so far.

    The noise comes in any speaker using any wire when played through the rear speakers. Tried different modes (non surround sound) as well and the static is still there. So, it's an internal problem. I've looked for a reset button, but nothing doing. There's no mention of it in the manual.

    I'll have to go to Circuit city or tweeter to check if the DVD I made sounds right there. For what it's worth, the receiver does have a "VDP" input. Think this stands for video disk player. They did have lazer disks back then.

    Any advice for a new receiver that will sound accurate enough to get a feel for what my movies will sound like in theaters, yet not break the bank? I'm wondering if the extra money I spent on Denon last time was a waste and I should go with JVC, Kenwood, (maybe even Sony, though they don't impress me in any way) or some other less glamorous brand rather than Denon, Onkyo, or something of that nature.
    Thanks for any help!
     
  5. Chuck Kent

    Chuck Kent Supporting Actor

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    ashley: It's been a while but I'm reasonably sure that older Denons can be reset. It's not one particular key but a sequence of holding certain buttons down on the front panel while the power is cycled. In all of the Denon manuals I've had, the procedure has been toward the back of the manual.

    Which Denon model are we talking about? Maybe I can try and find the procedure if the model's not too old...

    Except for the phono input (which is meant for a much lower signal level), any of the other inputs would fine. So, VDP, CD, AUX or whatever should work ok.

    If the Denon does have a terminal problem, and if you don't want to go back (why oh why not??? [​IMG] ), then my recommendation, from your list would be Kenwood. I like the better Sonys but not the entry level DE series. Same for JVC...I'll pass on their entry level series too.
     
  6. Roger Dressler

    Roger Dressler Stunt Coordinator

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    Ashley, it is possible (and maybe you did) make a DVD with 5.1 audio that has signal only in Ls/Rs that then plays only from the surrounds of a Pro Logic (or PLII) decoder. You just need to confirm that the DVD player's 2-ch downmixer is set for "surround" and not "stereo" mode. Not all DVD players give the choice, and if there is no choice, it is already the surround compatible mode. This mode will take all the signals from the Ls/Rs channels of the 5.1 Dolby Digital track, add them together, and apply the phase inversion necessary to make a surround encoded Lt/Rt signal that your PL decoder will see as a pure surround signal. The separation should be high enough to give you the effect you want. The only thing that will reduce the separation is if you also have some audio mixed in to L,C, or R front channels of the 5.1 source.
     
  7. Doug_B

    Doug_B Screenwriter

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    Roger,

    Appreciate the input. I was curiouis whether players could encode the "difference" info of the surrounds when downmixing to 2 ch.

    Doug
     
  8. Roger Dressler

    Roger Dressler Stunt Coordinator

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    Doug,

    The 2-ch Dolby Digital downmixer in DVD players does apply the 180-deg phase encoding to the surround channels. The stereo downmix mode does not.
     

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