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Is this how DD 5.1 works?

Discussion in 'Subwoofers' started by Ash007, Sep 26, 2005.

  1. Ash007

    Ash007
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    Can I just clear something up, to make sure I have understood Dolby Digital 5.1 properly.

    This is how I understand it.


    The .1 track is a dedicated discrete low frequancy track recorded on the disc, so the same noise goes down to the subwoofer from this track nomatter what system/setup you have and nomatter what the crossover point is set on the amp as, it is a feature of the disk. It has nothing to do with the crossover point.

    The crossover point is for the stuff that is supposed to go to the other 5 channels but is in reality too low for them speakers.
    So any stuff that is recorded on the 5 regular discrete tracks that happens to be below the crossover will be redirected down the subwoofer cable along with the .1 channel.

    Is this right?

    Also, with music from a cd, I presume its a simple case of everything above the crossover to the fronts and anyting below the crossover to the sub.

    again,
    is this right?

    Cheers,
    Chris
     
  2. Gary_W

    Gary_W
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    Bang on the money :)

    Unless you play CD's in 'direct' mode. In which case everything gets routed to the stereo pair and nothing to the .1 channel. The only time the sub will get a feed in this case is if you are also running a high level cable piggybacked off the speakers and are using the crossover on the sub.

    Gary
     
  3. Arif

    Arif
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    Chris mate - excellent question!!

    I never really had any issues with how 5.1 worked - but the distinctions you drew/queried were the sort of specifics that one never realised that one never actually knew. And very important to know, in my opinion - as it would have a bearing on key areas such what amp/speakers sub combination to get - depending on how much your emphasis will be on movies.

    Nice one!


    (Thanks to Gary, too!)
     
  4. kit1cat

    kit1cat
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    In this article http://www.audiorevolution.com/equip/surround/ it states that "The LFE channel on a DVD does not go to the subwoofer -- it goes into your system’s bass management. " If you have any of your speakers set to small you are only getting the LFE channel below your crossover.

    Barry
     
  5. mremulator

    mremulator
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    That's plain wrong The crossover on an AV receiver is for bass redirection on speakers specified as 'small'. The LFE channel is passed to the sub regardless, unless the crossover is set too low on the sub of course.
     
  6. Jase

    Jase
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  7. Mr Incredible

    Mr Incredible
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    Not true for my Denon 3805. When in Pure Direct by pressing the ENTER button you can not only adjust the levels of the fronts, but you can turn the Sub off or on if you want. So anything below crossover will also get routed to the Sub.
     
  8. kit1cat

    kit1cat
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    Perhaps the design of receivers has changed since that article was written, my old yammy amps had a fixed crossover of 90hz and the manual stated that the subwoofer out cut-off frequency was 90hz. My present receiver a Marantz SR7400 has variable crossovers and the manual states that LFE signals during playback of DD and DTS will be played through the subwoofer.

    Another article I read a few years back said subwoofer output was produced by combining full range copies of all speakers set to small with the lfe channel and then low-passing the sum.

    Barry
     
  9. kit1cat

    kit1cat
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  10. KoThreads

    KoThreads
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    I've a 3 year old Kenwood 9060 THX. The manual states that the LFE will always be output at the sub-out.

    If speakers are set to small all L-R front output below 80hz will also be output via the sub output. Speakers set to normal or large have full range bass.
     
  11. Mr Incredible

    Mr Incredible
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    This article certainly contradicts my understanding (and that of the thread starter). Apparently the .1 LFE channel does get low pass filtered AFTER it is summed with the LF from the other speakers when set to small. So crossover on the AMP does cutoff the LFE frequencies as well, if the article is to be believed. As a result anyone having mains set to LARGE with a low Crossover is actually missing a lot of LFE frequencies. Even THX crossover @ 80Hz will throw away frequencies above that. I never new that. We live and learn.

    The article stated :
    "If your main left and right speakers are genuinely full range (be honest now!), then you are better off running them full range as opposed to high-passing them at a ridiculously low frequency."

    Which is my situation, but TBH I also had (have) a 60 HZ crossover. Me thinks I need to rethink my strategy.
     
  12. Jase

    Jase
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    A lot depends on how your Amp/Processor/Receiver's Bass Management works. Some give you access to the LFE channel crossover, some don't. The new Denon models (A1XV, A11XV, 3806) now give you an option to adjust the LFE channel crossover as well as the other channels.

    Although, there's not much point in worrying about LFE content above 80hz as there might not actually be any. Depends if the soundmixer has actually included it or not.
     
  13. Mr Incredible

    Mr Incredible
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    Sounds like a reasonable move to have a separate LFE crossover in addition to the mains crossovers.
     
  14. Jase

    Jase
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    They get independent crossovers for different speakers as well. Fronts 80hz, Centre 100hz, Surrounds 120hz etc etc. :)
     
  15. Mr Incredible

    Mr Incredible
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    Grrr, want one.......... Definitley low on the WAF.
     
  16. Jase

    Jase
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    Sneak it in and swap the 3805 out. They look almost the same, she'll never know. :)
     
  17. Arif

    Arif
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    Yeah - but the darn remote control unit gives the game away, often!
     
  18. Jase

    Jase
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    You don't let your Missus have control of that do you? :eek: :rotfl:
     
  19. bob1

    bob1
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    I have read before that although lfe might got up to 120hz its made to blend in around the 80hz level, but like you say that all depends on the soundmixer.
    Even though i can set all the crossovers for each speaker i have them set at large and crossover at 80hz,if it wasn't the fact that i watch stuff other than dvd's then i would try the 120hz level ,which is shown as standard in the amps display rather than a number.
     
  20. Gary_W

    Gary_W
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    Is this the crossover on the sub or on the amp?

    If you are talking about the one in the amp, it will do diddly squat anyway as you have all your speakers set to large. It is only when you set any to small that the crossover in the amp comes into play. At least that's the case with my amp anyway :)

    Gary
     
  21. bob1

    bob1
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    Yes the one in the amp ,it does work because i don't have a crossover on the sub and i'm only getting lf out of it, my amp will make the option unavailaible if it can't be done.
    I must admit that the crossover on the amp isn't that great and the curve is a little erratic above the crossover point, enter the bfd :cool:
    Don't forget in the case of dolby digital you can't get anything greater than 120hz form the lfe channel, so yes the need to have a crossover is not needed so that must mean that my amp is letting me adjust the lfe channel.
     
  22. Troon

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    The LFE channel must go via the receiver's bass management system. One of the required setup possibilities of DD is to have "large" fronts and no sub - and the LFE goes to the fronts (and any other "large" speakers in the setup).
     
  23. Steve.EX

    Steve.EX
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    I am not wholly convinced that using millions of crossovers is necessarily a good thing. There is a train of thought that believes doing this is very complex, and does not always offer improvement over a more global setting.
     
  24. Mr Incredible

    Mr Incredible
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    If I've told you once, I've told you a million times........ DON'T EXAGGERATE.
    :D
     
  25. Knyght_byte

    Knyght_byte
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    the way it worked in my Sherwood 6106 (i think thats the right model number, havnt looked at it for a while..lol)......was that you set all speakers large or small i think......but also chose if you had a sub or not....you could still set your speakers to small even without a sub (which wouldnt be much use unless your neighbours suck..lol).....and according to the manual, if you set to large, the front Left and Right would get the .1 LFE channel information if you didnt have a sub.

    on my Denon 3803 which i use now it has similar options, except i can set my front, centre and rears independantly in regards to size....and have LFE or LFE+Main.......to be honest its rather confusing atm cuz im tired...doh..lol...all i know is i have it set as large fronts, also centre, my rears as small, and the sub setting as just LFE.......altho i do have my sub wired by hi-level as well.....

    it sounds lovely....
     

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