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pro-logic ?? complete novice

Discussion in 'Televisions' started by saddo, Mar 29, 2005.

  1. saddo

    saddo
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    Just brought a JVC tv with built in pro-logic
    i also have an analogue NTL cable box and a toshiba video and a phillips dvd player
    i have a few questions
    i hooked up the rear speakers but not much come out of them
    does the BBC or ITV broadcast pro-logic ?
    does NTL analogue cable broadcast pro-logic
    most dvds seem to have 5.1 sound do they also carry pro-loigic
    what about videos and pro-logic
    what use is the pro-logic ??
    do i sound like i have no idea what its all about

    Thanks to all you clever people out there
     
  2. Zacabeb

    Zacabeb
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    It's hard to explain the principle of Dolby Pro Logic without getting a bit technical, so bear with me. :)

    Dolby Pro Logic is primarily intended for programming that was mixed especially for it. Strictly, such programming is referred to as being Dolby Surround encoded. The system originates from movie sound, where it is part of the Dolby Stereo standard.

    Dolby Surround is based on the principle that in regular 2-channel stereo, there are greater similarities than differences between the left and right channels. That leaves room to "encode" surround sound by mixing it equally into left and right but with opposite polarities, making it different between left and right. The surround content can then be extracted upon playback by comparing the left and right channels, and steering the sound to each of the output channels with regard to the similarities and differences.

    A drawback is that when using this method, it's impossible to keep any naturally occuring differences between left and right entirely out of the surround channel. This produces "false surround" which may appear distracting, so Dolby Pro Logic uses a number of methods to reduce the audibility of it:

    • Limiting the bandwidth of surround content to 7 kHz, in order to reduces leakage of sibilants into the surround channel
    • Applying a tamed down version of Dolby B-type noise reduction in encoding and decoding, to further reduce the leakage a bit in the high frequencies
    • Adding a delay to the surround output relative to the other channels, to trick the hearing into ignoring the leakage (invoking what's known as the Haas effect or precedence effect)
    In a properly set up system, thanks to those methods there will be little audible sound coming from the surround speakers, except when sound was deliberately put there in the mix, or the sound has a very wide stereo spread. In the latter case, it's false (or "magic") surround but generally acceptable.

    Programming not produced in Dolby Surround may behave differently depending on how it was mixed. Most stereo TV programming works fairly well in Dolby Pro Logic because of the wide stereo mix, however. Somtimes, mixing techniques may produce significant surround content even when the programming is not specifically surround encoded. This happens mostly with musical scores and applause.

    In theory, Dolby Surround encoding survives intact in any stereo broadcast or recording. In the past, broadcasting equipment could damage the mix because of excessive processing, but nowadays most major broadcasters take precautions to avoid this when broadcasting Dolby Surround encoded programming. Most movies made in Dolby Stereo have inherited the Dolby Surround encoding from the theatrical mix and retain this so long as they are broadcast in stereo.

    As for DVD, most DVD's with Dolby Digital 5.1 soundtracks are produced so that the DVD player can downmix the 5 channels into Dolby Surround-compatible stereo. Generally though, when a DVD contains a separate 2.0 mix it may give better results in Dolby Pro Logic, as it is mixed specifically with respect to the limitations of the system.
     
  3. saddo

    saddo
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    ??????????

    i was hoping for a simple

    yes
    no
    yes


    ect
     
  4. Tight Git

    Tight Git
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    Zacabeb,

    It seems your efforts were not appreciated. :(

    For what it's worth, I thought your explanation was excellent! :thumbsup:
     
  5. mrtbag

    mrtbag
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    It certainly is a shame that some of the forum members efforts are not appreciated.

    Zacabeb, I also thought your answer was brilliant.

    saddo. Is it that you do not undertsnad the answer? Or is it that you do not want to read and learn it's contents?

    If you have read the answer and still do not undertsand, read it again. It is clear, and does answer your questions.
     
  6. Zacabeb

    Zacabeb
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    Thanks, but saddo's right in that my post was confusing. If you go from not having any prior knowledge to having take in that much info at once, it is daunting. It has always been confusing and not the least because of the inconsistent and changing terminology. :)

    But here's a breakdown of the specific questions asked, with more straightforward (and hopefully less confusing) answers:

    what use is the pro-logic
    Dolby Pro Logic is used to decode the surround channel from programming made in Dolby Surround or Dolby Stereo. The surround channel is mixed into the stereo signal in such a way that it can be recognized by Pro Logic upon playback.

    i hooked up the rear speakers but not much come out of them
    This is normal and intentional, unless you find that sounds which should clearly come from the surround speakers don't.

    does the BBC or ITV broadcast pro-logic / does NTL analogue cable broadcast pro-logic
    Any channel you receive that broadcasts in stereo can present Dolby Surround if the program was made in it. Most movies are made in Dolby Surround or similar systems, and many broadcasters also produce some of their own programming in Dolby Surround. Dolby Surround does not however work in mono broadcasts.

    what about videos and pro-logic
    Stereo VCRs can record and reproduce Dolby Surround programs, but mono VCRs can't. Movies on prerecorded tape are usually in Dolby Surround.

    most dvds seem to have 5.1 sound do they also carry pro-loigic
    Yes, the Dolby Digital system used to store sound on DVD was designed so that 5.1 content can be reduced to regular 2-channel stereo, including Dolby Surround.
     
  7. kevin19470

    kevin19470
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    Hi Zacabeb,

    Thank you for taking the TIME and the TROUBLE to be so precise, I for one have certainly learnt something; I hope this also applies to others.

    Kev
     
  8. red16v

    red16v
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    Hi, I too found Zacabeb's post most interesting and useful - well worth taking the time involved - thank you Z. Regards, yt.
     
  9. Cynthia 7

    Cynthia 7
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    Hi Zacabeb,

    I'm grateful to Saddo for posting his query as I would otherwise not have seen your brilliant clarification of Pro Logic. I only have vague knowledge of this until now although I have a Pro Logic television in the bedroom. Dolby Digital I understand as I have this in the sitting room and read about it.

    I have copied and pasted this for future reference. Thank you for putting us all in the picture about this sound mode and making your in-depth explanation so interesting.

    Kind regards
     
  10. saddo

    saddo
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    Thanks Zacabeb

    Thanks for your time to explain it to me in laymans terms
    i sort of understood the theory of pro logic. Its was the practcal
    application that was confusing me,
    After youe explanation all is clear
    just one more question
    does anyone know if NTL analogue cable is stereo ?
    my box only has one audio ouput so would it be better to use the aerial socket

    Thanks again
    Mike
     
  11. TopDog

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    Z Thank you for the explanation of prologic, can I assume that Virtual Pro Logic attempts to do the same processing with less expensive hardware? cheers.
     
  12. LV426

    LV426
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    Virtual Pro Logic tries (and usually fails IMO) to do the same thing with less speakers. True DPL uses 5 speakers - 2 rear, 2 front + 1 centre. Virtual DPL tries to produce a rear channel, from behind you (where it belongs) with no rear speakers (and sometimes, no centre).
     

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