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Confused about Dolby Pro Logic II

Discussion in 'AV Receivers & Amplifiers' started by FlimsyFeet, Dec 5, 2003.

  1. FlimsyFeet

    FlimsyFeet
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    I'm a little confused about Dolby Pro Logic II. This is what I have found out so far, but I would appreciate some clarification:

    1. DPL2 is a way of getting extra channels from a stereo analogue source, but where DPL only gives a limited frequency mono surround channel, DPL2 is full frequency stereo.

    2. If something says "Dolby Surround", like a VHS tape or NICAM TV broadcast, it has a soundtrack mixed for DPL receivers.

    3. A Dolby Surround mix will however sound better using DPL2 decoding, but not as good as a soundtrack mixed specifically for DPL2. Are there any films released on VHS with a DPL2 soundtrack? I don't know, don't buy VHS anymore.

    4. A soundtrack encoded with DPL2 will play correctly on a DPL receiver, but will not sound any different to a standard Dolby Surround soundtrack.

    5. DVD players will downmix Dolby Digital 5.1 to Dolby Surround for the stero output. There is no point in downmixing to DPL2, because receivers that do DPL2 decoding usually also have DD.

    6. If a DVD is played on a PC, there are programs (AC3Filter) that can downmix DD5.1 to DPL2.

    7. You can, in theory, rip the AC-3 (Dolby Digital) soundtrack from a DVD, and encode using DPL2 to a stereo WAV file. But there is still some discussion whether, if you back up this file to a compressed format like MP3, the compression encoding will affect the surround encoding.
     
  2. Reiner

    Reiner
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    Correct, that's one of the functions. DPL however wasn't designed to make surround of stereo-only sources, so it works only with DPL encoded soundtracks. Anything else just sounds terrible and you better use a DSP mode instead.
    Thus DPL2 has a new function, similar to L7 (Logic7).

    Correct again. The DPL signal is 'hidden' inside the stereo track, as such it doesn't effect stereo-only systems but DPL systems can extract the additional information and route it to the surround channels & center.

    AFAIK currently DPLII is only available with computer games.

    I guess.

    DVD players can downmix and not all add a DPL signal, some remain just plain stereo.
    Agree with the 2nd part, in fact then downmixing to DPL it isn't of much use either if you have a DD receiver.

    Dunno.

    Ditto (dunno). No clue about PC stuff ....
     
  3. FlimsyFeet

    FlimsyFeet
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    Thanks for taking the trouble to do all the quoting and make your replies easy to follow.

    The only thing I would question is where you said not all DVD players downmix to Dolby Surround - I read somewhere (I'll have to refind the link) this is part of the DVD standard. Some players can downmix to plain stereo, but this is an extra option.
     
  4. eviljohn2

    eviljohn2
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    I believe most DVDs have a stereo soundtrack included which is output from the stereo output (!). This would probably have been mastered for DPL (as with VHS, or some TV broadcasts (eg. films, Simpsons etc)).

    I don't think the DVD player actually does any "downmixing" as such.
     
  5. micb3rd

    micb3rd
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    DVD players must downmix Dolby Digital to stereo analog outs as not every one has Dolby Digital hardware, many people still use older hifi equipment.

    Quote from Dolby website.

    http://www.dolby.com/digital/l.in.9901.makingthemost.html
     
  6. dsw182

    dsw182
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    Am I correct in saying:

    PL2 (Music) -> Stereo source into multichannel
    PL2 (Movie) -> As PL1 but much improved
     
  7. lowrider

    lowrider
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    DPLII movie is the same as music, but center at max level, and no adjustements...
     
  8. jon2099

    jon2099
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    True, I have tested AC3Filter and it does downmix to DPL2 properly (i.e. the are distinct surround left and right channels). This only has limited use though, as most soundcards these days either have at least 5.1 channels or a SPDIF out.

    The surround information is encoded as a phase difference of the same sound between the left and right channels. When encoding in MP3 with joint stereo (usually the default for bit-rates <=160kbps), the phase difference is removed for sounds >2kHz in frequency. The reasoning is that the ear does not perceive this. However, DPL(2) decoders depend on this information so it ends up removing the surround information as well.

    You can either use a DPL-compatible MP3 encoder (which preserves phase information for sounds up to 7kHz) or encode in stereo (not joint stereo).
     
  9. Reiner

    Reiner
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    It would be output as PCM on the digital outs (optical or coaxial) and the stereo output.
    A stereo soundtrack is not mandatory and it doesn't need to be mastered in DPL (that would just depend on the title or if someone had made an effort to remix/-master it).

    They can.

    Found something regarding the downmix:
    From: http://www.dvdreview.com/faq/dvdfaq.shtml

    Note that it somewhere mentioned the downmix reduces dynamic range and discards the LFE, so if you have a stereo track present on the disc you are advised to use (select) that one - in case you are hooked up to a stereo only system or want to listen to a music DVD in in plain-old stereo only.
     
  10. cbemoore

    cbemoore
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    I read my amplifier's manual properly for the first time last night (Marantz SR6200). It explains things as follows:

    "DPLII Movie" mode is for replaying films that were originally recorded with a DPL or DPLII soundtrack.

    "DPLII Music" mode should be used for simulating surrround sound from a straight stereo recording (eg CD music, TV etc).

    I always used to use DPLII Movie for normal TV watching, but I've changed to DPLII Music. I now get much better surround effects during normal TV viewing, which is what you'd expect given the explanation above.

    Chris
     
  11. father alice

    father alice
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    sorry to but in,

    Does an hs2 dvd recorder record sound from dolby surround source as such, or simply as L & R sterio - ie, on playback would the dvdr sound better through DPLII music or DPLII movies?
     
  12. KraGorn

    KraGorn
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    Let your ears tell you. :)

    From my experience, "movies" puts more sound through to the surround channels where as "music" leaves the balance on the fronts while providing some lower-level output to the surrounds.

    AFAIK the recorder is a two-channel machine.
     
  13. jrpavel

    jrpavel
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  14. calscot

    calscot
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    Movie mode also uses the subwoofer, music mode doesn't.

    Movie mode makes more use of the centre channel.

    Music mode gives a wider soundstage rather than surround effects.

    Music mode is tweakable, movie mode isn't.
     
  15. lowrider

    lowrider
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    Music mode does use the subwoofer as does Movie... :lesson:
     
  16. cbemoore

    cbemoore
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