Difference between stereo and Dolby Surround 2.0?

Discussion in 'Archived Threads 2001-2004' started by Andrew_Cramlet, Feb 26, 2002.

  1. Andrew_Cramlet

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    Well, I feel like I don't know what I'm talking about anymore - so I thought I'd ask a basic question here.

    I always thought that all DPL did was convert stereo sound to a shadey surround sound (right,center,left,back). HOWEVER, it would seem that I was wrong.

    Could someone, with simple language, explain to me what exactly DPL is - and how Dolby 2.0 is different than "regular" stereo sound.
     
  2. Adam Barratt

    Adam Barratt Cinematographer

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    Well, Dolby 2.0 is usually stereo (2.0 simply means two channels, whether stereo or two mono channels), and can be used to convey ordinary 'vanilla' stereo or Dolby Surround encoded stereo. A Dolby Surround stereo soundtrack has four channels of information consciously 'folded' into it using a technique called matrixing. An ordinary stereo soundtrack does not.

    These matrixed channels can be 'unfolded' in your home using a Pro Logic decoder and heard through a conventional five speaker surround sound system. An ordinary stereo soundtrack was intended to be heard through two speakers only.

    If you run an ordinary stereo soundtrack through a Pro Logic decoder, you may well get left, centre, right and surround information, but what you get is entirely random. If a stereo soundtrack is also Dolby Surround encoded, the decoded channels are exactly what the soundtrack's mixing engineer intended you to hear.

    Dolby Surround soundtracks are usually labelled as such on the back of a DVD's case, while conventional stereo soundtracks never mention the word 'surround'.

    Adam
     
  3. BruceD

    BruceD Screenwriter

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    Also you need to remember that on a DVD a PCM soundtrack is essentially the same as that found on a CD, i.e. it is a lossless playback medium.
    Any DD soundtrack, or DTS for that matter, is a lossy playback medium. That means all DD and DTS such as DD2.0, DD5.2, DTS5.1, even DD1.0 (mono) is all content that has been compressed and doesn't contain all the original content like a PCM track.
     
  4. Ted Lee

    Ted Lee Lead Actor

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    also, dpl is mostly "old-school" now. remember that the rear channel signals are mono - the same sound is coming out of each rear-speaker.

    with the newer stuff (namely dolby digital and dts) the sound coming from the rear is discrete - you can have different sounds coming out of each rear speaker. it definitely provides a better sense of rear-surround, especially things like planes flying overhead, etc. imagine the sound starting in your left-rear and ending up in your right-front speaker. pretty cool...

    there's probably other advantages to dd/dts. if so, maybe someone will elaborate. i'm kinda curious myself.
     
  5. Andrew_Cramlet

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    Yeah, I know DPL is old school. I guess that is the reason I was clueless about it. I think I know a lot about digital, discrete surround sound.

    But a topic was raised about watching TV programs on regular cable "presented in surround sound." That is when I found my ignorance concerning DPL.
     
  6. Irv Kelman

    Irv Kelman Extra

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    Let me mention a few more things about Dolby Surround evolution.

    Dolby Surround: Matrixed four channel encoding. L - R - S - Sub Woofer. The vast majority of available movies are encoded in this format. With a Dolby decoder you can enjoy OTA TV broadcasts, Cable/satellite, VHS Tape, Laser Disk's and DVD's (CD's) in surround sound (if encoded).

    Dolby Pro Logic: Adds a matrixed center channel that improves dialog intelligibility. (Very important improvement) Will decode as above.

    Dolby Prologic II: Enhances Dolby encoded and non-encoded sound tracks.

    Dolby Digital: Up to six discrete channels. L - C - R - LS - RS - LFE. Available OTA HDTV, Cable/satellite, Laser Disk and DVD.

    Dolby Digital Surround ES: adds matrixed rear center channel to Dolby Digital.

    All Dolby incarnations are backward compatible.

    I hope this helps.
     
  7. Vince Maskeeper

    Vince Maskeeper Producer

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  8. Andrew_Cramlet

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    Thanks guys. I have one more question, though.

    What setting on my receiver do I use when wanting to hear an analog Dolby 2.0 or 4.0 surround source (cable, VCR, etc)?

    Unless the source is digital, my receiver doesn't recognize that is presented in surround sound, and simply outputs from the L/R speakers.

    If I manually set the receiver to "normal surround" it goes into DPL, but always makes use of the center channel (if I remember correctly - which I probably am not). Or was I simply trying to listen to non-encoded stereo? If I listen to encoded signal, will only the correct speakers output sound under this setting?

    I love this board. So much to learn, so little time...
     
  9. Vince Maskeeper

    Vince Maskeeper Producer

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  10. Wayne A. Pflughaupt

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    Andrew,

    Everyone has done a good job of explaining Dolby Pro-Logic here, but somewhere along the line one of your original questions got lost:
     
  11. Andrew_Cramlet

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    Thanks again.
    Things are a little clearer now than they were when I started this thread. But I have another basic question concerning this topic -
    Does regular old 75 Ohm Coaxial cable carry stereo sound? I ask, b/c if it doesn't, then this whole thread has been for educational purposes only.
    I have analog cable, that comes from the wall (beyond that who knows [​IMG]), and enters my TV and/or box via a 75 Ohm round cable. My cable box has both A/V outs and the afore mentioned round cable. I currently use the 75 Ohm cable.
    Aside from running only the video to the TV and the audio to the receiver, I can see no reason to use the A/V jacks. B/c the single cable feeds into the box, there shouldn't be any loss in quality by using it between the box and the tube, right? BTW, I'm using my audio out jacks on my TV to feed the receiver.
    If this type of cable does not support two channels of audio, then I really have no need for DPL at all - and have no way of viewing television "presented in surround."
     
  12. Michael Reuben

    Michael Reuben Studio Mogul

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  13. Vince Maskeeper

    Vince Maskeeper Producer

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    Like Michael said- the cable system does support and carry stereo sound.

    However- not all cable boxes can actually decode stereo. Even if they offer 2 channel audio outputs, often this is a hoodwink and it is mono.

    I'd try to tune in a music channel (MTV, VH1, something playing a video or one of thos digital music stations if you have them)-- and try to flick on the NORMAL SURROUND processing. Listen close to the l/r speakers. Are you getting ANY sound? If it is all coming from the center on music material, then you are probably getting mono sound.

    -Vince
     
  14. Andrew_Cramlet

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    Well...it figures.

    I tried those tests you mentioned (DPL - MTV, VH1, digital music stations). In some cases (music) I got NOTHING from the L/R mains. For cable TV (MTV, VH1, etc) I got very little from the L/R's and never anything from the front three at the same time.

    My cable is mono. Fantastic.
     

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