Still attempting to grasp DD v Pro Logic II and more

Discussion in 'Beginners, General Questions' started by Andrew O'Brien, Jan 6, 2004.

  1. Andrew O'Brien

    Andrew O'Brien Stunt Coordinator

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    I'm slowly getting all this HT stuff after playing around for a week and also do a lot of reading here. A couple of things are still confusing.

    When my receiver spots a Dolby Digital signal on my satellite dish the receiver display indicates that the
    L C and R speakers have signals plus the SL, SR, and LFE speakers. There is also a red display of the word "DIGITAL" and I think the Dolby sign next to it, maybe not (poor eyesight).

    There are other channels where I see the red DIGITAL word displayed but only L and R are indicated on the display. What is this ? HBO East has it while showing Sex In The City. If it is a digital signal why would it only have two channels of audio? Also, even though the display indicates only L and R, I do have audio coming from the center speaker as well. It does say Prologic II on the display, so this is distinct from DD, again why only two audio channels?

    Additionally, I have other channels that the display indicates Pro-Logic II but the red "DIGTAL" word is not present. So, what is the difference between Prologic II and Proglogic II with a "digital" presence indicated on the display ?
     
  2. Ed Moxley

    Ed Moxley Cinematographer

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    Dolby Digital isn't necessarily 5.1.......
    There's DD 2.0, and 4.0 and even DD mono (I think). It just means that the audio has been remastered to a digital signal, instead of analog.
    PL ll with Digital is DD 2.0 being processed to all the speakers.
    PL ll without the Digital is just a stereo (analog) signal being processed to all the speakers.
    Blazing Saddles is an example of a dvd that's DD, and not 5.1.....
    Young Frankenstein is another...........
    [​IMG]
     
  3. ChrisWiggles

    ChrisWiggles Producer

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    Dolby Digital is an audio format. IT is digital, and is a compression method for compressing UP TO 5.1 discrete channels. It can be ANY combination of those channels (as far as I know). This tends to confuse people, as Dolby Digital does NOT necessarily mean that a disc will be 5.1. As mentioned, it may well be plain stereo, or even mono.

    Pro Logic II is not a sound format, but a PROCESSING method, that is applied to stereo sources. This creates a surround soundfield from ANY stereo source you want, be it CDs, old VHS tapes, the radio, records, anything. Herein lies the confusion: say you have something that is in Dolby Digital, but only in stereo. You can then apply Pro Logic, PLII, or any other matrix processing, like Circle Surround, or Neo6, or whatever, to that stereo source (that is DD, btw).

    Does that make sense?

    Also see the HT Primer and FAQ, if you've not already, it addresses these issues, and more that I'm sure you'll find interesting:

    http://www.hometheaterforum.com/htfo...hreadid=120328

    Hope that helpS! [​IMG]
     
  4. Andrew O'Brien

    Andrew O'Brien Stunt Coordinator

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    Both comments are helpful and makes good sense. Thanks.
     
  5. Vince Maskeeper

    Vince Maskeeper Producer

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    An important detail to note in this specific case-- Just because a signal says "DIGITAL" doesn't mean it is Dolby Digital encoded. A Compact Disc features DIGITAL audio information, yet it is only 2 channels-- and your cable system providing digital audio signals is no different.

    There is nothing about the word "DIGITAL" that dictates the number of channels, the codec format (the digital "language" if you will), or the quality-- it simply means the audio data has been converted to computer binary data. The specific audio cedecs (languages) will dictate the number of channels and quality it will support-- but just bacause it's digital, doesnt mean anything more than the fact that it has been converted to data.

    In the case of your cable system, the audio might not even be Dolby Digital 2 channel, although it could be-- some cable systems provide a PCM encoded signal (similar to the digital info found on a CD) rather than dolby digital for their digital channels.

    As Chris said, in the case of talking about Dolby signals specifically it's important to think of Dolby Digital as a carrier TYPE, an audio "codec" (language) like Mp3 for example. There is nothing in the specifications for Dolby Digital that says it has to be used for only 5.1 material, and can be used to carry anywhere from 1 to 7 channels of audio...


    As far as the "Pro Logic" element- prologic is just a FILTER, a filter that can be applied to ANY audio source- in order to "simulate" surround sound.

    Any stereo signal can have Dolby prologic or Pro Logic 2 processing applied to it- you could actually run that processing on an audio signal coming off your CD player, a cassette or even an old record album. Pro Logic (and pro logic 2) are just a "special effect" used to simulate surround from stereo signals...

    Now, stereo signals can be created specifically with Dolby Pro Logic processing in mind... resulting in a more pleasing simulated surround... but even stuff that was created WITHOUT Pro Logic in mind will often yield a "surround" effect...

    Bottom line is, in your example- Sex in the City was carried with only a 2 channel stereo soundtrack... however you can apply processing like PL2 (which your receiver did) to simulate a surround sound output from a 2 channel source.

    -vince
     

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