What exactly is "PCM" Pro-Logic? Is it much better than standard DPL?

Discussion in 'Archived Threads 2001-2004' started by NathanP, Nov 12, 2001.

  1. NathanP

    NathanP Supporting Actor

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    I've been hearing "You don't really need DD 5.1 for Laserdiscs, PCM pro-logic sounds great!"
    What exactly is this "PCM" Pro-Logic?
    How does it improve on regular DPL?
    Is this a feature that comes with an LD player?
    Or is it encoded on a LD?
    I figured I might as well ask this as I'm about to buy an LD player on ebay.
    thanks,
    Nathan
    ------------------
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  2. Dustin B

    Dustin B Producer

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    I've only heard PCM used as an acronym for pulse code modulation, which is a way of storing sound information. As far as I know, it's usually used to store two audio channels (ie stereo CDs), and that's all that Dolby Prologic is anyways. Two descrete channels, where anything in both channels and in phase is extracted as the center channel and anything in both channels and 180 degrees out of phase is extracted and used for the rear channels.
    So unless some sort of compression technique is used that I don't know about for normal Prologic to make it smaller, as far as I'm aware, PCM Prologic is identical to Prologic.
    I think a stereo PCM signal requires 1.5 mbit/sec, a DD 5.1 requires 384 kbit/sec and a DTS 5.1 requires two or three times what the DD does, can't remember what that one is right now.
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  3. NathanP

    NathanP Supporting Actor

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    Can anyone answer my question?
    Probably a serious "laserdiscphile" could answer my question.
     
  4. Adam Barratt

    Adam Barratt Cinematographer

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    The 'PCM Pro Logic' these people are describing is ordinary vanilla-flavoured Dolby Pro Logic processing of a LaserDisc's uncompressed stereo PCM soundtrack.
    LaserDisc PCM audio is the same as that used by CD (or vice versa) and often sounds much better than equivalent two-channel Dolby Digital soundtracks commonly found on DVD.
    Adam
     
  5. NathanP

    NathanP Supporting Actor

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    Ok, so this will sound better than regular Surround 2.0 on a DVD.
    WOW, what I was doing for DPL on Dvd's is actually choosing Surround 2.0 and then select DPL on the decoder and it didn't sound that bad at all.
    Is PCM Pro-Logic on the LD's themselves? or a feature with a player?
    Thanks,
    Nathan
     
  6. Dustin B

    Dustin B Producer

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    Surround 2.0 on a DVD is Prologic. Whether it uses PCM or some sort of compression I don't know though.
    Both (sort of). The Laser Disc, DVD, VHS tape has to have the matrix encoding of the center (same in both stereo channels and in phase) and rear channels (really just the same signal sent to both rear speakers, and again in both the stereo channels, but this time 180 degress out of phase from each other) mixed into the stereo signal, and then your receiver or preamp has to be able to decode the center and rear channels out of the stereo feed (I suppose the Laser disc player could do this, but I don't think any actually do).
    ------------------
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    [Edited last by Dustin B on November 12, 2001 at 06:34 PM]
    [Edited last by Dustin B on November 12, 2001 at 06:36 PM]
     
  7. Vietor

    Vietor Stunt Coordinator

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    Its 2 Channel Audio Stored in the PCM format, and then the resulting stereo signal is run through DPL. Its just DPL on a 2 channel source.
    The difference between that ans that is on a DVD as 2 channel audio is the format. The DVD has the audio in a compressed format, DD, and the Laser Disk has the Audio stored in the same way as a CD.
    The only differnect is in the quality of the origonal 2 channel sound, the lossy compression of DD, as compared to the uncompressed PCM data.
     
  8. Tina_H_V

    Tina_H_V Supporting Actor

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    Hello Nathan.
    To answer your question further, yes, PCM is actually short for LPCM, which stands for Linear Pulse Code Modulation. Yes, it is indeed based on the same brand of digital audio formatting, which comes in the form of a series of 0's and 1's in the digital processing, which was initially placed on compact discs back in that format's inception by the early 1980s.
    In spite of being around at that time also, laserdisc only used an audio signal pattern which was compatible to that of FM-radio, accounting for a sound that surpassed pretty much anythign else analog. And unlike many of televisions of the time and in the early days of VCR's, all laser disc players were capable of putting out two-channel stereo sound.
    Then, by the mid-1980s, as engineers of laserdisc technology--especially those connected with Pioneer--made a serendipidous discovery: that there was mroe than enough space on the disc to allow for an extra set of stereo audio channels. With compact disc impacting as it was, the idea was to take that same brand of LPCM digital audio formatting found in compact discs and insert it onto the laserdiscs as well, giving not only an higher-quality alternative to the already-excellent analog stereo sound, but also allowing for filmmakers and LD manufacturers to get creative by adding audio commentary on an analog channel while leaving this higher-quality digital stereo audio feed intact--often times, with the original soundtrack from the film itself being mreerly transferred from the print master onto those digital stereo channels. This was initialized on early Criterion Collection titles, as well as a few other notable movies. This move, coinciding with the advent of presenting movies with their original widescreen aspect ration--whatever it would be--helped get going what would generally come to be known today as home theater. Also aroumd this time, LD players with digital-playback capabilities began to emerge on the market. Albeit a limited one given LD's history as a niche market, the impact was so well enough that by the end of the 1980s, all LD players were manufactured with digital audio playback capabilities as well as those analog.
    Although for a long time Dolby Surround was regarded to be the primary standard for Dolby Pro Logic playback of such-encoded software, actually, all laserdiscs with a two-chalen stereo digital track are actually LPCM tracks. Some people may take it as being the same...but it is not necessariliy so.
    The LPCM tracks of LD's were always presented as uncompressed, resulting in not only stronger Dolby Surround playback on DPL processing, but also a far greater stereo sound over many other home video forms available as well. Given DVD's propensity for compressing Dolby Digital data--whether 1.0 or 6.1 EX--even with the LD era formally past us, the Dolby Surround soundtracks found on digital stereo audio channels of laserdiscs remain the best of their kind in home theater to this day--even with the DVD r/evolution being as great as it is (and it is).
    Even today on some DVD's, there is both a Dolby Surround soundtrack AND a PCM soundtrack as well, with the PCM remaining uncompressed two-channel stereo yet suitable for DPL(II) playback which continues to be preferred for some to this day.
    Well, Nathan, that'll do it. Hope I was able to be of some help to you. [​IMG]
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  9. Chris PC

    Chris PC Producer

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    PCM stereo is good because its digital. The Dolby Surround and Dolby Pro logic on VHS video tapes is good, but it is analog. The dolby surround on Laserdiscs is digital whenever you see the "digital" thingy on the Laserdisc. The point is, even though Dolby Digital and DTS are the best formats with full range surround and discrete channels, PCM digital surround on Laserdiscs is far from lousy sound.
    In fact, if you play a LD with Dolby Pro Logic recorded via digital PCM and use a receiver with DPL II, I think it will as good as Dolby pro logic will ever sound.
     
  10. NathanP

    NathanP Supporting Actor

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    WOW!
    Tina and Chris-
    Thanks SO much, you've really enlightened me!
    I think I'll be getting that LD player soon.
    So, some people still prefer uncompressed DPL to DD 5.1?
    I really understand where they are coming from!
    Are the surrounds used more frequently in PCM pro-logic?
    Thanks,
    Nathan
     
  11. Patrick Sun

    Patrick Sun Studio Mogul

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    Does your LD player come with the AC-3 RF output in case you want the option of adding a AC-3 RF demodulator to get DD 5.1 audio playback? AC-3 is the old name for Dolby Digital 5.1. This AC-3 track resides on a track that's recorded so that it requires RF demoulation to extract the digital bitstream needed to provide the receiver's DD 5.1 decoder.
    For LD which have a dts soundtrack, the info sits on one of the digital tracks, and the other digital track can be used for mono sound or director's commentary.
    Most if not all LDs come with analog tracks in 2-channel form. This is the 2-channel output from the LD player that you can feed your receiver's analog inputs. Don't confuse them with the various digital outputs.
    Also, get this terminology correct:
    The soundtracks are ENCODED in the Dolby Surround format.
    The soundtracks are DECODED in the Dolby Pro-Logic processing.
    There isn't that much need to keep the "PCM" when talking about the sound format of LDs, it's all uncompressed audio tracks. And depending on the encoding, they are either in plain vanilla 2-channel stereo, or actually have rear channel information encoded on the tracks which are then extracted by engaging the Dolby Pro-Logic processing on the
    receiver.
    Whether or not the mono surround channel is used more or less for a Dolby Surround encoded soundtrack is totally dependent on the sound mix of the movie in question.
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  12. NathanP

    NathanP Supporting Actor

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  13. Patrick Sun

    Patrick Sun Studio Mogul

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    The video performance is more of a function of the comb filter in either the LD player (the expensive LD players have the fancy 3D comb filters that produce very nice video), or the TV itself.
    But a $200 DVD player will produce a video display that will be better than most of the expensive LD players, and a lot better than most of the average LD players.
    ------------------
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  14. NathanP

    NathanP Supporting Actor

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    Also, How many movies are encoded with DPL?
    Would you say a mojority of them?
    I've noticed that in DVD's these days, they tend to encode only DD 5.1 and DTS and are only encoding DPL in foreign lingo.
    Thanks!
    Nathan
     
  15. Patrick Sun

    Patrick Sun Studio Mogul

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    If there is no DOLBY SURROUND 2.0 soundtrack on a DVD, the DVD player itself will produce the 2 analog DOLBY SURROUND channel "on-the-fly" from the existing Dolby Digital 5.1 track, it basically downconverts the DD5.1 into a 2.0 soundtrack and sends it out of the DVD player's 2-channel analog audio outputs.
    There is no DPL ENCODING. Please get the terminology straight.
    You can't make a generalzation on LD audio tracks. Some had just plain mono or stereo audio tracks. Some are encoded with Dolby Surround, some are not. You have to look at each LD individually.
    ------------------
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  16. NathanP

    NathanP Supporting Actor

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  17. DaViD Boulet

    DaViD Boulet Lead Actor

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    quote: There is no DPL ENCODING. Please get the terminology straight. [/quote]
    Picky Picky.
    Dolby Pro Logic technically refers to the added feature of extracting the in-phase information from a stereo signal (which becomes the center channel) in addition to extracting the 180 degree out-of-phase information for the surrounds.
    In essence, all information in a stereo signal that is mono (in phase between the two speakers) is "ProLogic" encoded by default.
    Since we can validly talk about Dolby Pro Logic *decoding* it would stand to reason we could use the term "Dolby Pro Logic *encoding*" without too much offense...but if you want to be technical, it is called "dolby surround".
    It is true that DVD players can take DVDs lacking discrete 2.0 mixes and output 2.0 stereo via the analog (and digital) output jacks as the player can downmix the 5.1 DD into 2.0 on the fly. Interesting, even in this case most players have an option for a pure "stereo" down-mix vs. a surround *encoded* mix. Yes, even your DVD player will try to take the surround information from the 5.1 disc and mix it 180 degrees out of phase while doing the 2.0 downmix to create a dolby-surround *encoded* 2.0 signal [​IMG]
    Discrete 2.0 mixes on DVDs can contain flags telling the DD decoder to leave it alone during play back (play it back as true unprocessed stereo) or apply DPL decoding to the signal to extract center and surround information. Many DVDs that use 2.0 DD for mono films contain flags that will preserve the 2.0 stereo signal so the sound won't collapse into your center channel (as it would sound with a 1.0 DD signal).
    PCM is simply uncompressed linear digital audio. All DD compressed signals originated as PCM signals prior to compression. They are also decompressed back into PCM prior to D/A conversion (d/a converters only work with linear information).
    All (most?) LDs mastered after 1984 contain 2.0 stereo digital (16/44.1 pcm) just like standard CDs. This stereo signal cound be mono (the same information in each channel), regular stereo, or Dolby surround [​IMG] encoded. It could also be HDCD encoded. On Some LDs the 2.0 PCM stereo signal is actually DTS data that's pretending to look like normal 2.0 PCM to your LD player so it will cooperate and send it to the digital output. If you attempted to play this as normal 2.0 PCM via the LD players L/R analog outputs or a d/a converter you'd hear hiss.
    -dave
    [Edited last by DaViD Boulet on November 13, 2001 at 05:31 PM]
     
  18. Chris PC

    Chris PC Producer

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    Nathan,
    Laserdiscs come in these flavours:
    1) analog mono
    2) analog stereo
    3) analog dolby surround
    4) digital mono (I think ?)
    5) digital stereo
    6) digital stereo/surround
    7) Dolby Digital (DD) or AC3
    8) DTS or Digital Theater Surround
    The following is important:
    A laserdisc with DD (AC3) will also be able to be played and allow for dolby surround through either the analog or the digital surround sound tracks. So don't worry if the disc is DD and you don't have RF out on your player.
    A laserdisc with DTS will play on your player if you don't have DTS decoding on your receiver, you just use the digital tracks. If you don't have digital output on the laserdisc player, then you must use the analog tracks. The problem is, I think the DTS eliminates the analog tracks. So in order to use the surround soundtrack, you must use the digital tracks. Newer player in the 90's were like CD players and so they had DAC's in them. They read the digital tracks and fed analog out the RCA jacks. I think DTS discs are missing something because the DTS takes up so much space, but I can't remember which, but I thought it was the analog tracks. Someone else hear will enlighten me. (There is more to this, and others will hopefully fill in what I have missed).
    I would say that a good number of LD's are encoded with Dolby stereo or stereo/surround. But unfortunately, you can't generalize. It depends when the movie was put on LD etc etc. I bought a whole pile of used laserdiscs and I'd say 85% of them are dolby surround, the rest are stereo. There are quite a few DD or AC3 discs, but not as many DTS discs.
    It is very important what receiver you have, because any newer receivers might have Dolby Pro Logic "II" or "Circle Surround 5.1" can make produce a satisfying "surround" effect from even an analog stereo soundtrack. It is Dolby Pro Logic Surround, but it is a step closer to DD and DTS.
    Good luck with your LD purchase. I would advise looking for a Pioneer with auto side flip and digital out. If your receiver decodes DD or AC3 I would at least check out the players with that feature. You may not want to spend too much, but at least check out the cost etc. You never know, you may find its worth it. You might be lucky like I was and find someone with a very good player and tons of disc looking to ditch. I am happy I bought the player and discs I found.
    [Edited last by Chris PC on November 13, 2001 at 06:07 PM]
    [Edited last by Chris PC on November 13, 2001 at 06:11 PM]
     
  19. NathanP

    NathanP Supporting Actor

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    Thanks guys!
    Say,
    What Pioneer LD players would you recommend?
    Nathan
    ------------------
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    "Way to go Dallas!!!"
     
  20. Philip Hamm

    Philip Hamm Lead Actor

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    quote: A laserdisc with DTS will play on your player if you don't have DTS decoding on your receiver, you just use the digital tracks. If you don't have digital output on the laserdisc player, then you must use the analog tracks. The problem is, I think the DTS eliminates the analog tracks. So in order to use the surround soundtrack, you must use the digital tracks. Newer player in the 90's were like CD players and so they had DAC's in them. They read the digital tracks and fed analog out the RCA jacks. I think DTS discs are missing something because the DTS takes up so much space, but I can't remember which, but I thought it was the analog tracks. Someone else hear will enlighten me. (There is more to this, and others will hopefully fill in what I have missed).
    [/quote]I'll enlighten you. [​IMG] The DTS signal, as described earlier in this thread, takes the place of the digital stereo tracks. In order to listen to a DTS LD on a system with no DTS decoder, the analog tracks have to be used, using the analog L/R output of the LD player, like director's commentary. The analog FM sound is actually very good, my Eric Clapton Unplugged DTS Laser sounds great in stereo mode.
    Nathan, if you're not concerned with DTS and Dolby Digital, any Pioneer player with a model number X01 or higher will be good. Even a simple player like a CLD-S104 with analog L/R out and composite video will sound very good when played in stereo, and downright great in ProLogic for most movie soundtracks. If you're only getting the player for a few movies don't sweat the auto reverse, side switching for just a few movies isn't bad.
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    [Edited last by Philip Hamm on November 14, 2001 at 09:35 AM]
     

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