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View Full Version : Technical Mumbo Jumbo....


MISFITZ
06-27-2001, 09:03 PM
I'm pretty familiar with DVD technology. Here at my job, we have actually made a few disc and the settings and encoders I use have made me aware of the basics of DVD encoding. Now bring up how they are converting the ORIGINAL films to a digital source and the 'anamorphic' blah, blah, blah, and I can get a little fuzzy. Mainly cuz the disc we make don't use all the features a DVD can offer.

But my question is, how is the encoding done for Laser Disc? Is a Laser Disc 'compressed' less because of the larger size of the disc? And the CAV and CV formats. What ae some advantages and disadvantages besides being able to pause the film? I do notice a slight crisper image on SOME, but not all disc and so i don't know if that's related to it.

I know this answer could take up a few days, but any breif notes would be cool on how the Laser Disc holds its format. I get asked these questiosn when 'friends' see that I still have Laser Disc. I really can't answer them, but still pimp Laser Disc. Would help if I knew my subject more before i open my mouth. :rolleyes:

Paff
06-27-2001, 09:26 PM
I don't "know" all the answers, but I know enough to be dangerous, so look out...

The video on LD is actually ANALOG I believe. Sounds odd, but it is. This is one of the main reasons that companies like Criterion can't just go out and press a DVD even if they've made the LD. You have to "re-aquire" the DIGITAL rights if you want to press a DVD.

The issue of compression comes up more in the sound department. LD is capable of uncompressed Dolby Pro-Logic Pulse Code Modulated sound. There's a very large contingent that believes this is still the best sound ever created. I don't know if I agree, but it sounds damn good.
When you make a DVD, and you don't want to do a 5.1 remaster, you take that PCM mix and do a Dolby Digital 2.0 mix. Without a doubt, this sucks. Dazed and Confused on DVD is a dull, lifeless mix. But on my Laserdisc, the 70's come alive, man! Fantastic friggin sound.

Finally, the CAV/CLV thing. On a CAV disc, each "ring" contains exactly one frame of the movie. Thus, you get perfect freeze-frame since the disc spins in place, and the laser just reads that ring over and over again. With CLV, it has to read from more than one ring, thus you need a digital buffer to get freeze frame on a CLV disc. My Pioneer 704 does it, but it's nothing to write home about.

The best thing about CAV is just that every frame of film is on there. 24 clicks of the step-forward button = exactly one second of film.

But changing discs is still a pain in the ass, no matter how cool CAV looks. In the end, that's what matters most.

MISFITZ
06-27-2001, 09:36 PM
ok, here's another...

I can see your point about the PRO-LOGIC, but what are they doing to the sound when its in the AC-3 DOLBY SURROUND? That sounded pretty damn good too. (well, it seemed much louder if anything)

Paff
06-27-2001, 11:04 PM
Aw man, now ya got me started...

OK, we all know the basics of what AC-3 (now just called Dolby Digital 5.1) is, right? All digital signal, discrete speakers, etc.
But how does it fit on LD?
Well, one of the big problems was that when they started with AC-3, VERY few people had Dolby Digital receivers. Thus, the PCM Pro-Logic track would have to remain untouched, as 99% of all LD users needed it. So they "RF Modulated" the AC-3 signal and put it on Analog channel 2. Yes, it's actually an ANALOG signal. Imagine a wave, and all the "peaks" are 1's, and the "valleys" are 0's, and thats an RF modulated AC-3 signal. Then of course, you need an RF DEmodulator to convert back to normal digital signal before you go into your Dolby Digital receiver. RF Demodulators are now almost impossible to find, and VERY expensive (~$200)

Yet, despite all this "cooking" of the AC-3 sound, it's nowhere near as "cooked" as it is on todays DVDs!!

Here's why: They still have to compensate for the Luddites who don't have Dolby Digital receivers yet (c'mon people, these things are less than $200 now). But unlike LD, they can't put that pure PCM Pro Logic track on DVDs, otherwise most movies on DVD would require several discs!
Thus, they "dumb down" the DVD 5.1, so that any player can easily convert to 2.0, which is acceptable to a non-Dolby Digital receiver. This "dumbing down" of all 5.1 DVDs makes the sound very lifeless compared to the same 5.1 track on a laserdisc.

Now, I thought this was all snake oil for the longest time. But the demand for movies like The Matrix and Saving Private Ryan on LDs was huge. People swore up and down that the 5.1 sound on those discs blew away the 5.1 sound on the DVDs.
Well, a few months ago I found a cheap copy of Carrie on DVD. It was released the same exact time as the LD. Same packaging, same transfer, and a new 5.1 sound mix on both. I already had the LD, and I loved the new 5.1 sound (yes, I know, it's fake. Carrie was orginally recorded in mono. Work with me here). Every time Carrie "flexed" her power, the violin squeaks were thrown to the rear speakers for a cute effect. When Carrie heard the voices in her head ("They're all gonna laugh at you"), it swirled all about the room.
The DVD had little to none of that. The violin squeaks were only on my front speakers, and the swirling voices barely moved. First, I checked all my settings again with a sound meter and Video Essentials. In the words of Mona Lisa Vito, they were "dead-on balls accurate" to 75dB. I finally placed my ear to my rear speakers, and I could faintly hear what I was missing before. That ain't right.

Unfortunately, I had foolishly sold the LD when I got the DVD (sound familiar Misfitz?) so back to E-bay I went. Well, I have since re-acquired Carrie on Laserdisc, and the new mix sounds pure the way it should.

Believe it or not people, the sound on DVD you love is nowhere near as good as it is on Laserdisc. I move with the times, and LD is dead, DVD is where it's at. But lately I've been re-buying as many DVD movies on LD that I can get my hands on. They sound better, no question about it.

MISFITZ
06-27-2001, 11:34 PM
Very interesting.

HHHhhhmmmm. I gotta look at something at home.

But anyways,

then basically, the AC-3 on LD is better than some/all DVD 5.1?

Hhhhmmm. News to me. I can see how certain films on LD can still prosper with PRO-LOGIC then getting all 'whooped up" with all that mixing. To tell you the truth, I don't like listening to a lot of DVDs in the 5.1 mode. Maybe its in my set-up, but I can't hear sheet when they talk. I mean, i can, but, not like before. It always seems too low for me. It could be I'm just going deaf, but hey?! :confused: