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Why wasn't dual layer laserdisc not developed?
https://forum.lddb.com/viewtopic.php?f=32&t=6002		 Page 1 of 1
Author:  daro2096 [ 17 Jan 2016, 14:31 ]
Post subject:  Why wasn't dual layer laserdisc not developed?
Dual layer LD would have made changing disc less of an occurance so why was it never pushed?
Author:  substance [ 17 Jan 2016, 15:36 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
maybe because they barely made single layer efficiently produced. Dual layer, dual side DVDs all had issues in the early days.
Author:  je280 [ 17 Jan 2016, 19:29 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
substance wrote:
maybe because they barely made single layer efficiently produced.


Fair shout there.

By the time the pressing plants got everything sorted (mostly) any real future development had all but stopped by Pioneer & no one else was going to take up the cudgel on it as it was clear that the format had a rather limited lifespan by then therefore no money in it so it would have made no commercial sense.

Might have been an interesting development exercise though.
Author:  elahrairrah [ 17 Jan 2016, 19:36 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
From what I understand, you need a narrow band laser to be able to read two layers as in DVD and SACD.

Since all LD players outside some of the MUSE players and the CLD-1010 don't have a narrowband laser, you wouldn't be able to play a dual layer LD on 95% of LD players out there.
Author:  blam1 [ 18 Jan 2016, 00:02 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
Frankly, I think the whole thing was just beyond the technology at the time. Have to remember that DVDs, SACDs & Blu-rays are all digital mediums. LaserDisc is strictly analog. There would simply be too much signal loss in an analog domain trying to read through multiple layers. They would have had better luck moving into the digital realm, but then you've got the whole backward compatibility issue. Personally, I would have been much more accepting of a Digital LaserDisc and the huge storage capacity available over the DVD with it's limited bandwidth, resulting use of the horrible MPEG2 codec.
Author:  substance [ 18 Jan 2016, 00:49 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
Digital laserdisc didn't happen because affordable, smaller than toaster size microprocessors became available only in 1990s. They could use a room size computer to encode the mpeg compression for the master but then you would need similarly sized and mega expensive computer in your LD player to decode it.

When small and cheap microprocessors became available, narrower lasers also became available, they saw no reason to keep the size at 12", a 6" disc could hold over two hours video with higher signal ratio, twice the color and a 100 lines bump in luma resolution.

Dual layer indeed needs narrower laser, in analog domain, it could cause crosstalk. Larger surfaces are more difficult to deal with in clean room environment. Smaller discs also gave this advantage.
Author:  muzer [ 18 Jan 2016, 02:33 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
blam1 wrote:
Personally, I would have been much more accepting of a Digital LaserDisc and the huge storage capacity available over the DVD with it's limited bandwidth, resulting use of the horrible MPEG2 codec.

To be fair, though, they get around that by using high bitrates on DVDs that make MPEG2 compression artefacts not really a problem. I'm not really sure LaserDisc could have done any better, given the limitations available at the time, as you say. I mean, now we can look back and say that MPEG2 is pretty primitive (though modern compressors are pretty good by now), but at the time it was state-of-the-art.
Author:  blam1 [ 18 Jan 2016, 18:08 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
muzer wrote:
blam1 wrote:
Personally, I would have been much more accepting of a Digital LaserDisc and the huge storage capacity available over the DVD with it's limited bandwidth, resulting use of the horrible MPEG2 codec.

To be fair, though, they get around that by using high bitrates on DVDs that make MPEG2 compression artefacts not really a problem. I'm not really sure LaserDisc could have done any better, given the limitations available at the time, as you say. I mean, now we can look back and say that MPEG2 is pretty primitive (though modern compressors are pretty good by now), but at the time it was state-of-the-art.


I'll give you this, but I will add that I went into DVD kicking and screaming. I have always seen the compression artifacts, even in Sony's "Superbit" releases. I would personally much prefer the "limitations" of LaserDisc than watching the wood grain on a kitchen cupboard crawl with compression artifacts, or watch a cloud of fog either disolve into a complete blur or look like it is "alive".

I only purchased DVD because Image abandoned LaserDisc. On one hand, they promised to continue to release title on the format for 5 years, and 18 months later, they were done.

Compression is certainly better than it used to be, but for god's sake, don't stand to close to the screen during a credits scrawl with white credits on a black screen. That kind of stuff will make your eyes hurt.

I embrace Blu-ray completely, but until they find a way to perform lossless compression on the video like they've gone through great pains to do with audio, I will still miss LaserDisc to some degree. And as for the upcoming Ultra HD 4K stuff... encoding 60fps isn't necessarily the answer. Encode at 24 frames lossless and then we'll be going somewhere.
Author:  jjrclassic88 [ 14 May 2022, 16:29 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
Apologies for replying in a thread that's been dormant for 4 years. The dual-layer concept on a Laserdisc is something I've questioned before as well, since the idea for dual-layered discs had already existed in the late 60s early 70s.

1.) David Paul Gregg (a.k.a. the father of optical discs) briefly mentioned this principle in his 'transparent optical disc' patent from 1967 (the same patent that MCA purchased to develop their DiscoVision discs with Phillips):

https://patents.google.com/patent/US3430966A/en

Towards the bottom of the page, he states the feasibility of controlling a dual-sided transparent disc via the focus of the light lenses:

"In order to prevent the modulation of the light source by the recorded information on the side nearest the light source, the optical lenses of the light source are constructed so as to produce a cone of light rays converging on the bottom side of the recorded information nearest the reproducing transducer. In this manner, many bits of information are encompassed on the side nearest the light source, none are resolved, and the light intensity reaching the side to be reproduced is diminished only by an average amount equal to a large area of the lighted side, taken as a whole, together with the light attenuation provided by the diffusing layer."

He basically says that the lenses could be set in a certain position so that the data on one side of the transparent disc is read (while the other side is ignored). However he does not talk about automatically *re-positioning* the lens to read the data on the other side (like that of DVDs).

2.) Four years later in 1971, Phillips finished where Gregg left off when they filed a patent for the 'Apparatus for playing a transparent optically encoded multilayer information carrying disc':

https://patents.google.com/patent/US3999009A/en

"An apparatus for reading the information carrier is disclosed which there is inserted in the path of the read beam radiation from a source of radiation to a radiation-sensitive detection system an optical system for selectively converging the read beam on each track, whereby the tracks may be read without turning over the information carrier."

If you look at the second patent photo in the link (see below), there's a section view of a disc with each side containing two sandwiched layers of data (four layers total). Yes, the same basic design principles (later used in dual-layer DVDs), were being imagined by Phillips engineers in 1971...

I don't know what happened behind the scenes during the developmental stages of the Laserdisc. I suspect that early on, MCA/Phillips did attempt to produce a true dual-layer disc prototype with a refocusing lens, but unfortunately were not successful.

Of course, it wasn't until 1997 when the DVD finally turned that concept into a reality, despite technical problems early in their introduction...

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Author:  cplusplus [ 15 May 2022, 00:49 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
Very interesting. If I am understanding correctly, those are transmissive discs not reflective discs like LD.

Jordan Isailović briefly covers "Double-sided transmissive discs" in Videodisc and Optical Memory Systems. He mentions that indeed there would be no need to turn the disc over, but the discs are highly susceptible to damage and mentions having to house them similar to CEDs. The second patent above suggests adding a blank disc on top and bottom to prevent damage.

Isailović has a sections in Videodisc Systems: Theory & Applications where he mentions ways to increase capacity on LDs. One that stood out was removing recorded composite sync and having the player add it back. The other was reducing track pitch and laser wavelengths in the players. The latter was too expensive and not backwards compatible.
Author:  lonerangerface [ 15 May 2022, 04:45 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
From what I understand, CAV LD (30 min.) is equivalent to the single-layer DVD (4.7 GB), whereas CLV LD is equivalent to the dual-layer DVD (8.5 GB).
Author:  admin [ 15 May 2022, 21:18 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
lonerangerface wrote:
From what I understand, CAV LD (30 min.) is equivalent to the single-layer DVD (4.7 GB), whereas CLV LD is equivalent to the dual-layer DVD (8.5 GB).


I am not sure what you mean by "equivalent" but data storage version did exist and they were FAR from DVD specs.

LV-ROM (CAV) could store up to 324MB of digital information.
LD-ROM (CLV) could store up to 540MB.

It was more similar to a CD-ROM.

Julien
Author:  happycube [ 16 May 2022, 01:09 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
The digital datastream on an LD only used 1.5-1.75mhz of the disk's bandwidth (12mhz-ish), so the actual capacity would be multiplied by 6-7x, which puts CLV *somewhere* close to single-layer DVD capacity, but probably not all the way there.
Author:  jesuslovesgood [ 17 May 2022, 08:39 ]
Post subject:  Re: Why wasn't dual layer laserdisc not developed?
admin wrote:
lonerangerface wrote:
From what I understand, CAV LD (30 min.) is equivalent to the single-layer DVD (4.7 GB), whereas CLV LD is equivalent to the dual-layer DVD (8.5 GB).


I am not sure what you mean by "equivalent" but data storage version did exist and they were FAR from DVD specs.

LV-ROM (CAV) could store up to 324MB of digital information.
LD-ROM (CLV) could store up to 540MB.

It was more similar to a CD-ROM.

Julien


Pretty good Picture Quality for CLV and CAV for not a lot of MBs. I think these look like 4:3 dvds.

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