Talk:LaserDisc/Archive 2

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Archive 1 Archive 2 Archive 3

Accessing analog LD tracks

Hello and Help !! I have two perfectly working philips vlp-700 Laserdisc players (these are part of my classic AV collection) which I’v restored. I have a few discs which play no sound as they are Dolby Digital (all I get is a hiss both L&R) I know the players are analogue only. I know that somewhere on the discs is a Mono analogue signal. anyone know if this signal will be present outside the realms of the laser detection components. If so can it be taped into to get the mono sound track at any quality ? Any advice would be great. Regards Steve

Well, most newer LD releases always have at least one analog track available for playback (either the film's soundtrack itself, or a director's commentary on some discs), which is usually one of the analog stereo tracks (usually the Right channel, IIRC), for compatibility & playback on older players like your VLP-700s. (with the other analog track, usually the Left channel, being a modulated Dolby Digital stream). So, it should be accessible by your player. Is there is a control on your remote for the player (if it has one) to select the audio track to be played? My Pioneer CLD-1010 can be switched to play back either the Left or Right track by itself "duplicated" in both L&R channels. Maybe your player behaves in the same way? misternuvistor 19:29, 10 December 2005 (UTC)
Also another issue: if I'm not mistaken, the VLP-700 is a PAL-standard player, right? If so, this might explain things a bit more: PAL standard LDs only have one pair of audio tracks available (analog only for older LDs, and digital only for newer PAL LDs), while NTSC discs have 2 pairs (4 in all) of audio tracks (one pair analog, the other pair digital). This is because PAL video takes up slightly more bandwidth than NTSC on an LD, resulting in only enough bandwidth leftover on a PAL LD for only one pair of audio tracks. So, the only solution there would be only to play older analog-soundtrack PAL discs, that is, if your VLP-700s are PAL players. misternuvistor 21:28, 11 December 2005 (UTC)

WORM?

Just being a stickler for accuracy here, but first, notice that the following line is apparently missing the first part of the parenthesis: CRV discs existed as both pre-recorded releases and also as blank media that could be recorded once WORM, like CD-R) on each side.

Now, as for the reference to WORM. Technically, "CD-R" discs are not WORM technology in that they can only be written to once. If the CRV discs are truly "like CD-R discs" and can only be written to once, then the WORM reference should be removed. However, if the CRV discs are truly WORM technology, then the reference to CD-R should be removed.

Just my $0.02. Thanks.

--Gregg

Actually, WORM means "Write Once, Read Many", so CD-Rs are a WORM system. The WORM reference here would thus not be incorrect, but the phrasing is redundant.

--Scott

Duh. I think it's funny when he said, "CD-R discs are not WORM technology in that they can only be written to once." That's like saying, "CD-R discs are not Write-Once; Read-Many technology in that they can only be written to once." Ha. Thanks for making me laugh. - Theaveng 15:48, 11 October 2007 (UTC)
Gregg Scott Theaveng's right. Yeah, try saying that without larfing ;) CD-R does allow for writing multiple times. - When you do not close the session but leave it open to finish later. This is not recommended! - When you are making a multiple session disc. Where each session is closed and an updated filetable is written to the disc. - I had a job that weekly entailed a procedure of performing incremental backups using a Philips 2x writable drive (this weekly ritual became my Coffee Fetching & Consumption procedure.) At any rate a CD-R will always remain readable many times, until the disc becomes unreadable .... such as from scratches made by the unglazed bottom ring of a...... coffee cup! --Mikkel (mibm@tdcadsl.dk) 83.73.92.144 (talk) 00:56, 9 March 2008 (UTC)
It's true that you can write, say, one-quarter of a CD-R but once you've done that, it can't be changed. That first one-quarter of the CD-R is done. You can't go back and change the data, as you can with a floppy or flash drive. Hence the term "write once" versus a floppy which would be "write many". ---- Theaveng (talk) 12:08, 10 March 2008 (UTC)

Not sure if it is relevant, but in 1989 and 1990, when I worked for Interactive Information Systems (in UK) we used WORM disks for developing interactive video computer-based training material. (A computer program managed user interaction and displayed video sequences and stills depending on the user's input.) WORM disks were available for programmers like me to use before the production discs became available. (I assume they were cheaper or quicker to create than the final laserdiscs.) The WORM discs were a sandwich of two layers with an air gap in the middle. (No idea why.) Unlike standard laserdiscs, you had to store them vertically or they might not work. (Again, no idea why.) So you could not risk leaving them overnight in the laserdisc player, for example. —Preceding unsigned comment added by Everhard (talkcontribs) 00:01, 21 January 2010 (UTC) --Everhard (talk) 09:38, 22 January 2010 (UTC)

"Pre-recorded CRVdisc releases"...

I've removed the reference in this article to pre-recorded CRVdiscs, since this seems doubtful, due to not finding any info about such on the internet via Google (save for mirrored Wikipedia pages). Plus, CRVdisc was not marketed to the consumer, it was mainly a professional/industrial product due to it's high cost. So having pre-recorded CRVdiscs available (as if CRVdisc were a consumer product, which it was not) would seem a bit dubious, IMHO. misternuvistor 21:47, 11 December 2005 (UTC)

CRV...

I have also removed the CRV reference in the second paragraph:("Sales began on December 15, 1978 after the earlier CRV (Component Recordable Video) disc format had died out in obscurity."). AFAIK, there never was a "CRV" videodisc format that existed before DiscoVision/Laserdisc. There was the earlier prototype laserdisc system that MCA Disco-Vision introduced in 1972 at a press-showing that was referred to as the ROVS (Reflective Optical Videodisc System) that would later become the DiscoVision/LD format, but it was never referred to as CRV (and it wasn't recordable as that TLA implies), from my knowledge and research on the internet and elsewhere (especially here [1], a page about DiscoVision's history). Of course, there is the CRVdisc format developed by Sony (as I have mentioned about earlier in this talk page), but this was developed in the 1980s, long after DiscoVision/Laserdisc was released. misternuvistor 08:47, 13 December 2005 (UTC)

Recordable laserdiscs.....

I am removing the passage in the 2nd paragraph in the "Success of the format" section concerning recordable LDs ("Nonetheless, the recordable Laserdisc format was kept off the market to prevent high quality copying"), because of it's vagueness (which recordable LD format?), and due to the fact that there wasn't a recordable LD format that ever was "kept off the market" to begin with. Sure, there were recordable formats allright (such as CRVdisc and Recordable Laservision (RLV)), but they were simply too specialized, and too expensive to manufacture to ever be even thought of being marketed as a consumer format, only at a more professional/industrial market that could afford it (the cost to manufacture any recordable optical disc format in the 1980s heyday of the LD was simply quite high, due to it being such an very new technology). I don't think piracy was the reason.

I'm also removing the phrase "recording-capable units were not sold to the general public due to pressure from the film industry" in the 4th paragraph of the "Laserdisc vs. VHS" section, because once again, they were not sold to the public due to their high cost of manufacturing them instead, due in turn to being such an extremely new technology (recordable discs like RLV and CRVdisc, that is). It had nothing to do with piracy, or the film industry (I'm sure the film industry didn't pay too much attention to LD to begin with. They had bigger fish to fry, namely VHS and Betamax :) ). misternuvistor 01:58, 23 January 2006 (UTC)

I'm adding this back with more neutral phrasing, you two's objections of my lacking any evidence for sinister motives on the part of content providers and equipment manufacturers are neatly counterbalanced by the fact that you lack any evidence of recordable laserdiscs being inherently expensive at the time. Instead, all you can produce are dubious price extrapolations from the cost of recordable LD technology and media's microscopic production runs of the time, and vague statements of "it was really new!" (as if Laserdiscs themselves weren't at first :-p).
Whether or not you believe recordable LDs would have succeeded in the marketplace, the entire article should at least avoid contradicting their very existence and ignoring the possibility of their success. 207.177.231.9 16:44, 20 July 2007 (UTC)

Basic Specifications

How about a list of some basic specifications, in a simple form, with things like when it came out, how much they hold, etc. --202.164.193.221 21:13, 1 March 2006 (UTC)

I am going to get to that sooner or later, but sometime within the next five days within the date of this posting. As informative as the article is, with the introduction of the "CAA" information several walls of text need to be broken into subsections and other discrete subcatagories within the article. In gerneral, its time to clean-up this article.
The section most in need is "technical specicfication" which I plan to modify by adding software and hardware subsections. I will encourage other, more knowledgeable people to add subsections to "success of the format" as well as its comparisions with completing formats during its existance.--Caesius 22:23, 1 March 2006 (UTC)

Transparent vs. Reflective mode?

"By 1969 Philips had developed a videodisc in reflective mode, which has great advantages over the transparent mode" -- such as?

What are these two modes? It's never explained. —The preceding unsigned comment was added by Navstar (talkcontribs) 19:59, April 16, 2006 (UTC)

I would assume this means how the disc operates. But I've never ever heard of a transparent mode disc. All discs are reflective... Nil Einne 14:37, 12 October 2006 (UTC)
The Laserfilm system was transparent. The advantage of the reflective disc is that it can have two playable sides, the transparent disc has only one. --Blainster 08:02, 29 December 2006 (UTC)

The "original" design of the LaserDisc actually recorded each film frame as an optical image on the disk, which would presumably be scanned in playback by a flying-spot system. At some point, someone realized it would be much more efficient to record the video signal itself. The article doesn't make it clear when this occurred, or who thought of it. WilliamSommerwerck (talk) 20:55, 13 November 2010 (UTC)

LD pressing

"both players and software are no longer produced"

Certainly not in the US, however, I have read somwhere that the is at least one place in the world where LDs are still being pressed. Since they were still being pressed in the late 1990s, and that the pressing facilitys would have been comercialy availible, there surely must still be some surviving (if not operational) pressing equipment somewhere.203.214.75.127

Unfortunately, the article is correct in regards to both hardware and software no longer produced. I have no idea as when the last Laserdisc player was made but laserdisc production ended sometime in 2001 in Japan and facilties were converted to DVD production. By several credible accounts, Japan was the last hold out in Laserdisc support.
With the end of support and major financial investment in the machinery of Laserdisc production, I believe it all to be moth balled in the warehouses of these major corporations.--Caesius 17:22, 6 January 2006 (UTC)

Which came first?

Something just struck me while reading the "audio" section of this article: which was offered to the public first, a Digital Audio Compact Disc or a LaserDisc with digital audio tracks?--Kenn Caesius 15:30, 23 June 2006 (UTC)

Well, AFAIK, commercially (and with the exception of the PCM adaptors which came out shortly beforehand, which were more of a prosumer-market technology then), Compact Disc was the first digital audio format available to the public in 1982 staring in Asia, however, Sony, Philips and DiscoVision (along with Pioneer) did develop some experimental digital audio formats in the late 70's using LaserDisc. These experiments used the whole video bandwidth of the disc (much like how the previously-mentioned PCM adaptors operated wih videotape), instead of a more efficient separate FM-modulated subcarrier (containing PCM audio data) riding alonside the analog video and audio carriers, which what all commercially-released LDs with digital audio tracks (aka, discs & players with the "Digital Sound" logo) like you mentioned, use. Sony and Philips referred to this early experimental format as a DAD (Digital Audio Disc), (IIRC, don't quote me on that), and their work on this format (which never made it out to the market) formed the foundation for the development of the Compact Disc later on.
The first laserdisc player to have "Digital Sound" capability (as well as the first LD player to have audio CD playback capability) was released by Pioneer in 1984, 2 years after the introduction of CD (I forget which model number, I think it was a CLD-series player, though).
Here's a link to a page mentioning one of these prototypical LD-based "DAD"-type discs, this one developed by Pioneer & DiscoVision... misternuvistor 07:03, 26 June 2006 (UTC)
I think the nomenclature gives it away. Compact is a relative word, as CDs are bigger than the cassettes they replaced, so they were likely comparing the "compact disc" to a bigger optical disc. Ham Pastrami 05:12, 31 May 2007 (UTC)

The Last Laserdisc

As a useful trivia point, I think it would be good to mention the last movie released on laserdisc. Does anyone know what it is? -Litefantastic 20:55, 5 July 2006 (UTC)

Such information is already mentioned in the "History" section of the article.--Kenn Caesius 02:30, 6 July 2006 (UTC)

removed Twin Peaks

The version of the Twin Peaks pilot that existed on LD was not in fact the version aired in the States, but the "movie" version produced in case the show failed to air in the UK. Since this is an obscure, secondary version of the pilot and not the one sought by fans, it sort of seems less relevant (than as written) so I removed the mention entirely.24.33.28.52 20:02, 14 July 2006 (UTC)

Storage Capacity math

Since a normal CAV 12" disc can hold 54,000 still images, would that add up to 47GB of storage? (640 × 480 × 24bitRGB = 900KB) × 54,000 frames = 48600000KB / 1024 KB per 1MB = 47460MB = 46GB

--Navstar 06:38, 1 September 2006 (UTC)

Not quite. The signal to noise ratio isn't good enough to support 24 bits per pixel - plus the Hf response isn't great - additionally the color carrier only has a response of 1/4 the resolution. Basically you end up with:
video = (assuming approx 4 Mhz bandwidth) at 6 bits resolution = 3 megabytes a second or 100 k a frame x 54,000 = 5.4 gigabytes
audio = 275 megabytes (digital audio tracks) + 170 megabytes (encode DD on both analogue tracks)
Total is = 5845 megabytes.
Although you could probably cut that by 50% once you included any error correction to cope with drop outs / noise on the video track. A laserdisc size DVD would be much more interesting. Megapixie 07:01, 1 September 2006 (UTC)
How about laserdisc-sized Blu-ray Disc? On a later note does anyone know the capacity of these disks? Like 1 GB or something? Thanks in advance. Josh215 20:40, 12 March 2007 (UTC)

I feel the need to mention, just in case anyone is unclear, that LaserDiscs are analog. Their video is also completely uncompressed. Try recording 30 minutes of uncompressed video onto a computer and see what that gets you (it varies a bit, but still). I'll just say it's a lot more than 5845 megabytes. Point is, you can't accurately compare analog and digital storage. They're too different.

Laserdiscs and Super VHS tapes have a lot of commonalities. They store better-than-broadcast quality video, with a bandwidth of 0 to 7 megahertz. That said, when you use a Super VHS tape to store ADAT (digital audio) or Digital VHS video, you get about 12 gigabytes per hour of tape, and I suspect if laserdisc was somehow converted to store digital information, you'd get the same amount... around 12 GB per hour (per side). ----- Of course since laserdiscs are not digital, but analog, you'd have to use some kind of modulation (representing bits with sounds). - Theaveng 15:50, 11 October 2007 (UTC)

The ONLY specification of Super-VHS that is "better than broadcast" is luminance resolution - in EVERY other measure, Chroma resolution, noise, time-base stability, etc, S-VHS is vastly inferior. Ty Chamberlain (talk) 18:08, 18 July 2010 (UTC)

Market

Could someone try and write a section (or at least a few sentences in the introduction) on the international market for Laser Discs - I've never even heard of them before! Rogwan 21:19, 10 April 2007 (UTC)

No mention of Karaoke?

To my knowledge, Karaoke was the real impetus for adoption of the Laserdisc, primarily in Japan and as something of a fad in North America. Nearly every Laserdisc player has microphone inputs for this reason, a feature rarely found on commodity VHS or DVD players. The article doesn't seem to make any mention of Karaoke though. Ham Pastrami 10:05, 29 May 2007 (UTC)

Luminance Bandwidth??

I have looked and looked and looked, but I can not find a source to answer that simple question. Is it 5 megahertz? Someone should add the answer to the article, if it's available. - Theaveng 12:45, 10 October 2007 (UTC)

I don't know the exact bandwidth, but I think it is 5MHz in the NTSC version. This is slightly wider than the 4.2MHz broadcast standard.

VHS vs. LD, "air bearing", etc.

Although there is indeed an air bearing in normal operation, this (along with tape tension) is far from perfectly maintained and there is some contact, particularly during spin-up and spin-down times. Furthermore there is no air bearing at all on the control head as it is not on the drum... please note that the article does not specify "spinning", hence this is a valid interpretation. Additional details on the fine points of VHS machines really belong in the VHS article, not here. Jeh (talk) 15:51, 20 November 2007 (UTC)

The tape is not in contact with the drum when it is spun-up or spun-down. The drum starts spinning first. And then the tape is threaded around it second, so the air bearing is always present. ----- As for the control head, it would have some minor contact on the tape edge. That's true. But it would not degrade the actual picture. ----- As for these details not being in this article, my main concern was to get the facts straight. No point in making the LD v. VHS comparison if the comparison is invalid (i.e. claiming the playback/record heads rub the tape). - Theaveng (talk) 16:55, 20 November 2007 (UTC)
The control head contacts the tape across its full width. There are only gaps on the edge, true, but the width of the head unit (like that of all of the rollers, etc.) is that of the entire tape, so there is contact (scraping!) across the full width. And yes, the heads on the drum do contact the tape at times. If not, then why is cleaning sometimes necessary to remove shedded oxide from the gap? Jeh (talk) 17:59, 20 November 2007 (UTC)
Cleaning? What's that? I've never needed to clean my Super VHS vcr; just because they sell such items in stores does not mean you "need" them. They also sell undercoat protection at stealerships, which is totally un-necessary (the manufacturer already undercoated the car in the factory). But you make a good point about how the control head scrapes the tape as it crawls past, which is something I had not considered. - Theaveng (talk) 21:25, 20 November 2007 (UTC)
Yes, the cleaning TAPES are useless. That doesn't mean cleaning is useless. Any decent tech will manually clean (with swabs and similar materials) the tape path and heads of any machine entering the shop. They're going to play very expensive alignment tapes on the machine and they can't risk gumming up those tapes with the residue that might be on your machine. Jeh (talk) 17:43, 21 November 2007 (UTC)
Ah, I did a bit more research (I called a friend who's a master VCR tech). It's worse than I thought, and much worse than you thought. The air bearing does exist... but it's there to prevent contact between the tape and the overall surface of the drum, which otherwise would result in very high friction. The tips of the heads however protrude slightly from the spinning drum diameter and are in "intimate" contact with the tape AT ALL TIMES during normal operation. If they weren't, not only would they not need cleaning, they also would not wear out. But, they do, and they do, and they do wear into the tape surface.... so, there was no "making up lies" here. Jeh (talk) 18:21, 20 November 2007 (UTC)
And I might as well add that degradation of the control track most certainly CAN degrade the picture. The control track is where V sync comes from. If it's too weak the TV will never achieve vertical sync and the picture will roll forever. I suggest this definitely counts as degradation. Incidently this concept is not new with VHS. Way back when I was working with Ampex 2-inch quad machines, one of the adjustments was the head "tip"... how much the heads protruded and thereby how much they contact the tape. More "tip" meant better PQ but faster head wear. Jeh (talk) 18:31, 20 November 2007 (UTC)
My VCR makes it's own V-sync to stabilize tapes (and also live TV channels).
Yeah, I have a pro machine with so-called TBC too. It will stabilize the sync. It can't generate it from nothing. Jeh (talk) 17:43, 21 November 2007 (UTC)
Actually TBCs *do* generate sync. That's one of their primary functions. - Theaveng (talk) 20:46, 21 November 2007 (UTC)
A TBC cannot generate V-sync from nothing. Well, it could, but the result would be wrong 524 out of 525 attempts. The TBC circuit in such VCRs cleans up and stabilizes the signal from the source. Jeh (talk) 00:57, 22 November 2007 (UTC)
Anyway. If your master tech says the VCR heads scrape the tape, then I guess we have to trust his judgment, but I still have my doubts he really knows what he's talking about. (Translation: I want to see a citation that the play heads touch the tape.) I've torn-apart VCRs and the heads are flush with the surface of the drum. Plus: I'm still using a tape that I bought in 1985 with my first VCR & use as a semi-daily time shifter... I don't see any visible "scrapes" on the surface of the tape even after thousands of uses. If the master tech was correct, I should be seeing lines streaking across the tape; and I don't. - Theaveng (talk) 21:25, 20 November 2007 (UTC)
Well, here's one citation:

http://www.patentstorm.us/patents/5543990-description.html - "The configuration of projecting portions of the head tips, and the curvature thereof in a direction transverse to the tracks are optimized for uniform contact with the magnetic tape."

And another: http://www.freepatentsonline.com/5543990.html - "The head tips are held in good sliding contact with the magnetic tape for better recording and reproducing characteristics."

and another: http://www.sparkysworld.co.uk/vcrs.htm - "Placing the gap in contact with the sensitive surface of the tape causes the magnetism to be transferred to it."

and another: http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel1/20/4499/00179555.pdf - "VHS-VCR requires a tape having an MD stiffness of more than 250 mg in order to establish an optimum head-to-tape contact ."

I think that should do... Jeh (talk) 17:45, 21 November 2007 (UTC)

I am nonplussed at your edit to the article after I gave here the citations to the contrary that you asked for. This does not seem like a good faith effort on your part. Come now, be a man and admit you were wrong. Jeh (talk) 00:57, 22 November 2007 (UTC)