Talk:LaserDisc

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Laserdisc vs. DVD, analog vs. digital[edit]

I have once again corrected the following claim:

" The variable quality of analog media are theoretically capable of higher quality than the fixed quality of digital A/V carriers such as CD and DVD (example: ED Betamax produces over 500 lines of resolution, while DVD is commonly reported as only 480 lines by manufacturers). "

One: no, there is no inherent advantage (or disadvantage) of analog over digital, assuming that the basic specs such as analog bandwidth (resolution) and signal to noise ratio are the same. Please see Nyquist, Shannon, et al.

Two: The example given of ED betamax over DVD is irrelevant, because the basic specs are different. It is obviously possible to show opposite examples: digital media with far superior performance to analog. But if you match the basic specs, and if lossy compression is not involved, then the performance will be the same.

The LD/DVD issue is confused because lossy compression IS involved on the DVD side. But this has nothing to do with "digital media." It has to do with the storage and processing requirements of lossless-compressed video, which made it impractical to use such on a DVD-sized disc. Please, don't make this into an analog vs. digital (or head contact vs. air bearing) war. Jeh (talk) 02:21, 11 January 2008 (UTC)

You are correct. I have eliminated the phrase "analog media" and "digital media" to focus on the Laserdisc versus DVD comparison. ----- BTW digital media is not perfect. If you take into account the Kell factor (~0.8 horizontal), that reduces resolution. As does the lossy compression (which you mentioned). ---- Theaveng (talk) 13:17, 11 January 2008 (UTC)
An excellent rewording. Thank you. Jeh (talk) 00:26, 12 January 2008 (UTC)
I never said digital was "perfect", nor is perfection required here: Only that the claim of inherent superiority due to analog's "continuous" nature is unfounded. A digital signal chain with a given bandwidth (Flow, Fhigh, tolerance) and SNR will, within that tolerance, reproduce any signal that an analog chain of similar specs can reproduce - and, of course, vice versa. Jeh (talk) 00:26, 12 January 2008 (UTC)
BTW Kell factor is much more about stationary test patterns than real moving images. But even WITH Kell factor of 0.8, DVD's 720 pixels per screen width supports horizontal resolution of 432 line pairs PPH, so LD still doesn't have an edge. Then there is chroma performance, in which DVD is far superior, although again because of digital compression and 4:2:2 sampling and all that, it is different and difficult to compare directly. Nevertheless DVD can usually "resolve" details across a horizontal line that differ only in color much better than LD can. Jeh (talk) 00:26, 12 January 2008 (UTC)
A DVD at 432 lines (not pairs) would be only slightly better than laserdisc's 425 lines. If that DVD has been compressed to squeeze more video into 4.5 gigs, it's measurable resolution might fall below 400... inferior to laserdisc. (Overall the best format was actually ED Betamax with over 500 lines.) ---- Theaveng (talk) 20:33, 14 January 2008 (UTC)
Damn! I can't believe I made that "line pairs" goof! I know better, and I've even quoted the relevant part of the RS-170 specs at people who didn't believe that "tv lines" counted both the white and black lines, unlike photography's "line pairs"! Argh. Thanks for the gentle correction. Anyway, yes, very true. On the other hand, as the article states, LD performance isn't always right at the edge of the spec either. And very few images need that much detail everywhere at once -- the whole point of the compression algorithms is that they can put the bits where they're needed. And sometimes they do too much of that, or they do it too sloppily, resulting in blockies... Jeh (talk) 20:52, 14 January 2008 (UTC)
I hate blocks. On one of my DS9 dvds, there's a dark scene lit by a fire. The fire looks like it was made from orange-colored Legos instead of a natural plasma.  :-( I wish the engineer had spent more time cleaning that up. ---- Theaveng (talk) 13:03, 15 January 2008 (UTC)

One thing about ED-Beta being "better" than LD - ED-Beta's "500" lines of horizontal luminance resolution could only be maintained with super-duper clean heads - after an hour or so of playback, it would start to drop off below 400 until the heads were cleaned again - ED-Beta was INCREDIBLY sensitive to head-clogging. Also, the color resolution of ED-Beta was 40 lines MAX and often much worse - Sony originally claimed that the chroma res would be extended to 100 lines for ED-Beta but they didn't do it - S-VHS chroma sucked too. LD's chroma res was the full 120 lines for Orange-Cyan (I-Axis) colors (40 lines for RGB Q-Axis) and later Kurary, Sony DADC, and (finally!) Pioneer LDC mastered/pressed discs had 2 MHz of full RGB (not just I-Axis) chroma bandwidth - which was encoded with Faroudja's SuperNTSC system. The nasty Technidisc never bought a Faroudja encoder - their discs would have probably looked even worse if they had higher chroma bandwidth! Warner Bros WEA pressing plant started the higher chroma/luma encoding bandwagon which caused them problems when LD owners, who had their sharpness and color level controls set too high - they saw more noise and thought WEA's pressings were no good, when it was their televisions settings that had the problems. WEA was encoding 2MHz bandwidth and 450-460 lines of resolution a few years before the others started... by the time Faroudja had the SuperNTSC encoder available, WEA had shut down their LaserDisc pressing plant.

Oh, one other problem with ED-Beta and SuperVHS as compared to LaserDisc - their luma bandwidth is too high for the noise levels of the tape - in other words, they made ED-Beta and SuperVHS sharper so you could see more of the noise... in terms of the 'optimal' resolution level VS noise tradeoff, SuperBeta and Super High-Band Beta-Is were just about optimal. If JVC had set the resolution limit of S-VHS to around 300 lines or so, it would have been a much better 'match' to the noise levels of the format and a better picture would have been the result... it's amazing that neither Sony nor JVC increased the chroma bandwidth... JVC had numerous patents for VHS to expand chroma bandwidth to beyond 100 lines for all 3 colors but in a backwards compatible manner - it worked in a similar manner to the 16-bit, 48kHz digital audio extension to S-VHS that was, sadly, never allowed to be released here in the USA. It was encoded by a depth multiplex 11MHz carrier "under" the video along with the analog AFM audio.

Sorry for being so long-winded here - the LD format has been a passion of mine since we got our first player in the late 70's. I've talked to MCA DiscoVision engineers, Philips VLP engineers, have single-sided "flexible" test pressings from 1975/76, technical papers, patents, you name it... and I own every MCA DiscoVision title ever released - plus I have a new, still-in-the-box Magnavox Magnavision 8000 player bought by Bruce Springsteen on the launch day in Atlanta - he gave it as a gift and the recipient never opened it! It probably doesn't work now. Disclord (talk) 20:52, 26 December 2008 (UTC)

Fair use rationale for Image:PILF-2193.jpg[edit]

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BetacommandBot (talk) 00:57, 14 February 2008 (UTC)

Laser rot[edit]

It says in the article that a citation is needed to account for the statement on the rot of some of the early LD discs.

There is an excellent discussion mainly on this topic that took place in 2003 here: [1]

It also has one contribution from someone who has rot on his LD of the Clint Eastwood film Unforgiven issued by Warner Brothers - which dates to 1992 (which may or may not be the year of the production of his LD copy). Now this would indicate that some production plants still (1992-ish) manufactured discs that would develop laser rot in as little as 10 years, before 2003.

Not to confuse the concept laser rot with a similar defect found with some DVDs, the laser rot on LD occurs because some humidity was trapped between the sandwiched layers of the LD. While the DVD rot is a different beast, by which the discs aluminum surface is contaminated and develops corrosion. Both may render discs unplayable. Or affected audio tracks that are digital beyond listening while the analog audio track remains less affected. One of the benefits of the LD format is the level of backward compatiblity which enabled both digital and analog versions of the soundtracks on many discs. Although the NTSC format would allow for ocasional mastering of alternative audio track such as commentr on the analog audio track, it may make a film viewable one last time, or perhaps at a transfer to VHS, which - all faults aside - is a slightly more viable media, being entirely analog and not suspectible to the mares of the digital rot.

I do not know the etiquette and protocol of what constitutes a reliable source for a citation, but the discussion is made several years ago and remains quite sober and informative, and also gets around other subject of life with LD, offering an insight into the wealth of knowledge several of the contributors of the discussion has on the matter of LD.

As a newcomer to the LaserDisc format myself - I reckon have owned 8 films for less than 36 hours at time of writing as very new - reading the discussion linked to above left a very positive impact on me. Also I have owned a nice working Pioneer CLD-D515, unfortunately wo the remote, for little over half a year with no way to test it until now.

83.73.92.144 (talk) 00:21, 9 March 2008 (UTC) -Mikkel (mibm@tdcadsl.dk)

I own over 200+ LDs, and I have a good deal of minor to severe laser-rot. MGM LDs tend to get a minor degree of rot, displaying blue and red specs in weaker players (like the LaserActive models), which high-end players have no problems playing these LDs. Warner Bros. and Paramount have a good deal of rot, depending on the movie. For instance, DiscoVision version of Three Days of the Condor's sound is totally gone, as is the picture of The Shootist, and a copy of Superman II that I had to re-buy after rot totally wrecked the all of the discs. Sony-made discs are the worst. Brand new copy of Heavy Metal, and I watched it a mere two weeks later and it was totally gone, until I bought a very expensive model that takes up to two discs at the same time. The Lawnmower Man extended cut (New Line movie, but a Sony release) is also gone at the end Side B of Disc 1, and totally gone from Side C from Disc 2. So it's mostly hit and miss.

Recently, an old videophile has sold me LDs he's been storing in a shed in the middle of the Nevada desert on his property. It gets over 125 degrees in the summer in the shed, and below freezing in the shed in winter. All of his discs play just fine, and out of the 50+ movies I've bought from him, none have rot.

Just to conclude, Sony's discs have the worst cases of rot, MGM has the least cases of rot. Everybody else is in the middle. —Preceding unsigned comment added by Coffee4binky (talkcontribs) 03:56, 27 October 2008 (UTC)

ODC[edit]

"...and that company is still the world leader in optical disc mastering technology." If this is true, why isn't there even a stub for the company? I'm removing this, as it doesn't contribute to the article. —Preceding unsigned comment added by 161.165.196.84 (talk) 02:44, 11 August 2008 (UTC)

Merger proposal[edit]

I think that DiscoVision should be merged into this article cause discovison is a very small article and most of it just talks about the background of Laser/discovison and how Pioneer bought DiscoVision Associates. It should be easy to merge into the laserdisc history Speer320 (talk) 01:18, 24 October 2008 (UTC)

  • Support - As per the above stated rationale.--Kevin586 (talk) 15:17, 30 October 2008 (UTC)
  • Support - I'm all for it. 66.11.243.185 (talk) 00:15, 3 June 2009 (UTC)
  • Support - Agreed. LaserVision, LaserDisc and DiscoVision were essentially the same technology and were interchangeable. DiscoVision was not a known brand in Europe anyway.Delverie (talk) 13:28, 20 August 2009 (UTC)
  • Support - For all the reasons listed.24.190.34.219 (talk) 20:22, 27 October 2009 (UTC)
  • Support - As above. I would do this myself but I don’t have the user privileges yet. Jarl82 (talk) 18:38, 24 October 2011 (UTC)

Computer Chronicles Episode[edit]

There's an old Computer Chronicles episode that shows how LDs are made in a few video clips:

http://www.archive.org/details/computerchronicles

It's somewhere on that list.

Coffee4binky (talk) 12:20, 17 December 2008 (UTC)

Low-level format?[edit]

The article lacks any significant info on the low-level format used to physically store the signal(s) on the disk surface. Does it use the same "pits and lands" as a CD? Please add. -- 92.229.113.185 (talk) 05:07, 4 March 2009 (UTC)

Just for information, this is largely answered above, though with one or two errors. The video information is frequency modulated onto a carrier wave which is then converted from a sine wave into a square wave. The square wave can be written to the disc using a pit on the disc to represent the high level of square wave and a land to represent the low level (it would work equally well the other way around). The replay laser detects the lands which reflect the beam into a detector, appearing light, and the pits which scatter the beam and thus appear dark. The resultant recovered frequency modulated square wave can then be directly demodulated to recover the original video signal. It is not necessary to filter the square wave back to a sine wave as either can be demodulated equally well. Indeed in an analogue FM receiver, the sinusoidal carrier (at the intermediate frequency) is passed through a limiter which clips off the tops of the sine wave turning the signal ito something more closely resembling a square wave. Although the modulated square wave signal would appear, at first glance, to have inherent digital characteristics, it fails to qualify as digital because the pits and lands don't just represent 1's and 0's. The length of the pit or land is important and thus the signal is resolutely analogue. 86.180.84.186 (talk) 18:28, 15 February 2011 (UTC)
That is complete nonsense. Mainly because the signal is not frequency modulated as you claim. It is pulse width modulated (completely different). 86.144.88.101 (talk) 16:46, 26 May 2013 (UTC)
The frequency modulated carrier is pulse width modulated onto the disc. That is what was said above (though it was in a round about way). 86.171.173.14 (talk) 13:28, 21 December 2013 (UTC)

Advantage or Disadvantage?[edit]

Could someone clarify this:

"One important factor in newer DVD releases' small advancement over Laserdiscs is their opting for 16bit/44kHz sound in lieu of the DVD standard's little-known 24bit/96kHz capabilities."

It's under LD vs DVD - advantages. This statement is so confusing I don't know where to start. --Victoria h (talk) 06:39, 5 May 2009 (UTC)

I removed it. I don't know what point it was trying to make either. Lowest resolution DVD audio is 16-bit 48 kHz for starters. --Zilog Jones (talk) 20:24, 6 June 2009 (UTC)

Technical information[edit]

"All of these timing parameters are based on the NTSC standard of 29.97fps. The PAL and SECAM standards of 25fps increases the playback capacity of all the various formats by 20%."

I'm pretty sure this is wrong! While NTSC has 20% more frames per second than PAL, the latter has 20% more lines per frame than the former, so that the total bandwidth is virtually identical. Actually, since the NTSC frame rate is 30 * (1000/1001), or ~29.9700, fps, NTSC should take up ~0.1% less space than PAL, but that's only a difference of 3.6 seconds per hour.

Since I'm only about 6 hours old here on Wikipedia, I'm not going to make any changes to the actual page yet. If nobody else does it first or shows me to be wrong, I'll soon just delete the quoted sentences from the article. Since I won't be adding any content, I won't be adding any citations either. Aarons510 (talk) 07:30, 6 September 2009 (UTC)

Laser rot - A misnomer?[edit]

I read in the article that laser rot in LaserDiscs are caused by some stuff in the adhesive between the two halves of the disc. That stuff then makes its way into the aluminum layer, making it unreflective. Because the laser of the player probably has nothing to do with that problem, I suggest the name might be a misnomer. 210.4.120.4 (talk) 04:14, 15 October 2010 (UTC)

The word "rot" normally refers to organic decay -- and metals aren't organic (unless, perhaps, you're a silicon-based lifeform -- and before you jump on me, silicon isn't a metal). But the process produces holes in the reflective layer, which apparently grow larger with time. Is that not a form of "rot"? (Yes, that is a form of rot!) Calling it LaserRot is a reference to the system as a whole -- not the laser itself. If you want to get really picky about it... the term should be LaserDiscRot. WilliamSommerwerck (talk) 21:17, 13 November 2010 (UTC)

Deteriorating He-Ne Lasers[edit]

The article neglects to mention that, as helium passes easily through glass, He-Ne lasers can slowly deteriorate. Owners with this problem would remove the laser and stuff it in a helium balloon for several days. This would usually restore sufficient helium to get the laser working again. WilliamSommerwerck (talk) 21:17, 13 November 2010 (UTC)

Manufacturing Cost[edit]

The following is broadly incorrect...

"Laserdiscs were cheaper than videocassettes to manufacture, because they lack the moving parts and plastic outer shell that are necessary for VHS tapes to work, and the duplication process was much simpler. A VHS cassette has at least 14 parts including the actual tape while laserdisc has one part with five or six layers. A disc can be stamped out in a matter of seconds whereas duplicating videotape required a complex bulk tape duplication mechanism and was a time-consuming process."

Though it's true LVs could easily be stamped out, two were required for almost every recording, and they had to be carefully centered before being glued together. This largely offset any production-cost advantage. Though videocassettes had to be turned out one at time, this could be done with a bank of dozens of recorders, and the only "post-processing" required was sticking a label on the cassette. (By the way, LVs intended for use in "industrial" environments -- such as commercial video games -- were often glued to aluminum disks, to keep them from warping from the heat.)

LaserDiscs also use a different plastic than CDs and DVDs. The article doesn't discuss this, or the reason for it, though it might be better-covered in article on optical disks. WilliamSommerwerck (talk) 21:17, 13 November 2010 (UTC)

Interesting, as for the industrial LDs, was the aluminum disk portion used as the "dead side" of the disc, much like how white plastic was used for the dead side of later consumer single-sided LDs? misternuvistor (talk) 17:24, 14 November 2010 (UTC)

Disadvantages...and disadvantages.[edit]

Why are there two sections in this article about disadvantages? Somebody ought to merge them, preferably to the section right near the Advantages. 76.19.4.2 (talk) 01:23, 16 January 2011 (UTC)

One is disadvantages compared to VHS and the other is disadvantages compared to DVD. The article is messy, though, and anyone is more than welcome to try to clean it up.--Jorfer (talk) 05:05, 16 January 2011 (UTC)
I have merged the two disadvantages sections under a common heading. Jarl82 (talk) 18:36, 24 October 2011 (UTC)

There is a substantial amount of repetition throughout the article like: the audio formats supported, crosstalk, time of a CAV/CLV disc etc. This article is very disjointed and needs a common tone applying to it. A one person gentle and conservative edit? I would also suggest a tidy up of this discussion page too. Swapshop1 (talk) 23:53, 22 April 2011 (UTC)

I have begun to clean up the article to remove redundant information and make the tone more consistent. Jarl82 (talk) 18:36, 24 October 2011 (UTC)

Squiggly lines[edit]

Since 2004, I've noticed many of my LaserDiscs, made at least since 1993, are starting to get these "squiggly lines". I can't find any information on the Internet about these occurring on other LDs, but I have many, many movies with these problems. It could damage caused by extreme temp. variations, or discs being stacked. I don't know. Apple8800 (talk) 19:49, 8 February 2011 (UTC)

If you are storing your discs stacked they could be getting warped causing poor tracking. Ideally you should store them vertically. Jarl82 (talk) 23:51, 25 September 2011 (UTC)

Length of LD track[edit]

Does anyone know exactly how long is the track of a laserdisc? After doing a little math, my calculations appear to suggest 31 miles (49 km). However, I'm not sure if this is accurate. 119.93.67.178 (talk) 13:05, 12 February 2011 (UTC)

I make it 21.25 miles. (for a CAV 525 line disc playing for 30 minutes). 86.180.84.186 (talk) 18:33, 15 February 2011 (UTC)

Need for Editing[edit]

There is a need for this article to be edited and cleaned up as the LD format retreats further into the past I see a need for a clearer and more concise article that is less an omnibus with so many technical particulars and more a good general overview for readers. Currently, some sections read too much like a technical manual. Anyone have some ideas or suggestions? I also see the potential to split off a lot of the content from some sections into new articles. Jarl82 (talk) 23:49, 25 September 2011 (UTC)

Following from my original call for action I have made some initial changes to this article to start the process. I’ve cleaned up the Introduction and worked primarily on improving the Comparison to Other Formats section as I think this would be of particular interest to readers unfamiliar with LD. Previously this was split into VHS and DVD sections and I’ve merged this into one section with subsections for VHS, DVD, Advantages and Disadvantages. I also removed the former Comparison to other media section as it was overly technical listing resolution information that is easily found elsewhere without adding much to the article. I added a link to the relevent section of the video resolution wiki article in place of this section. I also removed the video game information from the Advantages subsection as there is covered elsewhere in the article under Variations and I edited the computer game information in this section. Any reactions or comments on these edits? Suggestions for further improvements? Jarl82 (talk) 18:32, 24 October 2011 (UTC)

Requested move[edit]

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was: not moved -- JHunterJ (talk) 02:05, 2 May 2012 (UTC)


LaserdiscLaserDisc – Consistency with pretty much every other CamelCase term in this place. If that's false, it needs to be corrected. Despatche (talk) 21:10, 24 April 2012 (UTC) Orig. time stamp 11:55, 24 April 2012 (UTC)

  • Oppose. From this n-gram it would appear that the CamelCase variant is less common than the current one. Favonian (talk) 21:10, 24 April 2012 (UTC)
  • Oppose. There is little evidence of consistency in usage out there. Favonian's ngram report is useful; this expanded one shows even more diversity and uncertainty, with camel case relegated to a very low position. Several of the external links for the article show internal inconsistency. This Googlebooks search, restricted to 21st century, gives further evidence of diversity. In such cases Wikipedia's preference for plain vanilla styling (see WP:MOSCAPS, and WP:MOSTM) resolves the matter simply and efficiently. NoeticaTea? 23:08, 24 April 2012 (UTC)
  • Comment - I'm going to use {{correct title}} right now. Therefore, you can decide whether it is right or now. --George Ho (talk) 19:39, 25 April 2012 (UTC)
    • Never mind, I must have misused it and realize it is intended for technical restrictions. --George Ho (talk) 19:45, 25 April 2012 (UTC)
The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Reverted[edit]

I just reverted a number of edits that were changing the spelling from Laserdisc to Laser Disc. The editor also uploaded his own artwork showing the different spelling, but I'm pretty sure that can't "prove" the spelling itself. I don't actually edit here, so uninvolved, but reverted solely because it was such a huge change from the consensus version and it looked incorrect, and under the spirit of WP:BRD, feel like now a discussion should take place. Dennis Brown - © 00:59, 19 May 2012 (UTC)

Encoding details? Picture formats?[edit]

The article woule benefit from a bit more technical details about the used encoding, similar to what can be found in the VHS article. How do you even record an analog signal using pits and lands? Does it use "color under" with the subcarrier recreated by the player, like VHS? Does it use FM? How is digital audio stored inside an analog video track? Does LD use specific frequency bands for color, luma and audio just like VHS? How is the motor speed regulated? Etc.

Also, what picture formats were common on LD? Were there anamorphic discs? Or was it mostly either 4:3? and if so, what was more common, pan&scan or letterboxing? Thanks! -- 92.226.3.37 (talk) 17:10, 26 July 2012 (UTC)

Spelling[edit]

The logo clearly reads "LaserDisc" as one word, with a capital L and a capital D. All occurrences of "laser disc", "laserdisc" and "Laserdisc" should therefore be corrected, in my opinion. 78.22.96.22 (talk) 15:07, 12 August 2012 (UTC)

"Binary Nature"[edit]

I hate to be that pedant everybody gets tired of, but I think describing laserdisc as being encoded in a "binary nature" ("although the encoding is of a binary nature...") is sort of inaccurate. The pits and lands do represent on/off and there's only two states, but they're not numeric, which I believe would be required to consider it to be "of a binary nature". Perhaps a more accurate way to phrase it would be "although the encoding does rely on pits and lands to represent states of 'on' and 'off' much like the binary encoding required for digital media" or something similar? I just don't think you can call something binary unless it's representing numbers in a base 2 manner.Cmactaggart (talk) 19:23, 26 August 2013 (UTC)

I just reread the above and realized that I must have been sick or something because that doesn't make any sense. I retract the above. Cmactaggart (talk) 17:23, 28 April 2014 (UTC)

Spiral Track Length[edit]

The page claims "The spiral track of a LaserDisc is 42 miles (67 km) long." This number is uncited.

I'm very confused about this number because there is a similar number given on the compact disc page: "The program area is 86.05 cm2 and the length of the recordable spiral is (86.05 cm2 / 1.6 µm) = 5.38 km."

Why does this bother me? Well, I can't find a precise number for the track width on a LaserDisc but everything I have found says that it's about the same as a CD. I don't know the program area either, but as an absolute upper bound it certainly can't be more than the physical area of a LaserDisc. So if we apply the same calculation on the CD page in reverse to the LaserDisc track length that implies a "program area" of 1072 sq. cm. A 30cm disc is only 900 sq. cm and that's before subtracting out the inner, unnused area. It's a completely unrealistic overestimate of the available program area yet apparently the LaserDisc's program area is even larger than that...

So there are a couple possibilities: 1. The track width in LaserDisc is smaller than for CDs by a non-negligable factor. I have not been able to figure out what this number is for LaserDisc, but everything I have seen says it's "about the same" as CD so I don't think this is the most likely explanation. 2. The calculation used on the CD page is wrong and the CD spiral length is more than 5.38 km. True this is a simplistic calculation that treats the data more like a series of annuli than a true spiral, but as far as I can tell that ought to be a fairly negligable difference. 3. The 67 km number is wrong. I can't find a source for this number, that's what I'm most suspicious about.

I actually have a textbook about this. It verifies that the "average track pitch" is 1.6 µm. I could not find any calculation for the length of the spiral track, but agree that 67 km seems long for the reasons you state. The length I calculate for LD is about half that; perhaps the writer intended this for a double-sided disc? Anyway, without a citation we can't verify the claim, so I think it's fine to get rid of it. Fnordware (talk) 21:54, 28 April 2014 (UTC)