What do you have to do to a CD to get it to skip?

Discussion in 'Archived Threads 2001-2004' started by KeithH, Oct 6, 2002.

  1. KeithH

    KeithH Lead Actor

    Joined:
    Mar 28, 2000
    Messages:
    9,413
    Likes Received:
    0
    How badly do you have to scratch a CD to get it to skip? I bought a new CD the other day (factory-sealed), and prior to playing the disc for the first time, I noticed two pits on the play side. One is especially noticeable, though it isn't enormous. Anyway, it looks like there are two chips in the polycarbonate. I had never seen such marks on a CD before, so I thought for sure the disc would skip. To give the disc the "best chance" of skipping, or at least so I thought, I played it on my fiancee's inexpensive Sony boombox. I figured the boombox would not have the greatest tracking ability or error correction. Without getting into a debate on that issue, I will say that the disc played just fine. I am now playing the same disc on her Pioneer DV-C503 DVD changer -- so far, so good. So, what does it take to get a CD to skip? How resilient are CDs?

    On a related subject, do those "Disc Doctor" devices work? Do they really fix damaged CDs? Can they actually damage CDs?
     
  2. Stacey

    Stacey Stunt Coordinator

    Joined:
    Feb 10, 2002
    Messages:
    174
    Likes Received:
    0
    Well I've seen discs that looked like they were attacked with sandpaper and work just fine even in a "cheap" player and discs with just one seemly little scratch skip in every player.

    As for the "disc doctor" people, some are bad, some are good and some are great. I find the quality of the repair really depends on the knowledge and expertease of the person doing the work.

    I've had a disc from one inexperienced person come out looking worse than I took it in and another very experienced person (using the same type of machine) give me back a disc indestinguishable from a new one.

    If you don't know weather to trust the "scratch doctor" in your area, try visiting them when a disc is being repaired and check out their work.
     
  3. TomCW

    TomCW Second Unit

    Joined:
    Jun 4, 2002
    Messages:
    339
    Likes Received:
    0
    In my experience (although some what limited), if the disc doesn't have and 'holes' in the aluminum backing, they generally play just fine. I get a lot of pawn shop CDs, and I hold them up to the light. No holes, I buy 'em!
    Tom
     
  4. KeithH

    KeithH Lead Actor

    Joined:
    Mar 28, 2000
    Messages:
    9,413
    Likes Received:
    0
    Stacey and Tom,

    Thanks for the feedback. I played the CD in question all the way through on my fiancee's DVD player, and as with the boombox, it played just fine. Still, I will try it on a number of different player just to be sure.


    Tom,

    I have never seen a CD with a hole through it. Is that a common flaw in your experience? I don't see that happening through normal use. Is this akin to "laser rot" that some people have seen with laserdiscs? As I recall, laser rot occurs when there is a bad seal between layers (materials) on a disc. The disc then "rots" because the aluminum comes in contact with air and moisture.


    Stacey,

    The "Disc Doctor" I referred is a device that one can buy at record store, not a person. I have a number of these types of devices, but I don't know if they really work.
     
  5. Benson R

    Benson R Supporting Actor

    Joined:
    Mar 24, 2000
    Messages:
    741
    Likes Received:
    0
    I remember my professor in digital signal processing telling a story about a project WAMO asked the engineering dept to do(WAMO is a major replication factory in the same area as my school). Anyway they were supposed to check how good the error correction was by drilling a hole through a cd. I don't remember how big a hole they were able to drill but I believe it was large enough to see with the naked eye.
     
  6. Joel Fontenot

    Joel Fontenot Supporting Actor

    Joined:
    Aug 9, 1999
    Messages:
    909
    Likes Received:
    174
    Location:
    Baton Rouge, LA
    Real Name:
    Joel Fontenot
    I've had many CD's with those extremely tiny pin-prick like holes in the aluminum coating that have always played just fine. I don't know how big those holes would have to be before the player mis-tracks, but the holes I'm talking about are in about 70% of all my CD's that I've bought since 1984 and have been there since the day I bought them.
    Scratches that cause mis-tracking are usually the ones that run along the spiral of the track as opposed to ones that run more radially out from the center. That's because a scratch that runs along with the tracking of the laser can cause the laser to follow the scratch just long enough to
    lose the real track itself - and it either re-tracks from the previous rotation back in the same spot (causing the repetitive "de-de-de-de-de-de-de-de" kind of skip), or it jumps over and misses a rotation of music altogether.
    I too have seen many CD's that look like someone ran sandpaper over it and it still plays just fine. That's usually because whatever scratches that do run with the track is usually short enough for the player to recover, and the CD's built-in error checking with the player's error corrections do a good job of masking all those other missing bits.
    I'm surprised when I see such badly scuffed CD's, but those are usually from people who weren't raised on LP's [​IMG].
    Joel
     
  7. Mike Broadman

    Mike Broadman Producer

    Joined:
    Aug 24, 2001
    Messages:
    4,951
    Likes Received:
    1
    The best way to get a CD to skip in my experience is to play it in the car. This is why I use MP3s for driving.

    It is very disheartening to take out a CD, play it, and hear the skips and jumps.

    NP: Cincinitti Pops / Kings Singers, Perform Beatles Music, SACD
     
  8. TomCW

    TomCW Second Unit

    Joined:
    Jun 4, 2002
    Messages:
    339
    Likes Received:
    0
    Keith,
    The 'label' side of a CD is the most subject to damage. Even a small scratch that goes through the label will damage the aluminum (or gold on DCC) discs, causing the laser to not be reflected back to the pick-up. If these holes are big enough, the error correction can't make up the 'bad' bits and it's either a 'pop' or a 'skip'.
    You can even buy test CDs that have calibrated 'holes' punched in them so you can objectively measure your player's ability to error correct. I think www.mcmelectronics.com has one.
    In any event, it's the label side, that causes most problems, not the 'shiney' side (you can polish the 'shiney' side with Crest or any mild tooth paste and buff with a little car wax to remove minor imperfections). I always try to lay my discs down so the label is protected. DVDs are the same and some rental outfits stick a protector over the label side to keep it from being scratched.
    Tom
     
  9. MatS

    MatS Screenwriter

    Joined:
    Jan 24, 2000
    Messages:
    1,593
    Likes Received:
    0
    what Tom said,

    Contrary to what many believe, it is the label side of the disc that is the most susceptible part. Cut an unwanted cd in half or scratch off the label side with a blade and look at where the data is contained.
     
  10. Christ Reynolds

    Christ Reynolds Producer

    Joined:
    May 6, 2002
    Messages:
    3,597
    Likes Received:
    0
    Real Name:
    CJ
     
  11. KeithH

    KeithH Lead Actor

    Joined:
    Mar 28, 2000
    Messages:
    9,413
    Likes Received:
    0
    Thanks for the information, everyone. Good stuff here. Anyway, the disc in question seems to play just fine despite the couple marks. I've played it in my fiancee's boombox and DVD player and my car player, computer CD-ROM at work, and a home player. No problems here. Also, I got a used CD today with what I thought was a bad scratch that. I thought it would skip, but I played it in the car, on my computer, and on a player at home, and once again, no problem! I always knew CDs were resilient, but I am impressed! [​IMG]
     
  12. Seth_L

    Seth_L Screenwriter

    Joined:
    Apr 5, 2002
    Messages:
    1,553
    Likes Received:
    1
    Supposedly the error correction on a CD is supposed to be robust enough to be able to play through a 1/4" diameter hole. I don't believe that myself though.

    Seth
     
  13. Ted Lee

    Ted Lee Lead Actor

    Joined:
    May 8, 2001
    Messages:
    8,390
    Likes Received:
    0
    it's so nice to see that more people are aware that the label side is the side you need to protect.
    i remember the first time i was told that...i was like, no way! [​IMG] now, i have to serve my penitance (sp?) by preaching to others.
    funny this thread came up. i just pulled out an old cd i must have bought in mid 80's (new order's substance) and i looked at the disc. my gawd...the thing looks terrible. considering how anal i am with this stuff i'm really surprised to see how bad it appears. scratch and scuff marks abound. anyway, it plays fine.
    btw keith - if you really want a cd to skip, just give it a really really really good whap on the side. i'm sure you'd love to do that with your 555es! [​IMG]
     
  14. Michael St. Clair

    Joined:
    May 3, 1999
    Messages:
    6,001
    Likes Received:
    0
    If you want to make a disc a skipper without scraping the aluminum off the top, make some large concentric (not radial) scratches on the bottom with a large needle or nail.

    This will hurt the disc a lot more than drilling a hole through it.
     
  15. KeithH

    KeithH Lead Actor

    Joined:
    Mar 28, 2000
    Messages:
    9,413
    Likes Received:
    0
    Michael,
    Thanks for the "tip". This thread is taking on a sadistic tone now. [​IMG]
    Ted said:
     
  16. KeithH

    KeithH Lead Actor

    Joined:
    Mar 28, 2000
    Messages:
    9,413
    Likes Received:
    0
    This thing about "holes" in discs really has me intrigued. I have seen these in some of my older CDs, none of which skip, and I don't think they are holes through the discs. I am thinking that they are holes in the aluminum that allow light to pass through. In other words, there are holes in the aluminum, but no holes in the polycarbonate layers. In any event, I am not about to take a pin to see if it go through the discs to find out one way or the other. What I can't figure out is, how can these discs play without skipping when there are holes in the aluminum? What does the laser do when it comes across a hole?
     
  17. Michael St. Clair

    Joined:
    May 3, 1999
    Messages:
    6,001
    Likes Received:
    0
     
  18. KeithH

    KeithH Lead Actor

    Joined:
    Mar 28, 2000
    Messages:
    9,413
    Likes Received:
    0
    Michael, it is my intention to copy a few older CDs onto CD-Rs. I appreciate the tips, though. I just picked up a used copies of the London versions of Rolling Stones Hot Rocks 1 and Hot Rocks 2 (UK releases). As you may know, these discs have stereo versions of a few tracks that are not available on the old US ABCKO and new remastered versions of Hot Rocks. The London discs I bought have a few pinholes, but they play absolutely perfectly (no skips), and they sound incredible. However, I plan on copying them onto CD-Rs tomorrow and never touching the original CDs again. I don't live near the ocean, and I figure the original CDs will be safe in the jewel cases. At least I am hoping that is the case. I am wondering if the pinholes formed when the discs were manufactured. These are old CDs (1985), and the manufacturing process (QC) probably was not up to today's standards.
     
  19. Michael St. Clair

    Joined:
    May 3, 1999
    Messages:
    6,001
    Likes Received:
    0
    Keith,
    Again, I strongly advise you use Exact Audio Copy (http://www.exactaudiocopy.de/).
    You'll want to have the program auto-detect the abilities of your drive. At least the first couple of times you extract tracks, use 'Copy & Test', and make sure the checksums come out the same. Then you know you have everything set up right and you are getting the best reads you possibly can for your setup (and the discs).
    I've done this for some ancient/rare discs also.
     
  20. Kevin P

    Kevin P Screenwriter

    Joined:
    Jan 18, 1999
    Messages:
    1,439
    Likes Received:
    0
    There are actually two types of "errors" that can happen on a CD, and both can be caused by scratches or damage. One is a data error, where bits are lost or misread by the laser. CD error correction is robust enough to handle the vast majority of these errors (even a pristine CD will have many such errors). If there are too many errors for the player to correct, most players will interpolate (average the samples before and after the bad spot) to fill in the gap. Data errors can be caused by damage to either side of the disc, especially the label side.

    The other type of error is a tracking error. This is the classic "skip", where the laser jumps to another part of the disc. These are mainly caused by scratches on the shiny side of the disc, which cause the laser to be refracted away from the data it's trying to read, and when the player tries to compensate, it jumps to another spot, causing the player to skip. Mechanical shocks to the player mechanism can cause tracking errors/skips as well.

    Most problems players have with scratched discs is with tracking. However some players handle scratches much better than others, and it doesn't necessarily correspond to the cost of the player. I've seen discs with very minor scratches skip in one player, and the same disc will play fine in another. Surprisingly, the player I've used that seems most resistant to skipping is a cheap Sony boom box I've had for several years. I've put discs that skipped in higher end players and this boom box would play them perfectly, or with a click at the worst. If you have some scratched or skipping discs in your collection, next time you're CD/DVD player shopping bring them with you and try them in the players you're interested in and see which ones skip and which ones don't.

    KJP
     

Share This Page