If a compact disc is really scratched up does this affect sound?

Discussion in 'Audio Hardware' started by ATSMUSIC, Nov 24, 2007.

  1. ATSMUSIC

    ATSMUSIC Well-Known Member

    Location:
    MD, USA
    I am asking because I have a few discs that play all the way through but I am thinking it is making the error correction work much harder. I don't know allot about this but am curious if anyone knows if this has an effect on sound quality.
  2. Metralla

    Metralla Joined Jan 13, 2002

    Location:
    San Jose, CA
    The error correction mechanism should be able to reassemble the data needed to drive the DAC. If it cannot, it will try to interpolate. If it cannot do that, it will mute the output momentarily.

    Scratches don't really affect the sound quality, although if you are getting a lot of interpolation, you may be able to detect that it does not sound as good. We are talking about a pretty extreme case though.
  3. EdipisReks

    EdipisReks New Member

    Location:
    Cincinnati, Ohio
    in my experience, as long as it doesn't skip, it sounds just fine.
  4. ATSMUSIC

    ATSMUSIC Well-Known Member

    Location:
    MD, USA
    sounds just fine isn't good enough for me :)

    Can anyone point me to any articles about this or other threads? I have a few discs that I am wondering if I should replace or not because they are really scratched but no skips. I ahve a feeling I might be wasting my money and time though but it has been bothering me.
  5. Jae

    Jae Forum Resident

    You're not alone there. I just spent a few hundred dollars replacing scratched CDs because I was worried about the effects of error correction, even though they sounded fine (it was just EAC that got upset).

    A waste of money? Perhaps. But hopefully someone here can answer that for sure...
  6. Mal

    Mal Phorum Physicist

    Location:
    Brighton, England
    Replace the worst offender in your collection and compare the sound of the mint disc with the scratched up one. If you can't hear a difference then don't worry about replacing the rest :righton:

    I used to worry about it but eventually decided I can't hear a difference as long as skipping wasn't occuring.

    Nowadays I rip my CDs to a HDD and listen by streaming the data to the Squeezebox (see here) - that way I no longer need to even think about damaged CDs. If they ripped in EAC OK then the correct data is on the HDD. You can even rescue discs that skip on CD players this way :)
  7. Joseph

    Joseph Active Member

    Location:
    Toronto, Canada
    If the disc is rare wouldn't copying to cdr eliminate the error correction issue?
  8. 3db

    3db New Member

    Location:
    Ontario Canada
    I wouldn't think so because error dection is still being used to read the data off the disc.
  9. Ski Bum

    Ski Bum Active Member

    Location:
    Long Island, NY
    :agree: This is the only way to truly persuade yourself of the result. (I don't think you'll hear a difference.)
  10. MikeyH

    MikeyH Stamper King

    Location:
    Berkeley, CA
    When you copy, you do get all the disc data. The reading mechanism is not the same (software processing wise) as the normal playing in a CD player.

    The reader should tell you if there were any errors significant enough to cause data loss. I can do a read test on my computer, and discs that 'skip' don't ever pass this. I haven't played with trying to copy them yet. Only one (a UK Wish You Were Here) is worth doing anything with. I would expect that once I got a clean read I could burn a perfect disc. If the read had noise, I'd expect the copy to have the same noise of course.
  11. tommy-thewho

    tommy-thewho Forum Resident

    Location:
    detroit, mi
    I have some very badly scratched disks that play great. I wouldn't think of replacing them till they start skipping...
  12. Dragun

    Dragun Member

    Location:
    Dallas, TX
    A local used CD store sells their somewhat scratched CDs for a little less than their other CDs. I've bought one or two of these and they sound just fine.
  13. ATSMUSIC

    ATSMUSIC Well-Known Member

    Location:
    MD, USA
    I think this is what I have to do. Unfortuantly the most scratched cd is a rough trade smiths self titled that I bought off ebay in excellent condition :sigh: so no too sure how much this one will cost to replace. I am guessing around 40 bucks.
  14. RDK

    RDK Active Member

    Location:
    Los Angeles, CA
  15. ATSMUSIC

    ATSMUSIC Well-Known Member

    Location:
    MD, USA
    I'm sure there was some point to this post but I don't get it :confused: :)
  16. kevinsinnott

    kevinsinnott Forum Coffeeologist

    Location:
    Chicago, IL USA
    There are scratch removal solutions sold. I've never really used one. I think, assuming I understand how CDs work, that the scratch, presumably, is on the protective plastic. These solutions fill those scratches, restoring the plastic to transparency. Does anyone know if these solutions work?

    It might save excessively scratched CDs.
  17. stereoptic

    stereoptic Anaglyphic GORT Staff

    Location:
    NY
    that's the answer! EAC will prove to you that the data that is playing is identical to the data stored on the CD. You can then listen freely without having that thought in the back of your head.
  18. Dave W S

    Dave W S New Member


    Yes, I do this whenever I happen to buy a used disc that looks overly scratched.

    I like this too, better yet, rip the mint disc and compare it to your ripped scratched disc, if they are bit-identical then definitely don't worry about it ever again- life's too short to waste time if there's no need! Now every now and then you'll get a really banged up disc and you might feel the need to check.
  19. RDK

    RDK Active Member

    Location:
    Los Angeles, CA
    Yeah, I had more to say but figured I'd just ruffle some feathers and be gorted... so why bother?

    In short, if you can't hear any difference and/or degradation in sound quality, then it's foolish to replace your discs. I'd rather save my money for a good shrink.
  20. SysteX

    SysteX New Member

    Location:
    Boston, MA
    CDs use two concatenated Reed-Solomon codes (alternating with interleaved bit blocks). The data blocks are originally 32 bytes long. First, the data is deinterleaved, then it is fed to a (32,28) R-S code that can handle up to 2-byte errors. This leaves us with 28 byte blocks. The data is then again deinterleaved and fed this time to a (28,24) R-S code that can handle up to 4-byte erasures (an erasure is when a data bit is known to be incorrect; the R-S codes can handle twice as many erasures--known bad bits--than it can handle errors--bits that are thought to be good, but actually aren't). This leaves us with 24-byte blocks that are deinterleaved yet again to produce the raw data stream that is fed to the DAC.

    This error correction scheme can handle up to 3500-bit error bursts before it starts using interpolation; this corresponds to a roughly 2.4mm long section of the disk. Only scratches that are larger than this (the 2.4mm is measured around the disk, in the direction the data is read--so this would correspond to a >2.4mm wide scratch running from the center of the disk to the outside edge, or a >2.4mm long scratch running circularly around the disk) would result in a non-bit-perfect data stream.

    Hope this helps!
  21. jt1stcav

    jt1stcav Say It With Single-Ended Triodes

    A bit OT, but why do people man-handle their CDs and scratch them in the first place?

    I can understand car disc players that suck discs into their transport mechanisms, which can ultimately scratch them (which is why I don't own one). But why can't the typical consumer handle their discs properly by the edges like a vinyl LP? It's unfortunant for those who purchase used CDs from these type of people who handle their own discs like frisbees...who wants a CD that looks like it's been carved on by a nail?

    I just don't understand that kind of mentality concerning people who just don't care about their collection and handle them haphazardly, getting greasy fingerprints, smudges, and scratches all over the data side of the acrylic surface. Why can't they be more careful when grasping them from their jewel cases or when putting them into the disc trays, etc?

    I have literally thousands of CDs; my earliest discs are from 1984 and they still look as new today as the day I bought them 23 years ago without as much as a single mark on them...honest! My vinyl albums are handled the same way (by the edges) and they're still clean and scratch-free.

    No, I'm not anal and clean my discs with cleaning solutions and a lint-free cloth...I just don't put my grubby mitts all over 'em and ruin them like so many others do. Sorry for the rant, but it's a pet-peave of mine.

    Carry on...
  22. motorcitydave

    motorcitydave Enlightened Rogue

    Location:
    Las Vegas, NV, USA
    Good advice, really.
  23. Jae

    Jae Forum Resident

    And that's the good thing about buying new CDs and LPs in the USA - they are usually sealed at manufacture and sold that way.

    But remember and spare a thought for those of us in Australia and Europe where sealed CDs are the exception rather than the norm. In Australia for instance, CDs are usually stripped from their cases (regardless of whether they are sealed or not) and stored by some snotty-nosed 15 year old in a paper sleeve "out back" for re-insertion into the jewel case when you take it to the counter (as a bonus you get to watch them slide the CD about with their fingers as they try to clip in on the spindle). The result? Scratched, scuffed and/or fingerprint-laden CDs *on purchase*.

    Even JB Hi-Fi, one of the few local stores that sells self-sealed CDs, is not immune thanks to human accidents.

    I can attribute all my scratched CDs and DVDs to this scenario, with most being purchased a many number of years ago *before* buying on-line was so easy.

    Now even having said this, I just bought a sealed US CD that is covered in scratches. It's the third scratched new CD I've received from the USA in just over a month. That annoys me.

    So whilst I agree with you in part, I think it a bit misguided to exclusively point the finger at consumers.

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