no more noah23?

June 8, 2005 6:53 PM

Ahhhhhhh nerts! I dropped one of my favorite music CDs and a small sliver shattered off of it. We're talking a circular arc maybe 2.5 cm long by .5 a centiment deep, knocked clean off the edge. It looks like a smurf bit it. Is there any combination of bubble-gum/hot-glue/duct-tape that will make this thing playable?

I have most of the chunk, but haven't been able to locate a small piece. All I want is to be able to play this once, so I can burn as much of the info off the CD, before chucking it. Is there any hope, or should I start checking the interweb for tracks from Neophyte Phenotype?

posted by slipperywhenwet to technology (18 comments total)

"a centiment"? Heh. Didn't catch that one either..
posted by slipperywhenwet at 6:55 PM on June 8, 2005

I would say that the odds of lining up the tracks well enough for the player are infinitesimal (although there are some correction factors so I may be wrong). Also, there is still the break there, so the laser would end up scanning a gap or a chunk of glue. And don't even get me started on the structural integrity compromise keeping the disk from spinning at an even speed.

If there's a piece missing, then there's no way you have all the data, and no way to play it through.

Better fire up that P2P app, slipperywhenwet.
posted by jenovus at 6:58 PM on June 8, 2005

so, take a look at the shiny side of the disc. You should see a transition between the silvery surface that's close to the center and the silvery surface that's close to the edge. As long as the chunk that got knocked off doesn't cross that boundary, then you should be fine.

The transition I'm talking about is usually closer to the outside edge than the inside edge (unless it's an EP).

Also, given the choice, if you can put it in a slower-speed cd-rom drive then you should. You want to spin the disc at as slow a speed as possible.

The biggest worry is that the disc will be lopsided and do bad things to your drive when it comes up to speed.
posted by bshort at 6:59 PM on June 8, 2005

(what bshort said) -- CDs are recorded from the inside out. You can usually see where the data ends (the transition in reflectivity).

Good luck with your drive -- damaging that is the risk you are about to take...
posted by omnidrew at 7:15 PM on June 8, 2005

The chunk where the silver is gone - it would be interesting to try to put it back, but I think the chances of sucess are close to zero.

Assuming you've tried this and it has failed, the next step would be to balance the CD, as a cd player will be unable to spin it up if the weight isn't equalised. The most straightforward way would be to remove a same-sized sized chunk from the opposite side of the disk, just take care not cut any deeper towards the center than the damage on the opposite side, else you start making playable sections unplayable.

The CD reads from centre outwards, so the beginning of the album should be ok. Unforunately, most of the data is near the edge, for the simple reason that there is much much more surface area near the outside than near in the centre, so you've probably lost 20-30 minutes. On the bright side, if the album is only 40 minutes long, that may mean you've lost nothing - merely the 30 minutes of unused space on the disk :-)
posted by -harlequin- at 7:24 PM on June 8, 2005

Incidentally, a good pair of scissors allows a controlled way to remove part of a CD, but you should practise on cheap CDRs, because you'd need to get the hang of not delaminating the edges as you cut, and not warping the plastic. It's easy to accidentally peel off some of the aluminium surrounding the cut, so practice :)
posted by -harlequin- at 8:12 PM on June 8, 2005

dang. Thanks for the answers guys. This is not so encouraging. Maybe DJ GJ, my CD source has a back up of this thing..
posted by slipperywhenwet at 9:06 PM on June 8, 2005

If you end up rebalancing it, make sure to rip it a the lowest speed you can. CDs can very easily be mini-frag grenades if unbalanced.
posted by easyasy3k at 9:18 PM on June 8, 2005

I would avoid the P2P option unless you can tolerate MP3's that were probably encoded poorly. Have you tried eBay? What about local used CD shops?

Also, consider backing up your CDs. Use a secure ripper like EAC or CDParanoia, with a lossless audio codec like FLAC and you can have bit-perfect copies of your CD stored safely.
posted by Monochrome at 9:44 PM on June 8, 2005

slipperywhenwet, check your email.
posted by louigi at 12:17 AM on June 9, 2005

If you put it in an old slow drive, you don't have to worry about it being balanced. Something 4x or slower should be fine. A nice high-quality old drive should let you, slowly, rip the disc without worrying too much about it ever spinning out of control.

Or you may have a drive with spin control, perhaps noise reduction. Turn that on to slow the drive down, then rip the disc at 4x.
posted by krisjohn at 12:43 AM on June 9, 2005

just to nit-pick harlequin's point - there is not more data per sq cm on the rim than near the hub - less in fact. CDs store a constant number of bits per sector of rotation, so they are more spread out near the rim. Like vinyl, audio CDs are played at a single speed (1x, in fact).
posted by cogat at 3:04 AM on June 9, 2005

Just to nit-pick my own nit-picking. Harlequin in fact said that there is a constant amount of data per sq cm over the disc. But there isn't.
posted by cogat at 3:09 AM on June 9, 2005

I hope this is a good lesson for you to back up all your music to hard drive.
posted by Civil_Disobedient at 4:31 AM on June 9, 2005

Balance is going to be more of a problem than you think. CDs can handle a bit of imbalance, but you've taken a large chunk out. I doubt the CD will spin up.

Modern day CD drives are variable speed -- they'll spin the disc as fast as they can to track, so you can try whatever you have. If it can spin at 1x, you can get the data. Some can read data on slower than 1x speeds (you'd have to rip it -- you can't play audio at less than 1x, unless you have a very smart CD drive that will buffer the track first.)

If it does, great -- rip away. If not, gamble time.

You need to balance the CD.

You cannot make it thicker.

You have two choices.

1) Make the identical cut on the other side. The chances of getting this balanced in one cut are very small, so..

2) As your last chance. Carefully glue the bit back in. Let the glue cure overnight. super glue might be tempting, and indeed, it's strongest in tension, which is exactly correct. But, personally, I'd use a mild two part epoxy [1]. Let. Cure. Overnight. That should restore the CD's balance enough to let it spin up, then grab every track you can.

If you do want to use super glue, you can -- but I'd still let it cure overnight. Throwing droplets of cyanoacrylic around the inside of the drive would be very, very bad.

The rub of this method: If the glue fails, you're going to have to open the drive to get the bit of CD out.

[1] Mild in terms of epoxies. Most epoxies are fairly nasty things, but the really amazing epoxies are also really amazingly nasty chemicals.
posted by eriko at 5:39 AM on June 9, 2005

Like vinyl, audio CDs are played at a single speed (1x, in fact).

This is incorrect, and -harlequin- is correct. CDs are recorded using CLV, a constant linear velocity of ~1.2meters/second. That means that the bit density remains the same throughout the disc, and that the disc does not spin at the same speed throughout. In order to maintain constant linear velocity, the disc must slow down as the laser moves to the outside of the disc, from ~500rpm to ~200rpm based on the position. This means that there is a greater amount of information on the outside edge of the disc - the bits are not more spread out as the laser reaches the outside rim. This page presents a good technical explanation of how CDs are encoded. You can actually hear many CD players adjust the rpm as you skip tracks and move the laser closer to the outside of the rim.

It sounds like you're thinking that CDs are recorded with constant angular velocity, which would mean that the density varies across the disc due to the rotation speed remaining the same. While this was true of early laserdiscs, it has never been true of audio CDs.

The "1x" speed is a meaningless distinction that came into play when faster CD-ROM drives were introduced; AFAIK it was not part of the original Red Book spec.

I disagree with the other posters that extensive rebalancing is necessary -- since CD drives clamp the disc in the center, where the disc is undamaged, it'll almost invariably spin up. The question is whether it'll be stable enough to get a good read; I agree that slowing the drive down through your ripping software to the slowest speed is your best bet. Gluing it back together would seem quixotic at best.
posted by eschatfische at 8:43 AM on June 9, 2005

For Bill Nye proof of eschatfische's point consider that a 3" CD-R holds only 185MB[1] of data and a 5" disc holds 650MB. If CDs were like records the 5" would only hold about double (because of the hub) the MB of the 3".

[1] Heh "only". I remember buying floppies that held less than that in KB.
posted by Mitheral at 12:03 PM on June 9, 2005

eschatfische:

The problem with an unbalenced CD spinning up is not helped by it being clamped in the drive, the problem is that it takes considerably more work to spin an offset weight at the same speed as it does a balanced weight, a CD player's motor is not designed for that extra load and in many cases simply will not have the strength needed to do it. (Nor is the structure designed for spinning weights that are offset that much (vibrator-motor style)).

But yeah, a high speed computer drive operating at a low speed is a good bet, because the motor then obviously has a lot of extra grunt in reserve that it can call on, hopefully enough to force the CD up to low speed, as the chip isn't all that big.

One of the big limiting factors on CD-ROM drive speed is that past a certain speed, CDs (as mentioned) can turn into frag grenades - even brand new good ones. Since this one might already be weakened by the structural damage so far, even if it gets balanced so it can spin up to full speed, it probably shouldn't be spun up to full speed.
posted by -harlequin- at 1:28 PM on June 10, 2005