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Initial Inspection

 

So the first step to making a good CD rip is to look at the CD itself. We want to identify any defects that might affect the audio, either to avoid buying damaged discs or, if it's too late for that, to work around the damage as much as possible in the later steps.

There are 3 problems which commonly affect CDs.

Surface scratches

CDs are made from polycarbonate. This is a sturdy, strong plastic that holds its shape well and resists breaking. You can fold a piece nearly in half before it'll snap. But on the downside it scratches quite easily, and a scratch can create spots that the CD player's laser can't clearly see. The designers of the CD format saw this coming however and planned for it. The Compact Disc flexes its digital muscles by including a heaping spoonful of error correction with every song. This allows CD players to infer a surprising amount of data based on the data which comes before and after a scratch. It's especially effective for scratches that extend from the center of the disc outward, instead of parallel to the spiral tracks on the disc. And even if the disc is heavily scuffed, CD polishing rigs exist which can smooth the surface so that it can be played again. So despite being the most obvious form of damage, a scratch is also the least likely to render a disc permanently unplayable.

The reason for this is simple. Unlike a record which uses grooves across its playable surface to store music, the data on a CD is actually on the opposite side, where the label and the polycarbonate meet. The CD player's laser shines clear through the plastic that makes up most of the disc to read this thin reflective film. So damaging the plastic is akin to scratching the glass of a framed picture. The imagine beneath is still the same, providing you can see it. And so a scratched CD isn't a good thing, but it's also not always fatal. But this brings us to our second problem:

Label side damage

For all the protection the data on a disc receives from its thick polycarbonate covering, it's still vulnerable to attack on its back side. CDs, especially early ones, are extremely easy to damage on their label side. This is simply a thin aluminum foil layer which has been electrochemically bonded to the plastic, with a bit of ink and lacquer overtop. And unlike normal scratches, there's no way to repair a spot which has been scraped off. The data that was housed there is simply gone. That's why the first thing I check when evaluating a CD is not how many scratches it has on the front, but rather if the label side is intact. This can be done by holding the CD up to a lamp and looking for bright lines or pinpricks of light in the otherwise nearly opaque surface.

This game CD has damage which cannot be repaired. Pass it up and keep looking for a better copy.

If you have a CD with label side damage but really need something off of it, all is not lost. Perhaps the damaged area is over a different song than the one you want, at which point you've narrowly dodged a bullet. If you're not so lucky, you can try to rip the damaged song as-is and patch over the bad spot in software. For quality reasons I hold this as an absolute last resort for cases where no other copies can be found. Filling in gaps in an audio file is a very difficult process and not one I recommend for most people. But still, it's better than the third problem:

Cracking/chipping

This one is a hit or miss situation. A disc which has been cracked or has a piece broken off of it will be very tricky to rip. Any music/data which has a crack running through it is very likely to play back with corruption/skips.

But it's worse than that. A CD is a carefully balanced disc, so that it can be safely spun up to high speeds without breaking apart. The fastest drives rotate at over 11,000 RPM. At those speeds, a slight imbalance or a weaked spot can cause the disk to wobble and tear itself apart. If you want to get data off of a cracked or chipped disk, you will have to be very careful.

First determine if the song you want is likely stored in the damaged area. The first tracks of an album will be near the center ring while the last ones will be at the outside edge. Perhaps you want the first track from an album, and you have a crack which only extends through the latter half the disc, or the very outer edge has been chipped. In that case there's hope.

If you believe you have a chance, there's a few options. The first CD-ROM drives could only read at slow speeds, such as 4x. And some modern drives can be software controlled to keep them at low speed. Search for CD-ROM silencer and you'll likely find several programs that can set a speed limit. In either case I suggest going as slow as you can. The slower the speed, the less force the CD will be subjected to and the less likely it is to vibrate itself to pieces from being out of balance.

Whatever you do, do not attempt to play it at full speed unless you can accept the disc exploding in the drive. I had that happen once in a brand new DVD burner, with expensive results.

Okay, so hopefully now we have some clean CDs without severe scratching, or any label damage, cracks or chips. Time to rip them!

On to part 2 - Mp3 Compression

Last modified September 30th 2013

I can see clearly now...