Copying badly scratched CDS to 'remove' the faults. Does that still work? And if so how?

I remember if you had a badly scratched CD that wouldn’t play properly you could make a copy of it with a CD writer and the resulting copy would be fault-free (no audible evidence of damage to the ‘data’)

Does this still apply on modern devices and CDs?

I heard that it was due to the fact that copying hardware was fundamentally different to reading hardware in the way it read the data. In other words if a scratch moved underneath a copier’s reading laser the thing would just carry on regardless, but if a scratch moved under a reader’s laser the hardware would lose track of where it should be reading from and it would ‘jump’.

Anecdote: I had a software CD that had a physical flaw in the plastic (It looked as if a small drop of molten plastic dropped onto the blank plastic sheet before it got rolled and cut into disks). I couldn’t install the software, but I could copy the disk, and was able to install the software from the copy.

The “import settings” on my copy of iTunes (9.0.2) includes a check box: “Use error correction when reading audio CD’s.”
Presumably, checking the box’ll let you import some CD’s which are too scratched to play properly.

There’s no fundamental difference in the way a CD player reads and the way a CD copyer reads. Think about a computer drive: on a hardware level, it doesn’t know if it’s reading a block in order for the block to be copied to a file or to be played on the speakers.

However, since copying isn’t real-time and playing a CD is, there’s certainly room for more intense error-correction (including multiple attempts to read) in copying software than there is in playing music.

But, I think more importantly, quite often (as in my case) a person’s computer drive might be newer and better at error-correction than the CD-player in their stereo. In that case, there are CDs (and again, I have examples) that can be read by the computer but not by the CD-player. A copy made by the computer will have no damage and be playable by the stereo, even though the original can’t be.
But there’s no reason you couldn’t have a scratched CD that an old computer drive would have trouble with, while a fancy new super-error-correcting CD player could read it.

Quercus has nailed it right there - PC CD drives quite simply have better playability, for the most part. A servo-engineer colleague from my Philips days would do the rounds of the high-ticket hi-fi companies sorting out their CD deck tuning issues, and he would often despair at the state that these items were in when released onto the market. Mostly it’s a resources thing, as CD drives for PCs are such high-volume items that there will be large teams working on single specialised areas, whereas in a smaller, lower volume hi-fi company there might be one guy tuning the servos or the laser parameters, and the results might be a little ropey. Also a PC CD drive will be required to read a cheap nasty CD-R at high speeds, whereas a hi-fi deck might just about read a nice CD-R in real time, the two market areas have different requirements and expectations.

I’ve copied corrupted audio discs on a PC and it’s copied some of the errors too. Once a disc is too corrupted, it’s unsaveable. This is because there are two layers of error correction in a CD: C1 errors are the first level, where an error occurs and it can be corrected by the redundant data on the disc (much of the disc data is purely for error correction). To minimise against data losses due to scratches, dings and dirt, the data on the disc is shuffled about a bit so a single small blemish will spread its bets with regard to data loss. But every error correction system can be overloaded, and too many C1 errors will lead to uncorrectable C2 errors. Many audio CD players will have a fudging system to deal with these C2s by filling in the gaps as best it can, but this is never perfect, just less grating than a sharp dropout.

This feature will digitally fudge over the uncorrectable C2 errors and then recode the data stream so these errors aren’t flagged as such by the device reading the copied disc. Some of the original data is still lost, so this won’t work for data CDs, just audio, and even then it’s not perfect.

Optical storage discs wouldn’t be able to work without error correction as there are always C1 errors on a CD (or PI errors with DVD). In fact, it’s a good yardstick of the quality of a CD and/or the quality of recording to a writeable disc. I’ve spent many a long hour making graphs of block error rates (BLER) in order to assess the quality of something or another.

The copy may be OK to listen but usually the copy program fills up the error with silence. If it’s small enough you won’t hear it.

EAC (Exact Audio Copy) makes this visibly clear during the copying process that you are getting errors but EAC fills them with silence.

You can use other programs like CueTools to check any CDs you rip against a database and compare it on Accurip with CRC checksums

Is this what they do? Why not interpolate?

I’ve seen both. Usually turning on the automatic correction will cause interpolation.

I also want to remind people that, ofttimes, even C2 errors are recoverable via polishing. The errors are only skin deep, as the data is actually a little ways in from the label side.

I’ve just tried this with iTunes. I just redid my whol CD collection that started in college. In 1999/2000 Napster and CD burners (direct sharing) were making it possible to totally amass whatever you could think of in your head as far as creating a music collection goes. The auto correction on iTunes does work ok, and it works overtime to try to get an audible track if one is physically ruined, but like folks are saying-it’s limited to how bad the disc is. I used i for CDs that were scratched and playable but were obviously going to get to the non-playable point. CDs that are already garbled are a goner. I polished stuff with an old MAXELL CD scratch remover kit.

http://www.google.com/products/catalog?q=cd+scratch+removal+kit&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&cid=7046305539273987660&ei=qz0FTeGNI8Sblge318nWCQ&sa=X&oi=product_catalog_result&ct=result&resnum=3&ved=0CCgQ8wIwAg#

IT’s basically a paste polisher (it’s probably just car polish) with a couple of cloths and a spray cleaner (maybe it does more but probably just glass cleaner) as the second step. You must be sure to go radially out with the hand polishing or you will just aggrevate scratch problems. Those two things in combination with a Labels/applicator and a scanner allowed me to restore original cds fairly easily. I just chucked the old ones or gave them away.
Now, I have a question of my own. Has anyone tried one of those more aggressive scratch removing machines that you can get in the store? Pictured Here. Some of my favorite CD are beyond wasted. I’ve been filling in the tracks with lesser quality tracks (MP3, etc.)that I can find online when I restore, but I’m curious about these machines…

http://www.cdscratchremover.net/

I know this thread is about error correction. I’ve gone just a bit beyond that because I’ve hit the limit with what that can do and people already broke that down fully.

Anyway, I’m updating this because I AM THE MAN.

Buy a Ryobi “White Rouge” stick at Home Depot or Lowe’s. It’s a polishing compound…You can get any scraches or nicks out that “error correction” can’t fix. Use it like crayon. I just did this. Brasso also works. I can’t even see the scratch I couldn’t get out previously anymore!! The CD plays perfectly! (You probably also need some felt or a some of those maxell wipes)

Brasso wil work sometimes, it depends where the scratch is. Most of the data on a CD lies just below the label. If you get a label scratch those are very hard to fix. If you get a scratch on the other side, brasso or another polisher can scratch off a protective layer and still leave the CD readable. Label side scratches are mostly unfixable.

Anecdote has it that toothpaste will also work, if you just have one or two scratched discs and don’t want to get a special product just for that.

Rippers like DbPowerAmp have an option to reread areas of the disk several times and attempt to recover data. They can even “average” the results to guess-timate what should be there. Helps a lot when trying to backup a damaged disc.

It can work, but it’s a lot of work. I’d try it on something you don’t really need. If you really need it, take it to some place to get it professionally polished, or buy a polisher yourself.