How can scratches and other physical dameges on CD affect the sound?

It's actually because the top side is a lot thinner than the bottom (play side). Scratches to the top side can allow the aluminium layer to oxidised and fail to reflect the laser. UK PDO discs that have bronzed were claimed to have been made with a silver instead of aluminium (the early ones used gold). The sulphur in the CD sleeves reacted with the lacquer, breaking it down. The silver then tarnished.
Technology: No silver linings for CD’s »

 

Handheld machines were sold in the past. I'm fairly sure they are the machines that cause the most damaged.

 

I doubt that even simplest machine can do more damage to CD that is already skipping/not playing Here is a video of one of the more pro device in work (same model is used in service near me)

 

Sometimes people buff discs that play perfectly although they have many scratches. Just to improve its appearance. Replacing original cases with modern crappy ones is another issue that bugs me.

 

Well this is pointless cause even profesional buffing, although it repairs schratches that are causing the record to skip, can make disc looking visualy worse (the machine cannot buf exactly to a micron on whole disc surface and you can sometime see that light reflexes different on some areas of the surface). Anyway, the disc should play well not look well IMHO Anyway, I doubt that buffing with professional device can result in playing problems on the disc that hasn't got such problems before so if anyone is doing this for "visuals"... well if it makes somone feel better , then why not ?

 

No, it doesn't look well under close inspection. However, it will look better under a quick glance/poor lighting. You usually have to tilt the disc to see the buffing. Some sellers will buff virtually every disc they sell. Of course, those sellers use a professional machine.

 

I guess it is just indiviudal if somone prefers light scratches or signs of buffing. They both doesn't affect playing so it's fine anyway. Other thing is that CD has a limit of times it can be polished so doing this on well playing one is rather not the best idea.

 

I 've always liked an old 100% cotton T-shirt.

 

Most shops that sell used video console video games will have a professional buffing machine and will buff discs for a small fee. If the buffing disc inside the machine is worn or the operator doesn't know what they are doing, it's very easy to ruin a disc. This is true even though these machines are highly automated.

 

As far as i know most of the modern machines have electronical systems that does not allow the device to be used after certain amounts of uses without replacing the polishing rag in the machine. Actually I never heard about a case in which profesionall machine made the disc worse after repair.

 

What I just said is info straight from the mouth of video game, record store owner whose shop I used to frequent often. I had quite a few discs buffed there. The failsafe features may be on the machines, but they are easy to override and ruin discs. Worn pads and problems with the water cycling in the machine can ruin discs too.

 

As to the topic of amateur disc repair, I heard of two methods I never tried myself. One is filling the scratches with some kind of car polish. The second method is polishing the CD quickly and carefully with one of these orange oil cleaners. These essential oils like the orange oil in those cleaners can ruin a CD pretty quickly and leave permanent milky white stains because they destroy the polycarbonate the CD is made of. But I once read somewhere that if you thin it and work quickly you can polish off the scratch and then quickly rinse the disc.

Of course I never would do that to my CDs and don't recommend to try it. I just wonder if someone did that already.

 

The only place in my area that has one of those pro-tier disc resurfacing machines is an independently owned video game shop… I only had to use that thing once, and it didn't help in the end because all the real damage was on the data/label side. But let me tell you, on the heavy setting it made the bottom of that disc (HEAVILY battered) look absolutely brand new. Incredible.


It was a rare early press Sony CD (pre-October 1982) I was hoping it would get me a disc readable enough to get a burst rip I could later correct with ctdb or something but it was still not enough to get it rippable at all. It's the label side damage that will get you.


Still, if I have any other discs that are heavily scratched up on the bottom surface I absolutely wouldn't hesitate to take them in. You really have nothing to lose. $5 and you're practically guaranteed to be able to get a clean rip so long as there isn't any label side damage.

 

I agree 100%! It bums me out when I buy an old used CD in supposedly excellent or like new condition only to find a new cheap and flimsy jewel case and a disc with signs of cleaning or buffing. I would rather have a beat up old style original case which are usually heavier and of higher quality and a disc showing light marks as long as it plays fine.

 

I totally agre about the case but scratches vs buffing marks doesn't mater to me as long as the disc works. I prefer to listen to the music than watching the disk's surface

 

Bad scratches in the TOC area may result in no sound at all even though the "data" is still present.

 

Luckily the Lead In area seems to be the hardest to scratch

 

It's the CD player which incorporates CD error correction and therefore there is a slight delay after the CD drive reads the disc before you hear the sound. The delay is even longer in car CD players and the portable "Walkman" type players.

 

Hey, I like wine! I'll drink to that!

 

No.

No. Depending on the severity, you may be completely unaware that the error correction (and interpolation, if needed) is operating. When interpolation fails (due to sustained errors), players mute the audio, which is obviously noticeable. Clicking/skipping is more indicative of a tracking issue than an error detection/correction/interpolation issue.

The Cross-Interleaved Reed-Solomon Code (CIRC) developed for CD is extremely powerful, and highly effective. I get the impression that many here do NOT realize that:

1. the raw audio data is NOT encoded directly on a disc;
2. the encoded audio data is scrambled via interleaving, so is not contiguous on disc;
3. the left and right audio samples are handled independently.

The concept is simple, spread the data over a wider range so any errors impact the audio as little as possible. Those who are interested, can read more about CIRC here:

http://www.extra.research.philips.c...chive/PTechReview/PTechReview-40-1982-166.pdf

http://www.pearl-hifi.com/06_Lit_Ar...kinson_John/The_Art_of_Sound_Reproduction.pdf (see Section 11.12)

http://cwww.ee.nctu.edu.tw/course/channel_coding/FEC_CD.pdf

http://www.theseus.fi/bitstream/handle/10024/32913/Reed-Solomon Encoding and Decoding.pdf (see Section 4.2)

The CIRC encoder looks like this:



Fig. 11.34 in the second link above shows how the encoder spreads code words over a large amount of data. As a result, you can drill a nearly 2.5 mm hole in a CD with NO impact on audio quality. A larger hole would require interpolation, until the limit of the code is reached, at which point the audio will be muted.

So, small scratches should not be an issue. The reason for suggesting cleaning from center to edge is to avoid scratches which follow the track around the disc (those are the worst).

It should also be obvious that the presence of an interleaver means that the data coming off a disc has to be buffered as part of the decode process.

Due to the way in which the interleaver distributes the data, and similarly the errors, 'degradation' of the audio of type less bass, worse image, less soundstage, etc. is impossible. Either the decoder can perfectly correct all the errors, or momentary, distributed interpolation is required, or the audio is muted.

A certain amount of 'slop' was built into CD to make it cost-effective to manufacture, as a result a new, pressed CD can have up to 220 correctable errors per second and still be considered a good CD. In practice, that rate is much, much lower (usually less than 10, and can be as low as 0 for CD-R), and there can be NO uncorrectable errors.

Hope this helps to put your mind at rest.

 

I'm telling y'all I've been using simple car wax (paste) for years on used cd's, and it's always worked like a charm.



Just remember to go center to edge when applying and removing.

 

You're not trying to speak Polish, are you? Just as I'm not trying to speak Spanish...

 

Some of the rental discs I used to get from Blockbuster that looked like they had been rubbed with sandpaper always played without a problem..

 

I've owned 1000's without incident. I have ONE where the silver (printed) side started peeling from the outer edges but I burned a copy, although the original still plays perfectly. Boy, things have sure changed from when CD's were 1st introduced. Back than, it was 'perfect sound forever' and how indestructible the discs were. I remember walking into a store and they had piles of CD's lying around, no jewelbox, no nothing, and the salesman making his point by demoing gear with these very roughed up discs and them playing perfectly! For myself, I've always treated my discs as I do my records, handle by the edges and return to storage immediately. ALL my CD's play just fine.

 

I remember back in school mid to late 1980ies when our music teacher told us how indestructible CDs were. He claimed that he and a friend had mistreated a CD with a screwdriver and could not scratch it badly enough that it would not play. One of those people you shouldn't believe half of what they're saying, and such people become teachers, ridiculous! Thank god I had the good sense not to try the screwdriver treatment on my own CDs. When I lended out my first on CD, I got it back scratched. Not too badly but it was noticeable. The culprit said something like: what do you want, scratches on CDs are harmless!