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

Never having been to Australia, I was unaware of this practice. I don't understand why this is even done, but I can understand your frustration on this matter. I did live in southern Germany for 3 years back in the mid '80s, and all my CD purchases on the economy were sealed by the manufacturers like they are here in the states...all my German-bought discs were new and unscratched (and remain as clean today as the day I bought them).

I'm thinking that the discs you purchased from the USA were possibly not new but customer returns that were sold to you as new, repackaged, and sealed with shrink-wrap and a heat gun by the retailer you bought them from. I say this since that's what we did at Guitar Center with returned merchandise from customers who either tore up the original packaging or threw it out completely. The CDs you bought from the states could very well have been treated this way and should not have been sold as new (if that's indeed what they did, unless you bought them as used).

 

I have always assumed that dirty or scratched discs require error correction, and that error correct inevitably leads to some degradation of the sound, but I've never tested that. I have a Jefferson Airplane MOFI that was buffed that I replaced because I hate buffed discs. Some day, maybe I'll compare the two.

 

Um, no?

EAC reads each sector eight times, and if a particular result is obtained 5 or more times, declares it to be "readable" and "correct". Your CD player only has a single chance to read, and if it doesn't get it, has to resort to error correction.

 

I always handle my CD's carefully, by the edges, but it's VERY easy to get slight marks/scratches on them, which are visible if you hold them under a light.

How you have managed to keep 23 year old CD's completely mark free, I don't know, but I envy you! Do you play them reguarly?

 

love my squeezebox!

 

Regarding this thread's thematic, consider the fact that there are SHM CDs out there. See the first post at this forum: http://www.euphonia-audioforum.se/forums/index.php?showtopic=4773

 

In my trips to Europe, CDs in the UK were generally not sealed, but a few would have a sticker to prevent one from opening the case. Most were open.

France had both sealed (mostly) and opened (few) cases. Germany (Bonn) had mostly non-sealed CDs - but there were quite a few sealed, depended on the label.

Back in the 80s when I bought some imports, they were all not sealed.

 

I think Stereoptic was referring to my assertion that ripping a damged disc error-free to a hard-drive and then listening from there was a great solution to worrying about sound degredation when listening to music on damged CDs.

 

I don't know why some people are concerned about the error correction "working harder". The error correction is handled in DSP that is designed for the task! Moreover, CD was designed to be economical to mass manufacture. That means NOT having perfect error-free discs at the production stage. Making a disc with no errors would be difficult and expensive, so the engineers built in mechanisms to handle flaws due to manufacture. It may surprise some of you but the Red Book specification allows a BER of 220 PER SECOND. New discs and blank CD-Rs will have BERs significantly less than that, but they won't be zero. Also, due to the multi-layered coding scheme (as described by SysteX), a player's DSP is always engaged in order to handle EFM-demodulation, error detection and correction and final sample computation when the corrected data is de-interleaved.

The error correction strategy was designed to minimze the damage fingerprints, dirt and scratches have on the audio signal. As has been pointed out, things have to get bad for some time for the error correction scheme to fail. That is why they make test discs with increasingly large drill holes in them to see how large a fault a transport can deal with.

If you still have reservations, I would suggest the following. Take the disc that you think sounds the worst (with CD looks can be deceiving, so it may not be the most scratched!), and buy a mint copy of the same pressing. Then record the SPDIF output of your transport playing both discs, and compare the WAV files you record. You may have some differences/misalignment due to recording this way, but the data should be the same for the majority of the files (you may have to align them in an editor). If the data are the same, you have nothing to worry about, if not, you need to replace the discs that give you concern. This is a real-time, read-once test, whereas the EAC test can involve multiple reads.

 

Whoops, sorry about that.

 

I don't doubt you, but I never experienced non-sealed jewel cases while stationed in Germany (from Jan. '83 to the end of '85). I do admit I only purchased CDs from one civilian audio shop in Ludwigsburg; all other music purchases were made at the Robinson Barracks PX in Stuttgart (AAFES always kept their CDs and LPs sealed).

I don't understand this practice of selling CDs in opened jewel cases...do the stores there let you listen to the discs first before you buy?

 

No.

It was common at better independent record stores in Australia and the UK to stock empty cases on the shelves. The discs were behind the counter.

For a big seller that was current, you'd get a sealed copy handed to you when you took the case up to purchase it; but if the record was from their deep catalogue, they would look in their racks for the little envelope and extract the CD and put it in the case.

Anti-shoplifting tactic.

(Whoops - LP Fan covered all this)

 

Here's the very first CD I ever purchased back in the summer of '84 in Ludwigsburg...every disc I own looks like this one! I know with such small pics it's hard to see any detail on the disc itself (I only cropped the images down so the file size can fit on this forum; no other Photoshop manipulations were made to doctor up and/or conceal any marks on the disc).

Aside from minute specs of dust and fingerprints on the disc's edge, this CD (and every disc I own) is completely scratch-free. I don't do anything special to them except play 'em (this disc has probably been played 100 times since I bought it new...I don't know else to tell ya).

 

I don't know what I'm doing wrong, but, I envy 'ya!

I would say though, if you have only played it 100 times in 23 years, it's easier to keep it scratch free than if you had played it more reguarly.

 

My worst scratched CD's were scratched as a result of poor packaging design, before they even saw the inside of a CD player!

For example, the stupid foam holders used for David Gilmour's 'On An Island' and the deluxe edition 'Help!' DVD

Also, CD's stored in wallets, such as the 30th Anniversary issues of ELO's 'Out of The Blue' and Bowie's 'Ziggy Stardust' and 'Aladdin Sane'.

You can pay more money for 'deluxe editions' with fancy packaging, and the packaging damages the discs! A pet peeve of mine!

 

Check the disc under a strong white light, sometimes a disc may look perfect in one light, but under the correct light, you would see hairline/micro scratches. i've played around with top loader cdps and regular tray loading cds, and for me, there is no way a disc is gonna be in perfect condition if i play it using a tray loading cdp, no matter how gentle i lay it on the tray. And also, certain cd surfaces are more resistant to scratches than others.

Anyway, for my ears, there is no difference in the sound as long as the scratches are not bad enough to introduce artifacts (clicks, pops etc) or skipping. I have 2 copies of a very clean sounding audiophile test disc, one really scratched up and another in flawless condition, i've ab'ed them and found no difference.

 

After close examination under my hologen desk lamp I did notice a singular micro-scratch or smudge less than an eigth of an inch long on the same disc. It's so faint I'm not even sure it was a scratch. Even so, I'm impressed with the fact that a CD as old as this one can still look this good after 100 or so playings.

I'm sure virtually all hard plastic disc trays on the majority of CD players at some point leave marks on a spinning disc...I can live with that. All my discs never leave their jewel cases; I don't use a shuttle/changer, paper/plastic sleeves or lend them out to others to man-handle. And it irks the hell outta me to see people grab them and slap 'em in a tray, or worse yet toss them all over a couch or bed or throw them onto a car seat or the filthy carpet!

I dated a girl back in '85 whom I let borrow one of my discs (Neil Young: Harvest)...when she finally returned it to me a month or so later, it was so badly scratched from God-knows-what that my Carver DTL-100 disc player could barely play a minute's worth of music from it! She apologized and bought me a new copy, but said she did nothing to the disc but play it on her 1st-generation Technics front-loading player! I seriously doubt the player was at fault...people just don't think about the proper care of handling CDs and think they're indestructable. That mentality drives me nuts!

Sorry for the rant (again)...I'll shut up now so y'all can go about the topic of this thread.

 

How does error correction work on a scratched CD? Even if it *sounds* generally okay, aren't you still getting imperfect information or artifacts buried in the music that can affect the feel or sound of the music? For example, I've seen people talking about how SACDs can hit high frequencies that by themselves are not audible, but do have an effect on the music.

Here's an optical illusion that gets at what I'm talking about. Your brain fills in the "scratches". You can read this passage fine, and even quickly. Buy you wouldn't be happy buying a book written like this.

 

To understand how the error correction works, you will need to do some background reading on polynomial codes (it's simply too big a subject for here). To begin with, you can start here:

http://books.google.com/books?id=VZ...&oi=book_result&ct=result&resnum=10#PPA168,M1

http://books.google.com/books?id=Ed...=X&oi=book_result&ct=result&resnum=3#PPA69,M1

and then go here if you need more info:

http://en.wikipedia.org/wiki/Cross-interleaved_Reed-Solomon_coding

http://en.wikipedia.org/wiki/Reed-Solomon_error_correction


You will only have changes to the original data when things get so bad that the error correction fails. In such cases, interpolation is attempted. If things are so bad that the error condition persists, eventually the player will be forced to mute, as it requires good data from which it can interpolate. If the interpolator does a good job, the only way to know that it is working would be either to record the data and compare to known good data, or probe the control signals within the player.

 

I share an earlier posters complaint about special packaging in general. I have some scratched up bowie discs from those deluxe editions too. I really think they like this packaging because its cheap to make, store and ship plus it provides for discs that will need to be replaced eventually.

I really hope the new Beatles discs will NOT be released in this packaging!

I sometimes wonder about non-tweeky folks who buy the stuff in this packaging and just keep it in there. Slide in-slide out. No mater how careful a person may try to be it's impossible to not have damage.

Another concern is now I see certain high end CDPs in ads that look like they load the disc with a slot instead of a drawer. I'm wondering how safe that can be. We have a mac computer that loads with a slot and it sometimes leaves marks on the discs....

J

 

Hmm, well, I disagree...although you kind of qualified your answer.

Elsewhere* I posted a story about how we could clearly see a scratch affecting the audio output from the CD player, due I believe to making the servo work harder (which then bled kickback through the power supply I further guessed)

[*seems to be in here, but I can't find my exact post, too many pages to look through
http://www.stevehoffman.tv/forums/showthread.php?t=181469 ]

 

Hmm, well, I disagree...although you kind of qualified your answer.

Elsewhere* I posted a story about how we could clearly see a scratch affecting the audio output from the CD player, due I believe to making the servo work harder (which then bled kickback through the power supply I further guessed)

[*seems to be in here, but I can't find my exact post, too many pages to look through
http://www.stevehoffman.tv/forums/showthread.php?t=181469 ]

 

Hmm, well, I disagree...although you kind of qualified your answer.

Elsewhere* I posted a story about how we could clearly see a scratch affecting the audio output from the CD player, due I believe to making the servo work harder (which then bled kickback through the power supply I further guessed)

NOTE: the point here is not about the bits out of SPDIF or whatever. The point is the player servo working harder disturbed the audio circuit of the player. If you were just using a digital output from the transport, then as long as the error correction could recover enough data it would be fine.

[*seems to be in here, but I can't find my exact post, too many pages to look through
http://www.stevehoffman.tv/forums/showthread.php?t=181469 ]

 

Use some toothpaste diluted with a little water to clean heavily scratched discs. Use alcohol and old clean cotton t shirt to finish. Works wonders.

 

If a disc does'nt skip I don't replace. The set level of error correction in a cd player itself can have an effect on sound quality according to Rega who mention it in the Jupiter cd player manual and their newer players have 3 different levels depending on the disc being played. Anyone who has a discman can flip the Shock control button on or off and hear the effects of more error correction versus less.