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In Reply to: RE: A bogus test for a CD player posted by Tony Lauck on October 13, 2009 at 20:39:39
I'm not so sure about that. It is an optical medium and no matter what is on the disc (we know it is a series of pits and lands, ie ones and zeros), the info has to be able to be read optically. The scratches block (by refraction) the reception of the lasers light. I see DVD ROM drives that have problems reading dics with fewer scratches and they should have more memory available. I should have a sacrificial CD around somewhere that I can bring to levels of horrible condition until it refuses to be read in order to test that theory of yours. It involves a little luck no matter how you slice it (pardon the pun) as you can occasionally find the tiniest of scratches in the wrong spot on some discs which will cause every player that you put it into to refuse to read that portion. I have a couple of those discs and no player will read those areas consistently.
-Bill
I worked for a computer manufacturer that developed optical disk technology and helped to standardize the CD-ROM format, so I am familiar with the technology and its limitations. In addition, I have practical experience with mastering audio CDs and a few "enchanced" CDs that included computer data as well as audio tracks. As it happens, one of these enhanced CDs had production difficulties and so I got to be all too familiar with all of the various limitations of the CD audio and CD data formats, and how problems can involve complex interactions between disks and players.
The nature of digital data storage is that it is designed to preserve data in spite of many errors. This is an illusion. It appears that one's data is perfect when it is on the very edge. One slight additional degradation and it's over the cliff... This property makes it very difficult to design and conduct valid experiments to test data reliability. I would say that doing this properly is almost impossible without in depth knowledge of the technology and/or without specialized test equipment.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
So are you saying that even a CD if badly damaged and which plays in the player does nothing to show that the player will play badly damaged discs? I do understand that your are distinguishing mp3 files from CD tracks. I also understand that it is hard to say when a disc will or will not play by looking at it. My only concern however is addressing the assertion that because one player will not play one disc does not mean that the lot of the players will not play any damaged disc, which I believe to be a huge assumption and a disservice to anyone interested in a good player. The assertion was made that a barely scratched disc had trouble being read in one player and so the argument there is that "then how can you expect discs with more damage to play". I feel that I can disprove that argument easily by playing a more damaged disk as the assertion does not address any technical argument, rather it is only a logical argument. That in itself is of course illogical ;-). So I feel justified in disproving the poor logic there. We will have to leave the technical fact that not every disc despite of its appearance will play in every player, regardless of manufacture, on the table. That's just not going to be disproved and I am not trying to do so. So I understand your point there, but you might also understand mine.
-Bill
I would summarize the situation as follows. If you want to understand the QC issues related to disks and disk drives, then specialized knowledge and specialized tools are required. If you have audio on CDs that you don't want to lose then you must treat the disks with the greatest care. In addition, without backup copies you are still at risk.
There is no way to intuitively understand issues related to the quality of data recorded on a disk or the performance of a disk drive in dealing with data errors. In particular, that fact that a disk plays well on a variety of players today does not mean that it won't suddenly deteriorate overnight. Similarly, the fact that a drive can play a bunch of damaged disks well does not mean that it will continue to do so, nor that it will play other damaged disks. This area is best treated as a "logic free zone".
When I get a CD I rip it to my computer system using software that takes special care to get it right. It turns out that there are no problems with perhaps 95% of disks, but lately I've come across some old CDs that can't be read even though they have no scratches. This is the case on three separate computers, each with its own drive. Unfortunately, this music is lost for me, because I never made a copy. Most of the bad disks that I get come from disks that I am ripping for an Internet download service. When I get one that doesn't read properly it is usually because of scratches. About half the time these bad disks can be read on one of my three drives without any errors. At this point it is possible to burn a good CD-R copy. The drive that seems to do the best job on bad disks is old and slow. Perhaps it works well because it has seen very little use over its 10 year lifetime.
I don't like the idea of being captive to a CDP manufacturer for a working drive. I've been that route and had to junk an expensive player because of a defective laser that was uneconomical to repair. Drives wear out. The last time this happened on my audio PC it took me less than 15 minutes to install a new CD/DVD reader/burner which cost me less than $40.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
I must be lucky but I've never had a CD fail, nor a CDR that I've made. And I've made many hundreds. I can't account for the problems people have with CDs (though I remember a Conrad Johnson transport/DAC combo back in the 90s that wouldn't play maybe 5% of my CDs; fortunately that's long gone). In the case of CDRs, though, I'm convinced that burning them at the slowest possible speed -- mine, via a Tascam CD recorder, are all at 1X -- is a good thing vrom a reliability/longevity perspective. I HAVE had CDRs that were made by others on their computers become coasters, but then I've never involved computers in the burning process myself.
I have yet to have a problem with a CD-R that I burned, including one that fell out of its jewel case and landed face down on a dirt road. Most of the problems that I've had were with CD-Rs burned by others (probably at high speed) and with pressed CDs that have been "pooched" by repeated mishandling. Recently, however, some unscratched CD's that I bought back in the 80's and early 90's have gone bad, including several titles in the "Compact Jazz" series. Probably some kind of rot. Is this the beginning of the end?
Please note that some of these CDs that have gone "bad" still play with no obvious audible degradation. The RBCD "error concealment" has simply interpolated the bad data and if there is not a lot of high frequency content or if the fault persists for a short period it is hard to notice the interpolation. One of my bad CDs would not rip without error correction turned off and then it had lots of pops and cracks. It sounded bad on my CDP in my car as well.
You are obviously taking good care of your CDs. Keep doing so and hopefully you won't have many problems. And definitely continue to burn CD-Rs at the best speed for the media and equipment. More important, back up any of these unreliable media before something goes wrong, rather than just placing blind trust in the technology.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
I do keep waiting for one particular CDR to fail (and have backed it up just in case). I have no idea where I got it and it has no markings of any kind. Thing is, it's so transparent you can read a newspaper through it! But it soldiers on, so far at least.
"There is no way to intuitively understand issues related to the quality of data recorded on a disk or the performance of a disk drive in dealing with data errors. In particular, that fact that a disk plays well on a variety of players today does not mean that it won't suddenly deteriorate overnight. Similarly, the fact that a drive can play a bunch of damaged disks well does not mean that it will continue to do so, nor that it will play other damaged disks. This area is best treated as a "logic free zone"."
This is what I was getting at and I agree with that assessment. I am simply suggesting that since it is a logical error, that I could illustrate that. I understand from your perspective though how disproving poor logic does not satisfy the physics of the situation. The problem that I see posed is not that of a physical nature but of a logical one as there seems to be a debate of what might happen rather than of what is possible. I appreciate your insight.
-Bill
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