Before beginning, I will admit that I have cheated a little. First, I used a disc with properties I know from previous samples. It's a "BrandX" 700-MB which writes well at 12x and 8x to about 650 MB, then picks up soft errors. The point at which errors appear varies from one disc to another and there are occasional "hard" errors which show up in the first blocks, but as you'll see they're all invisible to the simple "go/nogo" tests most people use. The second way I cheated is to use the big brother of CD-R Diagnostic, CD-R Inspector. I chose that because it provides a graphic output which is easier to see and use than Diagnostic, but everything you see below can be done with Diagnostic if you watch what's going on as you test. The disc had about 658 MB of data and it reads just fine in all my drives - a little slow in some, but without serious complaint.
Let's begin at the end: 0.00% unreadable. That's gratifying. There are no fatal errors; all that were detected were corrected by the error-correction code. The bad news came just before that. 1.05% recoverable errors means that the ECC was needed on 1% of the sectors read. We got through - but would we have been so lucky on another reader?
There's more information here. When the soft errors show up, the drive slows down. Those flaky blocks are reread to verify the ECC. In fact, the drive has a maximum speed a bit over 40x, but that's lost on this disc because of rereading. Incidentally, the test was repeated after the others were run and the results were identical.
Now we're getting 0.03% unreadable - errors which are not corrected. In fact, those occurred in reading the TOC and turned out not to affect the ability to recover the files. How do I know? I checked the data against the source files with WINDIFF (free from Microsoft). WINDIFF found no differences at the byte level. The errors were there, but it was possible to get past them - in this reader. There were fewer recoverable errors with this reader on the same disc used in the 40Max. Which, in my interpretation, means that this reader has slightly different sensitivity in reading a burned disc. As it happens, it's better tuned to the particular way the disc was written.
Note that this drive, which supposedly has maximum read speed of 32x, actually reaches well over 40x before the soft errors slow it down. Overall, it's twice as fast as the 40x. It starts at a lower speed but ramps up more quickly and doesn't hit those soft errors (which make it slow down) until later in the burn.
With this drive, we get the best results of all - except for the "unreadable" (i.e., uncorrectable) errors. Again, they did not interfere with WINDIFF ultimately recovering all the bytes correctly, but that was good luck. The errors are not really unrecoverable, but too difficult to read reliably for CD-R Inspector to regard them as valid. Again, the "unrecoverable" errors were in the first blocks, which probably explains the slow start.
There should be no surprise here. This disc is not well matched to the writer; in fact, it is probably not well matched to any of my writers from the tests I've run on them. For critical use, it's a "bad" line of blanks. However, simplistic tests - checking that the files are readable - would indicate no errors at all. If it had been recorded with audio instead of data, it would sound fine on any of the drives. However, the errors would be there and concealed by the electronics. On another reader - perhaps a car CD player - it might well fail in several ways. It might not track well; it might produce noise or sound dull; it might not progress correctly from track to track.
Does all that matter to you? Maybe not. If you know that the line works well when written in your drive and read in your players, you may not care. But the quality is missing and if you're relying on this disc to carry information to someone with a reader you don't know or to behave in someone else's CD player, you're running a major risk.
With the low price of quality discs today, I can't justify using these 700-MB blanks for anything that matters. I have others which cost about fifty cents each and check out free of all errors in all of my readers. They are well matched to my writers and at 14 MB per penny, they're less expensive than these "free" ones.
YMMV - Your Mileage May Vary.
E-mail me at cdrecording@mrichter.com
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