Hey, here’s a way to get your geek on! Thanks Aaron. I'll try this on the one commercial disc I have that suffers from fatal bit-rot - disc 2 of Mahler 3rd Horenstein on Unicorn-Kanchana. Disc 1, and the disc of Sym 1, are also badly tarnished, but I could rip those successfully. Disc 2 wouldn't rip via EAC or Media Center. A real-time transfer from a CD player didn't work without a few dropouts, although this has been successful on severely scratched up library discs when ripping wouldn't work. Apparently the gaps are too big. This is a pity, because these issues are hard to find and usually very expensive. Given their cult-like following, I'm surprised they didn't have a second round of reissue. They are UK PDO pressings.

Any other catalog series that are typically vulnerable to wasting? We should be proactive toward preserving such items. This Mahler went from okay to not okay in just a couple years. OTOH, the big kerfuffle over bit-rot predicted years ago seems to have been overstated. For USA collections, the vast majority of CDs remain playable, at least based on the collections I know. Are others finding more rotten beer coasters?

-----Original Message-----
From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Aaron Bittel
Sent: Tuesday, August 06, 2013 7:17 PM
To: [log in to unmask]
Subject: Re: [ARSCLIST] CD-R help request

I have had some luck recovering data from burned discs using the command-line tool ddrescue:
https://www.gnu.org/software/ddrescue/ddrescue.html

A version for Mac (OS X 10.5+) is available here:
http://tinyapps.org/blog/mac/200808220700_ddrescue_for_leopard.html

ddrescue doesn't itself do any error correction, but rather extracts the readable data bit by bit --
often at many times slower than real-time, depending on the number of errors -- to a disc image
file representing a complete read of the disc minus any bits that are missing. You can then mount
this disc image (OS X will do this natively) as if it were a CD-R and use the CD ripper/audio
extractor/error correction software of your choice on it, which may be more successful than on-
the-fly correction from the optical disc itself.

Another feature of ddrescue is that you can run it multiple times on the same disc, and each time it
will go back and try to fill in the bits that are missing. That obviously won't work with data that's
completely gone, but sometimes can recover data that didn't read correctly for some other reason.
And these subsequent reads are faster because the program is only addressing the missing data,
and skipping over the parts it has already successfully captured.

But the best case will be if you have two copies of the degraded disc. In this case ddrescue can
scan both copies, merging them into one image that will probably be error-free, since it's unlikely
both discs have degraded in exactly the same places. And again, only the missing bits are read
from the second disc in an attempt to fill in the gaps. [Disclaimer: I haven't used this particular
feature of ddrescue myself yet, but am describing it based on information on the project's web
page.]

It's a bit more involved than popping a disc in, firing up iTunes and clicking "extract," but it's
worked for me when nothing else would.

- Aaron

--
Aaron M. Bittel
Archivist-Librarian/Digital Projects
UCLA Ethnomusicology Archive