But when I fed a new music CD to the drive, it didn't rip. On investigation, I found
abcde: CDROM has not been defined or cannot be foundTwo useful threads I found were http://ubuntuforums.org/showthread.php?p=7849371 and http://ubuntuforums.org/showthread.php?p=7622858.
I found that for some reason, instead of /dev/cdrom I only had /dev/cdrom2. Editing /etc/abcde.conf, I defined CDROM=/dev/cdrom2. That fixed the problem for abcde.
The second thread showed how to get my CDROM drive at /dev/cdrom again. Following funkydan2's lead I moved /etc/udev/rules.d/70-persistant-cd.rules to one side and rebooted. The file was regenerated and /dev/cdrom reappeared.
That done, I reverted /etc/abcde.conf, commenting out the CDROM=/dev/cdrom2 line.