I learned a lot from the source of the following programs:

workbone-2.3
  didn't find a URL, I got this off a SuSE cdrom
amixer from alsa-utils-0.5.8
  http://www.alsa-project.org
xmcd-2.6 
  http://metalab.unc.edu/tkan/xmcd/ 
  (the disc id algorithm comes from xmcd)

Thanks go to:
Stefan Kamphausen <mail@skamphausen.de>
  for testing and suggestions
Stefano Barni
  for bug reports
