As most of the quality degradation is most likely done by a program as well, you could bring up your hex editor and try to recognize patterns, either in the encoded mp3 file or in the decoded PCM stream. For example, there are click-removal algorithms - those include click-detection, and if a file has too many clicks, it's most likely damaged.

But there are certain limits to those detection mechanisms, as simply using a too-low bitrate will degrade the quality of a record to an unacceptable level. Simply decoding the mp3 and then deciding whether the decoded result has acceptable quality is very hard, if you consider different kinds of synthesizer tracks - there are some very clean synthesizer sounds, but there are also filtered and voluntarily distorted sounds - your algorithm would have to determine whether that distortion was intrinsic to the original record or came to be through malintent manipulation - an impossible task.

So I guess it's simply easier to just record all your CDs instead of downloading them from the internet...

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web
[download]

Yes, you can go out and buy the CD if you like the artist to prove to the RIAA and others that file sharing is constructive towards their business model and maybe they should leave it alone :)

.02

cLive ;-)

--
seek(JOB,$$LA,0);