take your favorite piece of music, something fairly rich and compressed
already - i.e. without so much dynamic range.

Then take 10 second slices and attenuate each by 5 or 10 db or so,
intersperse them with silence.

This way you only have to run that 1 file and encode it and you'll have a
wide range of volumes right there.

Re-boost them back and you're done.

I.e.

10 seconds: 0db
5 seconds: silence
10 seconds: -10db
5 seconds: silence
10 seconds: -20db

etc. Should be easy to create in any audio program.

Regards,
Mark

--
http://www.marktaw.com/

http://www.prosoundreview.com/
User reviews of pro audio gear