If you get the MP3 plug in you can then save a track at different MP3 sampling rates and then show the differnce bw5een ten,

I have a Madonna track I use sampled at differet bit rates from 320 down to 8kbs. You can load them all into aduacity and switch between them hearing the same song but at different qualities. I'm sure that some 20second clips are probabaly 'fair use' but don't like the idea of emails from Warner Brothers Lawyers. I'll try and find a Creative Commons track that works. I used Ray of Light as it was particually good for this as the first 20seconds or so were sonically quite simple (harder to tell between the various quality) and then when the vocals kicked in it got more complex and so easier to compare.

I have used the track Seed of Sin by Further Adventures in Monkeyland simply because it was the first free track I found that has a quite bit and a busy bit.

http://www.jamendo.com/en/album/92051

What I did

1) Opened tarck into audacity

2) Deleted all but the fisrt 30 seconds, just to make life easier