After a rather interesting lecture on sound, especially regarding modern pop-music our lecturer demonstrated the so-called Loudness War. My fellow student Thomas also wrote a post on the topic.
As a nice visual demonstration the below YouTube video was used by our lecturer.
Secondly whily I was looking up some more information on the topic matter I stumbled upon a very funny illustration, however how internal its humor may appear. Originating in a forum thread at PSW Recording Forums.
Original picture here.
For some more actual sound wave examples and illustrations I liked The Death of Dynamic Range. WikiPedia also has a section on the Loudness War.