This is a song I wrote converted to mp3. It starts out with a bugle call, and then steadily morphs into a fast and violent techno.
The only real tempo changes are in the first few measures and the last few measures, and are just there to make the bugle call more dramatic. The buildup to the techno is all the same tempo, it just has faster and faster rhythms and eventually becomes double time.
A really cool thing I noticed about this piece is that is you listen for one particular instrument (knowing what instruments are in it) you can find it at almost any time. Yet, it still blends for a orchestrated sound.