I have had some experience with Audacity making tornado siren synthesizations. One of the vital tools I use is the chirp generator, for siren wind-ups and wind-downs. I have yet to figure out how to make wind-ups realistic.
This is an example of how a wind-up should sound: http://www.youtube.com/watch?v=kzFyGWdj6MI
But here is how the wind-ups I can generate sound: http://www.youtube.com/watch?v=DfISM-oP1Ic&feature=context-chv
Notice how the real wind-up rises at an increasingly slower rate, while the wind-up I can generate rises at a steady rate.
What I’m asking is,
How do I make a wind-up rise at an increasingly lower rate rather than increasing at a steady rate in Audacity 2.0?