How to generate non-linear chirps?

[sirendude2011]

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-oP ... ontext-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?

[kozikowski]

What you have is remarkably good. The hills and valleys echoes sell it immediately. Well, yes, if it's a mechanical siren, the motor torque backs away as the speed approaches normal alert, so the upsweep is non-linear.

Are you in Audacity 2.0? 2.0 has some impressive change-over-time tools you may be able to use. I've never used them, so we are now exactly even.

Koz

[steve]

Have a look at this topic: http://forum.audacityteam.org/viewtopic ... 60#p159187