The Rossler and Lorenz functions are iterated chaotic systems - they trace smooth curves
that never repeat the same way twice. Lorenz is "unpitched", having no distinct peaks in
its spectrum -- similar to pink noise. Rossler exhibits definite spectral peaks against a
noisy broadband background.
Time-domain and frequency spectrum of these two functions, as well as other info, can be
found at:
http://www.physics.emory.edu/~weeks/research/tseries1.html
These functions might be useful in simulating "analog drift."