  A stochastic model for intermittent fluctuations due to a super-position of
uncorrelated Lorentzian pulses is presented. For constant pulse duration, this
is shown to result in an exponential power spectral density for the stationary
process. A random distribution of pulse durations modifies the frequency
spectrum and several examples are shown to result in power law spectra. The
distribution of pulse durations does not influence the characteristic function
and thus neither the moments nor the probability density function for the
random variable. It is demonstrated that the fluctuations are intrinsically
intermittent through a large excess kurtosis moment in the limit of weak pulse
overlap. These results allow to estimate the basic properties of fluctuations
from measurement data and describe the diversity of frequency spectra reported
from measurements in magnetized plasmas.
