The central limit theorem for the number of level crossings of a stationary Gaussian process

Let $r(t)$ be the covariance function of a stationary Gaussian process with zero mean. If
$$ \int_0^{\infty}t(|r(t)|+|r'(t)|+|r''(t)|)\,dt<\infty, $$
then the central limit theorem for the number of level crossings in a large interval is proved to hold.