  The properties of the aperiodic variability in X-ray binaries with black
holes are considered. The power spectra of the luminosity variability for a
flat accretion disk that is an emission source with a power-law energy spectrum
have been modeled. At low frequencies the derived power spectrum has the form
of a power law with a slope $\rho\approx-1$ and a cutoff at a frequency
approximately equal to the fluctuations characteristic frequency at the disk
inner edge; at higher frequencies the power spectrum has a complex form. The
high-frequency variability is suppressed due to the arrival time delays of the
photons emerging in the different parts of the disk. The presence of azimuthal
accretion rate fluctuations in the disk and the azimuthal non-uniformity of the
disk surface brightness in the observer's imaginary plane caused by the
relativistic effects give rise to an additional variability at frequencies
$\sim$200 Hz.
