  Accreting neutron stars and black holes share a number of rapid variability
characteristics, such as quasi-periodic oscillations and broad-band noise. The
frequencies of these features were recently shown to be comparable to
fundamental general relativistic frequencies of perturbed test-particle orbits
near the compact objects. In this paper we propose a dynamical model for
producing modulations in the inner disk properties at these characteristic
frequencies. We postulate that a transition radius exists in the accretion disk
close to the compact object and investigate its response to a broad spectrum of
density fluctuations. We find that the transition radius acts as a low
band-pass filter with a broadband response that is constant at frequencies
lower than the inverse radial drift timescale and decreases above it as the
inverse of the frequency. Moreover, the response shows strong resonances at
frequencies nearly equal to the orbital, periastron-precession, and
nodal-precession frequencies, thereby accounting for the observed power-density
spectra of accreting compact objects and the correlations between their
characteristic frequencies.
