  We study an empirical model for a unified description of the power spectra of
accreting neutron stars and black holes. This description is based on a
superposition of multiple Lorentzians and offers the advantage that all QPO and
noise components are dealt with in the same way, without the need of deciding
in advance the nature of each component. This approach also allows us to
compare frequencies of features with high and low coherences in a consistent
manner and greatly facilitates comparison of power spectra across a wide range
of source types and states. We apply the model to six sources, the
low-luminosity X-ray bursters 1E 1724-3045, SLX 1735-269 and GS 1826-24, the
high-latitude transient XTE J1118+480, the bright system Cir X-1, and the Z
source GX 17+2. We find that it provides a good description of the observed
spectra, without the need for a scale-free (1/f) component. We update
previously reported correlations between characteristic frequencies of timing
features in the light of this new approach and discuss similarities between
different types of systems which may point towards similar underlying physics.
