  Based on the analysis of a large sample of RXTE/PCA observations of several
black hole binaries in the low spectral state we show that a correlation exists
between the spectral parameters and characteristic noise frequency. In
particular, the amplitude of reflection increases and the slope of Comptonized
radiation steepens as the noise frequency increases. We consider possible
implications of these results on the accretion flow models and discuss a
possible observational test aimed to discriminate between different geometries
of the accretion flow.
