  Using the RXTE/PCA data we study the fast variability of the reflected
emission in the soft spectral state of Cyg X-1 by means of Fourier frequency
resolved spectroscopy. We find that the rms amplitude of variations of the
reflected emission has the same frequency dependence as the primary radiation
down to time scales of <30-50 msec. This might indicate that the reflected flux
reproduces, with nearly flat response, variations of the primary emission. Such
behavior differs notably from the hard spectral state, in which variations of
the reflected flux are significantly suppressed in comparison with the primary
emission, on time scales shorter than ~0.5-1 sec. If related to the finite
light crossing time of the reflector, these results suggest that the
characteristic size of the reflector -- presumably an optically thick accretion
disk, in the hard spectral state is larger by a factor of >5-10 than in the
soft spectral state. Modeling the transfer function of the disk, we estimate
the inner radius of the accretion disk R_in~100R_g in the hard and R_in<10R_g
in the soft state for a 10M_sun black hole.
