  We study the rapid variability in Cyg X-1 observed with the Rossi Timing
Explorer (RXTE) on Jan 17 and 20 of 1997. The power spectra below 200 Hz can be
characterized by two ``shot noise'' components and a peaked-noise centered at
0.2 Hz. This is similar to those ``shot noise'' observed in another black hole
candidate GRO J0422+32 and a neutron star X-ray binary 1E 1724-3045. The
similarity suggests that the generation mechanism of ``shot noise'' and
peaked-noise is probably similar in both black hole systems and neutron star
systems, and in both high mass X-ray binaries (HMXBS) and low mass X-ray
binaries (LMXBs). We have also analyzed ~ 500 brightest shots selected from the
Cyg X-1 light curves. The time scale of the spectral variation around the shot
can be as long as ~ a few seconds, consistent with Ginga results. The
difference between the superposed shot profile in different energy bands can be
attributed to the time lag and the different shot width between different
energy bands. The shot width defined from the auto-correlation function of shot
profile does not show a bimodal distribution.
