  X-ray variability of the microquasar XTE J1550-564 is studied with time
domain techniques for the data from the RXTE/PCA observation in September 8,
1998. The 2--60 keV averaged shot is obtained from superposing shots with one
millisecond time bin through aligning their peaks. The spectral behavior during
the averaged shot exhibits prominent differences from that observed in Cyg X-1.
The hardness ratio of (13--60 keV)/(2--13 keV) or (16--60 keV)/(13--16 keV)
during a shot is lower or higher than that of steady emission respectively. The
correlation coefficient between intensity and hardness ratio of (13--60
keV)/(2--13 keV) or (16--60 keV)/(13--16 keV) is negative or positive
respectively. These results may indicate that physical processes in the low
state of XTE J1550-564 are different from those in Cyg X-1.
