  We investigate the accretion disk geometry in Galactic black hole sources by
measuring the time delay between soft and hard X-ray emissions. Similar to the
recent discoveries of anti-correlated hard X-ray time lags in Cyg X-3 and GRS
1915+105, we find that the hard X-rays are anti-correlated with soft X-rays
with a significant lag in another source: XTE J1550-564. We also find the
existence of pivoting in the model independent X-ray spectrum during these
observations. We investigate time-resolved X-ray spectral parameters and find
that the variation in these parameters is consistent with the idea of a
truncated accretion disk. The QPO frequency, which is a measure of the size of
truncated accretion disk, too changes indicating that the geometric size of the
hard X-ray emitting region changes along with the spectral pivoting and soft
X-ray flux. Similar kind of delay is also noticed in 4U 1630-47.
