  Based on spectral simulations, I show how focusing of the X-ray radiations
above 10 keV will open a new window for the study of microquasars. With
simulations of soft and hard state spectra of Galactic sources, I discuss how
SIMBOL-X can help to precisely measure the spin of black holes. Spectral study
on short ~1 s time scales will also allow the accretion-ejection connections to
be accessed, and the formation of jets possibly witnessed in X-rays. I then
turn to external galaxies, and demonstrate that spectral studies of hard
sources will be possible up to at least ~1 Mpc. For such sources, subtle
spectral signatures (e.g. a reflection bump) will clearly be detected. I
finally discuss the implications that these original results will bring on the
physics of microquasars and black holes.
