  We derive the wave equation for a minimally coupled scalar field in the
background of a general rotating five-dimensional black hole. It is written in
a form that involves two types of thermodynamic variables, defined at the inner
and outer event horizon, respectively. We model the microscopic structure as an
effective string theory, with the thermodynamic properties of the left and
right moving excitations related to those of the horizons. Previously known
solutions to the wave equation are generalized to the rotating case, and their
regime of validity is sharpened. We calculate the greybody factors and
interpret the resulting Hawking emission spectrum microscopically in several
limits. We find a U-duality invariant expression for the effective string
length that does not assume a hierarchy between the charges. It accounts for
the universal low-energy absorption cross-section in the general non-extremal
case.
