  We present a semi-analytic approach to forward-backward multiplicity
correlations in ultra-relativistic nuclear collisions, based on particle
emission from strings with fluctuating end-points. We show that with the
constraints from rapidity spectra, one can obtain bounds for the magnitude of
the standard measures of the forward-backward fluctuations. The method is
generic under the assumption of independent production from sources. For
definiteness, we use the wounded quark model for Au+Au and d+Au collisions at
the energy of $\sqrt{s_{NN}}=200$ GeV.
