  We present a sum-rule extraction of the decay constants of heavy-light mesons
from the two-point correlator of pseudoscalar currents. To this end, we compare
the perturbative expansions for the correlator and the decay constant performed
in terms of either the pole mass or the running MS-bar mass of the heavy quark.
The perturbative expansion expressed in terms of the pole mass exhibits no sign
of convergence whereas reorganizing this very expansion in terms of the MS-bar
mass yields a rather clear hierarchy of the perturbative contributions.
Accordingly, the decay constants extracted from the pole-mass correlator turn
out to be considerably smaller than those extracted from its MS-bar-mass
counterpart. Then, making use of the OPE in terms of the MS-bar mass we derive
the decay constants of heavy mesons with emphasis on acquiring control over the
uncertainties in the decay constants, related both to the input QCD parameters
and to the limited accuracy of the method of sum rules. Gaining this control
has become possible due to the application of our novel procedure for
extracting hadron observables based on dual thresholds which depend on the
Borel parameter.
