  The frequency dependence of the dielectric permitivity's maximum has been
studied for poled and unpoled doped relaxor strontium barium niobate
$Sr_{0.61}Ba_{0.39}Nb_{2}O_{6}:Cr^{3+}$ (SBN-61:Cr). In both cases the maximum
found is broad and the frequency dispersion is strong. The present view of
random fields compensation in the unpoled sample is not suitable for explaining
this experimental result. We propose a new mechanism where the dispersion of
quenched random electric fields, affecting the nanodomains, is minimized after
poling. We test our proposal by numerical simulations on a random field Ising
model. Results obtained are in agreement with the polarization's measurements
presented by Granzow et al. [Phys. Rev. Lett {\bf 92}, 065701 (2004)].
