  An abstract sampling theory associated to a unitary representation of a
countable discrete non abelian group $G$, which is a semi-direct product of
groups, on a separable Hilbert space is studied. A suitable expression of the
data samples and the use of a filter bank formalism allows to fix the
mathematical problem to be solved: the search of appropriate dual frames for
$\ell^2(G)$. An example involving crystallographic groups illustrates the
obtained results by using average or pointwise samples.
