  We compare within an unifying formalism the dynamical properties of modulated
and composite aperiodic (incommensurate) crystals. We discuss the concept of
inner polarization and we define an inner polarization parameter beta that
distinguishes between different acoustic modes of aperiodic crystals. Although
this concept has its limitations, we show that it can be used to extract
valuable information from neutron coherent inelastic scattering experiments.
Within certain conditions, the ratio between the dynamic and the static
structure factors at various Bragg peaks depends on beta. We show how the
knowledge of beta for modes of an unknown structure can be used to decide
whether the structure is composite or modulated. Furthermore, the same
information can be used to predict scattered intensity within unexplored
regions of the reciprocal space, being thus a guide for experiments
