  The transition from acoustic noise in the radiation-dominated universe to the
density structures in the matter dominated epoch is considered. The initial
state is a stochastic field of sound waves moving in different directions. The
construction of the initial state is compatible with the hyperbolic type of
propagation equation for density perturbations, and parallel to the theory of
stochastic background of gravitational waves. Instantaneous transition between
the cosmological epochs is assumed, and Darmois-Israel joining conditions are
applied to match solutions for sound waves with growing or decaying modes at
the decoupling. As a result a substantial amplification of the low scale
structures is obtained.
