  Nonlinear plane acoustic waves propagating through a fluid are studied using
Burgers' equation with finite viscosity. The evolution of a simple N-pulse with
regular and random initial amplitude and of pulses with monochromatic and noise
carrier is considered. In the latter case the initial pulses are characterized
by two length scales. The length scale of the modulation function is much
greater than the period or the length scale of the carrier. With increasing
time the initial pulses are deformed and shocks appear. The finite viscosity
leads to a finite shock width, which does not depend on the fine structure of
the initial pulse and is fully determined by the shock position in the zero
viscosity limit. The other effect of nonzero viscosity is the shift of the
shock position from the position at zero viscosity. This shift, as well as the
linear time, at which the nonlinear stage of evolution changes to the linear
stage, depends on the fine structure of the initial pulse. It is also shown
that the nonlinearity of the medium leads to generation of a nonzero mean field
from an initial random field with zero mean value. The relative fluctuation of
the field is investigated both at the nonlinear and the linear stage.
