  By comparing the impact of established laser smoothing techniques like Random
Phase Plates (RPP) and Smoothing by Spectral Dispersion (SSD) to the concept of
"Spike Trains of Uneven Duration and Delay" (STUD pulses) on the amplification
of parametric instabilities in laser-produced plasmas, we show with the help of
numerical simulations, that STUD pulses can drastically reduce instability
growth by orders of magnitude. The simulation results, obtained with the code
{\sc Harmony} in a nonuniformly flowing mm-size plasma for the Stimulated
Brillouin Scattering (SBS) instability, show that the efficiency of the STUD
pulse technique is due to the fact that successive re-amplification in space
and time of parametrically excited plasma waves inside laser hot spots is
minimized. An overall mean fluctuation level of ion acoustic waves at low
amplitude is established because of the frequent change of the speckle pattern
in successive spikes. This level stays orders of magnitude below the levels of
ion acoustic waves excited in hot spots of RPP and SSD laser beams.
