  We consider an overdamped Brownian motion in "quartic" potential subjected to
periodic driving. This system for the case of a weak periodic driving has been
intensively studied during past decade within the context of stochastic
resonance. We had demonstrated, that for the case of predominantly
suprathreshold driving the noise in the output signal is strongly suppressed at
certain frequency range: the signal-to-noise ratio demonstrates resonant
behavior as function of frequency.
