We show that a passive barrier separating two excitable chemical media can work as a transformer for a frequency of a train of pulses. The results of calculations performed for the FitzHugh-Nagumo type model and for the Rovinsky-Zhabotinsky model of the Belousov-Zhabotinsky reaction are discussed. Using the Rovinsky-Zhabotinsky model, we estimate the range of barrier widths and the range of frequencies of incoming pulses for which the transforming properties may be observed.