In response to white-noise stimuli, AP afferent axons of Rana catesbeiana and R. esculenta exhibit excitation, adaptation, and suppression simultaneously. After eigendecomposition of the second-order Wiener kernel, spectrotemporal properties of suppression and adaptation, in the individual axon, can be reconstructed by short-term averaging taken parallel to the main diagonal of the inhibitory subkernel. The results show suppressive spectra with deep, sharp notches in the vicinity of BEF. Spectral components outside the notch, on both sides of BEF, are effective in eliciting the suppression response; those very close to BEF are not. The results imply that the suppressive response (a negative dc shift in instantaneous spike rate) may occur with or without the presence of excitatory stimuli. It will be visible, however, only if there is background spike activity. The suppressive spectrum on the high side of BEF can extend beyond the highest AP BEF. In other words, AP axons can respond (negatively) to stimuli at frequencies beyond the highest BEF. The results further imply that a brief suppressive stimulus will be most effective if applied toward the end of a brief excitatory stimulus, or slightly after that excitatory stimulus has ended.