Full_Name: david stoffer Version: 1.9.0 OS: win xp pro Submission from: (NULL) (67.165.78.88) spec.pgram is supposed to plot the periodogram values in dB, i.e., 10log10(.). the value on the graph look ok, but the y-axis, plotted on dB scale NEVER shows negative values. in other words, all values are shown as positive.