The top left-hand side of Figure 6 shows a few stacked traces from a real 2-D seismic line. The top right-hand side shows the result of filtering the data with a ``blocky'' spectrum in which again the top third of the data are filtered with one filter, the middle third with a narrower filter and the bottom third with an even narrower filter. The bottom left panel corresponds to the result of filtering the dataset with a linearly changing spectra in the middle third of the trace. The bottom right shows the difference between the filtered datasets. This time the difference is small even in the middle third of the trace because the original data spectrum is not very broad as shown in Figure 7. In this figure the left-hand side corresponds to the time-frequency spectrum of the data and the right-hand-side corresponds to the equivalent plot for the dataset filtered with the linearly-changing spectrum. As noted before, there is no apparent frequency distortion arising from the sample-to-sample change in the trace spectrum.