Long description

This figure consists of four parts, each showing a screenshot from Signal Wizard. In each case, the ideal filter response is shown as a horizontal line at 1 below the cut-off frequency and a horizontal line at 0 above the cut-off frequency, with the cut-off frequency represented as a vertical line at 5000. The actual response is shown as a second line.

Screenshot (a) zooms in to the horizontal scale for the first filter in the previous figure, so that the transition zone around the cut-off frequency can be examined. The actual response deviates from the ideal response at a frequency of approximately 4200, descending at first slowly and then more steeply across the cut-off frequency, before easing off again to re-join the ideal response at a frequency of approximately 5800.

Screenshot (b) zooms in to the passband for the filter in screenshot (a). Almost no ripples can be seen.

Screenshot (c) zooms in to the horizontal scale for the second filter in the previous figure, so that the transition zone can be compared to that of the first filter. This time the actual response deviates from the ideal response at a frequency of approximately 4400, descending at first slowly and then more steeply across the cut-off frequency, before easing off again to re-join the ideal response at a frequency of approximately 5600. This shows that the transition zone is narrower.

Screenshot (d) zooms in to the passband for the filter in screenshot (c). In this case, a slight ripple is present.