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# Long description

This figure consists of three graphs. Graphs (a) and (b) are time-domain graphs, showing signal value against sample number. Graph (c) is a frequency-domain graph, showing spectrum against frequency. Graphs (b) and (c) are paired with a double-headed arrow.

Graph (a) shows samples that can be joined to make a smooth, symmetrical bell-shaped curve that starts at 0 for sample number 0, then rises smoothly to a peak at signal value 1, then falls smoothly back down to 0. To the right of the bell-shaped curve, the value is 0 for all sample numbers.

Graph (b) shows samples that can be joined to make the shifted sinc pulse seen in Figure 6.12(c). Again, the left cut-off point is at sample number 0. However, the lobes have been reduced and smoothed out. The same thing has happened on the right-hand side, so that there is no longer an abrupt right cut-off point but a smooth transition from the reduced lobes into the zero values. The peak of the sinc pulse corresponds with the peak of the curve in graph (a).

Graph (c), its frequency-domain equivalent, is at a value of 1 for frequencies below f subscript c, with no oscillations. The graph line then falls diagonally from a frequency slightly below the cut-off to a frequency slightly above the cut-off. It remains at a value of 0 for frequencies above f subscript c, again with no oscillations.