Long description

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

Graph (a) shows samples that can be joined to make the shape of the sinc pulse from the previous figure: a symmetrical curve consisting of a tall central peak with much smaller lobes on each side, alternating below and above the horizontal axis, and reducing in height the further away they are from the centre. The curve is centred on sample number 0.

Graph (b), its frequency-domain equivalent, shows a graph line that takes a value of 1 at frequencies below f subscript c and a value of 0 at frequencies above fsubscript c, with a vertical drop from 1 to 0 at f subscript c.

Graph (c) has the same shape as in graph (a), but cut off abruptly after a couple of lobes on each side. It has then been shifted so that the left cut-off point is at sample number 0. All samples above the right cut-off point have a value of 0.

Graph (d), its frequency-domain equivalent, has a similar shape to graph (b), but there are oscillations around 1 below f subscript c and oscillations around 0 above fsubscript c. Also, the graph line no longer drops vertically at f subscript c, but falls diagonally from a frequency slightly below the cut-off to a frequency slightly above the cut-off.