Long description

This figure consists of two graphs. Each one shows a sine wave being sampled. The sine wave is drawn above a horizontal axis. A series of evenly spaced vertical lines, representing the samples, extend from this axis to the sine wave. Each line has a small filled circle at the point where the line meets the wave.

In graph (a), seven samples are taken for five cycles of the sine wave. A single cycle of a lower-frequency sine wave is drawn through all seven filled circles, showing that there is an alias.

In graph (b), thirteen samples are taken for five cycles of the sine wave. The lower-frequency sine wave from graph (a) is shown again, but it does not pass through all the filled circles.