Aliasing

Aliasing occurs when the sampling rate is not high enough to correctly capture the shape of the sound wave. The recorded sound will have missing tones (Figure: Aliasing, top) or new tones that never existed in the original sound (Figure: Aliasing, bottom). These problem can be eliminated by using higher sampling rates or by using anti-aliasing filters. Figure: Aliasing

Higher sampling rates increase the number of sampling points. To see how this works, try adding a three points between each sampling point in the figure and redraw the graph. The recorded sound will more closely resemble the input.

Anti-aliasing filters remove all tones that cannot be sampled correctly. They prevent high pitched tones from being aliased to low pitch. Many sound cards include anti-aliasing filters in hardware.