Nyquist–Shannon sampling theorem
Alternatively, a signal may be intentionally sampled at a higher rate to reduce the requirements on the anti-alias filter. For example, CD audio typically extends up to 20 kHz, but is sampled with a 22.05 kHz Nyquist rate. By sampling at a rate 2.05 kHz higher than the Nyquist–Shannon sampling theorem calls for, both aliasing and attenuation of higher audio frequencies can be prevented even with less than ideal filters.