## 3. The Nyquist Limit | Home | Next |

The simplest sound wave is an oscillation between two amplitudes. A sampled waveform thus needs at least two sample points per cycle. Put another way, the wave's frequency must not be above half the sampling frequency. This limit is called the *Nyquist limit* of a given sampling frequency.

Sine wave at 1/2 sampling rate with two samples per cycle

If a sine wave higher than the Nyquist frequency is sampled, a sine wave of lower frequency results. This effect is called *aliasing*.

Sine waves above 1/2 sampling rate (blue) and resulting aliases (orange)

Since an alias is no different than a normally sampled wave of the same frequency, aliasing can be avoided only by removing frequencies above the Nyquist limit *before* sampling.