The minimum sampling rate of "2w" samples per second for a signal x(t) having maximum frequency of "w" $H_2$ is called as "Nyquist rate"

The reciprocal of Nyquist rate i.e. $(\frac{1}{2w})$ is called as the Nyquist internal.

Nyquist rate = 2w $H_2$

Nyquist interval - $\frac{1}{2w}$ seconds.

• If the signal x(t) is not strictly band-lined and/or if the sampling frequency fs is less than 2w, then an error called aliasing or fold over error is observed.

Due to aliasing some of the information contained in the original signal x(t) is lost in the process of sampling.

We use band limiting filter to eliminate aliasing.